Renewable Energy by the Numbers

A Survey of Renewable Energy Resources and their Potential for Breaking America's Fossil Fuel Dependence

Michael Minn (MichaelMinn.com)

February 20, 2007 (rev 5/31/2007)

Executive Summary

Energy use in the United States from all sources in 2005 was around 99,890T BTU. (not including 4,430 BTU of energy exports). At a population of around 300 million people, that works out to around 333M BTU per person each year, including not only only direct use of energy, but indirect usage, such as the energy needed to make paper or transport food. The DOE's 2006 Annual Energy Outlook projects demand in 2025 to be around 127,000T BTU. Therefore, completely weaning America from its fossil fuel addiction within the next two decades will require finding renewable replacements for at least 127,000 trillion BTU per year, and / or reducing demand to the amount of energy that can be produced.

The following are potential amounts of energy could reasonably be expected to be available from specific categories of renewables or by offsets from conservation. A detailed description of the categories and the rationale behind the numbers is given in the sections that follow.

• 50,000T BTU solar
• 27,000T BTU from elimination of fossil-fuel generating inefficiency
• 25,000T BTU conservation
• 20,000T BTU biomass
• 15,000T BTU wind
• 3,000T BTU hydroelectric
• 2,500T BTU geothermal

No single resource or technology will completely take the place of fossil fuels at any point in the foreseeable future and other technologies (such as wave/tidal or fusion) may gain prominance with further development. However, diversity in energy sources will provide redundancy to assure some availability even if there is a problem with one single component of the energy generation infrastructure (e.g. major drought or environmental disaster). And diversity provides a modest hope for decentralization of energy production and the end of energy cartels that have wrought such horrors on nature and civilization since the advent of the petrochemical age.

In this analysis, energy production and consumption is quantified in terms of British Thermal Units (BTU) per year as a common measure. This mitigates some of the confusion caused by the use of differing measurements when dealing with different fuels and demands(e.g. MWh for electricity or Mboe for petroleum products). While the transformations to BTU cannot be made with complete accuracy, use of this common measure makes it possible to make general comparisons and see potential supplies in therms of the larger picture of energy use.

A report that reaches similar conclusions can also be found on TheOilDrum.com

The Basic Physics of Energy

British Thermal Units: The common measure of energy used in this essay is the British Thermal Unit or BTU. A BTU is the amount of heat needed to raise the temperature of one pound of water at sea level by one degree Fahrenheit. While energy exists in other forms besides heat, the laws of Thermodynamics postulate that energy can be exchanged between physical systems as heat or work. There are relatively simple conversion factors between BTUs and other common measurements of energy or work:

• 1 BTU = 1,055 joules
• 1 BTU = 252 calories (heat)
• 1 BTU = 778 foot-pounds (kinetic energy)
• 1 BTU = 196 lumens for one hour (light)
• 3.413 BTU = 1 watt-hours (electricity)
• 3.8M BTU = 1 Megaton TNT (4.184 petajoules)

BTU Examples:

• 300 BTU in a typical fully charged laptop battery (14.8V / 5850 mAh)
• 2,000 BTU to make a single pot of coffee BTU per house
• 55,000 BTU (16 kWh) used per day by a medium-sized house in Sacramento during the summer.
• 950,000 BTU to drive from St. Louis, MO to Kansas City, MO (247 miles) in a 30 MPG Toyota Camry
• 2,000,000 BTU to drive from St. Louis, MO to Kansas City, MO in a 15 MPG Lincoln Navigator SUV
• 3,000,000 BTU to burn a 100W light bulb continuously for a year
• 22,000,000 BTU to drive a 40-ton GCW tractor trailer between Iowa City, IA to New Orleans, LA (1,000 miles, 6 MPG)

Units: When dealing with large amounts of energy, the following abbreviations are used in this essay. For consistency, this essay usually expresses energy from different sources in trillions of BTU. Energy documents often describe large amounts of energy in Quads, which are quadrillions of BTUs. For example, the total energy use in the United States from ALL sources in 2004 was around 100 Quads or 100,000T BTU.

• 1K = 1 thousand = 1,000
• 1M = 1 million = 1,000,000
• 1B = 1 billion = 1,000,000,000
• 1T = 1 trillion = 1,000,000,000,000
• 1 Quad = 1 quadrillion = 1,000,000,000,000,000

Watts versus Watt-Hours: In discussions about electrical generation or power usage, figures are often given in megawatts (MW or millions of watts), which describes the peak amount of power being delivered or used. A watt is a unit of power - the RATE of energy being used at any particular point in time. The AMOUNT of energy used is the rate multiplied by time and is measured in watt-hours, or the equivalent of using one watt of power for an hour. Watt-hours can be converted to BTU by multiplying by 3.413. For example: A desktop computer and monitor drawing a combined average power of 130 watts will use 1,040 watt-hours over the course of an eight-hour workday.

Energy in Fuels: The amount of energy that can be extracted from specific amounts of different fuels are fairly consistent, although they can vary based on the formulation and purity of the fuels. The following general conversion factors are used in this document and do not consider efficiency losses in the devices using the fuel:

• 1,027 BTU = one cubic foot of natural gas
• 52,000 BTU = one pound of hydrogen
• 76,000 BTU = one gallon of ethanol
• 91,330 BTU = one gallon of LPG (Propane)
• 115,000 BTU = one gallon of gasoline
• 131,000 BTU = one gallon of Diesel
• 135,000 BTU = one gallon of kerosene / fuel oil #1 / jet fuel
• 138,700 BTU = one gallon of compressed Natural Gas (used in transit)
• 5.8M BTU = one barrel (42 gallons) of crude oil
• 8M-15M BTU = one ton of biomass (e.g. agricultural residue)
• 15M-20M BTU = one ton of lignite/sub-bituminous coal
• 27M-30M BTU = one ton of bituminous/anthracite coal
• 20M BTU = one cord of Wood (a stack of dry logs 4x4x8 feet, around 1.2 tons)

Efficiency: Devices or media that store, transmit or convert power never output the same amount of energy that is input. Energy is lost, usually in the form of wasted heat. So, in looking at systems that transform energy from one form to another (i.e. power plants) or use energy to accomplish useful work (e.g. vehicles), more efficient systems are usually preferred to less efficient systems. Complex systems (such as home heating systems that use electricity from coal-fired plants) are the product of the efficiencies of all intermediate subsystems. Examples:

• 93% Long-distance electrical transmission lines
• 80% Lead-acid or Lithium ion batteries
• 55% Diesel engine
• 46% Natural-gas combined-cycle power plant (7,500 Btu/kWh heat rate)
• 34% Coal-fired power plant (10,000 Btu/kWh heat rate)
• 30% Spark-ignition gasoline engine
• 15% Commercial mc-Si solar cells

Capacity Factor: Power plants have a wattage rating that reflects their peak capacity. However, electricity usage fluctuates and all power plants must have downtime for maintenance and repairs. The difference between peak potential and actual generation in practice is measured as a percentage called a "Capacity Factor". A reliable coal-fired generation plant can have a capacity factor of 70%, although unlike wind, coal-fired generators can be more easily taken on- and off-line as needed. Wind turbines typically operate with a capacity factor of 30-35%. Given a power plant MW rating, assuming a 70% capacity factor, annual BTU energy production can be computed as:

• 1,000MW = 20T annual BTU

Current Consumption

Energy Sources: In 2005, American energy came from the following sources:

• 28,870T BTU (28%) Imported oil
• 23,050T BTU (22%) Domestic Coal
• 21,080T BTU (20%) Domestic Natural Gas and Natural Gas Plant Liquids
• 10,840T BTU (10%) Domestic petroleum
• 8,130T BTU (8%) Nuclear
• 5,390T BTU (5%) Other imports
• 2,781T BTU (3%) Biomass (wood, waste, ethanol)
• 2,710T BTU (3%) Hydroelectric
• 352T BTU (0.3%) Geothermal
• 149T BTU (0.1%) Wind
• 64T BTU (0.1%) Solar

Electrical Generation: According to the DOE's Energy Information Administration U.S. domestic electrical production was 13,383T BTU (4,054,688,000 MWH) in 2005. U.S. domestic electrical generating nameplate capacity was 1,067,010 megawatts in 2005, with a practical capacity of 1,015,227MW in winter and 978,020MW in summer. At the peak of the July 2006 national heat wave, Americans were drawing 740,000 of those 978,020 MW. By source that breaks down as:

• 6,871T BTU (50%, 2,013,179,000 MWH) from coal
• 2,669T BTU (19%, 781,986,000 MWH) from nuclear
• 2,587T BTU (19%, 757,974,000 MWH) from natural gas
• 1,244T BTU (9%, 364,519,000 MWH) from renewables (including hydroelectric)
• 490T BTU (4%, 143,588,000 MWH) from other non-renewable sources

Energy Use by Sector: The U.S. Department of Energy's 2005 Annual energy review broke down this consumption into the following areas:

• 31,980T BTU (32%) Industrial
• 28,060T BTU (28%) Transportation
• 21,870T BTU (22%) Residential
• 17,970T BTU (18%) Commercial

Industrial Consumption: The Department of Energy's 2002 Manufacturing Energy Consumption Survey breaks down 22,666T BTU of industrial energy consumption by industry:

• 6,816T BTU Chemicals and Plastics
• 6,799T BTU Petroleum and Coal
• 2,508T BTU Metals and Metal Products
• 2,461T BTU Paper and Printing
• 1,228T BTU Food and Beverage
• 1,059T BTU Non-metallic Mineral Products
• 685T BTU Appliances, Electronics, Machinery, Furniture
• 429T BTU Transportation Equipment
• 377T BTU Wood Products
• 304T BTU Textiles and Apparel

Transportation Consumption: The Department of Energy's 2003 Transportation Energy Data Book broke down 28,635T BTU (compared with 33,250T BTU in 2004) of transportation energy usage as follows:

• 9,255T BTU Cars
• 6,989T BTU Light Trucks (2-axle / 4-tire, including SUVs)
• 5,142T BTU Medium / Heavy Trucks
• 2,217T BTU Aviation (non-military)
• 2,203T BTU Off-Highway (agricultural, construction, etc.)
• 1,032T BTU Water
• 960T BTU Pipeline
• 626T BTU Railroad (freight and passenger)
• 187T BTU Buses
• 24T BTU Motorcycles

Commercial Consumption: The Department of Energy's 2003 Commercial Buildings Energy Consumption Survey accounts for 12,533T BTU of commercial energy usage. These figures do not include malls (or Wal-Mart?) but are adjusted to account for energy losses in electrical generation (around 66% of energy in source fuels is lost).

• 2,585T BTU Office
• 1,570T BTU Education
• 1,002T BTU Health Care
• 959T BTU Lodging
• 879T BTU Warehouse and Storage
• 857T BTU Food Service
• 752T BTU Inpatient facilities
• 728T BTU Retail (non-mall)
• 668T BTU Food Sales
• 637T BTU Public Assembly
• 590T BTU Service
• 488T BTU Other
• 288T BTU Religious Worship .
• 247T BTU Outpatient facilities
• 209T BTU Public Order and Safety
• 74T BTU Vacant

Residential Energy Usage: Combining data from the Department of Energy's 2001 Residential Energy Consumption Survey 2001 U.S. Household Electricity Report and compensating for electrical generation inefficiencies (66% loss) gave a picture for around 17,600T BTU residential energy usage in 2001 (compared with 21,870T BTU in 2005). With 107 million households and 300 million Americans, that represents 164M BTU per household or 56M BTU per person.

• 5,390T BTU heating
• 3,117T BTU electrical kitchen appliances
• 2,396T BTU water heaters
• 1,872T BTU air conditioning
• 1,194T BTU other electrical appliances
• 1,029T BTU lighting
• 843T BTU home electronics
• 778T BTU electrical laundry appliances
• 420T BTU gas appliances

Petroleum Usage: Americans used around 44,000T BTU (7,539 Mboe) of petroleum products in 2005. The 2005 DOE list of petroleum product supplied breaks these into the following categories:

• 19,319T BTU gasoline
• 10,635T BTU Diesel fuel and fuel oil
• 5,763T BTU other finished petroleum products
• 4,528T BTU natural gas liquids
• 3,484T BTU aviation fuel

Petroleum Imports: America used around 4,937 million barrels (28,634T BTU) of imported oil and oil products in 2005. The DOE breaks them down by source as:

• 839M barrels Persian Gulf
• 793M barrels Canada
• 601M barrels Mexico
• 550M barrels Venezuela
• 419M barrels Nigeria
• 1,735M barrels from 85 other countries

Remaining Fossil Fuel Reserves: The DOE estimated 7,409,653T BTU (74 years at current consumption rates) of U.S. domestic fossil fuel still in the ground on 12/31/2004:

• 123,952T BTU domestic oil reserves ( 21,371M barrels)
• 619,179T BTU domestic natural gas reserves ( 602,901B cubic feet)
• 6,682,800T BTU estimated recoverable coal reserves ( 267,312M tons @ 25 BTU/ton)

Foreign Fossil Fuel Reserves: Figures for proven and estimated reserves elsewhere in the world are a bit suspect, especially since 1985 when OPEC decided to link production quotas to reserves estimates, resulting in suspicious increases in reserves declarations. These numbers give a better understanding of some our foreign policy decisions of the past few years. Estimates of "years of total U.S. energy consumption" are based on the 100 quads of energy used in total, not the 60 or so quads of natural gas or oil-based energy used.

• Saudi Arabia: 1,502,200T BTU (259 billion barrels) or around 15 years of total U.S. energy consumption.
• Iran: 765,600T BTU (132 billion barrels) or around 7.5 years of total U.S. energy consumption.
• Iraq: 649,600T BTU (112 billion barrels) with a potential of over 1,160,000 BTU (200B+ barrels) or around 11 years of total U.S. energy consumption
• ANWAR: 35,954T BTU of gas (35T cubic feet) and 60,088T BTU of oil (10,360M barrels) or around a year's worth of U.S. total energy consumption.

Comparison with Europe: Energy consumption in both the UK and the EU as a whole is around 150M BTU per person per year - half the U.S. per capita consumption. Although European land development and consumption habits are different than in America, they are "first-world" countries and can therefore be more accurately compared than developing countries who have radically different lifestyles and energy use needs. Therefore, it is not unreasonable to suggest that Americans could someday have a European lifestyle on half the energy currently consumed to support our highly suburbanized culture. That 50% reduction would be equivalent to the subtraction of 50,000T BTU from current annual energy demand. Americans just consume twice as much of everything than Europeans. No single area of consumption seems to account for the increased energy usage.

• America has twice the amount of land per person: 107 inhabitants per square mile in America (300 million peoplein 2,812,500 sq mi) versus 296 inhabitants per square mile in the EU-25 (454 million people in 3,973,139 Km2)
• Americans use twice as much electricity: 13.2 Mwh/year per person in America (3,971 TWh for 300 million people) versus 6.9 Mwh per year per person in the EU-25 (3,121 TWh total electricity generation for 454 million people)
• Americans have twice the per capita Gross Domestic Product: $41,800 in the U.S. (2005) versus $18,500 in the EU-25 (21,300 euro @ 2003 1.15 euro/dollar)
• Americans have twice the home/apartment living space: 734 median square feet per person in America versus 404 sq feet in France, 432 sq feet in Germany and 474 sq feet per person in the UK.
• Americans do twice as much traveling: 17,603 per capita travel miles per year in America versus 8,178 per capita travel miles per year in Europe. (US 5,281B total passenger-miles, 4,348B auto/light-truck passenger-miles, 505B air passenger-miles, 6B rail passenger-miles) EU-25: 3,710B total passenger-miles (5,970B km) 2,761B auto passenger-miles (4,444B km), 279B air passenger-miles (449B km), 214B rail passenger-miles (345B km)).
• Ratios of Industrial/Transportation/Residential/Commercial usage are almost exactly the same: EU 29% Industrial, 31% Transportation, 40% Residential/Commercial; US 33% Industrial, 28% Transportation, 39% Residential/Commercial.
• Interestingly, Americans don't own twice as many cars...they just drive them farther: 450 cars per 1,000 Americans (135,077,031 registrations in 2005) 465 Cars per 1,000 Europeans .(2003)

Energy Sources

Solar (50,000T BTU per year)

Solar power has the potential to serve all of mankind's long-term energy needs. Because technological developments are ongoing at a rapid pace and uncertain in their outcome, there is no formal estimate on how and when solar could become a dominant American power source. However, following the example of France, which converted from zero to nearly 100 percent nuclear power in less than 20 years, only 25% annual growth in solar production from the 2005 64T BTU (around 0.1%) per year level, would yield 50,000T BTU annually by 2025 (half of current total energy use).

Energy from the sun drives almost all biological and environmental processes on earth and is at the root of most renewable energy resources. Fossil fuels are essentially ancient sunlight that has been preserved in the earth. The amount of solar energy that strikes the continental U.S. is stunning:

1,366 watts per square meter arriving from the sun (solar constant)
x 80% makes it through the atmosphere
x 65% makes it through the clouds
x 365.24 days per vernal equinox year
x 7 hours sunlight / day average year around
x 3.413 BTU per watt-hour
x 1,894 acres in the continental U.S.
x 4,047 square meters per acre
--------------------------
45,151,524T BTU per year (450 times 2005 annual consumption)

That number includes every single bit of land, including agricultural lands that are already harnessing the sun's energy and we could never hope to transfer that much solar energy to direct human use. But, an infrastructure that could capture even half a percent of that energy (at 50% efficiency) could satisfy ALL current domestic energy needs. As discussed below, a 100 mile by 100 mile solar farm in Nevada could equal all U.S. domestic electrical production. A 1995 study for the Texas Sustainable Energy Development Council estimated that of the 4,300,000T BTU of sunlight hitting the State of Texas annually, 250,000T BTU (2.5 times current total national energy production) could be practically accessed using available technology of the time mounted on residential, commercial and civic structures.

There are a wide variety of technologies for harnessing solar energy, most of them at high levels of maturity and many of them with ancient roots:

• Solar Photovoltaic systems are built from cells of semiconductors material. Photons from sunlight knock electrons loose from the atoms in the semiconducting material, causing electron flow. Photovoltaics have been around since 1953 with widespread use in the space program. Current photovoltaic systems convert around 15% of the solar energy that strikes them into electricity. Around 2,000 MW worth of photovoltaics are installed worldwide and almost every part of the U.S. gets enough regular sunlight to make photovoltaics practical. Photovoltaics are especially popular for situations with limited energy requirements in remote locations. The current generation of photovoltaics require a significant amount of energy for manufacture ( around 3.6M BTU per square meter) and it takes 4 to 7 years of a photovoltaic cell's 30-year projected lifetime to generate an amount of energy equivalent to what was needed for its manufacture. Photovoltaic production is currently limited by supplies of silicon although thin-film and other photovoltaic technology developments should significantly reduce production costs and increase availability.

  Photovoltaic cells are already use in a number of industrial-scale plants as well as numerous low-energy applications, especially in remote areas:

  • Parking meters
  • Road lights and signs
  • Buoys and offshore navigation aids, including all buoys operated by the U.S. Coast Guard
  • Calculators
  • Remote telecommunications systems
  • Remote Wi-Fi routers
  • Low-speed shuttle and ferry boats in London's Hyde Park and the British Lake District's Coniston Water.
• Concentrating Solar Thermal technologies use mirrors to focus heat from the sun to generate steam for turbine generators. Concentrating systems are the most efficient and powerful solar technology, although they can be complex to build and maintain and are most appropriate for industrial power generation rather than distributed residential installations. Trough systems, like FPL Energy's SEGS in Barstow, CA, use long curved mirrors to heat tubes of oil that is then used to create steam. Power tower systems, like the Solar One and Solar Two pilot plants in the Mojave Desert, use a field of mirrors to concentrate large amounts of energy on a central tower, where the heat melts salt which can transfer heat to a boiler or store the energy for overnight use. Dish systems like those produced by Stirling Energy Systems use a large mirrored dish to focus light on a photovoltaic module or a Stirling engine which converts heat to kinetic energy that drives a generator.
• Concentrating solar photovoltaic involves the use of mirrors to concentrate light on high-efficiency photovoltaic cells. This approach reduces the amount of silicon (and the associated expense) needed to capture the same amount of light energy as an analogous flat-panel photovoltaic installation. While the trend with flat-panel photovoltaics is toward cheaply making large numbers of low-efficiency cells, cells for concentrated solar photovoltaic are of higher quality, efficiency and expense. But while the actual cells are more expensive, the mechanical configuration is more complex and higher maintenance is required, the use of fewer cells for an equivalent amount of power can make them less expensive overall than flat-panel systems in appropriate situations.
• Passive Solar Architecture: Perhaps the oldest and simplest way of using solar energy is through architectural design, adapted to local conditions, that can directly use the light and heat from the sun. Daylight can be harnessed with large south-facing windows and clerestories as well as open building design with glazed apertures, light shelves and light pipes for transmitting light to the interior of buildings. Trombe walls incorporate absorptive materials built in south-facing walls that capture heat during the day and release heat at night. Glass rooms built on the south sides of buildings can provide 60 percent of winter home heating (with proper ventilation) and can also be very aesthetically pleasing. Design of South-facing overhangs and the strategic planting of deciduous trees can allow sunlight in during the winter and block it during the summer.
• Solar Water Heating technology is well established and currently in use in over 1.5 American million homes and businesses, representing a capacity equivalent to 1,000 MW. Most solar heating systems have roof collectors incorporating small tubes that run under thin black plates and either directly heat water or heat antifreeze that transfers the heat to a water storage tank. Solar water heaters typically reduce conventional water heating needs by 67% and can pay for themselves in 4 to 8 years in electricity or gas savings.
• Solar air heating works in a similar manner to solar water heaters, only with the final product being heated air. Solar air conditioning is also possible (although more technically complex) when solar heat is used to evaporate a refrigerant.
• Hybrid Solar Lighting devices such as those produced by Sunlight Direct capture sunlight with parabolic reflectors on a roof and route it through a building with fiber optics. These systems rely on conventional electrical lighting when solar light is unavailable.
• Solar Chimney Towers use wind turbines in a tower at the center of very large circular glass houses (2 - 30 kM in diameter). The air in the glass house is heated by the sun and rises through the tower, turning the turbine which can then power a generator. While the design and materials for such a facility are relatively simple, the process is rather inefficient, only harnessing around 2% of the solar energy that strikes the glass house. Solar chimney tower facilities would require extremely tall towers (up to 1km tall) and large areas of land to be practical. Scaling from a successful 50kW pilot plant built in Manzanares, Spain in the 1980s, a 10KM by 10kM area would be needed to replace a single 2,000MW coal-fired plant, thus severely limiting the number of areas where such facilities could be built. A huge plant in New South Wales, Australia has been in the planning stage for a number of years.
• Solar Power Satellite: A large photovoltaic power station in orbit could send its captured power back to earth in the form of microwaves. The idea of a space-based collection system has been around since 1968 and is attractive because solar power collection would be unobstructed by day-night cycles, clouds or atmospheric absorption. However, the extraordinary complexity and cost of launching equipment into space makes this option impractical until there is a radical (and unanticipated) improvement in launching technology and space-based manufacturing techniques.
• Artificial Photosynthesis would replicate the process that plants use to convert water and carbon dioxide into carbohydrates and oxygen. While the idea of bypassing the trouble of raising biomass crops and finding a way to emulate their basic chemical process is attractive, photosynthesis is an extremely complex process, despite it's ubiquity in the plant kingdom. Progress is being made, but, unfortunately, artificial photosynthesis remains a distant prospect.

Theoretical Case Study: If America wanted to build one huge photovoltaic farm in sunny Nevada to generate all its electricity (with some form of backup like distributed pumped storage reservoirs) using typical photovoltaic technology like 175-Watt Sharp NT-175U1 panels which occupy 14 square feet (62" x 32.5") per panel:

13,552T BTU (2004 U.S. total electrical generation)
/ 3.413 BTU / watt-hour
/ 175 watts per panel
/ 6 hours of usable sunlight per day (rough average)
/ 365.24 days per vernal equinox year
x 28 sq feet per panel (panels plus access roads)
/ 27,878,400 sq feet per sq mile
---------------------------------
10,399 square miles

So a 100 x 104 mile area in Nevada could theoretically satisfy all of America's current electrical generating needs. Current photovoltaic production techniques, limitations in the world supply of silicon, the considerable amounts of energy required to construct solar cells, and the cost of solar cell production would make such a deployment technically and financially impossible. However, this scenario provides some indication of what might be achievable with concentrating solar plants (which are a well-developed technology) or with more efficient photovoltaic production technology currently in the late stages of development.

Distributed Photovoltaic: Solar energy through photovoltaic cells lends itself especially well to distributed generation, rather than the current centralized system. As another fanciful scenario, suppose America got the notion to to install electric-generating solar panels on the roofs of most single-family homes. The Census Bureau's 2003 American Housing Survey listed 67,753,000 occupied single-family detached homes. The average single-family home in 2004 was was 2,349 square feet. If half of those homes used roof space equivalent to 1/4 of their interior square footage for solar cells, that would provide around 20 billion square feet for solar cells. Using the aforementioned 175-Watt Sharp NT-175U1 panels:

33,876,000 houses (1/2 of 67,753,000)
x 587 sq feet per house (1/4 of 2,349 sq feet)
/ 14 sq feet per panel
x 175 watts per panel
x 4 hours of usable sunlight per day (average - guess)
x 365.24 days per vernal equinox year
x 3.413 BTU / watt-hour
--------------------------------
1,200T BTU per year (1/3rd current residential electric consumption, 1% of total US consumption)

That would be 42 panels per house or 1,420,372,000 panels. At $1,000 per panel and assuming an installation cost equal to the panel cost, that would represent a $3 trillion dollar investment for the renewable equivalent of 1/4 of oil production in Iraq (at April 2006 rates of 2 million barrels per day).

Solar vs Iraq: Continuing the Iraq comparison, with current photovoltaic technology, Iraq is a better deal financially, since at $195M per day the occupation would have to take 42 years to expend a similar sum, which also exceeds the 30-year life span of photovoltaic panels. Of course, this does not consider the considerable political, human and moral costs associated with war. However, with the potential of thin-film technology, a cost-reduction factor of 10 would bring theoretical solar deployment costs in line with what the Iraq war will have cost by the end of the Bush administration.

A more realistic paradigm is the use of multiple existing technologies to make reductions in home energy consumption. Widespread adoption of this approach would stretch existing fossil fuel supplies in a transitional period while the technology, politics and finance develop for completely sustainable energy production. In an excellent article, Hacking your way off the grid, Brian McConnell detailed how he reduced electricity use in his San Francisco home by 80% in 2005 using a combination of photovoltaic panels, solar water heating, forced air solar heating and conservation measures. Even better, with reduced energy costs and the increase in home value, the system will pay for itself in under 10 years.

Elimination of Fossil Fuel Generating Inefficiency (27,000T BTU per year)

Since coal-fired power plants only convert around 33% of the energy in their source fuels to usable electricity, transitioning to solar and wind generation would eliminate this statistical loss and "save" 27,000T BTU in energy per year, or one quarter of current total annual American energy use.

In 2004, American utilities generated 13,552T BTU of electricity ( 3,970,555,000 MWh). With 300 million Americans, this works out to around 44M BTU (13.2 MWh) of electricity per person per year. The process of generating electricity usually involves heating water to produce steam, which then becomes mechanical energy that turns an electrical generator to produce electricity. An inescapable thermodynamic feature of this process is a loss of around 67% of the input energy as waste heat. While many plants recover some usefulness from their waste steam (such as selling it in urban areas for space and water heating), such losses are endemic to generation of electricity with fossil fuel. This means that, in reality, 40,100T BTU or 40% of American energy consumption was devoted to electrical generation.

Current wind and solar technologies are also inefficient (photovoltaic cells only convert 15% of light to electricity). But since the source energy (wind or sunlight) is essentially free, the costs of that inefficiency are only truly reflected in the increased size of generating plants. Transmission infrastructure and backup systems needed to provide electricity when the sun and wind are unavailable (such as pumped storage or hydrogen backup) would introduce additional inefficiencies, but only around 80%. And, again, since the source energy is "free", making up for those inefficiencies will only require additional generation capacity, not blowing the top off every mountain in Appalachia.

Biomass (20,100T BTU per year)

The Department of Energy and Department of Agriculture released a document, Biomass as Feedstocks for a Bioenergy and Bioproducts Industry: The Technical Feasibility of a Billion-Ton Annual Supply, which promotes a goal of sustainably harvesting 1 billion tons of biomass annually by 2030. At a conversion rate of 15M BTU per ton, achieving this goal would provide around 20,100T BTU of energy per year, a significant increase over the 2,900T BTU produced in 2003. This number breaks down as:

• 6,400T BTU crop residues (428M tons)
• 5,700T BTU perennial crops (377M tons)
• 5,500T BTU forest biomass (368M tons)
• 2,000T BTU municipal waste (216M tons)
• 1,600T BTU animal manure (106M tons)
• 1,300T BTU grains (87M tons)

Biomass is officially defined as, "Any organic matter that is available on a renewable or recurring basis, including agricultural crops and trees, wood and wood residues, plants (including aquatic plants), grasses, animal manure, municipal residues, and other residue materials. Biomass is generally produced in a sustainable manner from water and carbon dioxide by photosynthesis."

Perhaps the biggest attraction of biomass is that it is the only renewable source of liquid transportation fuel that can be used with the current carbon-fuel-based transportation fleet, fuel distribution network and industrial infrastructure. While American transportation may ultimately be largely powered by batteries, hydrogen or some as-yet-undeveloped technology, in the near-term, carbon-based fuels are the quickest path to renewable transportation energy. Ethanol, which can be easily made from all types of biomass and which is already in common use, will almost certainly be the renewable transportation fuel of the near future.

The potential 20,100T BTU from biomass represents 88% of annual motor and aviation fuel usage in 2005 (22,803 BTU) and 20% of total energy used in 2004 (around 100,000T BTU). The use of biofuels for aviation presents special problems due to the extremes of operating temperatures. As such, hydrogen will probably be the fuel for jets in the late 21st century.

While the bulk of American petroleum consumption is for transportation fuel, about 1/8th of the oil consumed is used to make a wide variety of products, including plastics, lubricants, solvents and alcohols. Many of these petrochemical-derived products can be replaced with with renewable biomass-derived products.

A large scale biomass to fuel industry will also be very labor intensive, providing numerous new domestic jobs, including work in rural areas that have been hard hit by changing economic conditions over the past 30 years. Due to foreign competition, over 220 forest products plants closed between 1997 and 2005, resulting in the direct loss of 120,000 high-paying manufacturing jobs, not counting the loss of additional service jobs in the communities hit by the mill closings. Those jobs could be restored with conversion of those often outmoded plants from traditional pulp mills to biorefineries. It will be nice to keep our money at home, rather than spending it to prop up corrupt oil families and fund jihadists.

There are 2,263M acres in the United States (1,894 in the lower 48 states) that break down as follows:

• 588M acres grassland pasture (26%)
• 504M acres of timberland (22%)
• 453M acres cropland (20%)
• 294M acres urban/swamp/desert (13%)
• 181M acres public facilities (8%)
• 168M acres low productivity forest land (7%)
• 77M acres unusable forest land (parks, wilderness)

Of the 190M tons of biomass used to generate 2,900T BTU of energy in 2003, most were wood products and wood processing byproducts (i.e. pulping liquors) that were burned to supply energy for wood processing plants:

• 44M dry tons forest products wood residues
• 52M dry tons paper pulping liquors
• 35M dry tons urban residues (municipal waste)
• 18M dry tons biofuels
• 6M dry tons bioproducts

There are numerous technologies for harnessing energy in biomass or converting the biomass into other types of fuel. Most of these technologies can be used across the variety of biomass sources.

• Ethanol, or Ethyl Alcohol is currently produced from crops with high sugar content (such as corn or sugar cane) by fermentation that creates grain alcohol. However, these crops are very energy intensive to cultivate, harvest and process, thus largely negating their value as renewable fuel sources. They also are vital as our source of food and the amount of corn needed to fill a 25-gallon tank with ethanol once could feed a person for a whole year The current synergy of agribusiness interest, depressed midwestern economies and a search for quick energy fixes is promoting an artificial market for ethanol that does practically nothing to reduce our dependence on fossil fuels. There is a reason that corn farmers do not use ethanol to power their corn farm machinery.
• Biodiesel is created by the transesterification of animal fat or vegetable oils with wood alcohol and lye into fuel that can be directly burned in unmodified existing Diesel engines. However, the vegetable oils required for biodiesel have the same production limitations as corn for ethanol, thus reducing their potential for displacing significant amounts of petrochemical fuel. They also imply a dependency on crops that are sensitive to environmental conditions and vital for feeding the nation.
• Cellulosic Ethanol: While traditional ethanol production has only used small high-sugar portions of plants, ethanol can be created from the cellulose, hemicellulose and lignin that make up the bulk of plant materials. Enzymatic hydrolysis uses enzymes to break down cellulosic components into sugars that can then be fermented into ethanol or further processed into useful products. Companies currently built around enzymatic technology include Iogen and Celunol Corp.
• Butanol or butyl alcohol can be produced using the same biomass materials and similar processes that are used to produce traditional or cellulosic ethanol and recent production technology advances have made butanol cost-competitive with ethanol. Butanol is a superior to ethanol as a vehicle fuel in that it does not absorb water as readily, has more energy per gallon and can be used directly in existing gasoline engines with no modification. Environmental Energy has been developing processes to make butanol more efficiently and Dupont and BP are collaborating on a butanol project.
• Incineration: Although the focus has been on the transformation of biomass into other products, biomass can also be directly burned in existing coal-fired plants to generate electricity. Aside from being able to use existing infrastructure, replacing coal with biomass eliminates the additional CO2 added to the atmosphere from buried carbon, since the released carbon is ultimately recycled in future biomass. Biomass also does not contain the nasty heavy metals (like mercury) that make coal generation so dirty. Co-generation in existing fossil fuel plants is a particularly promising approach, as demonstrated by the Chariton Valley Biomass Project. Fibrowatt has opened a 55 MW plant in Benson, MN that burns turkey litter, although there have been significant concerns with toxins released by the plant.
• Anaerobic Digestion: Large-scale animal farms produce more manure than can be safely used in its untreated form as fertilizer. Anaerobic digestors use heat to deodorize and sterilize manure, while producing methane gas for generating electricity and separating high-phosphorous liquid fertilizer. Although the remaining plant residue is currently treated as waste, it has the potential for being used as an additional biofuel or even as a substitute for sawdust in building materials.
• Gassification: When biomass is heated with no oxygen or only about one-third the oxygen needed for efficient combustion it becomes syngas, a mixture of carbon monoxide and hydrogen. This gas can then be burned very efficiently or further processed into liquid transportation fuel. This Fischer / Tropsch process was used by the Germans in WWII and can also be used to convert solid coal into liquid fuel. Some studies estimate that the European Union could use biomass to produce 17.6 trillion cubic feet of biogas (around 18,000T BTU) and replace all gas imports from Russia.
• Pyrolysis is a heating process similar to gassification causes cellulosic material to decompose into an oil. Pyrolysis is being explored by Ensyn Corporation, Dynamotive and Biomass Technology Group (BTG).
• Direct Hydrothermal Liquefaction emulates the processes that made petroleum deep in the earth by subjecting organic materials and water to high heat and pressure, causing them to decompose into an oily liquid that can be further refined into useful products. Changing World Technologies has a plant in Carthage, MO that converts the offal from a neighboring turkey processing plant into fuel oil. Other companies developing this technology include EnerTech Environmental and BioFuel B.V.
• A Hybrid Hydrogen-Carbon Process proposed by Agrawal et.al would create hydrocarbon transportaton fuels by chemically combining hydrogen produced by electrolysis using wind, solar and nuclear with carbon from biomass and coal. This results in a greater potential amount of energy available than from individual sources alone and mitigates the considerable technical and economic impediments associated with having to convert the entire transportation fleet to use ethanol, hydrogen or battery power.

Agricultural Crops and Crop Residues

The USDA and DOE project that production and crop yields could be improved and increase available agricultural biomass to 425M - 600M tons (6,375T - 9,000T BTU). Around 75% of this substantial increase would be from crop residues with an additional amount from increased production of crops (like corn and soybeans) beyond what is needed for food. These projections are based on anticipated (but uncertain) improvements in horticultural technology.

Of the 1.2B dry tons of plant material produced annually on 453M acres of American agricultural land, around 194M dry tons (2,910T BTU) are currently available for available for bioenergy and other bioproducts with current crop yields and collection technology. This includes 113M tons of crop residues (mostly corn stover), 60M tons of of animal manure and 15M tons of grains (for ethanol).

While corn (ethanol) and soybeans (biodiesel) are dominant in current American scenarios, other crops are being cultivated for fuel in other parts of the world. Sugar Cane is now supplying a significant part of the energy needs of Brazil. The Chinese and Brazilians have made a strong commitment to cassava, a root vegetable that can be used for ethanol with the stalks burned to create heat for the production process.

Meaningful usage of agricultural products to create liquid fuel is dependent on a transition from traditional ethanol production techniques to cellulosic ethanol (or butanol) production because the energy required to produce a gallon of ethanol by traditional means is a significant proportion of the energy content of the resulting fuel. Also, there is simply not enough corn produced to satisfy a significant proportion of America's energy needs. Statistics from the National Corn Grower's Association show that even if ALL corn currently grown in the U.S. were used for ethanol production (ignoring our dependency on corn for food), the yield would only be 2,362T BTU, less than 2% of total U.S. energy usage and less than 10% of the energy used for transportation in 2005.

81.8M acres of corn planted in US in 2005
75.1M acres of corn harvested in US
11.1B bushels of corn produced
147.9 bushels per acre
$1.90 per bushel average price
1 bushel of corn can yield 2.8gal fuel ethanol
 
11.1B bushels of corn / year
x 2.8 gallons per bushel
x 76,000 BTU per gallon of Ethanol
----------------------
2,362T BTU / year if ALL U.S. corn production converted to ethanol

Another limitation of the use of traditional agricultural products for fuel production is the large amounts of water that are required for agriculture. Many parts of the country already face water rights and usage issues and the problem is likely to only get worse with climate change caused by global warming. This issue could be mitigated considerably by instead using perennial plants, as mentioned below.

Perennial Plants

The USDA and DOE estimate that a market for perennial crops could result in 40 to 60 million acres being converted to biofuel perennials. This does not include the potential use of other, less-productive lands currently classified as pastureland. At an average of 3 tons per acre of switchgrass and 15M BTU per ton, this would result in 2,700T BTU annually of new renewable energy from perennial grasses. More dense woody crops (such a hybrid poplar, willow, and sycamore trees) could be raised on 5 million acres with an annual average yield of 8 dry tons per acre or an additional 600T BTU annually from woody crops, yielding a total of 3,300T BTU annually from perennial grasses and woody crops by 2030.

Perennial plants which grow from year to year probably represent the most plentiful and environmentally sensitive biofuel feedstock. The advent of cellulosic ethanol technology opens up a whole new range of plants that grow quickly and do not require the energy-intensive cultivation or use of fertilizers, pesticides and herbicides typical of plants like corn and soybeans. Perennials can often be grown on marginal lands that are not capable of supporting high-yield food crops. This can also offer some hope for areas plagued by non-native invasive species like Kudzu and Purple Loosestrife, whose fecundity in the absence of native predators could be turned from a vice to a virtue.

Switchgrass (Panicum virgatum L.), a warm-season grass that was an important part of the original North American Tallgrass Prairie, has received great attention as a biomass energy crop because it yields well on marginal soils with moderate inputs and has favorable fuel characteristics in terms of energy content, ash content, and chemistry. Switchgrass and other C4 grasses also contain low amounts of silica, the major component of ash. Switchgrass' dense root system filters pesticides and herbicides protecting groundwater and also trapping nitrogen and nutrients that escape other plant root systems. Switchgrass is a tough plant, requiring minimal care once it has been established. Switchgrass is also an excellent habitat for wildlife.

The Chariton Valley Biomass Project in Southern Iowa is an ongoing project to demonstrate the feasibility of raising switchgrass for burning in a power plant that can use both switchgrass and coal. The project thus far has been successful and much of the data above comes from the research results of this project.

Forest Products

The USDA and DOE estimate that an additional 226M tons (4,500T BTU) of products could be harvested from the nations forests:

• 89M tons from improved logging practices and from an increase in production (and associated residues) needed to satisfy increased consumer demand for wood products
• 60M tons of "fuel treatment" biomass to prevent forest fires. Most of this is high-value wood that would be harvested for sale as conventional wood products.
• 41M tons of residues from traditional logging or clearing of timberlands.
• 20M tons of urban wood and construction/demolition activities
• 8M tons of unused forest products industry residues
• 8M tons of urban tree trimmings, packaging and discarded wood consumer products

The current American timberland inventory contains 20,000B dry tons of biomass (around 400,000T BTU). In 2001, around 142M tons (2,850T BTU, 16B cubic feet) of material was harvested from forests. That included residues and pulping liquors that were burned to create 2,000T BTU of energy, most of which went back into the timber processing applications from whence they came.

Unfortunately, a significant part of the potential increase in production would be associated with increased production of wood for sale, not for conversion to energy. Of the 4,500T BTU of new wood, 3,500T BTU would be added to the current 2,000T BTU of current forest products energy biomass, a relatively insignificant proportion of the 100,000T BTU of current American energy consumption. The Healthy Forests Initiative is more about providing the forest products industry with trees and less about any greater good to current or future society.

Algae

While no formal models have been proposed for the use of biodiesel derived from algae, the high yield factors could reasonably be assumed place its potential in a 10,000T to 20,000T BTU range similar to all other biofuels combined. Because of the highly hypothetical nature of this number and the immaturity of the technology, algae numbers are not included in the summary estimates given in this document.

Microalgae are microscopic photosynthetic organisms found in both ocean and freshwater environments. Microalgae are the most primitive form of plants. Of the different types of algae, Diatoms (Bacillariophyceae) and green algae (Chlorophyceae, a.k.a. swimming-pool algae) are of special interest because they consume carbon dioxide and water and use light to produce oils and starches. Those oils and starches can be harvested quite efficiently to create biodiesel and ethanol. In fact, because algae are such simple organisms and because they live in close contact with water, they are capable of producing 30 times the oil per area of land as earth-bound oil crops like soybeans and canola.

Before the Gingrich-run congress shut down the Department of Energy's Aquatic Species Program in 1996, a considerable amount of research had been done on growing algae for biodiesel. Projections were that 200,000 hectares of algae ponds (an area 28 x 28 miles square) could produce 1,000T of fuel. Therefore, an algae farm on 11 million acres of flooded desert (a square 133 x 133 miles in size) could produce the equivalent of the 22,803 BTU of motor and aviation fuel used by America in 2005. However, there are more reasonable approaches than destroying a tenth of the Sonora Desert:

• Algae farms can easily be distributed around the country. The algae ponds could also be used to recycle farm runoff, agricultural waste and civic sewage input as a nutrient stream into high-nitrogen fertilizer that could then be sent back to the farm.
• A company in New Zealand, Aquaflow Bionomic, is successfully working with a sewage treatment plant in Marlborough to use "wild" algae with excess pond discharge, ultimately hoping to produce a million liters of fuel by April and improving discharge water purity at the same time.
• Here in America, GreenFuel Technologies is using algae enclosed in plastic tubes to trap carbon dioxide, nitrous oxides and other pollutants from coal-fired plant exhaust and convert them with sunlight into solids that can then be fed back into the plant as fuel.
• The oil-drilling firm PetroSun recently announced the formation of an Algae BioFuels subsidiary to perform algae R&D in Arizona and Australia.
• Marine algae blooms, which are caused by agricultural and sewage runoff, are becoming an increasingly severe problem for ocean life. However, it would be possible to harvest that algae relatively economically and convert it to ethanol, thus solving multiple problems at once.
• LanzaTech has developed a process using nongenetically-modified bacteria isolated from natural environments for producing ethanol from carbon monoxide via small-scale fermentation. Carbon monoxide is the byproduct of a number of industrial processes (including steel manufacture) and this technology could provide energy while also solving an environmental issue for manufacturers.

While further behind in development than other biomass technologies, thanks to the "small-government" policies of '90s Republicans, algae has the potential to be a significant contributor to the energy needs of 21st century America.

Wind (15,000T BTU / year)

Wing is the fastest-growing and highest-profile source of renewable energy. At the end of 2004, the U.S. had 6,740MW of wind generation with at least 5,000MW scheduled to come on line by 2010. Although there are some issues with wildlife and aesthetics, wind generation is environmentally-benign and technologically-straightforward. There are significant limitations on the number of areas where the wind blows strongly and consistently enough to make utility-scale power generation practical - most in the west and Midwest, few in the deep south.

Estimates by the National Wind Technology Center from 1993 indicate the potential average power from areas at wind class 4 could be 500,000MW, yielding 15,000T BTU per year. With efficient storage technology for when the wind is not blowing, this would be adequate to replace the 13,383T BTU (4,054,688,000 MWH) generated by American utilities in 2005. A 2006 study by the University of Delaware estimates that Mid-Atlantic states (nine states from Massachusetts to North Carolina) have 330,000 MW potential wind generating capacity, which could yield 3,000T BTU per year (900,000,000 MWH), or enough to satisfy the electrical needs of those nine states (185,000 MW) with room for 50% growth.

In looking at the power ratings of wind power plants, one must consider the major drawback that wind does not blow 100% of the time at full strength. Power plants have a wattage rating that reflects their peak capacity. However, electricity usage fluctuates and all power plants must have downtime for maintenance and repairs. The difference between peak potential and actual generation in practice is measured as a percentage called a "Capacity Factor". A reliable coal-fired generation plant can have a capacity factor of 70%, although unlike wind, coal-fired generators can be more easily taken on- and off-line as needed. Wind turbines typically operate with a capacity factor of 30-35%.

For example, at the end of 2004 there were wind farms with a total capacity of 6,740MW. However, with a capacity factor of 30%, average capacity was really 2,022MW. Multiplying that by 8,766 hours per year (365.242375 days per vernal equinox year) and converting to BTU, that gives 60.5T BTU per year currently available from wind generation - a drop in the 100,000T BTU bucket.

However, using the 500,000MW average figure from the National Wind Technology Center (which already takes capacity factor into account), we get a potential annual 15,000T BTU that would be equivalent to total 2004 electrical generation. This also does not count additional generation from small home turbines in areas that are not available for or amenable to commercial wind generation.

A 1991 report by the Pacific Northwest Laboratory, "An Assessment of the Available Windy Land Area and Wind Energy Potential in the Contiguous United States" (PNL-7789) listed the top 20 potential wind energy state in billions of kWh per year:

• North Dakota - 1,210B kWh per year
• Texas - 1,190B
• Kansas - 1,070B
• South Dakota - 1,030B
• Montana - 1,020B
• Nebraska - 868B
• Wyoming - 747B
• Oklahoma - 725B
• Minnesota - 657B
• Iowa - 551B
• Colorado - 481B
• New Mexico - 435B
• Idaho - 73B
• Michigan - 65B
• New York - 62B
• Illinois - 61B
• California - 59B
• Wisconsin - 58B
• Maine - 56B
• Missouri - 52B

Adding these figures, converting to BTU and then reducing by the 30% capacity factor gives a number in line with the aforementioned estimate from the National Wind Technology center:

Dealing with the low capacity factors of wind plants is not an issue now since existing coal and natural gas-fired plants have the capacity to take up the slack when wind power is unavailable. However, as wind becomes a larger percentage of American power generation, facilities will have to be developed like the peaking plants currently used to deal with peaks of demand during the summer months. As part of a diverse mix of generation resources, the British system includes artificial Pumped Storage water reservoirs at Dinorwig and Ffestiniog that are filled at time of low demand and serve as hydroelectric peaking plants during periods of high demand (or low wind power). The St. Mary's Canal Project is an American pumped storage facility proposed to be integrated with wind generation in Montana. Proposals have also included the use of Wind-generated electricity to electrolyze water into hydrogen that can be stored in the wind turbine tower and used to generate electricity whether or not the wind is blowing.

The simplicity and cleanliness of wind generation also makes it amenable to small-scale wind generation systems that allow consumers to significantly reduce their use of electricity from the utility grid. A typical residential home system will still be connected to the electrical utility and will draw from the grid when the wind turbine is not generating enough power. In fact, if the turbine is generating more power than the home needs, the Public Utility Regulatory Policies Act of 1978 allows homeowners to sell unused electricity to the utility, thus causing your power meter to run backwards and reducing your utility bill. Conventional small wind turbine towers are generally around 30 feet tall and require at least an acre of land, making them inappropriate for small suburban lots. They also often require building permits and (for the good of community relations) approval by the neighbors.

The ubiquity of wind is inspiring numerous different approaches to harnessing wind power, some that hearken back to older technologies:

• Aerovironment, among numerous other research projects, is working on low-profile wind turbines that can be integrated into the structure of large buildings to supply a portion of a company's electrical needs.
• The Bahrain World Trade Center incorporates a group of 29 meter wind turbines integrated into the building design that will provide 10-15% of the complex's energy needs.
• SkySails is working on large kites that can augment the propulsion of large cargo ships with up to 6,800 HP of towing power (under optimal conditions) While not eliminating the need for traditional power plants or relegating ocean travel to the old, unreliable days of sailing ships, projections are that annual fuel costs for a ship can be lowered by 10% to 35%.
• Sky WindPower is exploring the potential for large tethered flying wind farms that could harness energy from high altitude currents which are stronger and more constant than ground winds. A major technical hurdle is developing control actuators that are durable enough to operate for longer periods of time in autonomous flight than have ever been experienced by transportation craft.
• While most wind generation systems use horizontal axis turbines that look like large airplane propellers, WindStor and PacWind are among the companies that are reviving older Vertical Axis Wind Turbine, a simpler, low-maintenance technology that can be used in small-scale and portable applications.

Municipal Waste (2,000T BTU / year)

The EPA reported that in 2003, Americans generated 236M tons of municipal waste, of which 72M tons (30%) were recycled and the rest was burned or placed in landfills. The largest portion, 83M tons (35%), was paper or paperboard, with plastics, fabrics and woods coming in at 62M tons (26%). In total, around 216M tons of organic material (including recycling) theoretically represents 2,160T BTU energy (at 10M BTU/ton), or around 2% of total 2004 U.S. energy consumption.

Municipal waste is a much more complex product than other forms of biomass and presents a difficult set of issues. The core of the problem is that municipal waste is mixture of a wide variety of items, making it difficult to recycle or convert to energy. Although it has the potential to be a significant energy and materials resource, the current state of technology causes it to be a disposal nuisance and environmental horror.

Incineration has been used for decades, but even with stunning improvements in technology, the toxins that are emitted from smokestacks and / or left in residual ash present a serious environmental issue. The list of pollutants is long, but perhaps the most insidious are dioxins, which come from burning chlorinated plastics, linger in the environment surrounding a plant and can cause a number of hideous health problems. The technology required to scrub plant emissions is extremely complex and expensive, further limiting the attractiveness of waste incineration for electricity generation. And even where pollutants can be removed from gas emissions, the pollutants are left in the ash, which has a concentrated toxicity greater than the garbage that entered the plant. (Global Alliance for Incinerator Alternatives)

Even where the environmental issues can be addressed, political issues make it extremely difficult to build new incineration plants. The most sensible place to put an incinerator is near the source of the garbage in urban areas. But few things motivate civic involvement like rumors of a garbage incinerator going up in the neighborhood.

One promising alternative under exploration is the use of the same Direct Hydrothermal Liquefaction process used with biomass. Changing World Technologies has a pilot plant in the Philadelphia Naval Yard that is processing garbage with heat and pressure in a process that mimics the forces that created petroleum deep in the earth over the centuries. The process separates the minerals, leaving an oil that can be further refined for energy or as a feedstock for products normally created with petroleum.

Another waste destruction technology involves the use of plasma (extremely high temperature gas) to break waste down into its elemental components. A project in St. Lucie County Florida run by GeoPlasma will process new garbage as well as existing garbage in landfills into syngas, which will be burned to create electricity, and an inert, obsidian-like material that can be used as aggregate for construction and pavers. Plasco Energy is also working with plasma arc technology. Although the process is touted as a closed-loop, emission-free process, there is a question about whether this can be guaranteed on a large scale with diverse inputs, especially chlorinated plastics.

The twin needs for waste disposal and energy generation could make small-scale waste-to-energy systems attractive in remote situations (such as some military application). Purdue University is working on a "portable biorefinery" that converts organic waste into ethanol and low-grade methane gas that are burned in a flex-fuel diesel engine that powers an electrical generator.

In a world of diminishing resources, municipal waste represents potential value, although a minimal one in terms of energy. The limitations of current technology mean the best solutions to the issues surrounding municipal waste are probably low-tech: separation by consumers, reduction of waste production levels and composting or recycling useful waste products.

Hydroelectric (3,000T BTU per year)

Often forgotten in the discussion of renewable energy is the most mature and widely available source of renewable energy - hydroelectric. However, because most of the limited number of areas with high hydropower potential have already been exploited, hydropower can only be expected to provide its current 2,500T to 3,000T BTU per year for the foreseeable future. An additional 800T BTU may be available by using underwater turbines to harnass the energy of free-flowing rivers (30,000 MW) and industrial flows/canals (10,000 MW). The National Hydropower Association identifies potential total growth potential of 90,000 MW, more than doubling 2007 capacity of 80,000 MW, using small-scale plants and new technology like run-of-the-river plants that divert but do not completely block river flow.

The harnessing of hydropower dates to antiquity with water-driven mills used by the Greeks. The first American hydrogenerating facility was built in 1882 in Appleton, WI. 25% of the world's electricity is currently generated with hydroelectric power. There are around 850 large dams in the United States with hydroelectric capability, providing a hydropower capacity of 95,000MW. In 2004, hydropower accounted for 2,725T BTU (almost 3% of U.S. energy consumption).

While there is no official figure for theoretical American hydropower potential, a Army Corps of Engineers study in 1979 indicated that if all possible sites were fully exploited, the U.S. could have as much as 512,000 MW of hydroelectric capacity providing 15,300T BTU per year of electricity. However, most of the high-capacity hydroelectric sites in the United States have already been developed and community opposition on environmental and aesthetic grounds to further hydroelectric development means that there is little potential for significant growth in industrial-scale American hydroelectric power. There is some potential for growth in small hydroelectric sites, including a number of facilities abandoned in the 1950s and 1960s when the price of coal and oil was low.

Geothermal Energy (2,500T BTU per year)

The U.S. Geological Survey (USGS) Circular 790 identified around 23,000MW of known resources and a potential of up to 127,000MW of undiscovered resources. Since geothermal electricity plants can be operated on a fairly continuous basis (90% capacity factor), this represents a potential of 500T - 2,700T BTU per year.

Geothermal energy is heat that flows from the earth's interior. Estimated total geothermal energy emitted by the earth is 42M megawatts or 1,256,536T BTU per year (12 times current annual American energy usage). This is a practically inexhaustible resource, since the interior of the Earth is expected to remain extremely hot for billions of years to come.

The problem with geothermal energy is that there are a limited number of geographic locations where there is enough of this heat concentrated close enough to the surface where it can be accessed and exploited with a practical amount of effort. Most American geothermal sites are located in the West: California, Nevada, Arizona, Idaho, Utah, New Mexico, Alaska, Nevada, Hawaii. While these numbers make geothermal a relatively limited resource in terms of total American usage, as with tidal/wave energy, exploitation of these resources makes sense locally in the areas where the resources exist.

The Geothermal Energy Association website contains a significant amount of information on geothermal technology and potential sites.

Wave and Tidal Energy

If all continental American wave energy could be captured at 100% efficiency, that would represent 7,000T BTU, which is around half of 2005 electrical energy generation or around 7% of total domestic energy consumption. It is questionable whether those estimates are politically practical or attainable with existing or developmental wave energy technology, but wave energy could be useful in certain locations and as part of a diverse portfolio of resources. Energy in Hawaii is already expensive to import and harnessing even a small portion of the 1,000T BTU of wave energy striking its shores annually would satisfy a significant amount of the state's energy needs. Because of the immaturity of wave and tidal energy capture technology, wave/tidal is not included above in the model for replacing America's 100,000T BTU total energy usage.

Ocean waves are small disturbances in the ocean surface caused by the force of blowing wind. Since the source of wind power is heat from the sun, wave power is essentially indirect solar power. Tides are variations in sea level caused primarily by the gravitational pull of the moon, with additional help from the sun and the rotation of the earth. Therefore, tidal power is essentially indirect lunar power.

Research into wave and tidal energy is ongoing and a 2005 report from the Energy Policy Research Institute (EPRI Global WP 009 - US Rev 1, Jan. 14, 2005) estimated the total amount of power in waves striking the U.S. West coast at 1,501T BTU and the East Coast at 409T BTU, for a total of around 2,000T BTU. The U.S. total wave energy including Alaska and Hawaii is estimated at 2,100T watt-hours per year or 7,165T BTU per year. A World Energy Council report provides a similar estimate of 2,300T watt-hours (7,849T BTU).

There are a number of variations on floating buoys that convert wave motion into continuous kinetic energy that can be used to generate electricity. These devices are in advanced stages of development and the initial stages of deployment.

Energy from the oceans can also be extracted by capturing energy in the water motion caused by tides. Until recently, the primary means of capturing tidal energy was by building a dam across the mouth of a tidal basin that allowed the rising tide to enter the basin and then using the outflow from the basin of the sinking tide to drive a hydroelectric turbine. Although this principal had been used in Europe as far back as 900 AD, the first modern plant was a 240MW plant that came on line in St. Malo, France in 1965. Aside from the detrimental effects of the dams on wildlife and navigation, there are a limited number of tidal basins with wide ranging tides where construction of dams are practical.

More recent approaches involve the creation of artificial offshore lagoons and low-velocity turbines that capture river or sea currents caused by tidal changes. Six test turbines are currently located underneath New York's East River with the potential that an expanded configuration could produce 26M kWh per year (0.089T BTU).

Fusion

Fusion power is energy generated by nuclear fusion reactions when two light atomic nuclei are fused together to form a heavier nucleus and release energy. Fusion is the energy that fuels the sun and the major current human use of uncontrolled fusion is in nuclear weapons. Controlled fusion experiments are just now reaching a break-even point where the amount of energy released is greater than the considerable amounts of energy needed to cause fusion to occur.

Fusion has the potential to create staggering amounts of energy with a very small amount of fuel. Einstein's famous E = mc² equation states that energy equals mass times the speed of light squared. In unit-specific terms:

joules = kilograms * (299,792,458 meters/second)².

Using a conversion factor of 1 BTU = 1,055 joules with 2004 U.S. energy usage of 100,000T BTU, squaring the speed of light, doing a little algebra to solve for mass and converting to pounds:

105,500,000,000,000,000,000 = mass x 89,875,517,873,681,800

mass = 1,173.85 kg = 2,587.89 lbs

This means that a tank of deuterium (an isotope of hydrogen currently used for fusion) containing slightly more than half the mass of a 4,587lb Lincoln Navigator could theoretically satisfy all of America's current annual energy consumption.

However, the technology is young and each advance uncovers more problems that need to be solved. As such, all proposed fusion power plant designs are wildly hypothetical and, therefore, fusion power cannot be figured into near- or medium-term energy plans. Fusion also presents potential problems with the creation of radioactive waste tritium and irradiated structural materials. While nuclear fusion could be the power that sends mankind to the stars, for now it remains only a long-term prospect.

Energy Storage

Solar and wind power are intermittent energy sources and require some form of storage in order to satisfy continuous human needs. Vehicles also require some form of energy storage (fuel) that is portable, efficient and reasonably sized. Numerous media and technologies exist in various stages of development.

Hydrogen

Despite often being mentioned in conjunction with renewable energy, hydrogen is a storage medium, not an energy source in itself. Energy is required to produce hydrogen, which can then be burned or fed into a fuel cell which releases the captured energy. Hydrogen can be easily produced from carbon-based fuels or by passing electricity through water (electrolysis) to release hydrogen and oxygen. Since almost all hydrogen exists bonded to other elements (like oxygen in water), it cannot be looked on as a fuel source that can be harvested.

Hydrogen is the simplest and most common element in the universe. In its simplicity hydrogen has the highest energy content by weight of any fuel at 52,000 BTU per pound. However in its pure, gaseous state, hydrogen also takes up a great deal of space relative to its weight: 0.000089 grams per ml vs 0.00128 grams per ml of air.

Given it's low density, hydrogen presents formidable storage issues. Storing compressed hydrogen requires large, heavy tanks that are strong enough to hold gas at very high pressure. Cooling hydrogen to a liquid (as was done in the Apollo space program) reduces it to a manageable size, but but cryogenic storage is too dangerous and complex for widespread consumer adoption. Different kinds of chemical hydride technology are limited by capacity or difficulty regenerating chemicals for reuse.

For example, a 5,000 PSI tank that can hold around 2,730 BTU (0.8 kWh) per liter of size. Since a gallon of gasoline (approximately 4 liters) contains 115,000 BTU, a hydrogen tank equivalent to a 20 gallon gasoline tank (2,300,000 BTU) would need to hold around 843 liters of hydrogen (210 gallons) and would occupy a cube about a yard on each side, not counting the bulk of the heavy walls or mounting structure.

For now, perhaps the best storage medium for hydrogen is simply renewable carbon-based fuels.

Fuel Cells

Fuel Cells are often spoken of in tandem with hydrogen since they can be used to combine hydrogen and oxygen in the presence of a catalyst to efficiently (80%) produce electricity, water and some heat. Fuel cells can be be used directly with hydrogen or with a reformer that extracts hydrogen from carbon-based fuels like methanol, yielding significant improvements in efficiency over internal combustion engines. Fuel cells currently use platinum catalysts that make them too expensive for widespread use. There are also limitations to current hydrogen storage technology that were described above. Hopes are that currently active research will lead to cheaper fuel cells that can be part of a transition to extensive use of hydrogen fuel.

Pumped Storage

Pumped storage uses large artificial lakes that are filled using excess power and drained through hydroelectric generators. Pumped storage is currently used with conventional fossil-fuel plants to permit the fossil-fuel plants to be run at full capacity and high efficiency, even when power demand is low. Pumped storage can also be used in conjunction with wind and solar to provide power at night or when the wind is not blowing.

While efficient and very practical for some situations, pumped storage facilities are quite expensive to build and maintain, require access to large quantities of water, and are impractical in arid climates or flat terrain.

Batteries

Batteries are a mature and improving technology whose primary disadvantage are price and some modest limitations in range. The Tesla Roadster uses a 1,000-pound collection of 6,831 small lithium-ion batteries (i.e. laptop batteries), has a range of 250 miles on a single charge and goes from 0 to 60 in four seconds. While gasoline engines only use around 30% of the energy in gasoline, batteries return around 80% of the energy used to charge them (not considering significant inefficiencies in coal-fired electrical power plants), giving the Tesla Roadster an equivalent energy efficiency to a 130 MPG gasoline-powered car. Unfortunately, it lists for $80,000, placing it a boutique car category with the Porsche 911 Carrera S.

Compressed Air

Compressed air can be used to store energy in tanks that can directly drive a piston or turbine engine. Tanks can be recharged quickly at charging stations or with home air compressors, possibly even using rooftop photoelectric energy to drive the compressors. The technology scales well and can be used for larger vehicles.

General compression is has implemented dispatchable wind turbines that compress air rather than generate electricity. Ordinary wind turbines have an upper limit of wind speed they can handle without damaging their electrical generators. Turbines that incorporate compressor pumps have no such limitation, which allows them to more fully utilize the energy available in high wind areas. The compressed air can also be very efficiently stored in tanks, permitting consistent power generation even when the wind is not blowing. The amount of reserve capability is limited only by the size of the tanks and underground structures like abandoned mines can be utilized for high-capacity storage.

Flywheels

Flywheels store kinetic energy in rapidly spinning metal or carbon composite disks balanced on magnetic bearings. Flywheel powered gyrobuses were used in Switzerland in the 1950s, although they were not commercially successful in an era of cheap gasoline. Flywheel systems are commercially available as stationary uninterruptible power supplies. Flywheels are extremely efficient storage devices (typically 90%) and can be charged and discharged quickly.

Cold Storage

Refrigerated warehouses (cold storage) are used for storing food and are large energy consumers. Since the temperature differential with the outside represents a form of energy storage, cold storage could potentially be used as a grid buffer with intermittent wind or solar power. At times when generation exceeds demand, the warehouses could be cooled up to the minimum temperature. When demand rises, the warehouse cooling system is turned down or off, alleviating drain on the grid and freeing energy for other uses as the warehouse temperature slowly rises to the upper maximum. A pilot project was initiated in the Netherlands in 2007.

Ultracapacitors

Capacitors are devices commonly used in electrical equipment for storing small amounts of energy as electrical fields. Ultracapacitors are are extremely high capacity capacitors that can be effectively used as batteries. The the primary distinction is that batteries use various chemical reactions to store electricity, creating limitations in charge time and useful lifetime. While ultracapacitors have been around since the 1960s, the technology is only now becoming available to build them with useful levels of capacity in a cost-effective manner. MIT's Laboratory for Electromagnetic and Electronic Systems is developing technology using vertically aligned, single-wall carbon nanotubes EEStore, a Texas-based company, claims to have developed an ultracapacitor technology that could charge in five minutes and provide enough energy to drive a medium-sized automobile 500 miles at only a modest premium in cost above conventional gasoline engines, although the lack of released details make the validity of this claim uncertain.

Conservation

While conservation cannot eliminate demand for energy or the need to develop renewable energy technology and infrastructure, conservation with existing technology and techniques could reduce American energy consumption by as much as 25,000T BTU annually (25% of current usage), easing the path to a renewable energy future.

Smaller Cars

If everyone switched to 36 MPG Honda Civics or Mini Coopers that could cut energy consumption by around a third and save around 6,200T BTU annually. Individually, switching from a 15MPG Lincoln Navigator to a 36 MPG Corolla cuts your automotive energy consumption in half. This does not count the differential in the amount of energy needed to manufacture a 2,500lb Corolla vs. a 4,587lb Navigator. Since passenger cars and light trucks constitute 17% of total energy use, improvements in passenger car efficiency would have a significant overall impact.

In 2003, there were 135,669,897 registered passenger cars that traveled a total of 1,660,828,000,000 miles. That travel required 74,590,137,000 gallons of fuel (almost all gasoline), resulting in an average fuel economy of 22.3 miles per gallon. Light passenger vehicles (cars, light trucks, motorcycles) used 16,268T BTU.

A significant amount of driving, notably commuting, involves solo drivers and such drivers could save considerable amounts of energy by switching to extremely small cars:

• Venture One has plans to produce a three-wheeled two-passenger hybrid based on the Carver that can get up to 100mpg. The vehicle incorporates a hydraulic mechanism for tilting when going around curves for added stability. It is also very cool looking and, supposedly, a blast to drive.
• Smart has plans to produce an extremely small two-passenger car (9'x5'x5') that gets aroung 40mpg. Their extremely small size makes them ideal for crowded urban areas and Smarts have been a presence at the NY Marathon for a number of years.
• Zap will be offering a collection of three-wheel electrics and micro-sports cars.

Diesel Engines

Diesel engines are more efficient than traditional spark-ignition gasoline engines. America produced around 19,319T BTU of gasoline for passenger and commercial vehicles. Transitioning all of those vehicles to Diesel (with no change in mileage or vehicle size) would reduce fuel needs to 12,751T BTU, giving a 6,568T BTU annual energy savings using Diesel engines instead of gasoline engines. Reductions in vehicle sizes would, of course, increase this value even more.

Thermal efficiency is the efficiency of an engine in converting the energy available in fuel to useful work rather than waste heat. Even the best traditional automotive gasoline engines have a thermal efficiency of 30 to 33%, and then only at full throttle. Diesel engines, by contrast typically have thermal efficiencies over 50%, meaning they get more power from the same amount of fuel.

This improvement is somewhat distinct from the observation that Diesel-powered vehicles have higher MPG ratings. The amount of energy in petroleum-based fuels is actually relatively consistent across different products BY WEIGHT. The difference is that Diesel fuel is more dense. One gallon of Diesel has more energy than one gallon of gasoline, meaning that a car burning Diesel will get more miles per gallon of Diesel than a comparable car burning regular gasoline. This also explains why conventional gasoline engines using ethanol or ethanol blends get a lower MPG - because ethanol is less dense than gasoline and a gallon of ethanol contains less energy than a gallon of gasoline.

Diesel-powered passenger cars currently make up only 3% of sales in America (vs 50% in Europe) and have a poor reputation for noise and dirty exhaust. However, engine technology has improved considerably in recent years, to the point where they can now meet California's stringent emissions standards. The engines are still more expensive (and heavy), although the fuel cost savings can more than compensate for the additional expense.

Electric Vehicle Engines

Transition from inefficient spark-ignition engines for cars and light trucks to electric cars using energy stored in high efficiency Lithium Ion batteries could save 9,500T BTU annually in transportation energy, not including manufacturing energy saved building these simpler and lighter vehicles.

Spark-ignition engines are even more inefficient than coal-fired steam-cycle plants, achieving only 30% efficiency at optimal conditions. Use of grid electricity to charge Lithium-ion batteries (80% efficient) for electric cars and light trucks save a large chunk of the 11,000T BTU wasted of 16,244T BTU annually used by those vehicles, not to mention the improved quality of life resulting from removal of their pollution from the air we breathe.

However, this savings can only be realized after a significant amount of our electricity is generated from wind or solar. Using electricity from current coal-fired plants simply transfers the inefficiency from the gasoline engine to the power plant. Coal-fired plants only operate at around 33% efficiency, which is essentially equivalent to current gasoline-engine efficiency, not including power lost in transmission or battery charging. Even the 46% efficiency of natural-gas combined-cycle power plants is below the 50% and greater efficiency of modern Diesel engines.

A 26 MPG Toyota RAV4 uses 4,423 BTU per mile. A comparable vehicle powered with batteries or fuel cells uses only 887 BTU per mile or the equivalent of around 130 MPG. The main issues are limitations in range, high cost and mysterious political and business forces opposed to their adoption.

The major issue with electric vehicles is energy storage. There are numerous technological options (none of them perfect) for efficient energy storage that could be viable with additional development and infrastructure investment. Storage technology is discussed above.

Hybrid vehicles are basically conventional gasoline-powered cars with an electric drive motor and limited battery storage capability. Hybrids only have an efficiency advantage in urban stop-and-go traffic. In highway driving their performance is not much better than non-hybrid gasoline vehicles. At their core, hybrid vehicles are just expensive, slightly more efficient gasoline vehicles that serve only as a transitional technology toward all-electric transportation and make little actual, practical difference in themselves.

Replace Trucks with Trains and Barges

Heavy trucks use around 18% (7,000T BTU) of the total 28,635T BTU used for transportation. If 50% of that was replaced by class 1 or short-line rail, we could save 2,800T BTU annually, not counting the ancillary benefits of reduced road congestion and improved air quality. While current traffic patterns, rail infrastructure limitations and business-logistics practices make that target of dubious practicality, it does point out the amount of additional energy wasted by the 20th century move from rail to