Home | About | Contact | Store


AIPG Position Statement - Domestic Energy: Other Resources

AIPG Position Statement - Domestic Energy:
Other Resources
(October 2009)

Authors:  Art Becker, CPG-09001, Gary Edmondo, CPG-11089, Rich Greiner, CPG-08681, Don Harris, CPG-10819, James Howard, CPG-02536, Keith Long, MEM-0795, Joel Renner, Michael Root, CPG-06386, and Claudia Stone, CPG-06048

Biofuels, biomass, hydroelectric, solar, geothermal, and wind make up the largest renewable energy resource group in the world.  These resources are renewable and sustainable, so a statement of current reserves is generally hard to estimate, with limiting factors such as water, land and the materials required to build a facility often more important than the resource.  Additionally, aside from biomass and biofuels, these energy resources do not produce a carbon footprint, except during construction.

Of the US energy consumption in 2007, 6.3% came from renewable sources, with the following distribution:  hydroelectric (38.5%), biomass (33.8%), biofuels (15.9%), geothermal (5.5%), wind (5.0%), and solar (1.3%).  This represents an 11% growth in the use of renewable resources since 2003.

Table 1
US Energy Consumption by Source

Energy Source
Quadrillion Btu




% Growth 2003-2007

Fossil Fuels










Natural Gas













































Total US





Sources: Non-renewable energy: Energy Information Administration (EIA), Monthly Energy Review (MER) March 2008,  DOE/EIA-0035 (2008/03) (Washington,DC, March 2008,)  Tables 1.3, 1.4a and 1.4b. Renewable Energy: Table 2 of this report.

Table 1A
The Role of Renewable Energy Consumption in the Nation's Energy Supply, 2007

An exploding pie showing the total percentage of renewable energy consumption in the Nation’s energy supply.


Table 1B
US Consumption of Hydrocarbons as a Energy Source
US Consumption of Hydrocarbons as an Energy Source

Historically, renewable resources have been used for electric generation (hydroelectric, biomass, geothermal, wind, and solar), heat generation (solar, biomass, and geothermal), and fuel (biofuels).  However, they generally constitute only a small percentage of overall energy generation because of costs compared to traditional sources (coal and petroleum), technology availability, and reliability (Table 2).  Additional research and development is paramount to making these more cost effective in the future.  At present the national average cost of electricity is $0.121/kWh.  Key problems facing alternative energy are:  intermittency, specialty metal requirements, water consumption, land use, and distribution.

Table 2
Cost to Produce


Cost/Gallon to Produce

Federal Subsidy

US Yearly Production Capacity

US Capacity under Construction

Plant Construction Costs










12.4 G gallons

2.1 G gallons





2.24 G gallons

1.23 G gallons





















Cost/KWH to Consumer

Federal Subsidy



Plant Construction Costs































Costs to produce are operating costs only, and do not include capital.  Capital costs are estimated from recent startups (2003 to 2008) in the US.

Existing Resources

Hydroelectric generation remains the largest source of renewable energy in the US (2007).  However, overall contribution to the energy grid is declining because no new facilities have been built since the 1980s, and US electricity consumption continues to rise.  At present there are 2,378 hydroelectric plants online in the US, down from 3,100 in 1940.  Only 3% of the dams in place within the US currently have hydroelectric capability.  The National Hydropower Association estimates that an additional 4,300 MW of capacity could be brought online from existing facilities.  Additionally, the Idaho National Laboratory states that of the approximately 300,000 MWa of US natural stream energy resources, only about 10% has been developed.  From this 300,000 MWa, about 30% is located in areas where development is unlikely, and the remaining 60% has not been developed as an energy source.  Hydroelectric power in the US, including both small and large scale projects, is largely untapped because of the environmental and social stigma associated with this resource.  INL also states that of the 60% of untapped resource, approximately 100,000 MWa could be feasibly developed using low power and small hydroelectric projects.  Large projects have been under taken in China and Africa in the past 10 years.  However, social and environmental stigma associated with these projects prohibit development in the US.  Production costs are low, since most of the capital is required for dam building.  Some development of turbines in fresh water streams (Hudson and Mississippi) is currently underway in the US.  However, this is largely an untested and untapped resource in the US.

Biomass electrical and heat generation is the second largest source of renewable energy in the US.  This requires combustion of organic material for generation of heat and/or electricity, which produces many of the same emissions as fossil fuels.  The contribution to US energy use via biomass rose slightly from 2003 to 2007, but has not experienced the rapid growth of other renewable energy sources as a result of carbon dioxide generation and product requirements.  In the US, biomass energy is generally produced either from combustion of municipal waste (trash) or trees/saw mill waste.  Some research shows promise for use of grasses and other fast growing organics.  Environmental concerns have prevented biomass energy generated via timber harvest in the US from being a larger more economical source.  At present, this resource is largely untapped in the US.

Biofuels, specifically biodiesel and ethanol, is currently the third largest source of renewable energy in the US.  This energy source requires conversion of recently harvested biological materials into a usable fuel source.  These two sources are popular alternatives to traditional petroleum-based fuels, but production costs are generally much higher.  There is no reduction of carbon dioxide with these fuel uses, but there is a reduction of foreign oil dependence.  Federal subsidies have been required to make this a profitable venture.  Increased production capacity (4x since 2003) has resulted in increased corn and soybean prices, which translates to increased production costs and increased food costs.  At present the US goal is to double biofuel production by 2022, but rising costs and availability of agricultural land may limit growth. Water use (3-7 gallons/gallon of fuel produced) and available agricultural land are two major concerns identified with biofuels.  Land use and competition with food crops is the most serious issue facing future development of biofuels.  Use of nonrenewable resources such as stainless steel, fertilizer, and other products is also important.  Biodiesel also cannot be used in the bulk of the US passenger car and small trucks, which rely on unleaded gasoline.  Additionally, both biomass and biofuels face problems with distribution to a larger market, away from source materials.

Geothermal energy is the fourth largest source of renewable energy in the US, but along with biomass has not seen the significant growth of other alternative sources.  At present the US is the world leader in online capacity, however, only six western states (AK, CA, HW, ID, NV, and UT) currently have geothermal power.  There is also a small experimental plant operating in Wyoming at this time.  Geothermal power relies on heat energy stored in the earth, with the deeper the source point, the greater the energy potential.  At present there are two types of geothermal energy, low and high temperature.  Low temperature resources are generally used for local heating and cooling of space through heat pumps or direct heating by circulating the geothermal fluid through heat exchangers.  High temperature is generally from deeper sources, and uses the geothermal fluid to produce electricity, usually via steam turbines.  Geothermal power is capital intensive (5-7 times a fossil fuel system), but has a low operation and maintenance costs.  It is estimated that $800 million to $1 billion in capital expenditures will be required to increase US geothermal use from 3 to 10%.  Estimated geothermal resources are 130,000 times current development in the US.  Traditional geothermal resources have been estimated to be as large as 150,000 MWe with an additional 100,000 MWe from heat co-produced from oil and gas operations and from geopressured-geothermal in the Gulf Coast.  Experts have estimated that more than 60,000 MWt of energy are available for direct use and greater than 120,000 MWt can be saved by using geothermal heat pumps.  Beyond these conventional resources, are so called Enhanced Geothermal Resources, or resources without adequate fluid for traditional recovery methods.  A Massachusetts Institute of Technology led group estimated that 100,000 MWe of base-load electrical generation could be on line in the United States by 2050 with a reasonable investment in R&D.  For comparison, 150,000 MWe  with 40% efficiency will supply electricity to approximately 44,500,000 homes a year.  The use of hydrocarbon fluids and bromine based heavy liquid in geothermal plants as a fluid agent to spin the turbines is an additional requirement. 

Wind generated energy is the fifth largest source of renewable energy in the US.  This source has experienced almost 200% growth over the last five years. Capital costs for a large wind farm have been steadily declining from $2,500/kw in the early 1980s to the current range of $900 to $1,200/kW, but this still represent approximately 70% of the total investment over the life of the plant. Intermittency is the biggest issue regarding wind energy.  Wind generated energy is dependent upon wind conditions, which behave erratically by nature.  Support of a wind based system, with other energy generation sources is required to keep a stable electrical grid.  Storage studies have been under taken, but the associated batteries require metals production not currently available in the US (lithium, nickel).  Resources are unlimited, but capacities are generally in the 20-35% range, compared to conventional sources (95%), as a result of the unpredictable nature of the energy generation source.  Use of nonrenewable resources such as steel, copper, and petroleum based products is important to consider.  Land use and visual impacts have also been important for the wind farm industry.

Solar generated energy is the lowest source of renewable energy currently in mass use in the US.  Growth has been steady over the last five years, but solar has not experienced the exponential growth seen in other sectors.  Energy generation growth in 2008 was approximately 9%, as solar panel capacity increased 78% from 2007.  However, no new plants came on line during 2008.  At present, large plants are 30% efficient, and construction costs are similar to traditional coal or gas plants.  Current plants are in the 30-100 MW generation capacity, and require $200-400 million in capital.  Lead time for materials manufacturing and construction is also long, with a concentrated solar power (CSP) plant taking 6 years and a photovoltaic facility requiring 4 years to complete.  Upfront capital costs are high, as are electrical generation costs (20-50 cents/ kWh), which makes it difficult for solar generated energy to compete with other renewable sources.  However, costs have been in steady decline as a result of increased efficiency, technology improvements, and economy of scale.  Intermittency, as with wind, is one of the biggest issues facing solar energy.  Use of specialty metals and other nonrenewable resources, and land use are important concerns.  All exotic metals required are currently mined abroad, not in the US.  Water use, and other heavy liquids, used in CSP plants are an important concern, as most areas of high solar activity are also low in available water.  Tax benefits, incentives, cash rebates, and net metering help make solar installations more economically attractive to homeowners.

Developing Resources

There are other sources of renewable energy that are currently under investigation in the US.  These range from algae based biofuels to tidal generated power.  At present these sources are generally higher cost then traditional sources and are in the early development stages. 

Tidal energy contains significant potential, as all coastal areas experience two high and low tides over a 24-hour period.  However, to be effective, tide differences must be at least > 16 feet.  Nearly 40 sites on Earth have fluctuations this large, including Hawaii, the Atlantic Northeast, and the Pacific Northwest.  There is no current capacity in the US.

Ocean energy, which uses wave energy and turbines, also contains potential for isolated island regions, such as Hawaii, Guam, Canaries, Azores, South Pacific, where other sources of energy are limited.  As with tidal energy, this is in the development stage and is 10-15 years from full production.

Biodiesel production from algae is also being evaluated.  Limited production is underway in Florida and the southwestern US.  Research into commercial production is a very early stage, with cost generally significantly higher than traditional biodiesel sources from corn.

Table 3

Air Pollution Production from Use

Alternative Energy

Sulfur dioxide  per kWh (lbs)

Nitrogen oxide per kWh (lbs)

Co2 per kWh (lbs)

Toxic metals

Wind Farm





















Similar to Coal Plants



















Natural Gas





Sources:  California energy commission, Wind Energy comes of Age, Paul Gipe, 1995, American Wind energy association, EIA Annual Energy Review, 1998.  Some geothermal systems contain toxic metals within the steam or fluid, these may plate out on operating components of the geothermal plant.


Avery, W. H. and Wu, C., 1994, Renewable Energy From The Ocean - A Guide To OTEC, Oxford University Press, 1994. Covers the OTEC work done at the Johns Hopkins Applied Physics Laboratory from 1970–1985 in conjunction with the Department of Energy and other firms.

Cornett, A., A Global Wave Energy Resource Assessment, Canadian Hydraulics Centre, National Research Council, Ottawa, Ontario, Canada  ISOPE 2008-579

Cruz J.; Gunnar M., Barstow S., Mollison D. (2008), Joao Cruz, ed., Green Energy and Technology, Ocean Wave Energy, Springer Science+Business Media, pp. 93

Cruz, Joao (2008), Ocean Wave Energy - Current Status and Future Prospects, Springer

Eidman, Vernon R., 2007, Ethanol economics of dry mill plants, in Hauser, Robert J., ed., Corn-based ethanol in Illinois and the U.S.:  Department of Agricultural and Consumer Economics, University of Illinois, p. 22-36.

Energy Information Administration, March 1998, Monthly Energy Review,  Official Energy Statistics from the US Government.

Energy Information Administration, March 2008, Monthly Energy Review,  Official Energy Statistics from the US Government.

Engelhaupt, Erika, 2008, Growing energy on unused agricultural land:  Environmental Science and Technology, v. 42, no. 15, p. 5,380.

Engineering Committee on Oceanic Resources — Working Group on Wave Energy Conversion (2003), John Brooke, ed., Wave Energy Conversion, Elsevier, pp. 7

Gipe, Paul, Wind Energy Comes of Age, Wiley Publishing.

Goldemberg, Jose, and Guardabassi, Patricia, 2009, Are biofuels a feasible option?  Energy Policy, v. 37, p. 10-14.

Good, Darrel L., Hauser, Robert J., and Schnitkey, Gary D., 2007, Ethanol economics at the Sector level, in Hauser, Robert J., ed., Corn-based ethanol in Illinois and the U.S.:  Department of Agricultural and Consumer Economics, University of Illinois, p. 7-21.

Green, B. and Nix, R.G., November 2006, Geothermal – The Energy Under our Feet, Geothermal Resource Estimates for the United States.  National Renewable Energy Laboratory, Technical Report NREL/TP-840-40665

Henniges, O., and Zeddies, J., 2007, Biofuels; experiences and perspectives in industrialized and developing countries: Quarterly Journal of International Agriculture, v. 46, no. 4, p. 349-371.

Hill, Rachelle, and Younos, Tamim, 2008, The intertwined tale of energy and water: Virginia Water Resources Center [www.vwrrc.vt.edu/watercooler_apr08.html]

Huo, Hong, Wang, Michael, Bloyd, Cary, and Putsche, Vicky, 2009, Life-cycle assessment of energy use and greenhouse gas emissions of soybean-derived biodiesel and renewable fuels:  Environmental Science and Technology, v. 43, pp. 750-756.

Johnson, J.J., 2006, Technology assessment of biomass ethanol; a multiobjective life-cycle approach under uncertainty:  Cambridge, Massachusetts Institute of Technology, PhD dissertation.

Kim, Hyungtae, Kim, Seugndo, and Dale, Bruce E., 2009, Biofuels, land use change, and greenhouse gas emissions, some unexplored variables:  Environmental Science and Technology, v. 43, p. 961-967.

Low, Sarah A., and Isserman, Andrew M., 2007, Ethanol and the local economy, in Hauser, Robert J., ed., Corn-based ethanol in Illinois and the U.S.:  Department of Agricultural and Consumer Economics, University of Illinois, p. 63-96.

Massachusetts Institute of Technology, 2006, “The Future of Geothermal Energy” p. 29, 30
NGWA National Ground Waters Association, 2006, “Energy Woes Create Unprecedented Opportunity”

McCormick, Michael (2007), Ocean Wave Energy Conversion, Dover, ISBN 0486462455 , 256 pp.

Oak Ridge National Laboratory, September 2006, Biomass Energy Data Book, Department of Energy,   Report No. ORNL/TM-2006/571

Ocean Thermal Energy-OT International Energy Agency, 2006. Review and analysis of ocean energy systems development and supporting policies.

Perrin, Richard K., Fretes, Nickolas F., and Sesmero, Juan Pablo, 2009, Efficiency in Midwest US corn ethanol plants; a plant survey: Energy Policy, v. 37, p. 1,309-1,316.
Petrou, Evangelos C., and Pappis, Costas P., 2009, Biofuels, a survey on pros and cons: Energy and Fuels, v. 23, p. 1,055-1,066.
Sims, E.H , 2008, Hydropower, Geothermal and Ocean Energy, Massey University, New Zealand, International Energy Agency, France

Solar Energy Research Institute, November 1989, Ocean Thermal Energy Conversion: An Overview. SERI/SP-220-3024. Golden, CO: Solar Energy Research Institute; 36 pp.

Takahashi, P., Trenka, A., 1996, Ocean Thermal Energy Conversion, Publishers: John Wiley & Sons, 1996

Thorpe, T., 2008, "An Overview of Wave Energy Technologies: Status, Performance and Costs" (PDF). wave-energy.net. http://www.wave-energy.net/Library/An%20Overview%20of%20Wave%20Energy.pdf. Retrieved on 2008-10-13.

Tomson, Bill, 2006, Most of idled farm land in U.S. to remain fallow:  Wall Street Journal, November 20, 2006, p. C4.

J.W. Tester, B.J. Anderson, A.S. Batchelor, D.B. Blackwell, Ronald DiPippo, E.L. Drake, J. Garnish, B. Livesay, M.C. Moore, K. Nichols, S. Petty, M.N. Toksöz, and R.W. Veatch, Jr., The Future of Geothermal Energy, Idaho National Laboratory External Report INL/EXT-06-11746, Idaho Falls, ID (2006) 396

Twidell, John; Weir, Anthony D.; Weir, Tony (2006), Renewable Energy

Wakeley, Heather L., Hendrickson, Chris T., Griffin, W. Michael, and Matthews, H. Scott, 2009, Economic and environmental transportation effects of large-scale ethanol production and distribution in the United States:  Environmental Science and Technology, v. 43
Westcott, Paul C., 2007, Ethanol expansion in the United States; How will the agricultural sector adjust?  US Department of Agriculture, Economic Research Service Report FDS-07D-01, 18 p.

General Website References

  1. The Marine Power Project Welcome Page – www.esru.strath.ac.uk
  2. National Renewable Energy Laboratory, US Department of Energy – www.nrel.gov
  3. University of Strathclyde, Tidal Power, www.esru.strath.ac.uk
  4. Ocean Thermal Energy Association – www.ieaoceans.org
  5. www.qa.water.usgs.gov
  6. www.zebu.uoregon.edu
  7. www.enviroliteracy.org
  8. www.biomass.org
  9. www.eren.doe.gov
  10. www.nrel.gov
  11. www.ott.doe.gov
  12. www.eia.doe.gov
The American Institute of Professional Geologists (AIPG) was founded in 1963 to certify the credentials
of practicing geologists and to advocate on behalf of the profession.

AIPG represents the professional interests of all practicing geoscientists in every discipline.
It's advocacy & efforts are focused on the promotion of the role of geology and geologists in society.