Renewable Energy


The promise of renewable energy has remained a major area of controversy. Advocates claim that feasible, widespread use of renewables plus proper conservation policies can satisfy US (or World) energy requirements in the near future. The only barrier is said to be that the energy establishment and governments are not trying hard enough to develop the cheap, non-polluting, and enormous power sources that are out there, waiting to be tapped.

However, skeptics of the broad utility of renewables point to their still minuscule contribution to US energy sources (apart from hydropower, which has been present for decades, is not expanding and is variable from year to year). Renewables today contribute little more in absolute energy supplies in the US than on the first Earth Day (and less, as a fraction of total energy consumption). The primarily causes for variation are the effects of long-term droughts and silting on hydropower, which is the largest renewable energy source (and by far the largest renewable source of electricity) in America1. However, this is only one aspect of the matter. Some renewable sources, such as biomass, are beginning to make significant contributions to energy supplies in several developed nations, including the US; photovoltaic cells are economically viable in some circumstances even today, and wind power, while still a tiny fraction of the energy mix, is rapidly expanding in the United States and in several European countries2.

One question is whether the rapid expansion of these sources over the past decade puts us early on the rising slope of the "S" curve, implying more rapid growth in the future, or whether we are approaching a plateau, with the absolute value of renewable energy production not likely to increase greatly for many decades still. Table II.3.1 shows the recent contributions of renewable energy to the energy mix in the United States.

Table II.3.1: U.S. Energy Consumption by Energy Source, 1990-1994 in quads/y, 1015 BTU/y.
Source: Renewable Energy Annual 1995, Energy Information Administration, p. 9, Table H1
Energy Source (quads/y) 1990 1991 1992 1993 1994

Renewable Energy
  Hydroelectric Power 3.113 3.196 2.871 3.156 3.037
  Geothermal Energy 0.327 0.331 0.349 0.362 0.357
  Biomass 2.632 2.642 2.788 2.784 2.852
  Solar Energy 0.067 0.068 0.068 0.069 0.069
  Wind Energy 0.024 0.027 0.030 0.031 0.036

Total Renewable Energy 6.163 6.265 6.106 6.403 6.350

As usual, the truth lies somewhere between the extreme views sketched above. The question is, just where? A look at current basic technical and economic facts provides a good starting point to answer this question for photovoltaics, wind, solar thermal electricity, and biomass-produced electricity. Because of the ease with which electricity may be transported and converted to other energy forms, because of the great advantages that non-or low-polluting renewable electricity sources would bestow, and because of electricity's potential to contribute significantly more than it does today to the major sector of transportation, this chapter is confined to electricity production by the four renewable technologies listed above.

Of course other sources are of some importance. Geothermal energy is a quasi-renewable source that has been exploited for many years in the US, although at a relatively low level. Geothermal sources are not inexhaustible if too much energy per unit time (power) is removed from too small an area, or if the dry steam in place is removed without adequate replacement (as is happening in the Geyserville, CA geothermal field).

Both solar thermal and biomass also have obvious energy uses in producing heat and for some industrial and residential processes (such as cooking). The latter is a major source of energy in less developed countries, and the former is used in countries in all stages of economic development. Biomass also has clear applications in the transportation sector through ethanol and methanol production.

There is little disagreement that if renewable sources of energy were to prove technically practical and economically feasible in the quantities needed, they would be greatly preferable to current methods of energy production.

  • First, by definition, the supply would be renewable, allowing indefinite or, at least, extremely long-term, use in most cases (hydropower excepted).
  • Second, pollution would be greatly reduced, usually limited to the pollution released in manufacturing and building (and recycling and reclaiming) the equipment needed to produce electricity (e.g., smelting aluminum reflectors, producing wind vanes, producing storage batteries). Carbon dioxide would not be added to the atmosphere, reducing greenhouse concerns. There would, however, be some pollution from biomass sources, (Table II.3.2).3 In addition, there would still be issues of land use and waste disposal.
  • Third, renewables could provide energy self-sufficiency (or, at least, greatly reduced energy dependency) for the US, which may become increasingly important from the national security perspective.

    Table II.3.2. Estimated Emissions from Electric Power Generation in tons/GWatt-hour. Source: Renewable Energy Annual 1995, Energy Information Administration, p. xiii, Table FE1. (SO2 = sulfer dioxide, NOx = nitrogen oxides, PM10 = particulate matter with diameter less than 10 microns, CO2 = carbon dioxide, VOCs = volatile oganic compounds)

    Fuel (tons/GWatt-h) SO2 NOx PM10 CO2 VOCs

    Eastern Coal 1.74 2.90 0.10 1,000 0.06
    Western Coal 0.81 2.20 0.06 1,039 0.09
    Gas 0.003 0.57 0.02 640 0.05
    Biomass 0.06 1.25 0.11 0 0.61
    Oil 0.51 0.63 0.02 840 0.03
    Wind 0 0 0 0 0
    Geothermal 0 0 0 0 0
    Hydro 0 0 0 0 0
    Solar 0 0 0 0 0
    Nuclear 0 0 0 0 0


    The Department of Energy reports that system costs have been reduced by a large fraction since 1982 and that the market is growing by 20% per year. The levelized costs of photovoltaics (presumably with batteries or other storage) are estimated at between $0.25 and $0.50 per kWh, relative to about $0.05-0.15 per kWh for conventional large-scale electric sources in the US today. This technology is cost effective today for small consumers over 1/4 mile from an electric grid, although still much too high for broad market penetration.

    On average, some 200 watts/square meter of sunlight reach the US, although the distribution is, of course, quite uneven. This level provides a natural limit on the energy production per area of land for all solar collection systems. Photovoltaic (PV) systems have made major progress over the last 10-15 years, with efficiencies reaching over 10%. But these fundamental limitations pose large area and, therefore, material requirements on widespread, large scale use of this technology. Nevertheless, in principle, 0.3% of the land in the US could supply all of its electricity.

    In 1987, 22 MW (peak) of PV modules were produced worldwide; in 1989, this number reached 40 MW; in 1993, production reached 60 MW and, in 1996, about 100 MW is anticipated4 . In 1988, about 12 MW (peak) capacity of PV modules were produced in the US -- 0.002% of the total supply, neglecting the actual efficiency of insolation. By 1993, this number had grown to about 20 MW, of which 40% was for domestic use. A total of 78 MW (peak) has been shipped for use in the US since 1982, resulting in an estimated production of 0.002 quads in 1994. Clearly there is moderate growth in demand and capacity, although since national demand for electricity is roughly four orders of magnitude greater than the PV contribution, these numbers by no means indicate an imminent market takeover.

    According to the DoE, the global production of PV modules is now 48% single-crystal silicon, 30% polycrystalline silicon, and 20% amorphous silicon. The latter category has been a long-term hope for cheaper modules, but amorphous silicon PV units been plagued by shorter lifetimes. On a hopeful note, a major gas company, Enron Corporation of Houston, is seriously examining building a 100 MW PV plant in the planned Solar Enterprise Zone in Nevada, on the Nuclear Test Site. They hope to achieve coats of 5.5 cents/kWh (bus bar cost) with non-concentrating thin-film technology5 . Present conventional electric costs range in the US from 3 to 15 cents per kWh.

    The problems facing larger scale market penetration are principally cost and the need for backup storage systems. The latter add to cost and complicate matters for individuals who might otherwise contemplate purchase of PV technology for residential use6 . Government and industry sources anticipate further cost reductions in the future, to be achieved by improved manufacturing technologies and, possibly, from the development of more efficient and cheaper photoelectric cells.

    Solar Thermal Electric

    Although not widely heralded or as exciting to the media as PV technology, the use of solar thermal energy is far more advanced and has a much longer successful history. Solar thermal water heaters, patented by Clarence Kemp in the United States in 1891, have been commercially available for over one hundred years. Rooftop solar water heaters and solar collectors for space heating have become increasingly common in the U.S. and in some cases, have become standard practice overseas (e.g., in Israel). However, more recently, the idea of using solar heat to produce electricity at a central facility has progressed to reality in a number of locations, the best known example being the private sector effort of Luz International in Southern California. Total US energy production using solar thermal technology is estimated at 0.069 quads for 1994 (less than 10% was electric).

    The technology is relatively simple, relying on solar collectors/reflectors to heat a fluid from which energy is extracted. The fluid may be water, in which case steam may be used to drive a turbine, or a molten salt (having the advantage of being able to store the energy), which is then used to drive a heat engine. Luz built nine plants, with support and technical assistance and advice from the US Department of Energy, totaling 354 megawatts in generating capacity in the Mojave Desert between 1985 and 1991. At that time, the firm went bankrupt while constructing its tenth plant. It had succeeded, however, in reducing construction and operating costs considerably, to $3011 per installed kilowatt (quite competitive with many conventional electric generating plants) and 8 cents per kWh (a 50% reduction over 6 years). Luz's bankruptcy was attributed by Department of Energy sources to several factors, including a prospective loss of tax credits, higher property tax liabilities relative to gas-fired electric generating plants, overextending its own resources, and competition from unexpectedly low gas prices. The plants continue to produce electricity, operated by a utility consortium7

    A small high-technology addition to U.S. solar thermal capacity was inaugurated in spring 1996 in the Mojave Desert. Solar Two, sponsored by the Department of Energy and private utilities, uses molten salt to boil water to drive a 10 MW steam turbine8 The molten salt has a time constant of several hours, permitting some storage capacity. In addition, on a much larger scale, there are proposals for constructing up to 841 megawatts of solar thermal electric capacity in the Solar Enterprise Zone in Nevada.


    This source of electricity has been most developed in California over the past two decades, notably at Altamont, but European nations, particularly Denmark, are beginning to develop wind resources as well. This is the only renewable source (aside from hydropower) whose cost is competitive with conventional power production. In 1990, the costs of some newer systems were reportedly as low as $0.05/kWh, a decrease of 84% in one decade (DoE). There are 1700 MW installed in California and an additional 1000 MW in Europe. About 3.4 billion kWh (about 0.035 quads) are produced per year in California, which is 1.2% of the electricity demand in that state. Capacity factor in California is thus only about 22%, due to the fact that wind is not always present at the right velocities with sufficient steadiness. Total wind generation of electricity in the United States has grown from 0.024 quads to 0.036 quads from 1990 to 1994. This 50% increase over five years may indicate that wind energy may contribute significantly in the future to energy supplies.

    The range of useful wind velocities may be extended by improved turbine design, thus adding to effective capacity. Turbines (at least, those of lower cost) experience problems at low temperatures, especially in the presence of snow or ice. This hampers their development in some attractive, windy areas, such as the Dakotas (North Dakota alone could theoretically produce over a third of current electric demand in the US). Turbine lifetimes are estimated at 10 to 20 years. The DoE estimates that the US could produce some 20% of its electricity demand from wind power at those locations with average annual wind speeds of 16 mph or more. The area required would be 18,000 square miles (0.3% of the area of the lower 48 states), most of which, however, could still be used for farming or ranching. Less than 5% of this area would need to be devoted to roads and other infrastructure.


    Biomass includes such primitive energy sources as the use of wood-burning for heating and cooking to sophisticated plans (and some functioning plants) that gasify plant material for burning to produce electricity. It also includes the production of ethanol and methanol for fuel to be used by internal combustion engines for transportation. In 1994, about 2.85 quads of energy were produced by biomass in the U.S., amounting to 45% of renewable energy consumption. Wood-based biomass accounted for 2.266 quads (almost 80% of biomass energy). Over 60% of this energy was derived from "black liquor," a wood waste product of pulp and paper mills, which is often used to provide energy for the mills themselves. In addition, the burning of waste and garbage added about 0.5 quads of energy, with most of the balance of biomass sources arising from the use of ethanol as a transportation fuel (0.1 quad).

    Electricity capacity based on biomass reached 11,000 megawatts in 19949 compared with 200 megawatts in the early 1980s. Waste burning facilities have been increased in capacity, but several were stalled or shut off because of pollution concerns (as the Hempstead plant in Long Island, New York, where PCV's among the waste material became an issue).

    In principle, energy crops could be grown to provide fuel for biomass electric plants. For example, grass or willow or poplar trees could be grown for this purpose on some of the millions of acres set aside for cropland recovery under the Conservation Reserve Program. The technology to produce electricity is not an issue, but the economics will be determinant. Another issue will be the minimization of polluting emissions from such plants.

    The first plant of a new wave of biomass power was a 50 megawatt plant built in Burlington, VT in 1994. Several hundred megawatts of capacity were built in California under a ten-year plan started in 1985, under which guaranteed prices for the generated electricity were contracted for by utility purchasers. However, after ten years, the plants were not advantageous economically and 500 megawatts of capacity were retired after the guarantee ran out. Currently, such plants produce electricity at between 4-7 cents per kilowatt hour, which is not competitive with coal-fired plants at the margin. A federal tax credit, instituted in 1992, of 1.5 cents/kWh for "closed-loop" biomass electricity, in which biomass crops are grown, burned for electricity, and renewed by the operator, might assist in the future, although there are no current plants operating in this mode. Improvements in technology could, in principle, increase the economic viability of this option.


    In several areas, the outlook for renewable energy may be bright. Renewable sources currently supply about 7.2% of domestic US consumption of energy, somewhat less than the 7.7% from nuclear power, for comparison. Over 12% of electricity is produced by renewable sources. Outlook for significant growth in hydroelectricity or geothermal electricity does not seem great, but the use of biomass, solar electricity, and wind show promise for increased use. Currently, only wind seems to be in a stage of rapid growth, primarily because it is economically the most competitive in a number of locations across the country. There are plans for increased use of PV and solar thermal electricity, particularly in plans for the Solar Enterprise Zone in Nevada, which is partially federally-supported.

    In general, the Energy Information Administration reports that the future of renewable energy is uncertain10. Most potentially viable renewable energy technologies are not yet economically competitive and would require favorable tax treatment as well as federal and state support to develop. It can be argued that such tax incentives would be wise policy both to reduce pollution and to develop energy sources, which will be needed in the future. It is argued by many supporters that the renewable approach would be highly competitive if external costs (e.g., pollution, health and environmental effects, costs related to national security) were properly considered in setting energy prices. However, the Federal Energy Regulatory Commission ruled in early 1995 that states may not regulate energy utility prices in this fashion, so this major possibility of support for renewable energy production has currently been lost. One option for promoting renewable energy in the marketplace would be for governments at all levels to purchase preferentially energy from renewable sources. It remains to be seen whether technological improvements, future constraints in conventional energy supplies, or public demand for governmental intervention will permit renewable energy to achieve the major market penetrations that had once been envisioned by many enthusiastic supporters. Clearly, there are many areas in which further research and development would bring results. Recent trends in federal R&D funding for renewable energy research are discussed in section IV.1 of this report.


    1. Energy Information Administration, US Department of Energy, Renewable Energy Annual 1995. (Washington, DC: US Department of Energy, 1995); D. Bodansky, "Overview of the Energy Problem," [The Energy Sourcebook, eds. R. Howes and A. Fainberg (New York: American Institute of Physics, 1991)] shows that US hydroelectric power consumption in the first half of the 1970s ranged from 2.65 - 3.31 quads. In 1994 renewables provided 3.04 quads. The other significant renewable source is biomass, which provided about 2.85 quads in 1994, and 2.9 quads in 1984. Data for biomass in the 1970s is uncertain, but was probably about the same. Biomass is mostly accounted for by wood waste and pulp to produce energy for paper mills and, to a lesser degree, by home heating. Geothermal sources account for less than 0.4 quads. Consumption of hydroelectric energy varies significantly (by 10-20 % from year to year) due to varying precipitation patterns.
    2. Renewable Energy Annual 1995, op. cit. footnote 1, pp. 4-5, 9-12, 85, 103, 105-106, and Energy Fact Sheets, US Renewable Energy Laboratory, US Department of Energy, October 1994. See also the DoE Website:
    3. An exception would be biomass which, although providing no net increase in carbon dioxide to the atmosphere, would produce air pollutants during the combustion process. The details of the magnitudes of this source of renewable pollution would depend heavily on the type of biomass burned and the means used to do so. [See Table II.3.2]. Some biomass forms (notably wood and wood products) produce nitrate compounds and more volatile organic compounds and particulates than most coal and than all oil (per unit energy output). See Renewable Energy Annual 1995, footnote 1, p. xiii.
    4. Energy Fact Sheets, US Renewable Energy Laboratory, ibid. The information in this and the following sections is largely derived from this source and from the Renewable Energy Annual 1995, op. cit., footnote 1
    5. Renewable Energy Annual 1995, op. cit., footnote 1, p. 106.
    6. The energy storage problem is mitigated somewhat by the fact that both solar power and electrical demand peak during the daytime.
    7. Renewable Energy Annual 1995, op. cit., footnote 1, p. 102
    8. Science, Feb. 23, 1996, p. 1061
    9. Renewable Energy Annual 1995, op. cit. footnote 1, Table 5, p. 15.
    10. Renewable Energy Annual 1995, op. cit. footnote 1, p. xxxii