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The National Renewable Energy Laboratory (NREL) is one of ten federally funded national laboratories. NREL has offered to provide answers to technical questions from Home Power readers about renewable energy.

Question: What is the efficiency of conventional power plants?

Answer: The question is rarely asked about conventional power plants. The answers may be surprising. Usually, people ask about the conversion efficiencies of renewable energy sources. For comparison, flat-plate PV system energy efficiencies (sunlight to ac electricity) are 10%-12%, and have potential for improvements. Concentrator PV systems can potentially reach up to 30% efficiency. Solar thermal central receiver systems are projected at around 25% efficiency. And, wind energy systems can average around 25% efficiency.

Energy efficiency is defined as either work out or energy out, divided by energy in. There are many ways to define those terms, depending on the application or purpose. Typically, the energy efficiency is calculated for a very specific system. Calculating the efficiency for a class of power plants, as in this article, becomes dangerous. Average efficiencies have an inherent error, because every power plant and utility is unique.

I define the energy out as the ac power supplied to a home or other end user. The energy in is more difficult to define, as it varies with the fuel and generating technology mix. Usually the energy content of the fuel can be directly measured or calculated. However, for a conventional power plant, it takes energy to get the fuel to the plant and to transmit the power over power lines. The energy of mining or extracting the fuel and delivering the electricity to a home should also be included in the energy in term for the efficiency calculation, as should mining reclamation and the mitigation of negative environmental effects.

As an example, the following is an estimate of the energy efficiency of a coal-fired power system. First, the coal is mined, either surface or underground, transported within the mine, crushed, washed, and then transported to the power plant. Additionally, there is reclamation, or an attempt to return the mine to a natural state. All of these steps involve energy, and there are material losses. The energy efficiency of all those steps is estimated at 91%-93%. This efficiency is calculated from the energy content of the delivered coal divided by the sum of the energy content of the mined coal and the energy required for mining, crushing, washing, transportion, and reclamation.

For most power plants that use combustion of a fuel, the energy efficiency varies from 30%-40%. This efficiency is calculated from the electrical output of the power plant divided by the energy content of the fuel. The efficiency varies considerably depending on the energy content of the fuel; the type and age of the combustion furnace; the combustion, boiler, and cooling temperatures; and any extra energy required for emission controls, such as scrubbers.

The transmission and distribution system includes everything between the power plant and the home or end user, such as high-voltage transmission lines, substations, and transformers. The exact losses depend on variables such as distance, voltage used, type and age of the wire, and temperature. The average transmission and distribution system efficiencies vary from 87%-92%.

A complete coal power system can have an energy efficiency ranging from 24% to 34%, by multiplying the energy efficiencies of the fuel extraction (91%-93%), power plant (30%-40%), and the transmission and distribution (87%-92%). The dominant factor in the complete system energy efficiency is the power plant efficiency, which is representative of any combustion type power plant.

Now for the disclaimers: The efficiencies used are averages of estimates. Also, the energies required for waste disposal, such as fly ash from coal, are not included in these analyses. The energy losses from choosing one alternative over another, such as when surface mining of coal replaces the energy content in the grazing land, are not included. Land reclamation is not 100% efficient, and the loss of energy productivity from unrecoverable land is not included in these analyses. Because energy costs have increased since 1975, energy efficiency and productivity have become more important and some of the efficiencies may have improved. However, the energy efficiencies quoted in this article are representative of current power plants and electric utility transmission and distribution systems.

General conclusions that we can draw are 1) that the conventional combustion-type power systems have better efficiencies than current flat-plate PV systems: and 2) that concentrator PV systems, high temperature solar thermal electric systems, and wind energy systems may have comparable efficiencies. Given the uncertainties and known omissions from the above energy efficiency calculations, the conventional power plant system efficiencies are most likely the best case. When the omissions are included, the energy efficiencies will be lower.

Energy efficiency is important, but should never be used as the only criterion. The basic human energy cycle of sunlight, plant growth, eating, and physical work is estimated at 0.25% efficiency. Yet, very few people advocate eliminating the human population. Home owners, companies, and governments also use economics (pollution, societal, and investors costs), energy security (fuel interruptions, transmission, reliability, and long-term sustainability), environmental concerns, and sometimes, personal preferences when making a decision. Its never an easy decision.

Access

Energy Alternatives:A Comparative Analysis, published by The Science and Public Policy Program, University of Oklahoma, Norman, Oklahoma, May 1975.

Author: Byron Stafford, National Renewable Energy Laboratory

Send your technical renewable energy questions to: NREL, c/o Home Power, PO Box 520, Ashland, OR 97520 • 916-475-3179 voice/FAX . Email via HPBBS 707-822-8640 or Internet Email to [email protected] iÉi

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Of the People

Don Loweburg and Bob-O Schultze

©1995 Don Loweburg and Bob-O Schultze

With the Republican take-over of the House of Representatives and the Senate, there will be a wholesale change in committee leadership. Out go the Dems and in come the Reps. There are some legitimate concerns about how the changes will effect the nation's energy policy.

According to a report issued by SEIA, the most important changes, in terms of energy, will come from the House Energy and Commerce, House Science, Space, and Technology, and Senate Energy And Natural Resources Committees. Whether the House committees remain intact, get shuffled into a different incarnation, or get axed entirely is anybody's guess. The Senate E&NR Committee will be chaired by Senator Frank Murkowski (R-Alaska). Sen. Murkowski has supported some RE projects in the past, but is sure to try opening Alaska's National Wildlife Refuge for oil drilling. Also in limbo is the E&NR Subcommittee on Renewable Energy And Energy Efficiency. If it survives at all, the likely Chair will be Sen. Don Nickles (R-Oklahoma) That's Oklahoma with an "O" — as in OIL. Get the picture?

By the People

A survey of 1,000 randomly selected voters was conducted during December, 1994 for the Sustainable Energy Budget Coalition. When asked, "If the government is to continue funding research and development for specific energy sources, which source do you think should be highest priority?" — 42% choose RE sources like solar, wind, geothermal, biofuels, and hydroelectric, 22% chose energy efficiency and conservation, 15% chose natural gas, 9% nuclear, 7% fossil fuels (oil and coal) and 6% had no choice.

Judging by this poll, the American voters would choose RE over over oil and coal by a 6 to 1 margin. Will our legislators heed the message and govern "For the

People" or ? Time will tell, but it couldn't hurt to remind your representative that she/he was looking for a job when they found this one.

Good News for Californians

Legislation may be introduced in the California State Legislature to mandate net metering. Although Southern California Edison has for some time selectively used this policy, a state-wide mandate for all utilities is welcome news. The legislation will focus specifically on small producers, under 50 kw, allowing net periodic metering to parity. Excess production will be purchased by the utility at avoided cost. The new law is targeted at residential customers producing their own electricity with wind, solar or hydropower resources. We will keep you posted on the details, as they happen.

IPP, DRA (Division of Ratepayer Advocates of the California Public Utilities Commission), UCAN and TURN (ratepayer advocate groups representing both Southern and Northern California) have adopted a joint position opposing utility ownership of customer sited PV and other forms of distributed generation. We believe that the competitive potential of photovoltaics is best realized by commercializing customer-sited photovoltaics as a competitive alternative to utility generation." A copy of the full statement is available on request.

The Home Power Movement?

I get uncomfortable with sociological studies in general but thought this one interesting. IPP member Peter Smith dug this up while doing an online text search. Two studies (1989-1990) by J.S. Tatum, titled "The Home Power Movement and the Assumptions of Energy" and "Policy Analysis and The Home Power Movement: Technology, Behavior, and the Environment" detail some of the following findings:

"Participants in the home power movement have come to be among the most efficient and technically sophisticated of residential energy users, not only adopting but contributing to the development and marketing of super-efficient refrigerators, well pumps, and other residential appliances." "The apparent success of the movement and the effectiveness of the motives involved suggest that more attention should be given to PV-based home power systems as a means for dealing with energy and environmental problems than would otherwise be justified by a simple comparison of costs per kilowatt hour." "As a part of this movement, both the adoption of radical energy efficiency measures and the choice of electricity supply systems more than twice as expensive as traditional sources go well beyond traditional models of consumer behavior. These characteristics of the movement suggest (asking) important questions about energy policies that rely on the assumption that traditional patterns of energy related behavior are close to optimal and need only be examined at the margins. The decision making processes of movement participants also suggest a more formidable capacity for integrating the complex implications of energy choices into coherent action than is generally ascribed to ordinary consumers. In all of these respects, the movement appears to have implications for energy policy making out of proportion to the number of home-power homes."

Thank you Bill Gates.

Among the stacks of colorful catalogs arriving in early December was a software catalog from Microsoft featuring its "At Home" line of software for home businesses. I glanced through it and handed it to Cynthia. A few minutes later she handed it back and asked if I noticed anything about the cover. I looked and then suddenly, bingo, it hit me. The lovely rustic house, lit up at dusk surrounded by a snowy winter scene, had PV modules on the roof! No reference or mention of the PVs were made. It was just there. Did anyone else catch this?

"Distributed Generation appears inevitable. The question is whether it will be planned and controlled by utilities." UPVG (Utility Photovoltaic Group, DOE corporate welfare recipients), ["Photovoltaics: On the Verge of Commercialization" June 1994, p. 32]

"There are two possible future scenarios for ownership of PV power systems: they will either be owned, installed and maintained by the utility as part of its generating plant or, the systems will be owned and operated by private entities that are both customers and suppliers of electricity to the utility." Dr. Robert Wills, The Interconnection of Photovoltaic Power Systems with the Utility Grid: An Overview for Utility Engineers, Sandia National Laboratories 1994.

These quotes — part of a long list from as early as 1989 that I've collected — clearly reveal where the utilities are at. It's like there are two realities, the sweet talk of collaboration versus these documented goals and statements of utility policy.

We're Growing

Membership is now in excess of 90. IPP encourages all people who share our views to join. There's lots to be done and a role for all whether you are an installer, dealer, manufacturer, distributor, user or advocate.

Access

To Join IPP: By E-mail: [email protected] By phone: (209) 841-7001 or (916)-475-3402 Write and send tax-deductible donations to: IPP, PO Box 231, North Fork, CA 93643

Authors: Don Loweburg, PO Box 231, North Fork, CA 93643 • 209-877-7080 • Internet: [email protected]

Bob-O Schultze, POB 203, Hornbrook, CA 96044 • 916-475-3402 • Internet: [email protected]

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