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Status and cost improvements of solar technology.

The public and decision makers at the corporate, utility and governmental levels need to be informed about the current status of solar technology and the dramatic technical and cost improvements it has undergone during the past few years. This can best be accomplished by demonstrating the effectiveness of photovoltaics in some exciting new, eye catching ways. I think that PV central power station, base load generation of electricity lies far into the future. One might even argue that intermittent, low voltage DC electricity supplied by photovoltaics is not well matched to the present central power grid. Power conditioning to convert to higher voltage AC accounts for typically half the cost of a complete PV power station, and storage adds substantially more to the cost and operating complexity. On the other hand, the present electrical distribution system is attempting to meet needs that might be much better served by photovoltaics. Let me suggest four areas in which I believe that the use of PVs could become cost effective and begin to displace conventionally supplied electricity during the 1990s: air conditioning, water pumping, chemical hydrogen production and transportation.

Air Conditioning

The most rapidly growing market for electricity in the US and many tropical countries today is for space cooling. Meeting this demand with centrally generated power is very expensive because of the high capital cost and operating expenses needed to meet short term peak demands. If ever there were a match between the availability of solar isolation and the local demand for solar electricity, this is it. By avoiding the need for expensive storage and by competing in the most expensive, peak demand conventional market, central solar thermal electric stations, supplemented by small amounts of natural gas are able to provide competitively priced power in Southern California and other tropical countries.

Alternatively, air conditioning demand might be met on-site by PVs powering a high efficiency (either brushless or reactance) DC motor driving a conventional refrigerator compressor. This strategy does not need expensive energy storage, avoids losses during transmission and DC to AC conversion and competes in the most expensive market. By avoiding about one quarter of the losses, one can have a proportional decrease in the size and cost of the PV array, and by eliminating expensive power conditioning equipment, lower significantly the capital cost of solar air conditioning. If one wished to extend the cooling time of the system into the evening hours, it would be less expensive to add either a backup AC motor or an AC to DC converter that operated from the conventional grid than to build a complex electrical storage system. An even simpler and cheaper cooling strategy involves PV powered DC attic ventilation fans that could greatly reduce building air conditioning demand. Clearly, the most cost effective PV powered air conditioning system would combine the cooling fan and a relatively smaller heat pump with the most efficient motor available and a modest PV array. Such a total solar space cooling system would be ideally suited to large flat roofed commercial and manufacturing buildings whose owners are more likely than householders to invest in a new technology.

Similarly, PVs are ideally suited for powering the small motors used to pump heat exchange fluids in solar hot water and pool heaters. In order for any of these uses to penetrate the market,it will be necessary to develop complete PV powered that are easily installed by the home owner or a contractor. After all no one, would buy a solar powered calculator if it were necessary to buy the components separately and wire them together before balancing ones check book.

Water Pumping

Let's examine a second familiar application from a different perspective. Solar powered water pumps have long seemed attractive applications for PV electricity because the demand for delivered water is less constrained by the intermittent nature of solar power, and water pumping is often needed far from existing power lines. We tend to think of solar water pumping as small scale, of the order of a kilowatt or so, but what if we used PV powered pumps to move irrigation water for some major projects and other arid regions? One could envision distributed solar arrays built on top of the aqueducts, many of which should be covered to reduce evaporation losses anyway, and along the adjacent right of way. This arrangement if carefully engineered could significantly reduce the costs of structural supports and land acquisition of the PV system. Once again the close proximity of the electricity source to the end use reduces line losses, and the use of efficient DC powered pumps eliminates conversion losses and equipment costs relative to central station alternatives. A plan to transport and desalinize ground water in Australia by long distance pipelines using PV powered DC driven pumps has been proposed by Lonrigg[1]. He has also carried out a general analysis of this approach as well[2]. California will be negotiating new electricity contracts for pumping water in the 1990s and is expecting to pay much higher prices. Such a strategy might significantly reduce the pressure to construct additional fossil fuel power plants.

Chemical Hydrogen


One area for which the low voltage, DC output of photovoltaics is ideally suited is in the electrolysis of water to produce hydrogen and oxygen. As in plant photosynthesis, the desired product becomes the storage medium so that solar intensity variability is not a serious concern. Hydrogen is an important feedstock for the chemical industry particularly for the manufacture of energy intensive chemicals such as ammonia, NH3. It is also produced in major quantities for the petroleum refining industry, and large quantities are utilized in the food processing industry to hydrogenate edible oils. The potential market is surprisingly large as the energy content of US produced hydrogen is nearly 2.5 per cent of total energy use[3] and since it is typically stripped from methane, CH4, significant amounts of CO2 are released in the process. According to an analysis by Joan Ogden and Robert Williams, high purity, merchant hydrogen, generated by photovoltaic driven electrolysis could begin to compete economically with current sources for this market by the middle of the 1990s[3]. The economics are enhanced by the co production of another important industrial gas, oxygen, and by the inherent clean air benefits of such a solar based industry. What is needed is for a manufacturer to assemble and market an integrated PV hydrogen production system consisting of a solar array, an electolyzer and gas storage system.


The transportation sector is a significant contributor of greenhouse gases and to regional and local air pollution. The world's 500 million motor vehicles each year add more than 800 million tons of carbon as carbon dioxide or 15 per cent of the fossil of fuel contribution[4]. Furthermore, this amount has been increasing both in absolute terms and as a percentage of the global total. As the major source of carbon monoxide which increases the atmospheric lifetime of the methane, and as a significant producer of tropospheric ozone and hydrocarbons, vehicles contribute additional gases to the greenhouse effect.

The principal technologies proposed to replace our carbon fueled transportation system are hydrogen powered internal combustion engines or fuel cells and electric motors. To address the greenhouse problem, both electricity and hydrogen would need to be produced by non-fossil fuel powered systems. The available technologies include photovoltaics, solar thermal, hydropower, wind, biomass and nuclear power. Because of their modularity, simplicity and ability to be located on site, photovoltaics are especially attractive for both options.

Electric vehicles are an especially attractive option if the problem of onboard storage of energy can be solved. The low voltage DC output of solar cells is perfectly matched to any imaginable battery system without the need for any power conditioning equipment. One could readily envision a fleet of small commuter vehicles that could be recharged during the day by PVs mounted on the roof of covered parking lots and commercial building. Additional PVs on the roof of homes could charge spare storage batteries that could be readily substituted when needed. While battery technology has been slow to improve, major advances have been recently made in the design and performance of the vehicles themselves as was recently illustrated by GMs Impact. Also the recent announcement by Isuzu that it had developed a new, low cost electricity storage system based upon a super high energy density capacitor may make electric vehicles practical in the very near term.

Ogden and Williams have proposed that PV produced hydrogen become a transportation fuel in the sunny Southwestern United States. The advantages for local air quality, acid rain and the greenhouse effect are obvious since the principle product of hydrogen combustion is water and a few nitrogen oxides. These latter emissions should be readily controlled by a one way catalyst since there are no hydrocarbons or carbon monoxide to complicate pollution control. Ultimately, they might be eliminated entirely by using hydrogen to power a fuel cell. Currently, BMW, Siemens and the Bavarian government are building a 600 KW PV-hydrogen production system in Germany to fuel test vehicles. Both BMW and Daimler Benz have prototype, hydrogen fueled internal combustion cars, and Daimler will begin production of a hydrogen powered urban bus in the near future. Additional work needs to be done on hydrogen storage systems, but the basics of the technology are well understood. Once again, end use efficiency plays a synergistic role with a solar technology since greater vehicles fuel economy reduces the hydrogen storage problem and the size and cost of the PV array per vehicle.

Ogden and Williams estimate that if photovoltaics get into the price range of $ 0.40/peak watt, that hydrogen as a fuel would be competitive with gasoline at $ 1.50 - 2.00/gallon around the turn of the century. It could begin to make inroads by being utilized in fleet vehicles and buses. Unlike other synthetic fuels programmes, because of the modular nature of the production facility, it is possible to get started in producing PV hydrogen in a 5 to 10 MW facility for as little as $4 to 12 million[4].

The displacement of fossil fuels by hydrogen represents one of the few strategies that could simultaneously address energy security concerns, the severe photochemical smog problem of sunny regions, acid deposition and the green house effect.


[1.] P. Lonrigg, Use of PVs to transport and desalt ground water supplies using brushless DC motors, Solar Cells 85 (1984) 231. [2.] P. Lonrigg, Alternative energy in agriculture, in: Photovoltaics in Agriculture,, Vol. 2, (SERI, Golden, CO ch. 2. pp. 5.46.) [3.] J. Ogden and R. Williams, Solar Hydrogen: Moving Beyond Fossil Fuels (World Resources Institute, Washington, DC, 1989). [4.] M. P. Walsh and JJ. MacKenzie, Driving Forces: Motor Vehicle Trends and Their Implications for Carbon Dioxide Emissions and Global Warming (World Resources Institute, Washington, DC, 1990).
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Author:Zaidi, Zafar Iqbal
Publication:Economic Review
Date:Apr 1, 1992
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