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cells of $100 per peak watt the power costs of the residential power unit and those of the central power station are approximately equal.

Everyone in the industry agrees that individual residential arrays will come on line first. However, to many the critical test will come later, when large central power facilities are constructed. It is, however, possible that we need never get to the stage where we need very large generating facilities. In general the cost per watt of photovoltaic arrays will not vary with the system size. The limiting factor is usually rooftop space and the amount of sunlight the roof area gets. Doctor Joseph Loferski has estimated that in Rhode Island and, indeed, in most of the country, 20% of the rooftop space could generate enough electricity for a Rhode Island's electricity needs. 18 In

the October 15, 1974 Forbes Magazine Jerold Noel, a solid state physicist working with Tyco Laboratories is quoted as saying, "We have made a calculation that the roof of an average house around Philadelphia could produce enough energy to supply the needs of the home, with enough left over to, say, charge an electric car." According to Doctor Martin Wolf, about three times the present average household consumption of electric power can be collected from an average sized family house, even in the northeastern part of the United States which 19 doesn't get as much sunlight as other sections of the country."

Still, there will be limitations. High rise buildings, for example, probably do not have enough rooftop space for their energy needs. Certain industrial processes, like aluminum manufacturing, require enormous amounts of energy. And, even in high density areas of the city, with townhouses, or apartment houses, or even in areas where single family dwellings are surrounded by towering shade trees, one might find it not feasible to have rooftops generating electricity. It is also possible that there are certain storage technologies which would make it more economical for individual residences to share storage facilities on the block or neighborhood level.

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However, even where existing rooftop space is inadequate we find that the next step up is not metrpolitan or regional generating facilities, but on-site, nearby electric generation from relatively small plants. According to the Spectrolab report in the Task Force Report photovoltaic power system cost

characteristics do not change significantly with size over approximately 4

20

MWe peak output. That is enough to fuel around 800 homes.

According to this

report, the optimum size plant, in terms of dollar per output in watts probably falls in the 4-10 MWe range (around 800-2,000 homes, about the size of a small neighborhood in the city, or a subdivision in the suburbs.

Local Government and Solar Cells

Federal funding for solar cell development has increased from $660,000 in 1974 to more than $1.2 million last year, and the proposed budget for this coming year includes a request for almost $10 million. It is possible that Congress will increase this sum significantly. However, many experts in the solar cell field agree that this kind of funding will not bring about major cost reductions quickly. The main reason is that the millions are broken down into grants of $100-250,000 among many different organizations. These small grants support research and theoretical experimentation, but cannot justify the automation of facilities and the sort of learning curve which industries usually go through during their infant years. There is general agreement that what is necessary is the creation of an artificial market whereby government will buy cells when their cost is high in order to permit industry to automate facilities and reduce the cost quickly. When the price drops below a certain level a natural market will open up.

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No one is sure when the natural market will increase greatly. One

professional in the field estimates that at $10 per peak watt it will be very Others talk about $2 per peak watt. Most

close to a competitive number."

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agree that $1 per peak watt is a minimum number for other than central power station applications and will probably be competitive with fossil fuel generation by the year 1980.

Basically, what is required is the creation of sufficient orders in advance so that production can be geared up to mass production techniques. Such increased production will lead to the initiation of a learning curve; that is, you learn more about how to make a product as you produce more. Consequently you produce

it at a lower cost. This experience curve turns out to be remarkably similar for many industries, from washing machines to transistors. The Boston Consulting Group, in a book called Perspectives on Experience, traced the experience curve for many industries The next three pages contain three tables which indicate the experience curve projected for silicon cells compared with that which occurred with transistors and how this affects price. The learning curve predicts that for every doubling of volume you can expect a 20-30% reduction in cost. Many in the solar cell industry use the transistor industry experience as a good

indicator of future projections for solar cells. As one person noted:

There was a Department of Defense need for a very lightweight electronic replacement for vacuum tubes, even though they were very expensive, $20 for one transistor. They eventually got down to 25 cents or 30 cents per transistor. But even though they were $20 there was a particular need for them. That is the key point.

Now, in the case of the solar cell, we have the same kind
of situation. It is satisfactory, from a technological
standpoint, and the usefulness of the device, well, it is
there. But there is no major market for a $20 per watt solar
power system. In the case of the solar cell, there is not
really a large market for an expensive cell as there was for
the transistor. 23

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1973 SSPS "Blanket Cost Projection

1972 EFC Ribbon Solar Cell Cost Projection

Ref. Currin et. al. 9th IKKE PSC

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