At the end of the day, the information available suggests to me that the Energy Return on Energy Invested (EROEI) for photovoltaics is less than or about equal to 1:1. If I'm wrong, and it is more like 10:1 and will steadily rise indefinitely with futher research, then a strong case for "Star Trek" optimism (and hence "Roddenberrys") can be made. There is no doubt in my mind that improvements in photovoltaics will be made--the real question is whether the return on these investments in technology (in complexity) will provide linear returns, or whether they will be subject to diminishing marginal returns. Here is a recent project from the Solar 2006 convention in San Jose last month:
SunPower is approaching a 23% efficient PV. This helps it take business from typical 17% efficient PV. Dr. Richard Swanson, CEO, SunPower gave the conference good reason to expect continued high growth. He pointed out that in 1975 solar modules cost $100/watt. By 2002, the cost had fallen to $3 per watt. The industry learning curve of 30 years has been consistent – each time that production doubles, cost drops 81%. Dr. Swanson expects $1.40 per watt by 2013 and 65 cents per watt by 2023.
This Dr. Swanson of SunPower is making the case for a kind of "Moores Law" for improving solar panel efficiency. Is this really a linear decrease in cost? Right now there is about 5300 MegaWatts of installed PV capacity worldwide. The US alone currently generates on average over 1,000,000 MegaWatts of electricity (just electricity...this won't power a hydrogen fuel scheme). So existing PV would need to double eight times in order to just match the current US electrical generation. If, per Dr. Swanson's linear decrease in cost projection is true, after eight doublings in capacity PV cells would cost 0.005 cents per watt. You could build enough PV to power the entire United States for $5,095. Something tells me that the reality is not linear! No, the reality is most likely best expressed by some form of logistics curve, such as the diminishing marginal return curve suggested by Joseph Tainter:
The rapid increase in efficiency of photovoltaics coupled by the decrease in cost per watt from the '70s to the present is represented by the return on investmen tin complexity, which rises rapidly from 0,0 to C1,B1. The salient question is: what point on the curve represents the return on current marginal investment in PV complexity? Probably somewhere between C1,B1 and C2,B2. Projections, like Dr. Swanson's that assume linearity in cost decrease per watt are basing this assumption on the roughly linear increase represented by the curve between 0,0 and C1,B1. But the reality is that the benefit from each marginal investment in photovoltaics at this point will return less and less. This technology cannot save us from the ultimate ramifications of diminishing marginal returns.
There is, in fact, some evidence that PV technology is already at the peak of the diminishing marginal return curve (C2,B2). Sunpower, the same company where Dr. Swanson extolls the historical decreasing cost of photovoltaics, recently made this press release:
...Overall, these changes result in a 43 percent increase in power, said Julie Blunden, vice president of external affairs at SunPower. Each panel can generate 315 watts of electricity and will have roughly the same cost per watt as the existing line, she said.When you improve "efficiency," but the cost of doing so keeps the cost per watt stagnant, then you have peaked on the diminishing marginal returns curve. Future increases in efficiency are most likely possible, but they will become so costly as to actually increase the cost per watt. Investment in complexity is inelegant, and will always run into exactly this problem...