Common Tragedies

Thoughts on Environmental Economics

Solar statistic of the day

Posted by Rich Sweeney on February 12, 2008

Average number of solar hours per day in sunny southern California: 5.5

That is from John Supp, of California’s Solar Initiative. What this means is that even in southern California, a PV panel produces at its optimum output only 22% of the time. In northern California this figure drops to 18% (4.5 hours).

While there have been a lot of exciting developments on the PV front in recent months, the practical realities remain discouraging. Unless we figure out how to store this energy (or how to make the sun shine longer), its going to be a long time before PV makes a significant dent in our coal/ natural gas consumption.

More to come on the economics of PV later today (I hope).

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3 Responses to “Solar statistic of the day”

  1. Tmoney said

    Rich, while I definitely agree with you that energy storage is going to make solar a lot more attractive from a base-load perspective, I disagree that its predictable intermittancy is discouraging. Solar power production tends to peak at the periods of highest demand, especially in a climate like southern california, meaning that a solar power producer who sells at the market clearing rate is earning the highest dollar possible for each of his solar kwhs.

    Now, you may argue that only getting 5.5 or 4.5 hours a day of production is a financial problem, and I’d definitely agree. Right now solar isn’t generally competitive (on an amortized basis with reasonable financing assumptions) with coal or gas without generous subsidies. But when and if Nanosolar or the other “holy grail” cheap producers get their production in full gear, the financial picture will probably change. The same could be said for taxes on carbon or cap’n’trade. When and if coal has to pay for its emissions, solar (even at 4 or 5 hours a day) will become significantly more attractive.

  2. Rich Sweeney said

    Mr. Money,

    Good points. I think my comments may have overstated my real skepticism on PV. As you know, I’m pretty bullish on solar in general, and have been consistently amazed by the speed of innovation in recent years. I was just really surprised to learn that even in southern California a PV panel only produces at nameplate capacity about 5.5 hours a day. I knew that the capacity factor was low, but something about that number just really stuck out. Kinda like when one of my team members at RFF was describing her experience using a solar backpack: she said it really made you realize how often you’re in the shade.

    With all that being said, I’m going to play devil’s advocate for a second and point out two other factors to consider that may support my feigned initial skepticism. The first goes to your point about the time of PV production. You rightly note that those 5.5 hours occur during peak demand periods. But PV diffusion has two effects on peak period consumption. The first is to obviously reduce demand for those that bought PV. Yet this will in turn reduce congestion/ cost of electricity during this period for all other end users. The net effect could be a much smaller reduction in peak fossil generation than expected.

    Second, one thing that gets overlooked in these discussions of renewables is reliability. The electricity grid is fragile and at the end of the day certainty of electricity availability trumps all other concerns. What that means is that even if we meet growing demand in places like southern California with PV and wind, these intermittent sources have to be backed up by reliable, dirty generators. This phenomenon is known in the industry as “browning up the grid”. The reality is that to bring online new wind or pv, utilities need to bring on new coal or gas plants.

  3. Re: PV diffusion effects on peak period consumption

    Reducing congestion allows cheaper distant generation to serve consumer demand. On the assumption that the costly close-by generation is typically older and fossil fueled, it seems likely that a relatively larger share of the distant generation will be non-fossil fueled.

    Or, to look at it another way, there are no nukes or large hydro projects or wind farms in Los Angeles, but those sources of power contribute substantially to serving demand for electricity in Los Angeles. To the extent that L.A. PV tends to relieve congestion, those non-fossil power sources can contribute a larger share.

    Of course the capacity factor is a issue. But if your device will only generate power for 4 or 5 hours a day, at least solar naturally works during the hours when it typically is needed most. This bit of good luck for solar doesn’t overcome all of its cost disadvantages, but a good analysis will consider the dynamic value of power.

    Now, if retail rate structures would only allow retail customers with small solar facilities to capture some of the time-of-day value…

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