Wednesday, March 18, 2009

Getting more out of Utility Scale Solar PV—Dynamic Solar Arrays

In recent years we have seen a growing interest on the part of companies and individuals in using solar power in the US. The interest has translated into installations in the states that offer the best incentives. Just in the last 18 months we have begun to see forward leaning utilities bid/announce projects in the hundreds of megawatts (i.e. utility scale solar). It is exciting to see some utilities making real investments in solar power, because those of us in the solar field need utilities as our partners to realize the full potential of solar power.

And speaking of the full potential of solar power, for years many utility executives have dismissed solar because it is intermittent—i.e. the utility cannot control the output of today’s solar panels at any given moment. Despite such lack of control solar power is beginning to make inroads, but wouldn’t utilities be even more interested in solar power if we could give them some control over the output of their PV panels?

What if we could not only give a utility executive more control over the output of a solar panel, but also improve the performance of the solar panels at the same time?

Talk about win-win!

So how might one provide greater control over the power output of a panel AND enhance performance of the panel at the same time?

By building a system that allows one to control the temperature of the solar panel.

It is well documented that solar PV panels produce less power at elevated temperatures. The obvious corollary is that PV panels produce more power (all else equal) if one lowers the panel temperature. The amount of power increase (or decrease) is small for each individual degree change, but can add up to a considerable fraction of total output over multiple tens of degrees (20%+ of total output would be quite practical).

One simple way to control the temperature (and hence the power produced) of a panel would be circulate a fluid, such as water, across the panel. Assuming the water temperature is cooler than the panel, controlling the flow of water across the panel allows one to reduce the temperature of the panel—and thereby increase the power that panel produces.

Obviously one would need a large reliable source of cooler than panel temperature water, luckily in most places the ground itself (if you dig down several feet) offers a consistent year-round reservoir of cooler than panel temperatures that are multiple tens of degrees cooler than the temperature most solar panels operate at. Cheers to the geothermal folks.

Finally if one maintains two fluid reservoirs at different temperatures, one can control the temperature of the solar panels (and hence the power output) at any intermediate temperature by simply mixing the fluid from both reservoirs together as needed. This means the utility would be able to dial up (or down) the amount of power produced by its solar panels as desired between the limits imposed by the reservoir temperatures.

So how might a utility use a Dynamic Solar Array? The simplest (and most logical to those in the solar industry) would be to turn the temperature setting to the coolest point and generate as much additional power as possible. But another possibility would be to make adjustments to maintain as stable an output as possible over the course of a day--i.e. dial up the power 10% to offset a drop in power due to a passing cloud and lower the power back down 10% after the cloud passes. Or the utility could set the temperature at some intermediate point for most of the day, but boost the output from the panels to maximize production at a period of peak demand. Obviously the utility could use a Dynamic Solar Array in many different ways (that’s the point of giving them more control!) depending on its other generating assets and objectives.

Is this extra control (you still need sunlight!) worth the expense of adding plumbing to solar panels and across the entire solar plant while maintaining relatively large fluid reservoirs at different temperatures? That is a question the solar industry and utilities must determine together.

I’m optimistic that adding relatively simple technology, like plumbing, and one which utilities have considerable experience using throughout their operations, that can potentially boost solar PV panel output by 20% or more would be given serious consideration all on its own. Offering utilities greater control over a relatively expensive asset they have complained about not being able to control in the past seems like one of the purest expressions of “adding value” I can think of.


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