October 21, 2009
Electric Utilities Embrace Solar Power

An article by David Wagman about big electric utilities embracing solar power discusses some of the trade-offs of photovoltaics (PV) versus concentrating solar power (CSP). Turns out PV versus CSP is about more than just average cost per kwh. PV can produce power under lower lighting conditions in areas closer to the poles and with more clouds. The article hits a lot of issues with utility-scale solar power. Worth a read.

PV can produce at least some electricity under less than ideal conditions, such as low sun angles and overcast skies. That characteristic is why utilities in places like Massachusetts, Michigan and New Jersey can become solar energy players alongside their brethren in the desert Southwest.

On the other hand, since PV instantly makes electricity when photons hit it the electric power outputted is noisier when clouds pass over. CSP, by contrast, involves heating liquids up to high temperatures in order to eventually generate steam. The temperature of the liquids does not drop rapidly when clouds pass over. So CSP is more dependable in response to passing clouds.

PV also offers the advantage of modularity and scalability. Utilities and large energy users can start relatively small and scale up as demand grows and as they become more comfortable with the technology. But scalability can have its drawbacks, too. For one thing, the larger the deployment the greater the likelihood that cloud cover will affect output.

For similar reasons CSP also can provide power in the evenings. The very hot flowing liquids can heat up molten salts in insulated containers as a way of storing the heat. Then in the evenings as the sun goes down CSP can still provide electric power. It is cheaper to store heat in molten salts than to store electricity in batteries.

Since CSP doesn't work in lower light climates this means that solar far has more growth potential for evening use in the American southwest and under areas with high insolation such as Australia and North Africa.

Share |      Randall Parker, 2009 October 21 10:12 PM  Energy Solar

Brett Bellmore said at October 22, 2009 9:45 AM:

Of course, CSP generally requires focusing the light, which is difficult with diffuse light, so clouds might not cause an instant dropoff in output, but they'll cause a greater net dropoff in power output.

not anon or anonymous said at October 22, 2009 11:20 AM:

So CSP is more dependable in response to passing clouds.

I've never understood this notion of "dependability"--surely a bank of supercapacitors can smooth out the power output as well or better than a CSP-based system. The remaining problems can be solved with flexible market pricing.

anonyq said at October 22, 2009 4:01 PM:

Not even necessary. Roof based PV are spread out over a large area so change in production due to weather will be slow

Eric Johnson said at October 22, 2009 8:50 PM:

> surely a bank of supercapacitors can smooth out the power output

But is it economical? I wouldn't know myself, I'm just asking.

> Roof based PV are spread out over a large area so change in production due to weather will be slow

What scale do you mean exactly? A city can easily all be cloudy at once, of course. You can transmit city-to-city, but that costs - I think that's why you hear more about storing energy than transmitting it. I know little about this, though, and could be wrong.

Randall Parker said at October 22, 2009 10:00 PM:


You should click thru and read the full article. Rooftop solar is much more expensive. The utilities are thinking it makes sense to build a larger number of smaller (still quite large) solar farms over a wider area in order to reduce the effects of local clouds.

Randall Parker said at October 22, 2009 10:16 PM:

Actually, here's where I recently came across a comparision of residential solar costs versus much cheaper larger scale solar.

Also, installed costs show significant economies of scale—small residential PV systems completed in 2008 that were less than 2 kilowatts (kW) in size averaged $9.20/W, while large commercial systems in the range of 500 to 750 kW averaged $6.50/W.

Residential solar makes no economic sense unless you want to live off-grid. Though in an area with high electric power costs (e.g. SoCal) and lots of sunlight the tax advantages of a residential solar installation might still make it cost effective to the individual even as it is a bad deal for taxpayers.

My problem with the idea of living off-grid: Where is electric power not reliably available that still has broadband access to the internet?

anonyq said at October 24, 2009 7:35 AM:

A city is rarely cloudy at once and the problems are then not electricity. Say a city is 1 km across, With windspeeds of 60 km/s it will take a minute for the whole city to drop output. A CSP plant is much smaller so the drop off of solar radiation is much faster. Other issue is that you need backup for the chance that the CSP plant breaks (small but not zero change) while there are so many rooftop solar units that in aggregate they can be seen as unbreakable but slowly degrading.

The reason why electricity companies don't see a future in rooftop is because they have a competitive disadvantage in it which is so large that they don't have a future in it.

A big advantage of Residential Solar is that you don't need planning permission.

A reason to have residential solar is not to live permanently off-grid but to have (intermittent) electricity after the Big One hits California.

Randall Parker said at October 25, 2009 12:31 PM:


I agree there are survivalist advantages to having solar panels.

The Big One: I think water is the biggest problem. My sense of it is if the Big One is going to knock out electricity and internet connection for months then I'd want to hike out (or sail out) of California at that point.

Post a comment
Name (not anon or anonymous):
Email Address:
Remember info?

Go Read More Posts On FuturePundit
Site Traffic Info
The contents of this site are copyright ©