Spain's PS20, the worlds largest solar thermal Power Tower electrical generating plant came on line this week, in another step of progress in the steady march of the world's solar power industry. Instead of using photovoltaic panels to directly generate electricity, concentrating solar power, CSP, uses thousands of mirrors, called heliostats to reflect and concentrate the suns rays on a boiler that generates steam to rotate turbines to generate electricity.
This picture is of a different Brightsource CSP Power Tower
Although, solar photovoltaic’s have other advantages, the advantage of CSP is that heat can be stored so the plant can continue to generate electricity overnight. From what I can tell, PS20 is one of the older boiling water designs that can continue to generate power for about 7 hours after sundown. In the last year, most new designs for Power Towers have converted to molten salt as the storage media, giving much higher heat retention, and the ability to run all night.
Sean Sullivan, of CleanTechnica.com reports World's Largest Commercial Solar Power Tower Goes Online. As it is only the second, this is not a large competition.
Abengoa Solar operates the new plant, which has a power capacity of 20 megawatts, enough juice to power about 10,000 homes.
The plant uses 1,255 heliostats (motorized mirrors) to reflect sunshine onto a fixed focal point. The heliostats follow the sun’s path throughout the day to catch maximum rays. Like a legion of faithful followers, the mirrors face upward and pay tribute to the towering idol in their midst. That would be the 531 foot tall collection tower, the object of their reflection.
With a surface area of 1,291 square feet each, the massive mirrors working together focus over a million and a half effective square feet of sunlight on the apex of the tower. It gets hot. Very hot. That heat energy can be used to boil steam to turn turbines, or stored for later use.
What to do when the sun’s not shining has forever been solar power’s nemesis. While we can’t alter the sun’s behavior, we can store its power for later use. Electrical batteries have offered somewhat of a solution toward this end, but they are expensive, tough on the environment and impractical for utility-scale power storage.
Current technology can store solar-generated heat for up to seven hours, and the US National Renewable Energy Laboratory is looking forward to stretching that to an amazing 12 hours!
In sum : Concentrating solar power walks very softly yet carries a big stick. It has the potential muscle to compete with fossil fuels in terms of megawatt output, yet treads very lightly indeed on the earth. With its new PS20 plant, Abengoa is making great strides toward this end for the solar industry and clean energy.
So you get a glimpse of a battle within large scale solar energy generation industry between photovoltaic panels and CSP. While CSP has a big advantage with storage, it does require water, and after the 50% drop in solar panel prices over the last two years, it is apparently not as cost efficient.
But, rapid technology change makes it challenging to keep up. I've read several recent articles about advances in the molten salt storage now being used with the BrightSource Power Tower that provides a huge advance in the efficiency of overnight storage solving the "intermittency" problem solar and wind face to replace fossil fuels and nuclear as base load generation.
I'll write a more substantive comparison of the pros and cons of PV versus CSP soon.
I hope this article brightens your day.
PS Also please check out my other recent diaries:
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Desert Sun Announces 550 MW Solar PV Generating Farm, the Largest Yet