Solar: Ivanpah and concentrated sunlight

Some have asked why not just build a big greenhouse to collect the sun's heat?

Let's do a simple carnot efficiency calculation.

Round off 25C to 300K.

Let's suppose your greenhouse gets up to 120F/322K.

Then your systems efficiency is never better than 1 - (300/322) = 6.8%.

Ivanpah is designed to run at 1013F/818K or 1 - (300/818) = 63%.

So it will cost 1/10 as much as the greenhouse.

http://www.energy-tech.com/article.cfm?id=32913

As a standalone solar thermal system, I suspect the economics on this plant are very bad because no matter how hard you look for the details of the contracts they have with the utilities, the only thing you can find about the cost per kWh is that it's a secret. Obviously it is so high that everyone involved is scared to death of the public/ratepayers finding out. And like everyone else, I have to ask "where do they go" to lower costs.

If you assume a future where a higher percentage of sources are unreliable then obviously there is more value in a reliable source. But if you look at thermal storage, no one has been able to make that economical and how do you lower the cost of salt to improve that?

But Ivanpah has one trick up its sleeve: they cleverly sited themselves right next to a large natural gas pipeline. If the utilities have a need for more on-demand power, Ivanpah simply needs to install a natural gas burning boiler and they will be able to make steam and turn the generators any time needed.

Another future possibility would see Ivanpah converted to a hybrid facility called an integrated solar combined-cycle plant. On the generation side, it would be a two stage turbine like any other combined cycle plant: first a high temperature gas turbine whose exhaust goes into a boiler for a steam turbine.

On the hot side, the working fluid would first run through the solar tower for preheating and then into the gas fed "boiler" for superheating.

GE is working with eSolar to develop this kind of technology.

http://www.technologyreview.com/news/425012/ge-invests-in-solar-thermal-company/

The sad thing is that solar power doesn't get any better than Ivanpah. 

The site is ideal: desert with lots of useless land and clear weather to give maximum solar intensity. It's as far from Germany as you can get in terms of site suitability.

The technology is elegant: the collection method is simple and cheap glass mirrors. No toxic chemicals for manufacturing, no toxic waste to dispose of when panels reach EOL and the price just doesn't get any lower.

The electricity generation process has merit too. Their unique ultra-high temperature system means high carnot efficiency: 63%.

Compare that to the typical solar cell's efficiency of just 15%.

http://physics.ucsd.edu/do-the-math/2011/09/dont-be-a-pv-efficiency-snob/

Still, the economics look bad and this system basically proves it's impossible to improve it very much.

Of course, Carnot efficiency is a "not to exceed" value. In reality, it is expected to

"operate at 18 percent efficiency and earn a capacity factor of 30 percent.

This performance should make the 392-MW facility more efficient than plants with crystalline-silicon panels, thin-film cells or rival thermal technologies using parabolic mirrors, according to analysts, as the efficiency of utility-scale crystalline silicon and thin-film plants is likely less than 12 percent."

http://www.greentechmedia.com/articles/read/is-ivanpah-the-worlds-most-efficient-solar-plant