03.29.13

We should use Concentrated Solar Power ONLY after sunset

Posted in Uncategorized at 3:40 pm by Administrator

There is an ongoing battle between Photo-Voltaic (PV) solar which converts sunlight into electricity through an electro-chemical reaction and Concentrated Solar Power (CSP) which generates electricity using steam turbines.  Based upon the nameplate capacity under development today PV is winning the battle hand's down. Some projects that were originally designed to use CSP have recently been converted to PV.

However, there is one very problematic characterisitic of PV that can be avoided with CSP.  PV, with its direct dependence upon sunlight, fades in the late afternoon and is not available in the evening when electricity demands peak.  CSP, on the other hand, can be equipped with molten salt Thermal Energy Storage (TES) which can be used to extend electricity production well past sunset.  The Gemasolar plant in Spain generates electricity 7x24x365, as shown by the production graphs below.

The big disadvantages of CSP are cost, complexity of the facilities and the length of time required required to construct them.  Typical CSP installations with TES run about $6-8/watt compared to $2-3/watt for PV.  CSP requires the installation of thousands of large mirrors as well as construction of a steam generation plant and salt tanks.  All of that takes time;  typically 2-4 years or more. For example the Solana plant in Gila, Arizona broke ground in December, 2010 and will be completed in August, 2013.

CSP facilities like Solana and Gemasolar divide the solar energy received into two streams. Part of the energy is used to heat molten salt for energy storage and part is used to produce steam for the turbines that generate electricity during the day.

But what if 100% of the energy was used to heat molten salt? That way a much smaller and less expensive facility could be used to generate electricity using the energy stored in the molten salt into the evening and all night if necessary.

Less expensive PV could be used to supply the electricity needs during the day.

Using this approach would produce the most cost-effective, 100% solar solution possible. All of the grid connectivity and transmission infrastructure could be shared by the two generating sources.

In many parts of the world, including the Southern U.S. this one-two combination of PV during the day and CSP at night would make a lot of sense.

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30-Nov-2015: Update: I came to the conclusion that PV + CSP was an optimal configuration on my own in 2013. However, I have recently found out that NREL wrote a paper discussing the advantages of this combination back in 2011. It is a very comprehensive and convincing analysis.

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