Solar After Dark

Photo Credit – US Government
Solana Power Station

One of the challenges of renewable energy is dealing with intermittency and providing power when it is needed.  In this piece it is pointed out that in the Southwest there is a partial mismatch.  It leads to a rapid ramp in power demands over a relatively shore 1 hour period.  This is hard for utilities to manage, particularly when they are adding lots of renewables which, for the most part are not dispatchable.

Graph Showing Swing In Demand, Current and Projected, Due to Solar Sources Turning Off as the Sun Goes Down

Graph Showing Swing In Demand, Current and Projected, Due to Solar Sources Turning Off as the Sun Goes Down

The  Solana Generating station has an approach that addresses this nicely.Solana is a solar plant with molten salt storage allowing it to continue to generate electricity after dark.

“it will also be able to continue providing much of that power for six hours after sunset thanks to an innovative heat-storage system”

More good photos

Coordinates lat 32.920080  lon -112.975894

32.920080, -112.975894

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6 Responses to Solar After Dark

  1. Looks like an amazing system. One question: I checked out the NREL link. A yearly generation of 944 GWh translates to a capacity factor of 38%, which is probably more than the theoretical maximum for the location. I suppose some of the generation must be based on CNG, which is the backup. Any idea, how much of the total generation will be purely based on solar emergy?


    • Enoch1680 says:

      They do not provide the peak power conversion. The MW ratings are for the turbine and since the system has molten salt storage the turbine does not need to be matched to peak power production from the sunlight. I think that the 944GWh is solar production and does not include the gas.

      Did you use the turbine rating in your calculation of the capacity factor? If so that would explain the puzzling result. The sunlight is used to run the turbines during the day but also to store energy in the molten salt. So I am confident that the array performance would be well in excess of the 250 MW net or 280 MW gross ratings of the turbines. That would lead to a lower capacity factor more in line with what you would be likely to see.

      Another way of saying it is that the plant has an effective capacity factor of .38 if run at 250 MW operation is extended after dark. But that the 250 MW is lower than the peak solar power conversion. Having the molten salt has the added benefit of allowing you to use a lower rated turbine than if you had to convert the peak power from the system to electricity immediately.


      • You are right, the turbine power rating for this plant is much less than the peak solar power rating. A solar field aperture of 2.2 million sq meters translates into a peak power of about 700 MW. With this power rating, capacity factor is calculated to be 15%, which is reasonable. Secondly, 944 GWh from 1257 hectares translates into an energy density of 75 kWh/sq.meter/year. This is a good number.


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