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Comment by Manuel_D | Hacker News Reader

What does this add over existing [1] solar thermal plants? The approach seems to be roughly the same: heat a material with solar power and then operate a heat engine with it. Is storing heat generated by photovoltaics better than using solar energy to heat material directly?

1. https://en.wikipedia.org/wiki/Solar_power_tower

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When you're dealing with solar (or any renewable really), you have to think about the generation of electricity and storage of that electricity.

Solar thermal plants can be used to generate energy, but they're not great at storing it for dispatch at later times. Even the link you provided has thermal storage as a component of the system-- you need to figure out how to dispatch electricity at night.

What's proposed is a cheaper storage solution, and they state it can still provide power after 10 hours.

Solar thermal inherently has built in storage: the molten salt heated during the day continues to provide energy through the night.

> Even the link you provided has thermal storage as a component of the system-- you need to figure out how to dispatch electricity at night.

This is referring to the thermal storage of the molten salt tower.

What I'm getting at is why is solar PV -> electricity -> thermal storage preferable to solar mirrors -> thermal storage. Is solar PV less expensive than mirrors?

Solar PV performs better under imperfect illumination conditions. Concentrating solar thermal power can't make use of diffuse light on partly cloudy days, whereas solar PV can. Solar thermal also has to reach a minimum operating temperature before it starts generating steam/electricity. PV actually works better on bright, cold days and will generate full power the instant an array reaches full illumination. These factors, plus the greater mechanical complexity and maintenance requirements for thermal solar, make it very hard for new thermal solar plants to deliver a lower levelized cost of energy than new PV plants.

Existing solar thermal plants using nitrate salts, which are stable up to 550 C or so.

NaOH doesn't boil until over 1300 C. The temperature range from melting to boiling is over 1000 C.

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