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Comment by cinquemb | Hacker News Reader

> This study thinks we can achieve this with only ~200 MWh of storage.

Agree, very unrealistic.

One thing that always disappointing to me about these conversations is that solar == photovoltaics, batteries == li-ion electrochemical… luckily the world isn't limited to these asumptions and developments have been and continue to be made, even if they are mostly ignored/overlooked by the HN crowd.

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Things like kinetic storage are geographically limited. Most places with available hydroelectric storage already generate electricity from dams.

Chemical storage in the form of natural gas produced by the Sabatier process is very inefficient. Currently it's at 55% efficiency to go from power to gas. Even the most efficient combined cycle plants are currently 65% efficient. End to end efficiency is ~1/3.

Also, using synthetic natural gas requires a means to capture the exhaust of gas plants to actually make it carbon neutral. Converting the fraction of a percent of carbon dioxide in the atmosphere is not currently possible.

The conversation is mostly about batteries because that is the only known option at the moment, other than geographically limited ones.

There's also many kinds of thermal energy storage systems in use (I think molten salt systems are the most promising[0], esp if you design salt mixtures that have have higher delta k's[1] and more efficient HEX and steam turbines to about ~60% efficiency of converting heat to electricity[2]), not limited by geography.

Going of the example powering 100MW turbine with a working temp range of ~278C[0] and using an eutectic mixture of calcium chloride and magnesium chloride (ionic halide salt)[1] with a working temp range of ~1440C, can make the "tank of about 9.1 metres (30 ft) tall and 24 metres (79 ft) in diameter to drive it for four hours by this design." last for nearly a day, though with higher upfront cost than a typical NaNO3 + KNO3 system, but nowhere near nuclear costs (except for the similarities with dealing with supercritical water for electricity generation).

[0]: https://en.wikipedia.org/wiki/Thermal_energy_storage#Molten-...

[1]: https://gist.github.com/cinquemb/015f8b0775db2381513f0e20186...

[2]: https://www.solarpaces.org/vc-funded-thermal-battery-based-m...

Solar thermal plants [1] effectively already use this system. They heat a model salt container, which drives a heat engine. The molten salt remains hot enough enough to keep producing energy through the night. However this scheme requires both solar collectors (in the form of mirrors) as well as the molten salt tank plus a heat engine. The resulting levelized cost is about the same as nuclear power [2].

If this startup does manage to produce energy storage at the efficiencies and costs as advertised that'd make intermittent sources more viable. Ultimately building solar and wind is betting that we'll be able to build efficient, cheap, and massively scalable energy storage.

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

2. https://www.lazard.com/media/450784/lazards-levelized-cost-o...

Yes, I had CSP in mind, however most CSP systems today use the kn03+ nano3 eutectic mixtures, and the LCOE is based on that assumption, as well as assuming you can have no baseload from the storage, and cannot distribute storage separately from collection. And even with their assumptions the range for solar thermal capital costs/kwh is about 20% less than nuclear on the top end, 41% less on the bottom end. One also has to consider the political costs that nuclear comes with and that CSP doesn't.

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