> The purpose of Standard Thermal is to make energy from solar PV available 24/7/365 at a price that is competitive with US natural gas.

They compare to natural gas. Not the cheapest alternative.

>Pipes run through the pile, and fluid flowing through them removes heat to supply the customer

Just basic district level geothermal heat pumps do the same. You don't need to heat the soil. Just drill down and install pipes. Earth generates heat. What is the cost difference now?

> Just basic district level geothermal heat pumps do the same.

This doesn't with everywhere though? Because of geology?

Why go throught the extra solar -> electricity -> resistive heating -> soil instead of directly doing solar -> heating a metal rod -> soil?

Cutting out the conversion steps should be more efficient.

If the electricity is free, efficiency does not matter that much. The capex of the storage system might matter a lot more. In which case, heating up a big mass might be more economically feasible than battery installations.

They skipped a few real competitors that'll shrink their market:

1. In places with underground water reservoirs, these can be used for heat storage very similar to this. It's location dependant but I think there's European district heating networks doing this already.

2. Heat pumps for process steam are gaining ground. The temperature at which heat pumps lose competitivness is slowly rising over time. They mention storage at 600C. Heat pumps win under 80C and are up to 160C and aiming for 200C though at those temps cheap gas will probably win for now. Heat pumps can also recycle process heat and cool and heat at the same time.

3. Wind doesn't get mentioned. Wind doesn't pair as neatly with batteries as solar does but in places with seasonal storage issues the batteries can be used for solar and wind during summer and wind plus whatever (biogas/nuclear/hydro) in winter. They need to worry about both centralised big batteries and customer sited ones.

In general I'm supportive of the idea, but similar to the Nordic sand battery, when they start talking about generating electricity from the stored heat I take that as a signal that they've realised the alternatives above combine to really squeeze the market they have left and undermines my faith in the rest of the product.

Yeah, Form Energy exists to basically disprove this:

  Batteries will still be too expensive to arbitrage these seasonal differences effectively. Thermal electricity storage is orders of magnitude cheaper for storage, but worse at daily cycling

Form, like the authors, agrees that Lithium-ion is great for intra-day cycling and not suitable for is seasonal storage. Unlike the authors, Form believes it can engineer chemical storage with the requisite properties. Form’s batteries have something like 10 days of capacity relative to the size of their inverters.

Form's basic idea is that low round trip efficiency can work as long as it's cheaper enough.

They've always had $20/KWh as a notional price but there's already talk of Sodium batteries in China getting near that price point, while having nearly double the round trip efficiency.

Energy storage yes, electricity storage no. Very limited utility and questionable use of solar PV, which has about a 20% conversion efficiency of solar energy to electricity. Seems like a lot of extra steps to make heat.

One of the biggest uses of residential energy is heating/cooling. Especially in winter months where PV generation is significantly lower (I have seen numbers of 2-5x summer generation), having "free" heat could be quite valuable.

Now, do the economics shake out for storing heat to deliver in winter? No idea, but the idea is not far fetched. Outside of bitcoin mining, there are few uses which can soak up the increasing glut of midday PV generation. Anything that can seasonally store that (even at terrible efficiencies) is valuable. What is going to be the most economic option? No idea. My personal bet is iron-air batteries, but there are a lot of contenders in the space that are competing for widespread adoption.