[hef19898]

Winter heating in Germany is covered by gas, not electricity. There is no competition here. In fact, one could use surplus renewable energy at close to zero marginal cost to produce green LNG, the efficiency wouldn't matter. Store that gas for winter or something like that.

[Schroedingersat]

Sodium acetate has a heat of fusion of 289kJ/kg and a price of around $400/tonne

For low grade heat you can just store it directly using some black pipes at $5/kWh of storage skipping the electrolysis and the pv steps.

Might need some kind of cleaning after 5 years, but it should break even especially if scale pushes prices down a bit.