IMHO opinion
As a battery (electricity in and out) the 40% (or less) efficiency is a show stopper.
Wasting 60% of the energy you buy (to charge it) means your sale price ($/MWh) needs to be 2.5x your buy price plus your amortised capital cost, and that's just to break even. As other more efficient storage devices come online the competition will reduce or eliminate opportunities to obtain such high arbitrage, i.e. The battery could end up under-utilized and costing money just to replace the energy loss due to leakage of the stored heat.
As for using the stored heat to warm up a greenhouse; there are more efficient ways to achieve that e.g. a heat pump.
