Thermal Energy Storage System, page-2

The article doesn't any indication about the losses involved in going from stored thermal energy to electrical energy.

To be a serious contender for the storage of electrical energy they would have to declare their efficiencies in converting electrical (high grade) energy to thermal (low grade) energy and then more importantly converting it back again. An electric kettle can do the former quite easily but transforming heat to electricity on a small scale without 50% losses would be a huge breakthrough.

If they could do that the PV solar panel industry would be history. A set of solar thermal panels combined with storage could supply hot water, room heating and household electrical needs, just a little bit too good to be true.