From the description, it sounds like a giant Peltier device, not a steam turbine (otherwise why would they care about having a cold tank?). Solar farms also have a ton of space in between turbines so I’m not sure that metric is relevant. Additionally, since this device uses very safe materials (salt and coolant), there’s no reason you couldn’t dig a really big hole and shove the device inside...it would also provide some nice natural thermal insulation. When it comes to storing energy far from urban areas, cost is a much higher priority than energy density.