Domestic scale CSP with rock storage

One of the "green" team's latest projects is to heat air using parabolic troughs and then use it to heat rocks stored inside a vacuum insulated chamber. The idea is to then use the heat later when you need it. We are hoping to achieve rock temperatures of around 300C and retain the heat for 2 to 3 days. The heat can be used for water heating or even for factory process heat if we scale up the size of the system.