My understanding is this is for excess PV capacity. But I think they should address this! Their plan is to heat deep inside a big pile of dirt using resistive h

My understanding is this is for excess PV capacity. But I think they should address this! Their plan is to heat deep inside a big pile of dirt using resistive heating elements and then pump the heat out in pipes. Maybe it's hard or expensive to add solar heating into the system? But why couldn't they pump it in? Maybe they don't have extra space because the dirt mound is covered in PV panels.