Tesla's latest thing with powerwalls is to build "virtual power plants". This means the batteries are all under central control and can absorb extra power if wind/solar/nuclear are providing more than needed and later reduce load by running from battery when loads are higher.

In this case the schools probably just provide a convenient set of distributed locations, owned by a single authority. The money they earn from providing this service can be partially kicked back to the schools to offset air con costs.