Parsons Switch Ltd. announces new switch pack.

The Parsons Switch will monitor the inverter output and when a preset value is reached, a purpose made dual element immersion heater is switched on so that it will only operate when sufficient light is available to provide free electricty to power the 1kW element.
This replacement immersion also incorporates a 2kW element to provide back up heating from the existing switched circuit in the conventional manner. In practice the domestic consumer could heat a water cylinder during the day while out at work for free and save on existing fuel bills.
http://www.parsonsswitch.com