Thanks Ellen The reason is, I have solar-siphon hot water system with electric boost.If I get boost during night time, solar hot water system does nothing since all of my family take shower in the evening. If I can have day time control load, solar hot water warms water temperature reasonably (like 25 degrees during winter time) then electric boost heater can do rest of it (e.g. after 1PM to 3PM). I also have small solar PV system at home which is not enough for heating element and need mains p ...