Immersion Heater time control

[cj]

This must be a common scenario?

I have dual 3kW immersion heaters, (although top one does not seem to be wired/working, no matter).  I have Economy 7, with solar pv. Gas condensing boiler for DHW & CH.

During summer when generation exceeds domestic use, I would like to use day-time electricity (rather than gas as that is more expensive), particularly during peak generation times, but the lower one is on continuously only controlled by the thermostat and the wall switch.

A conventional plug-in timer is no use as the current is over 13 Amps. 

What is the best timer to use so that I can readily adjust the times, possibly using a solenoid that could have an intelligent sensor (in the future) to only switch on when generation exceeds immersion heater demand?

It would also seem sensible to change the lower immersion heater to a much lower power, say 1kW, as the import cost is so much more than the export value, thus being on for longer, and more nearly matching the average daytime generation.

[davec]

CJ,

Horstmann do a hardwired Economy-7 Immersion controller. You can set E7 and optional daytime ON/OFF times; there's also a 1Hr 'boost' button. I got mine off eBay a few years ago, it's called an 'Electronic 7; Maxistore'. You'd need to double check the max current for twin immersion but no probs with my single 3Kw.

Dave.