well, yes, but it depends how you wire it - it is easy enough to know if you are exporting electricity or not and to operate a contactor accordingly - it is very common to put a car charger under such an arrangement, so as to minimize charging at grid prices.. And the Misubishi Ecodan you allude to is a range of heat pumps - so how is water being heated anyway ?

Mike

I have been wondering about this. My aim would be to avoid gas consumption in summer. A battery could take care of cooking the dinner, but an immersion heater would be required for the hot water. A potential problem is that a normal immersion heater takes 3 kW. That would be fine, but if it's a cloudy day, it would defeat the point if some of the leccy had to be bought in. Happily, lower powered immersion heaters are available.

So what I'd like is some form of logic control. So, step 1, send leccy to any current consumption and the rest to the battery. If PV output minus consumption > 2 kW, send it to the immersion heater instead of the battery. If full 4 kW output, send it everywhere. Obviously if battery is full and tank is hot, export the surplus. Is that a possibility?

Well I was wondering  if  there were setting on the internal controller for such options or would it have to be  with a Eddie and a second supply to a second element 

There are a number of products out there that claim to do just this.

There are some which modulate a second immersion's power input based on some CTs clamped around the incomer as a simple solution.

There are much more sophisticated arrangements available now; for domestics these are often driven by the inverter datalogger, and generally use the same logic as required for EREC G100 export limitation schemes and for controlling the battery charge/discharge.

I don't work with domestic schemes very often though so can't recommend specific products, but the installer will probably be more than happy to discuss options.

(* No connection, and no experience with them in the field, just seen them at a number of trade shows)

As has been said, PV immersion diverters are readily available - although it maybe makes more sense to run the heat pump to warm the tank than use an immersion - presumably the heat pump will run anyway if there is demand, so really you'd be asking the heat pump to run when there wasn't demand (but 'free' electricity available) and put the excess heat  in the tank ... which might suggest a need for a larger tank that you might otherwise have?

The idea of "free" PV electricity might be going away though - the "deemed 50% export" is going to disappear as smart meters measure actual exports and suppliers seemed to be obliged to switch to paying on a metered basis even for existing FIT contracts, so using excess generation locally will start to cost actual money.  Granted the per unit price is still smaller than importing - but the difference is declining - my supplier is already offering 10p/kWh in some circumstances - so getting to be in the same ball park as importing gas, especially when you factor in the cost of the extra equipment.

   - Andy.