Twin Immersion Coils.

[Miller3857]

Looking for guidance with a 750 litre thermal store which has twin tappings  for immersion coils, one near the bottom the other half way up. We have 4KW of solar PV so want to make the best use of this. Would it be best to have two separate immersion coils or one? If it's one coil which tapping would be best top or bottom? If two coils are the way to go is it possible to control (automatically) each one separately allowing half the store to heat up before switching to the other (assuming the lower) coil? Any advice would be gratefully received. Thank you in anticipation! Rich

[ProDave]

With 4KW of PV you won't get more spare than one can handle for much of the time, so for simplicity I would have one solar PV diverter feeding one immersion  heater.

 

However I would probably consider a manual summer / winter changeover switch that switches it from the bottom to the top one.

 

Alternatively make that changeover with a contactor. Some solar PV diverters have a switch output to do that. So for example heat the top one first, and then that reaches it's cut out temperature, switch to the bottom one.

 

The ability to do things like that is one reason why I preferred to make my own,

[joth]

I think Eddi one such diverter? I had wondered why it supports them sequentially only, but this makes sense.

(we're looking at 8kW array I was actually researching diverters that can enable single or both coils, depending on the excess export available)