How hot to make a hot water cylinder heated via PV?

Reed_Richards

Bendy_House said:

Reed_Richards said:

I have my immersion heater thermostat set to around 75 C.  There is a second thermostat with a thermal cut-out for heating via my "boiler".  Although in principle this operates at 82.5 C it is occasionally triggered by the immersion heater-heated water and has to be manually reset or water from the boiler bypasses the cylinder.  There is a TMV on the outlet from the cylinder which takes the hot water temperature down to around 40 C.

On a sunny summers day I still generate more electricity than I can use.     

Ah, that sounds like what I was suggesting to my friend.

Is this a standard hot cylinder, or a Thermal Store? Vented or un?

So, surplus PV leccy is used to charge it up, and you have this set to around 75oC? Why not higher?

Ah, the boiler gets this up to 82-ish, so I'm guessing this is a TS? Which will therefore be designed for such temps?

And, in summer, the TS gets charged up fully, so you have 'free' hot showers and DHW? Do you have any thoughts on just how effective it is - eg, on a sunny day, how well would your system heat up the tank from cold?! (I guess that depends on what other call is made on the PV, so a silly Q...)

I wonder how much it helps on sunny winter days?

I have a conventional cylinder, unvented.  My "boiler" is an ASHP; it could not actually heat the cylinder much beyond 50 C so the thermal cut-out must be there entirely to satisfy regulations; as far as I can tell.

I could heat my cylinder (to 50 C) much more efficiently with the heat pump than with the immersion heater but the heat pump requires more power than my solar system can provide so it's cheaper to do it free with the immersion heater if I have enough spare solar power.  This only happens in summer when I don't require electricity for heating. I don't heat the cylinder from cold, just as cold as it has become after 20 hours plus using hot water.  This usually takes between 80 and 120 minutes at 3 kW.