PV Switch

[Johnuready]

I am successively running a PV switch to switch spare electricity away from the grid to our immersion in a solar thermal 210 ltr tank. As its working very well I'm looking to install a 125 ltr pre heat tank to feed the main tank. Anybody have any ideas on a circuit to sense the main immersion thermostat turning off when main tank is hot and switching to the pre heat tank. On the main thermostate asking for heat it switches back to the main tank.

Only have one immersion thermostat and no auxiliary contacts. Could use temperature sensor on main tank as input source? Would prefer sold state switching, not a relay.

 

[danesol]

You can only use so much hot water though ....... would it not be better to send it off to batteries ??

 

[Johnuready]

I'm building a very low energy bungalow and have no gas hence the reason to maximise the use of PV spare power and solar thermal.

I think I have found an answer today.

Put an accurate temperature sensor on tank 1 with a change over contact fed by a common and two outputs.

Normally closed change over contacts sends a live to an MK Contactor that feeds tank 1 immersion.

When tank 1 reaches the temperature the change over relay will disengage Contactor 1 (tank 1) and engage (tank 2). Using another relay switched MK Contactor on to tank 2 immersion

If temperature in tank 2 reaches max then immersion thermostat turns it off

If temperature drops in tank 1, relay closes and re engages Contactor on tank 1

Feed both Contactor on a separate feed from my PV switch.

That should work

 

[danesol]

If you have no GAS, wouldnt you better off circulating all this hot water through central heating rads as well as a hot water cylinder ??