On Tuesday, 3 November 2015 18:04:02 UTC, rick wrote:
My solar PV system, produces a significant amount of unused electricity.

I have a Thermal store based heating system .... providing mains
pressure DHW off one heat exchanger and underfloor heating from the
other ... the water content of store being circulated around the boiler
when heat demand is called.

A consideration is to install a 2nd hot water cylinder, and use the
excess PV power to feed an immersion heater .... creating a large store
of heat.

Any call for DHW will result in thye incoming cold mains being
pre-heated by this store .... when store is depleted, the normal heat
exchanger function within the Thermal store would maintain DHW supply,
topped up if necessary by boiler.


I did ask a few weeks back about just using Solar PV excess direct into
Thermal store immersion, but as this is kept 'at temp' don't really see
a way to easily do that.

This pre-heat method would seem a suitable alternative ... and using the
mass of the water as an energy store.

I haven't run the numbers but expect you'd be better off all round to feed the electric heat into the existing tank. The water wil go above set point, and not need other heat sources until the temp is back down again.


NT