Getting my head round using solar PV to heat water - basic question (I hope!)

[StephenStephen]

I'm getting the home heating system replaced.
current setup is: https://www.diynot.com/diy/threads/too-many-boilers-for-the-22mm-pipe.511647/#post-4248767 post 9

It looks like we're going for:
-a single gas boiler
-unvented 3 zoned central heating
-large area roof solar PV with excess electricity feeding into the immersion heater in the cylinder

So I'm guessing that the PV electricity can only be used to heat hot water for taps etc, and cannot be used to supply radiators - is that right?

I don't understand the basic setup, in terms of the relationship of the:
-pipes through the boiler
-pipes through the radiators
-pipes through the cylinder
If anyone has a diagram of such a system I'd be very grateful.

Thank you, much appreciated, Stephen

 

[ianmcd]

what is to understand, the set up you suggest is very specialized, not something you could do yourself

 

[StephenStephen]

what is to understand, the set up you suggest is very specialized, not something you could do yourself

Hmmm - I'm confused - in what way is it specialized? - isn't it a standard central heating setup with (an increasingly common) electricity feed from solar PV to immersion?
I'm trying to understand the setup of a single gas boiler with unvented 3 zoned central heating and hot water cylinder - which coils heat which water etc - I'm interested in looking at a diagram. That's what I want to understand.

Of course I'm not installing it, but I do want to understand it.

 

[JohnD]

So I'm guessing that the PV electricity can only be used to heat hot water for taps etc, and cannot be used to supply radiators - is that right?

No.

Electricity can be used to supply any electrical device.

But it would be absurd to try to use electricity to heat radiators when you already have a gas boiler.

Since you say you have a gas boiler, heating the HW cylinder is very poor use of your PV. The immersion control device costs about £250, and the amount of gas you will save on hot water is unlikely to repay that in your lifetime.

If you are having an ordinary domestic installation, peak PV will be 4kW or less. Considerably less in winter. Which will not be enough to run your radiators in winter. For an hour or two per winter day, it will sometimes be enough to run a 500W electric heater. For a couple of hours per week in the winter, you might be able to use your washer or tumble drier at the right time on the right day to save on its heating costs. If you're at home during a sunny spell.

 

[hard-work]

PV panels are used to heat hot water in a storage cylinder/thermal store that is used as a preheat for a combi. Thermostatic blending valves are available that will by-pass the combi and send DHW directly to the taps when he DHW is hot enough in the cylinder.