Can you use a heat battery for central heating?

[Pete Lea]

Hey all,

Excuse me if I get some facts wrong, I'm a complete noob when it comes to anything other than replacing radiators.

We're about to get PV Solar Panels (~6kw) and a large battery storage array (2xTesla Powerwalls for ~27kwh storage and ~10kw output). I'm looking to replace my old potteron powermax gas combi boiler and go all electric. We're going to sign up to Octopus Go so we can try and pre-charge as much stuff in the 4 hours of the night when electricity is cheaper because my projected bills with two teenage daughters is going to be astronomical.

For Domestic Hot water, it seems like it's a no-brainer to get something like a Sunamp Thermino, I have a big tank of water in my loft, which I assume I would keep for this system and two mixer showers that I believe pull from this big tank? (correct me if I'm wrong). I also plan on getting solar divert so excess PV energy comes to this heat battery.

For Central Heating I'm not entirely sure what options I have (ASHP is out of the question for various reasons). Here come the silly questions:

Do I need a new Electric Boiler just for the central heating? Or could I get another Sunamp Thermino (as I believe the have immersion heaters at the bottom of them) and just use that? Or could I use an electric boiler in combination with a heat battery? I'm not sure how these would work together. There seem to be multiple types of Electric boilers, I assume I don't need a combi if the Sunamp is handling hot water?

I'd like to not draw more than 10kw peak at any given time so I can fully utilise my electric batteries and not have to draw from the grid at peak times, so the idea of using heat batteries seems appealing if I can spread the load out.

If someone could give me some pointers so I can research the right things that would be super helpful, I've read a ton of things about individual technologies but I can't seem to piece how they all fit together.

 

[ShaunCorbs]

The sunamp replaces the cylinder

Can I ask why ashp is out of the question?

 

[Pete Lea]

The sunamp replaces the cylinder

Can I ask why ashp is out of the question?

Sure, all the pipework to my radiators is only 10mm and the radiators aren't massive themselves. I suppose I could ask a company to do a heat analysis report or whatever it's called to rule it out. We've spent the last few years renovating our doer-upper so the thought of replacing the pipework and the newer radiators seems a galling prospect.

 

[ShaunCorbs]

The problem is the electric boiler route isn’t the best tbh I would suggest staying on gas if that’s your only option

 

[Pete Lea]

The problem is the electric boiler route isn’t the best tbh I would suggest staying on gas if that’s your only option

Is an electric boiler (~100% efficient?) using energy that was consumed and stored at 5p/kw - as cheap as a gas boiler (~85% efficient?) at 4p+/kwh if it's only used for central heating? At least I wouldnt be paying the standing charge for gas if I can disconnect it. (I pulled those figures from memory so they may be completely wrong)

 

[ShaunCorbs]

Nothing is 100% efficient and gas boilers are around 93-94% I suspect your elec boiler will be around 85-87%

Also when do you have our most demand for heating winter time where you solar set up may be 60% accessible weekly / usable depending on snow etc

 

[Pete Lea]

Nothing is 100% efficient and gas boilers are around 93-94% I suspect your elec boiler will be around 85-87%

Also when do you have our most demand for heating winter time where you solar set up may be 60% accessible weekly / usable depending on snow etc

Okay my numbers were wrong . So do you think a good combo would be to keep the gas and replace my massive old combi boiler (the parts and servicing cost a fortune now) with a more efficient newer one and couple it with a smart hot water tank or a sunamp?

 

[ShaunCorbs]

Tbh yes I’m not totally convinced on the sun amp two reasons I haven’t played with one long term and price

There great if you haven’t the space for a tank

Me personally I would go as big as array as you can with 400-450w panels

Batteries are unless it’s a good deal on the tp you can / should be able to save a bit on these I would price for one now eg 10kwh the reason why I say this is you need 5-6 hours with full cap on your panels to re charge them with no load which tbh is a unicorn

And depending on the feed in rate this would pay for your gas depending on the deal you could get etc seen upto 35-38p a kwh on peak times

 

[Pete Lea]

Tbh yes I’m not totally convinced on the sun amp two reasons I haven’t played with one long term and price

There great if you haven’t the space for a tank

Me personally I would go as big as array as you can with 400-450w panels

Batteries are unless it’s a good deal on the tp you can / should be able to save a bit on these I would price for one now eg 10kwh the reason why I say this is you need 5-6 hours with full cap on your panels to re charge them with no load which tbh is a unicorn

And depending on the feed in rate this would pay for your gas depending on the deal you could get etc seen upto 35-38p a kwh on peak times

Thanks for your time, that's been really helpful. It's given me some more stuff to research at least

 

[Judith]

Hi Pete it’s been 7 months since your post and just having solar panels with battery storage ourselves. Was wondering if you went ahead with the heat battery for the hot water and what did you decide on the central heating.