FoxESS Community - Owners & Installers Forum

Hi,
I have three MiraHV25 batteries and a 4.8kW array. We're on Octopus Go because we charge a PHEV and an EV most nights, but that means we get a low feed-in tariff. Our electricity bill is really low, but I'd like to make use of our surplus to heat some water. The only snag is that we have a combi boiler and no tank!
Is it practical to add a tank to the existing system, or is it a question of waiting for the boiler to expire and then going a different route?

Hi
You are asking a question about plumbing and I can share what I know of the options - there are various ones and you may need good advice for your home depending on whether you are trying to reduce your carbon footprint or get better payback on your excess energy.
Pressurised direct hot water tanks/cylinders (HWC) are readily available but need an expansion vessel to allow them work as you need plus other safety elements which add cost. They also tend to be large (typically a bathful of water or more for larger households) so you need space to put one. I doubt you'll find an HWC plus ancillaries for less than £800 inc VAT, and you'll have substantial installlation costs.
However, it can work in combination with your Combi boiler - essentially if the hot or warm water from your HWC is piped to feed into the cold water input of your boiler, then the you should only use gas to add whatever extra energy is needed to achieve the set temperature.
NB this plumbing solution can certanly outlive your boiler and can be future proofed to permit water heating from alternative solar panel, air-sourced-heat pumps or electric, etc.
If such a solution and cost means you are still interested, then you should be able to find either a good up-to-date plumber or a renewables installer who deals with more than just solar PV to quote you for somthing specific.
Good Luck,

Alan

That's great, thank you for the reply! I'm looking to reduce my gas consumption and this sounds like a great interim solution (our boiler isn't very old). It amazes me how much we can generate even on overcast days.

I consider doing something similar but already know I will need indirect untenanted cylinder with immersion heater (needed for e.g. heat pump in the future).
You will need some monitoring/automation e.g.
-something to tell you when battery is full,
-something to monitor water temp in tank
-it should be relatively easy to switch off/bypass gas boiler and rely just on immersion heater during summer m-ths.
Think I would start with estimation of amount of excess energy and calculate what amount of water I could heat up with it.

Just remember your installation needs to comply with building regulations (or it might invalidate your insurance).