Should I replace my gas combi boiler with an electric boiler?
A supporter asks us: I am installing solar panels and my gas combi boiler is getting old. Should I replace my boiler with an electric one so that the spare electricity produced by my solar PV panels can be used to heat water to heat my house? TTL’s Julia Waterlow responds.
It sounds like a sensible idea but the short answer is – no.
The longer answer is that it won’t stack up financially. I did a quick back-of-an-envelope calculation for my house and just using electricity for hot water and heating would cost me £1,500 a year rather than the current gas and electricity bills total of £480. Yes, some of the energy from the solar panels that I’m not using in the house could be diverted to heat hot water and reduce that a bit but:
- There are only about six months of the year when the surplus could meaningfully heat the water and that is mostly notwhen you need it for your heating. It can work for hot water heating during the summer, dependent on your usage and the size of the immersion heater, but that is a complex and individual calculation.
- You would need to install an immersion hot water tank (neither our correspondent nor I have one, nor the space for one). Plus you’d need a diverter to move the spare PV electricity to the immersion tank, which could cost you between £250 and £550 to install.
- an electric cylinder with storage is usually more expensive to install than a gas boiler
I also thought it would be a good idea to put in batteries at the same time as solar PV.
Yes, that could work but not if you were trying to heat hot water as well. You have to choose where your spare solar power goes: to the grid, to a battery, or to heat hot water. Trying to do all three is possible but is unlikely to stack up financially.
The difficulty with batteries that most people don’t realise is that most are quite small, unless you want to fork out a fortune. This is ‘small’ in the sense that although a battery may say it’s a 5kWh battery, the 5kWh is actually its storage capacity. However they can only take about 2kW or give out 2kW at a time.
So if like our correspondent (and me) you have an electric shower that uses 7 kW, then the battery can only supply 2kW of that and the rest has to come from the grid. The same would be the case with supplying a hot water tank: a battery can only supply a little at a time. Batteries are great for background electrics and smaller appliances up to about kettle standard. But turn on the oven, have a shower and watch TV and the battery won’t supply your needs.
So if I want to ditch my gas boiler and keep my existing radiator system, what can I do?
Air source heat pumps (about which we have talked extensively in our Lewes Eco Open Houses Online Events) are considered the answer at the moment although they are expensive. You need space outside to house one and you may need some larger radiators. Additionally, you should also consider that most gas suppliers will charge you to have your gas supply removed.
Alternatives to gas central heating is a major question the government has to address given that heating accounts for around a third (31%) of total household CO2 emissions.