Gas Combi boiler needs replacement.I have PV what options are there?

rugbyleaguesmate

Hello I wonder if you could help? I have a 6.72 electricity producing PV on my roof purchased nearly 4 yrs ago based on advice from this forum and I wonder if you could help me again?

My gas COMBI boiler which heats water for taps/radiators and showers needs to be replaced and I am quite keen to see if there is an option to use my PV to supplement hot water production. I've done some research but I'm not really coming up with anything (electric boilers, std boilers with tanks and heating via a immersion etc)

I do not want to spend more money than using PV would save me but apart from running the house and sometimes charging the electric car I do feel I export too much to the grid.

Has anyone else had this opportunity and what did you do to sort it?

Thanks in anticipation.
Ian

Coastalwatch

Hi Ian, we've recently replaced our GCH with a couple of ASHP's, so gone totally electric. I've sent you a pm with our experiences, although it may not be compatible with your property or outlook.

The link below is a good place to start if you've an inclination of relying soley on electricity in future.

https://forums.moneysavingexpert.com/discussion/4715287/discussion-ashp-air-air-with-solar-pv/p1

michaels

What about water heating - we use loads of it with 5 of us all having multiple showers/baths each day.  Do heat pumps actually make sense for the required temperature or would a big storage tank heated using night rate electricity on something like the octopus 4p tariff make more sense?

Petriix

If you've already got all the plumbing for gas water heating then you're not going to find a cheaper setup than simply replacing your boiler with a new, efficient gas boiler. Remember that gas costs 1/5 of the price of electricity and less than half the price you are paid to export your surplus. Crucially, any electricity you export directly displaces gas being burned at a power station so it's no worse environmentally to burn gas at home.

If you are on deemed export payments *and* you are exceptionally high users then there is a potential to save money with a hot water diverter (Eddi, Iboost etc). You have to do the correct sums to work out if this is the case: calculate exactly how much you currently spend heating water each year by looking at your meter readings for a month when the heating was not in use and multiplying that by 12. Assume that you will be able to save about half of that figure each year because you won't be able to heat much in the winter so divide by 2 to get your potential annual saving. Now multiply that by the guarantee period on your chosen diverter to get your total saving. Now, take that figure and deduct the total installation cost including plumbing and electrical work and any parts etc. If you're left with a positive number then it's probably worth your while.

In my house we use less than 2000kWh of gas heating hot water each year which costs around £50 with a new condensing boiler so a diverter would never break even.

Unfortunately, most people do the wrong calculation by basing the estimated savings on the hypothetical cost of the diverted electricity rather than the (much lower) cost of the gas saved.

Solar for space heating is generally not practical because you mostly use the heating when it's not very sunny. Unless you have a way of storing the energy for when you need it. There are some products out there, but they are expensive when compared to the 10 year cost of ownership of a new gas boiler.

Petriix

Having said all that, the ASHP discussion is interesting, especially if you consider combining it with cheaper TOU tariffs. Probably not ideal for heating a whole house in winter though.

Martyn1981

michaels said:

What about water heating - we use loads of it with 5 of us all having multiple showers/baths each day.  Do heat pumps actually make sense for the required temperature or would a big storage tank heated using night rate electricity on something like the octopus 4p tariff make more sense?

Why can't you use night rate electricity to run the heat pump to heat the large storage tank?

rugbyleaguesmate

Hi there and thanks for your responses....Whats becoming clear to me is that in order to exchange the boiler for something which can use the Pv means quite a change (Installing tanks, heaters, diverters etc) and I don't think will be financially viable. I was hoping there would be a boiler that maybe was duel fuel and smart enough to take from either depending on whats available.
Mart you were the one that persuaded me to get PV. Well I've generated 24.64mw since Sept 2016 with no issues.....absolutely delighted and thank you for putting me on this road!

michaels

I think you need hot water hot enough to warm up a bath that has gone cool which means 55 degrees or so,my understanding is that heat pumps rapidly lose efficiency when trying to get above 40 degrees.

Martyn1981

rugbyleaguesmate said:

Hi there and thanks for your responses....Whats becoming clear to me is that in order to exchange the boiler for something which can use the Pv means quite a change (Installing tanks, heaters, diverters etc) and I don't think will be financially viable. I was hoping there would be a boiler that maybe was duel fuel and smart enough to take from either depending on whats available.
Mart you were the one that persuaded me to get PV. Well I've generated 24.64mw since Sept 2016 with no issues.....absolutely delighted and thank you for putting me on this road!

No probs. If you are willing to make a big change, then have a look into an ASHP. I've tried but we just don't use enough gas overall (approx 6-7k total (heating, DHW and oven)), but if your heating and DHW (of course HP's supply hot DHW too) is around 10,000 kWh's pa or more, then the maths may work out with the RHI, and you wouldn't need a solar diverter for DHW in the non heating months, as the COP multiplier would make the HP far, far more efficient, and cheaper than gas when efficiencies are taken into account.
In the US, a lot of people have their electric water heater in the garage, basement etc, a non heated part of the house, so switching that unit for a heat pump water heater, which costs more to buy, actually saves a massive amount of money, but of course you need an area that can be cooled, with ventilation (like a garage), and that's a very different picture to the UK, where we mostly have gas fired hot water in one way or another. Oh well.

Been helping my sister with the research and liaison for her to get her new (but very old) home converted from two oil boilers to ASHP. Her and her husband will be running a small holding, and well being centre, and for some reason just don't want to be burning diesel in the countryside. ;-)

Fingers crossed for 3-phase too, so they can have a monster PV system, even bigger than yours!!!