Solar and battery vs ASHP

Northern_Line

Hi everyone,

I wanted to test some of my thinking on either of these options for my house. For background, we originally brought a newly renovated property in September. It has internal wall insulation, high performance glazing, loft insulation and good roof insulation. Overall, we really like the property but there’s one drawback- we’re off the gas grid, which means we’re all electric.

The developers who did the renovation went cheap on the heating and as a result, it currently has wall mounted electric panel heating as it’s only heating source. The design means it’s got high ceilings and is open plan. While this heating gets it to an acceptable temperature most of the time, it was completely inadequate during the current cold snap and it obviously costs a fortune to run. We will likely spend £4000 a year on energy, £3000 of which will be space heating and hot water.

I’ve been considering options for bringing the costs down or changing the heating system. It seems like I’ve probably got two options. Supplement the current electric heating and tackle the costs with Solar PV and battery storage. The challenge here is we live in a valley. Our South East facing roof has is banked by a big hill and trees which provide shading. The only option would be a 4.2kw array on a North East roof. I’ve had some good quotes( and a lot of snake oil merchants try to flog my fantasy systems that won’t work) that suggest this would generate about 2300kw per year, but I’ve also had a few people say that the location of the house in the valley means that’s even potentially optimistic. As a result, two guys said they could quote but they thought it would be a waste of my time and money.Given this uncertainty, estimating a payback period is difficult. 

The second option is to do away with the electric heating and install an air source heat pump. This would require installing underfloor heating downstairs and plumbing in wet radiators upstairs. While I’m skeptical of the cost savings for ASHPs, I actually think that as our current option is direct electric heating, which is only second to burning money to keep warm when it comes to cost, we could potentially cut our bills by anywhere from 1/3 to 2/3 with this.

Both These options would set us back about £10,000. I’m inclined to believe the ASHP might kill two birds with one stone, deliver a long-term uplift in the EPC and in our case pay for itself relatively quickly. However, I wanted to test these options with the forum to see if my thinking is sound.

Thanks 

Alnat1

To throw another idea in, what about ASHP and batteries without solar. 

You could opt for a tariff with cheaper overnight prices, heat your water and fill batteries overnight. The ASHP could then run in the day on the cheaper energy from the batteries.

Not sure if this is cost effective but worth doing a few sums.

ABrass

Not solar, not to help with heating. A NE facing array will deliver virtually nothing when you'd want the power.

The ASHP might be a good option. Even at a poor COP of 2 it would be halving your heating cost. You can keep the existing system as a backup or to provide a boost option if it's really cold or you want to warm up faster.

ispookie666

You could use PVGIS with your roof orientation to see how much it would produce. 
For AShP with batteries, you would need a reasonable size probably upwards of 20Kwh or even 30.  

Unless the SE is fully in shade, I'd still stick some panels up.  You could look into microinverters or optimisers, theoretically they are better in shading scenarios. 

Another cheaper option, Air to Air AShP, but you will need planning permission ☺️

Rodders53

Solar won't provide anything useful at the time you need it most (winter, short days, cold).  Dismiss that idea, probably.

Also consider air to air heat pumps --- Planning will be needed, but they are cheaper and likely less disruptive than fitting radiators, pipework and/or UFH for a wet ashp.  A new HW tank is likely to be needed to utilise a wet ASHP for hot water?

UFH done properly (pipes buried in a heat-retaining screed) may be too disruptive?  If so, larger low flow temp radiators could do a similar job?  Or one of the 'overlay' UFH systems may work - you'd need site specific advice probably?

When going down the wet CH install route don't forget to cost out Kerosene and Bulk LPG (propane) boilers.  One would hope ASHP would be competitive on a complete new install, but...

Go over to the Energy forums https://forums.moneysavingexpert.com/categories/lpg-heating-oil-solid-other-fuels where there are threads on heat pumps etc.,. that will provide useful reading for you.

Coastalwatch

Hi NL and welcome to our mad house! I can certainly agree with both previous posts and would like to add another suggestion into the mix. That being Air2Air heat pumps. IMHO they are more economical to install and run without the intrusion and complexity of underfloor heating and radiators. We have two that satisfactorily supply all our space heating in combination with a thermal heat store to cover DHW and all installed for circa £4k. As Alnat1 suggests, a battery charged via a cheaper overnight tariff would assist in reducing consumption in daytime hours at the higher rate.

Probably worth having a look at the thread below if seeking further info. Don't be put off by the with solar aspect as that was the original intention way back in 2013. It is still appropriate, but even without solar they are a very efficient means of heating being comparable to that of GCH in terms of running costs.

https://forums.moneysavingexpert.com/discussion/4715287/discussion-ashp-air-air-with-solar-pv/p44

Reed_Richards

Solar power is a terrible match to heating requirements.  You get very little solar power in months like December and January when you need the most heating and more power than you can use in the summer months.  The appraisal that it was a waste of your time and money was honest, at least insofar as expecting it to make a significant impact on your heating bills.  

I have an ASHP and I'm very satisfied with it.  However under current EPC regulations it will do nothing whatsoever for your EPC rating, although there have been mutterings that this may change in future.  Whilst an ASHP alone might cost you under £10k, I suspect that installing a central heating system, pipes, UFH, radiators and a suitable hot water cylinder will cost you a lot more.  If you go with a mix of UFH and radiators, make sure that you can get an ASHP that can make best economic use of this and reduce its output flow temperature when the radiators are not calling for heat.      

fenwick458

I'd rule solar out on a NE roof
battery storage in my opinion is overpriced and won't be around for much longer , with the advent of EV's and bi-directional charging as standard you won't need to spend £10k on a measly 10kw battery you'll just get a 70kw battery in the form of an EV at no extra cost
Insulation seems a safe bet, just put all your money into insulating the house

Northern_Line

Thanks all. 

I’ve looked up the property and PVGIS and to be fair, it’s largely in line with the two reputable quotes I’ve got. What I’m still skeptical of, and I don’t know if PVGIS accounts for this, is the gradient of the surrounding area. It’s difficult to describe but as we’re in a valley, we’ve got a 25 metre hill covered in trees standing over our SE roof. That to me makes any sort of install difficult if not impossible on that side.

I have considered air-air. I don’t know why but the planning process puts me off slightly. It also seems daft in my view you need planning for that but not an air-water system! Does anyone also know if air-air can be centrally controlled or if it works on a room by room basis?

I agree the UFH install would be disruptive. However as luck (or lack thereof) would have it, the down stairs floor needs to come up any way as the contractors “forgot” to screed it. So I’m thinking if we combine those two things, it might feel less disruptive. 

I am hoping the ASHP install would come in about 10k total (that includes discounts from  the BUS grant). So the price would be fairly comparable to Solar. Air-air would be much cheaper but I still have a few reservations. My other thought at the moment is that the current heating system is probably going to impact future sales of the house. Unless we see a structural change in the energy market that is at best at least 5 years off, I can’t see anyone wanting to buy a house off grid that is reliant on electric heating. Well, fewer people at least, which makes me think sorting the heating first also makes sense. 

Rodders53

Only one wet ASHP external unit and under a certain volume size is 'permitted development' and you may have PD rights limited in many cases (conservation areas for example) so requiring Planning in any case.

Air to air units can have WiFi modules added or some now come included (maybe at a premium indoor unit price).  Those will allow centralised control.  They can also support wired controllers (rather than IR hand units) and data bus integration into fully fledged building management systems if desired.

You can get multi-splits (one outdoor many indoor) and outlets in ceilings rather than outside walls (think shops/offices/hotels to see examples) and even go the whole hog and get systems that can cool one room while heating another with 3-pipe VRF systems.  The more complicated they are the more expensive of course.

Just visit any makers website  (Daikin, Mitsubishi Electric, Mitsubishi Heavy Industries etc.,.) to see the options.  Most if not all also do wet ASHP systems.  

ispookie666

I do have a NE roof and have 12 panels on there, it produces sweet fa at this time over the year, over the year it's around 35% loss compared to perfect south facing.  The south-west facing one has significant shading from a large tree. Hence the reason for enphase system.
You should not rule out the South facing roof due to shadowing as the sun is high up relative to horizon for a good part of the year.  

If finances was not a limiting factor, this is what I would do 
1. Solar on pretty much all the roof - will need to go through G99 and you can limit how much you export 
2. Solar power diverter to heat up hot water 
3. Planning permission and Air2 Air Air source heat pump - At least 2 or 3 units.  Multi splits are more expensive to buy.  
4. Keep the infrared panels for the once in a life time (which seems to have every year) cold snap.