Electric combi boilers / solar panels / eco heating solutions

Would be interested in opinions on a solar quote I’ve had, or on any of the components in it.

Around 8 months ago I got a few quotes (Octopus/Eon/local) for ~12/13 panels and a 9kWh battery which all seemed to be around £14k, which seemed expensive and too long a pay back period.

I signed up to a Solar Together Surrey group buy interest list and have had the following initial quotes (these are just prices without a visit to confirm).

Pricing seems a lot more reasonable, just interested if people more knowledgeable than me have any thoughts on either the pricing, the components used or questions I should be asking:

————
19 panel Quote

PV Package Pricing
19 panels £4,962 (19 * 430w = 8170w)

Storage Pricing
9.2kWh £3,009

Shading optimisation £950 (£50 per panel)
Bird Proofing £600
Extra roof scaffolding £1,000 (2 * 500) (panels spread across three roof sections)

£10,521
————
13 panel quote

PV Package Pricing
13 panels £3.913 (13 * 430w = 5590w)

Storage Pricing
9.2kWh £3,009

Shading optimisation £650 (£50 per panel)
Bird Proofing £600
Extra roof scaffolding £500 (1 * 500) (panels spread across two roof sections)

£8,672
——
Panels:
Exiom TOPCon 430W All Black Module - 430W

Inverter:
Growatt - MIN 2500~6000 TL-X

Battery
Growatt Ark 10.24kWh (Usable capacity 9.2kWh)

I paid £12k for basically the 19 panel package (I had 18 panels) with solar together back in Jan.

They were great and that seems like a decent price. I would go for it if you’ve got the ££.

Depending on how heavy your electricity usage is, it might be worth looking at extending to 15 or 20 kWh. Especially if you’re thinking about a heat pump later down the road.

Thanks, that's really good to hear!

Electricity usage isn't particularly heavy so even 9.2kWh sounds a lot. I assumed batteries were the easier part to expand in the future (no scaffolding etc etc) and one area where tech/cost may change more rapidly.
No plans for a heat pump but I should probably read into it a bit more.

They’re super easy to add on but you’d have to add VAT as they’re only exempt as part of a solar installation. So effectively a 20% discount and no increase in labour cost.

Good point about the labour costs etc.

I think since Feb this year they're VAT free even just on their own:
https://www.gov.uk/guidance/vat-on-energy-saving-materials-and-heating-equipment-notice-7086

2.19 Batteries for storing energy converted from electricity ... the installation of a standalone battery for storing electricity from the
grid (the mains electricity)

but yep that's not forever so worth thinking about

Looks very reasonable compared to mine. I had 16 panels installed and a 7.2kWh battery, and I think it cost about £11k. That was also part of a Solar Together scheme.

Thanks, that's really helpful to know.

My octopus quote comes in at
13 panels (13 * 440w =5720 w)
13 x inverters
2 x 10Kwh batteries
Bird Proofing
Scaffolding
Installation
£10,2205

Which seems reasonable to me.
Tempted to ask for 2 more panels as our intent is to dead off the oil central heating and install electric underfloor heating throughout

install electric underfloor heating throughout

Please don’t do this, you’ll have a really bad time.

Leccy UFH is unbelievably juicy, especially retrofitted to a suspended/poorly insulated slab floor; your 20kWh of batteries won’t touch the sides.

UFH in bedrooms is also a bad idea for comfort, for many reasons.

Get one of the big energy companies to install a heat pump and massive radiators; you prob know this already but the £7.5K grant makes it cheaper than a boiler install. Don’t waste your money on unnecessary UFH, and certainly not electric UFH!

^ this.

We're getting electric UFH installed this week for a tiny en-suite but that's as far as I would go. Certainly not a whole home solution.

This is what worries me most about trying to go for a heat pump tbh - really difficult to see where I can fit really big rads or which I actually like the look of...

You don’t need new, massive radiators for modern R290 based heat pumps to work; it’s fine to use existing.

Upgrading the rads will allow the heat pump to run at lower flow temperatures, and be more efficient however.

Allegedly cast iron rads are ok with heat pumps: https://www.castrads.com/en/product-category/cast-iron-radiators/

Any heat emitter will work with any heat pump (or any other heat source).

Sorry, I should have clarified - I mean apparently they're able to deliver an efficient COP.

Depends how big, how many, which house etc etc.

This is the problem for us. House is single skin brick so rads prob need to be good / we need to insulate wherever else we can, but there aren't lots of good wall spots for rads.

I'd understood cast iron were not likely to be as efficient but they do look nicer (IMO)

When I looked at this before the suggestion seemed to be that they were pretty inefficient when running at a high temperature and runnng costs were pretty high because of that (higher than the equivalent gas boiler).

I couldn't find much actual solid data though, mainly lots of best case scenario stuff which wasn't that useful.

UFH in bedrooms is also a bad idea for comfort, for many reasons.

What makes you say this?

That’s not the same as it’s heated with the air source, they are talking about electric pads, you’d need to be mental to install that in your house unless you’ve got a hooky meter

Radiators at the end of the day are radiators, as long as you have the correct BTU for the room it’ll heat no matter what kinda of input.

Price wise they ain’t cheap tho

Really slow response if set in dry screed, compromised performance if retrofit overlay/between joists. Ideally you want decent response time to achieve an overnight setback temp and recovery; I know I find a 21deg bedroom uncomfortable to sleep in.

Also poor ratio of emitter surface to room volume; bedrooms usually have a lot of furniture about the place, including a bed taking up a big chunk of floor.

Sure, but don’t they have a higher internal volume which means more water heated which means worse COP?

Look at it this way: unless you're in the Highlands, in the UK we only really get a week or so of truly cold weather a year, and this is the only time your heat pump will approach its max design flow temp with lower efficiency. The rest of the time, it'll be ticking over at a much lower flow temp, achieving a CoP and running cost that will be comparable to gas even without using a tracker/time-of-use tariff, whilst keeping your house at a constant, comfy temp all year round.

If/when you eventually begin upgrading radiators, the efficiency will only increase.

There's also the inevitable re-balancing of the 'green tax' from leccy to gas to consider, which will make running heat pumps even cheaper.

Internal volume is only relevant as part of a series of factors which contribute to overall BTU output at a certain delta-T, and with other factors being equal, more water volume actually = better CoP.

Material, form factor, size only matter in so far as the goal is to maximise water volume and emitter surface area, and minimise flow temperature and flow resistance on the circuit.

Talking of radiators, most fancy ones, especially the ubiquitous 'column'-style ones that mimic cast-iron style, have significantly lower real-world outputs than their stated BTU values, which are often just made up. Orthodox P+, K2, K3 panel rads are a known quantity with a uniform design having been through multiple test labs which reliably confirms their actual outputs.