Electric combi boilers / solar panels / eco heating solutions

It might be old news, but Octopus Energy are now allowing Octopus intelligent go and Octopus Go electricity tariff users to go on the fixed rate export tariff, at 15p / kw for Intelligent octopus users or 8p / kw for Octopus Go users.

Previously you would go onto their 4.1p SEG tariff for export.

Thats means that for me, with the intelligent octopus go tariff, I can purchase electricity at 7.5p/kw between 11:30pm and 5:30am (6h) and export during the day at 15p/kw.

In theory I can set up my home battery to fill up, charge the EV at night at 7.5p, and export all daily solar panel generation at 15p.
No incentive any more to use surplus solar during the day.

Seems almost wrong...

My referral link if anyone needs it!
https://share.octopus.energy/blond-horse-546

In theory I can set up my home battery to fill up, charge the EV at night at 7.5p, and export all daily solar panel generation at 15p.
No incentive any more to use surplus solar during the day.

That's basically what I'm doing at the moment. Battery dips to around 80% before sun starts adding back to battery during the day. When it gets to 100%, it's all export.

Last night I was pulling down ~20kWh charging both cars and the battery overnight.

Who needs heating when you can just huddle round the inverter to stay warm...

Is your inverter within the thermal envelope?

Having written off an ASHP for our imminent total house refurb/extension we've been discussing it again in light of reports of prices dropping. It's still not clear whether we can get a grant for it as part of a complete thermal upgrade of the house or whether you would have to delay the installation of it until after all the insulation, windows etc. are done in order to apply for the grant.

If it doesn't turn out to be feasible (either due to a lack of a grant or it not being possible to put the external unit anywhere sensible) one other option that might be worth considering is a solar panels driving wet under-floor heating (since our roof is bang-on south-facing), with a gas boiler backup. I've read that such systems exist, but I've not found a schematic of them. Is there a separate expansion tank for the ufh loop with an element in it?

We’re currently claiming the full £7.5K BUS grant for installing ASHP as part of an ongoing refurb/extension; just find a friendly independent MCS-certified installer and it’s not a problem.

Solar on its own for heating won’t work (unless you have a field you can cover with PV panels). Most efficient system is solar PV charging a battery and running ASHP to ‘charge’ a thick, well-insulated UFH slab during off-peak periods of a smart energy tariff, then running your house from the battery and exporting solar at a high rate during the day.

Initial outlay for such a setup is very high, and payback often long enough to make it not worthwhile if your only criteria is reducing energy bills.

Sack off the gas if you can afford to.

That's really interesting. This bit confused me as to how you're meant to apply if you're getting a whole house refurbed including insulation and an ASHP in place of a gas boiler:

"Your property must have a valid Energy Performance Certificate (EPC) with no outstanding recommendations for loft or cavity wall insulation."

https://www.gov.uk/apply-boiler-upgrade-scheme/check-if-youre-eligible

...but you're still applying for the grant despite getting everything done at once?

I'm not thinking that PV would heat the house under all circumstances. I think we'd have to rely on a combi boiler a bit, but we could substantially reduce our use of it from the PVs. What I'm struggling to understand is what an electric wet-UFH system looks like. Where does the element go? Is there a buffer tank and an expansion vessel? How big are they?

If by ‘electric’ you mean ASHP, then it’s exactly the same as a ‘system’ boiler, with a hot water tank, pump, buffer/volumiser as necessary, rads, wet UFH etc, with the only difference being that you have an outdoor monoblock heat pump unit heating the water being pumped instead of an indoor gas boiler. The only direct electric resistance ‘element’ in the system might be a backup immersion heater for the hot water cylinder, but this isn’t essential.

The flow temperatures should ideally be lower with ASHP, therefore any rads should be larger.

As for the EPC requirement, you can check if your house has one on the gov.uk website, most do. If it doesn’t, obtaining one isn’t hard or expensive.

If anyone's interested, we just got quoted £3.7k all in (including replacement rads) for an ASHP from Octopus. I think that had all the various grants included (not means tested). 3 bed Victorian terrace.

Basically if the installer states that any loft insulation etc is getting done at the same time it’s fine. BUS will probably ask them for a photo or other proof.

I'm about to drop them for a local installer.

They're super competitive price wise but the closer I get to install date, the more concerned I am about the system design they've put together. Got a local installer over last week and we spent 2 hours reviewing the approach and there were so many things that Octopus had failed to consider and we're in a new build (2019), so I dread to think what it's like in an older property.

They've also changed the spec of system (different rads and cylinder) since original itemised quote. On both occasions, I'm getting lower spec equipment without a reduction in price.

You may have a better experience but I'm done.

I think this is the reality, they are designing for gas efficiency equivalence, so you get a higher temperature, low cop system at a price that helps them get market share. You don't get a well optimised system but if that matters depends if you're capex or opex rich

If you look at the league table of publicly available system efficiencies, octopus installs don't do very well

By electric, I don't mean ASHP, I mean water for UFH heated by electricity generated by PVs. I know you can get solar-powered UFH, I'm just struggling to visualise the system diagram for it. Where does the heating element go? In the buffer tank?

I have an iboost which rather than export uses excess Solar electricity to heat the hot water tank, the boiler is turned off for six months a year a a result

Solar thermal seems less popular these days but seems the better option for a wet system but solar in the UK for heating is always going to be a seasonal miss match between generation and demand and why a ashp is the best compromise

Unless you live in a passivhaus, the space heating will be thirsty, and using direct electric resistance elements to do this will be wasteful as you could only ever approach 100% efficiency, or a ‘coefficient of performance’ of 1.

Using the same amount of leccy, whether from the mains or augmented by solar/battery etc to run a heat pump will achieve a much higher CoP, usually 3-4, meaning you get 3x the heat energy for a given input compared to direct resistance heating. So again, unless your house needs hardly any energy input to stay warm, you’d be mad to use anything other than a heat pump to heat your UFH.

Like I said before, it's entirely possible that we won't be able to get an ASHP since where we want to put the external unit might not be feasible . If that turns out to be the case we'll have to stick with a gas boiler for our heating. If that is the case then we may be able to afford PVs, which we could use to augment the heating system and/or heat our DHW, which would save cash and carbon. If that is the case, how would that be integrated into the heating system, since boiler-based heating loops don't have a tank that you can put an element in?

Immersion element in the hot water cylinder, job done.

That would be the hot water cylinder that contains your domestic hot water? The stuff that you run into your bath? So presumably not the water/inhibitor mix that's running through your radiators?

I feel like I'm missing something here.

Perhaps this https://www.tepeo.com/ ?

I really liked the look of these, but hardly any reviews, other than the fella from fully charged on YouTube.

This is what I have, a few people at work have them as well
https://www.marlec.co.uk/product/solar-iboost/

You mentioned “and/or heat our DHW”… Yes, immersion element in the hot water cylinder.

If you really want to electrify, just make an ASHP work however you can. Anything else would be a big compromise.

He's convincingly enthusiastic...but agree, not much to go on

Something like this is probably what I need. It has the buffer tank stacked on top of the DHW unvented cylinder and an immersion in both, so you could presumably use surplus power from PVs to top up the heat on either.

2 quotes for ASHP installs both coming in at £25k - wtf am I doing wrong? 4 bed detached house with mixed oil/gas system. One quote mentioned 2 x Mitsubishi PUZ-WM85VAA- 8.5kW. I haven't got back to them yet as only just received them.

Seems about 15k more than I was expecting lol.