Hi, we currently have a Gen1 5kw hybrid with an 8.2 battery. We are looking at having a heat pump installed in the future but also wanting more battery storage. what would be the sensible way forward, sell the old setup and fit an AIO plus new inverter or replace the Gen 1 with a Gen 3 hybrid plus a 9.5kw battery?
There’s a lot of differents parts to that simple question!
I’d start off with what is your daily consumption in winter and do you have a predicted consumption for your heat pump (have you got as far as quotes, heat loss surveys, etc)?
The difference between an 8.2 and a 9.5 battery is negligble difference so changing the battery adds little value as you won’t get enough from selling the old one to recoup the additional cost of the new one. Maybe if you have the 8.2 and the 9.5 together it’d be worthwhile but then you are likely to be constrained by your inverter throughput if you are trying to charge the battery overnight to run the heat pump. This is where the Gen 3 or AIO do score better than the Gen 1 inverter.
Another key factor is what tariff you are on and what tariff you want to be on. The best efficiency for a heat pump is to run ‘low, slow and long’, basically to have the pump on as low as temperature as possible to maintain the house heat against heat loss from the outside. There’s a recent heat geek video evaluating different tariffs on this efficiency, concluding that trying to run your home on just the cheap rate periods of Cosy or Go isn’t practical.
To give you my own practical experience. We’ve had a heat pump for 2 years now, and just over a year ago had our GivEnergy battery and inverter system fitted. We use about 14kW a day in the summer for domestic use + hot water with the heat pump, and I estimated an average of 22kW EXTRA a day for the heat pump although this was very variable - on very cold days it could be 40 or 50kW and worst case I saw this winter 90kW. We have a large house but it sets in context the sort of demand a heat pump can draw.
So given this high consumption I knew we simply wouldn’t have enough battery storage to see us through a day so elected for Octopus Agile and used Home Assistant and Predbat to automate the battery charge/discharge based on predicted solar generation and house load (including the heat pump).
For most of this winter we only had the 5.2kW battery (4.2kW usable) on a Gen 1 hybrid inverter which was enough to cover us through about 4-6pm in the peak agile period (typically 30-35p/kWh). The rest of the time I was drawing from the grid. Average price in November was 18p/kWh, I think February was 13p/kWh.
So key message out of this is that its unlikely you can buy enough battery storage or charge it up in the cheap period to run your house and ASHP, you don’t need a large battery, but you do need to be prepared to manage your battery actively to minimise your spend.
Personally more battery storage is good but the economics of it (what you save by charging overnight and discharging in the day) do not make for happy reading. A 9.5kW battery will cost about £4k fitted, a Gen 3 hybrid will give you 3.6 instead of 2.6 charge/discharge rate and cost about £1-2k fitted.
AIO gives you great discharge and charge rates, whole home backup but you’ll need to buy a separate solar inverter and at the moment you can’t daisy chain multiple AIO’s together.
I would suggest you stick with what you’ve got, maybe add extra battery storage but work out the economics, charging throughput and whether it’ll pay off in anything like a sensible period or not
Fridgeman
I would re-iterate everything that geoffreycoan has posted.
In August 2022, I had solar panels installed (SolarEdge inverter with optimisers as I had 3 roof orientations). I had a GE AC3.0 coupled inverter (3kW) feeding a GE 8.2kWh battery.
Over the winter, I decided to go for a heat pump and more panels installed. In April, I had my panel array increased up to 9.75 kWp and a 2nd GE 8.2kWh battery installed.
In summer 2023, I was on Flux and made a good profit (June was +£300 to me!)
My heat pump was installed at the end of July 2023.
In mid October, solar generation and temperatures decreased and my batteries couldn't last to the 4-7pm peak on Flux alone (from 1am-4am charge and solar). In afternoons, I was often charging from grid.
I then shifted onto Cosy with Outgoing 15p, which worked better with the extra 1pm-4pm charging slot. If I had a good winter solar day with 'warm' temperatures, Cosy worked with the heat pump.
With my GE inverter, in 3 hours I could import 10 kWh but only 8.3 kWh went into the batteries, the rest being used for my house load and heat pump. A 5kW inverter would obviously help here but my average base load (including heat pump use) was 24 kWh, sometimes much higher.
My AC coupled setup, can't get enough charge into the batteries.
In mid January, I transferred onto Agile import + 15p outgoing, supplemented by predbat at the end of January. I wish I had done this much sooner! My average import since 30th Jan has been 10.31p and my overall cost has been £32 (omitting Standing Charge).
I have wondered since whether I should have stuck with the one 8.2 kWh battery! But 2 batteries is probably nearer to the sweet spot.
My conclusion is that I can use lower priced 30 min slots from the grid to charge the battery. And anything less that 15p (minus conversion losses) is cheaper than using solar! Predbat has carried out my charging and discharging for me. If I hadn't gone with Predbat, I would have tried Wonderwatt.
I initially contemplated another battery but I wouldn't do so now.
It is a big decision!
Rob
Thanks for the replies, we are on Octopus go intelligent due to having an EV, so we get quite a few cheap hours (currently). I'm dumping my remaining battery to the grid in the evening as it pays to do this with any left over charge. We would be keeping the 8.2 battery and adding the 9.5 along with the higher output inverter. All the downstairs is heated by underfloor (water) so operating temps are lower than radiators, upstairs heating rarely comes on. Also have 2 multifuel stoves so we are hoping that an ASHP would save us a fair bit due to being on LPG. Think we need to get Octopus round to have a look and see what price they come up with for the ASHP. Thanks again.
Curve ball is switching it for a Polar-ESS setup. For the same rough cost of the AIO you'd end up with around 20kWh of battery and 6kw charge/discharge.
I have looked at the website for Polar-ESS.
Where have I seen that app before?
I ended up wondering whether this was an elaborate April Fool. We will see ....
Rob
Agreeing with all the above, but maybe to simplify it a bit without a ton of facts and figures, is that basically you can't expect to run an ASHP solely from batteries (in my opinion 🙂 ). The peak energy needs per day will be too high, and the instantaneous power throughput requirements will be too high.
Having a battery certainly will help take the sting out of it, and it's better than not having a battery, but the energy consumed by ASHPs is usually just too high (assuming a reasonably sized or even large house).
I've had an ASHP for almost 15 years now, and I absolutely love it, could not recommend them more. I have found the most economical way to run it is to bias it, so as to run on night rate prices 'as much as possible'. I'm probably lucky in having a very simple dual-tariff setup and get 9hrs of off-peak prices every day.
I simply charge heat/energy into the UFH for my 9 hours off-peak, then during the day I very rarely need to import any more power to top up the heating... The only controls I use really are the built-in controls of the Heatpump, which is all based on return water temperatures and Delta-T.
(and understanding you will find hundreds of conflicting opinions, but this genuinely works for me, for 10 years +).
Your current battery is already a 'good' size, and adding another one will make it 'better', but I don't think I'd factor in an ASHP too much when making this decision...
When I was selecting my own battery system (I went for an AIO - and love that too!), I also thought long and hard about how large of a battery I needed, but since I have installed it, maybe 6 months ago, I have come to the above conclusion, ASHPs are just bigger animals that batterys can cope with...
Agree with the points @paddyb makes about heat pumps are just too big for batteries. I see mine pulling 4-6kW at times, not so much now its milder, but certainly have seen that last month. Batteries take the sting out of it but you can’t totally eliminate the peaks and larger draw that heat pumps have.
Couple of points in follow-up @Fridgeman as you’ve got UFH downstairs that is a great match to an ASHP. As paddyb. says you can run the heating overnight and heat the floor up more than you need it, acting as a heat sink for the rest of the day. This very much matches the long and slow for the heat pump.
I wasn’t sure from your second message whether you were going to keep your existing gen 1 inverter with the 8.2 and fit the 9.5 and gen 3 alongside, or swap the existing inverter over. Just beware that other than multiple gen 1’s together (which is what I have), multiple gen 2’s or 3’s can suffer from cross charging each other.
Definitely be interesting to see how polar ESS develops and what is ‘cut down’ vs givenergy. Appears that the app is subscription (it says on the website that there’s a starter offer of it free for first year), but what else is different?
At the moment they have quite small batteries and inverters but there is more in the pipeline and they appear to be keenly priced
Fridgeman do octopus allow you to dump your battery to the grid for 15p/kwh then? As surely that’s detectable as brown energy and thus ineligible?
Smk82 I believe Scottish Power don’t allow brown export but Octopus don’t disallow it, in fact they explicitly allow it in the FAQ’s https://octopus.energy/blog/outgoing-faqs/
“What can I use an export tariff for?
We haven’t put a limit on this. Export via any source capable of feeding energy back to the grid. So that’s not just solar PV…
YOU CAN: get a micro-wind turbine installed, charge up home batteries when energy’s cheapest to feed back into the grid later, or (if you’ve managed to get your hands on a vehicle-to-grid charger) use your electric car’s spare battery
YOU CAN'T: build a home-brew nuclear power station, or run a cable from your neighbour’s house and jack up their bill by sending their electricity back to the grid. That’s just not cricket.”
“Join Outgoing Octopus and use home batteries (or your EV battery, if you've got hold of a vehicle-to-grid charger...) to take advantage of low consumption prices on our Agile tariff and high export rates on Outgoing Octopus. It’s a balancing act.
Store electricity at times of the day when the Agile prices are super low or even negative (on December 8 2018 Agile dropped to -2.31p per kWh). Then export from your battery when energy on the grid is most in demand, and most expensive. Not only are you powering your home with cheaper stored energy, but supporting the grid when energy is in high demand, and making money off anything extra you export.”
geoffreycoan
They may be supremely relaxed in their FAQs, but in their export terms (see 4.5.1) they make it clear that they don't have to pay for Brown Exports.
Though obviously they can do, and have chosen to do so. Long may it last.
Have a look at A2A. We have two pumps and 5 internal units which we run on 19kwh of batteries on all but the coldest days i.e. well below freezing. We rarely use peak rate grid power and where there is a risk of that on a few freezing days, typically Dec/Jan, we pop the gas boiler on. But that is very infrequent and only when the ASHP COP falls right off. The beauty of A2A is that you don't need to run it all the time and you are flexible with heating in different rooms. We're never cold and heating bills are next to nowt. We do have an 'A' energy rating for the house and insulation makes a big difference. I'm glad we didn't go with A2W to be honest. 4 bed detached house.
sponev Daikin MultiSplit system per chance?
Octopus are quoting for air to water - upside £7.5 grant - downside they want to 'upgrade' every radiator. That's why I'm looking at A2A.
Slartibartfast yes, Daikin, well two actually. Very flexible heating (and cooling). You will need a hot water solution although I think A2A with a cylinder is on the horizon. We still use gas for water currently as it's still cheap on Octopus tracker. We had a look at heat pump cylinders but can't justify the cost vs gas just yet.
Yes I have seen that A2A is much less energy intensive than A2W as well as giving a summer aircon option, Tim & Kat and The EV Puzzle on YouTube both have A2A.
As well as the no boiler upgrade replacement grant and you need something still to heat the hot water, from what I've seen they can be more invasive to fit to a home as you need to run new pipes into ceiling positions where the A2A units have to go. Depending on your room layout that may be more of a problem.
Slartibartfast do you have detail of what upgrades Octopus are quoting for the radiators?
We had pretty much all of ours replaced as part of our A2W ASHP installation, but in the most part its just swapping a single panel for a double panel of the same dimensions so its not really all that disruptive.
One of our radiators was installed bigger than the original (but that was in a room that I'd previously already changed two rads for a single larger double panel rad), and one in the hallway was smaller.
geoffreycoan we were able to install 5 units with zero visible internal ductwork and no condensate pumps due to the layout of our house. But we were fortunate and I suspect quite a few folk wouldn't be so lucky to get away with that. Indeed I think Tim and Kat needed some substantial duct work?
I enquired and they seemed to be wanting to replace most of my radiators and the hot water cylinder for their price estimate (before any survey). Since I designed the system for a 45°C boiler output temperature when I installed it 35 years back and have run it that way since then, I saw no point in replacing any of those components. Even after the grant, the cost would be more than doing it myself without the grant.
might all be a no go now if the new regs are true, unless they are not enforcable yet. current system is in the middle of the house under the stairs
Fridgeman Its still a proposed spec at this stage so the regs don't apply yet.
geoffreycoan Just got the detailed quote. They want to replace 8 out of 11 radiators. One in the living room is 1100mm x 500mm - they want to replace it with a 1800mm x 450mm one. I'm not sure where they get their rads from ...
However I have found Stelrad Compact K3 rads (triple panel). If they are connected correctly (bottom to top) then the out put at Delta30 is enough. Time to negotiate.
Slartibartfast I got something similar - one radiator much wider than what's there, and one much narrower. I pushed back and they came with rather more sensible alternatives.
(They're changing 6 of 10.)
Slartibartfast From personal experience, don’t skimp on the living room radiatior. This was the only rad we didn’t agree with the proposed sizing and had a smaller one installed but still larger than the existing one that was there.
We found in practice that the room was never quite warm enough, especially as you tend to be sitting down in the living room, so less active. We ended up installing a larger one a year later, in fact I fitted the largest I pretty much could fit in. Now if I turn the radiator up the room can get too warm which is a much better situation to be in.
I would also look carefully at towel rail recommendations. None of ours were recommended to be replaced but we found the kitchen (large ladder towel rail) and utility room (smaller towel rail) just never got warm enough. We had those replaced this year with a large vertical radiator and a conventional rad respectively. No warmth issues now at all in any of the rooms.
K3’s are good if a bit expensive. I considered one for our hallway which is where the master thermostat is but decided that actually I didn’t want that room over-heating as then it would shut the entire system off when it reached temperature. Keeping the new rad that was fitted in the install has proved to be the right choice.
Slartibartfast I had an A2W ASHP system installed last July and some of my K2s were swapped out for K3s. The K3s neatly fitted in the same positions as the old K2s so I didn't need any pipe runs changing. It sounds like your Stelrad Compact K3 might serve the same purpose.
The K3s certainly provide heat. I run solely on weather compensation and heating curve with no internal thermostat control, which has worked well. But this is A2W. I still have TRVs which are all open. If any room does overheat, I do have flexibility to turn the TRVs down.
you can't expect to run an ASHP solely from batteries (in my opinion 🙂 ). The peak energy needs per day will be too high, and the instantaneous power throughput requirements will be too high.
Agreed!
Rob
geoffreycoan Living room has a 4kW log burner - so no worries when it gets a bit chilly. One thing I did notice - it looks as though they ignored the MVHR system when they calculated heat loss.
I wouldn't count on getting much for selling your old system as GivEnergy doesn't really support 2nd hand gear very much - essentially no warranty on them and most installers don't want to install it due to the warranty issues and having to take over the whole install when doing so
On the topic of ASHPs I found this relatively informative:
comms
Then you should absolutely check out his follow up video 😊
https://www.youtube.com/watch?v=BesfqnHPxLU
To be fair to the man, he was challenged on his opinion, took it on board, and made a video on what it looks like when done right. I was actually following this drama in realtime, its was a lot of fun. And it will very easily lead you down a huge rabbit hole of distraction in youtube (or at least, it did for me!) watching videos from the Heatgeeks and the Urban Plumber…
Same as most things in life, if you choose the wrong system/size/solution for any project, then compound issues by also installing it incorrectly, it’s probably not going to work. The guys in that follow-up video did that fix for free, and a very well know HP manufacturer donated the equipment for free...some honest, diligent and passionate people showing how things ‘should-be’. Huge respect to them!
Rob_Quads picked my last Gen 1 Hy5 up for £75 so yes I'd agree the second hand market is not great. Shame really as if you know what your doing they are relatively easy to resurrect.
hoggy Wow that's incredible. How did you get it installed then past the "installer has to commission it"?
geoffreycoan well given I'm a spark I have installer account so cheating a bit, but even if not (and you forego the portal access) it's not like these things cease to operate via GivTCP or any other local control method.
hoggy Definitely something to think about when my warranty expires. Thanks