Question for those with ashp, battery and solar

I’ve been looking at ashp for a while and yesterday I started to wonder how people are running these with relation to their battery/s and panels. In cold periods obviously they use a substantial amount of juice so do people just run the battery down and then run off the grid? If so what tariffs have been found to be best? Or do you get the system set up as we have for the EV so that it runs separately from the battery? Extra batteries seems a nice idea but will add considerably to the cost.

To give an idea, we run two heat pumps from 19kwh of batteries which gives us coverage for around 95% of the time without grid draw. However, we have A2A which I consider to be a lot more flexible than A2W in that we can heat rooms selectively and don't need them to be on all the time. So we manage quite easily for everything but the very coldest days. On the ten or so days where it gets very cold and COP falls off, we put the boiler on for a few hours. This is because gas on Tracker tariff is very cheap at the moment, so it's a cost issue and not that the ASHP couldn't handle the heating requirement. I can see from the various heat pump forums that those with A2W don't fare so well in many cases and also very sensitive to the quality of the installation. We do have an A rated EPC which really helps. We are currently on IOG but may switch to Flux as we also export a lot. In terms of max power draw, we only see it in excess of our 3.6 limit for a few minutes if we turn both pumps on, then it ramps right back as the pumps modulate.

We’ve just got the EPC up to a B from a D so that should help. Was looking at ashp as we really want a straight swap for the oil boiler, which is already outside the house, with the gain of replacing standard gravity fed hot water tank with mains pressure, and gaining garden from losing the oil tank (about 9sq m). Last years (the first) bill for everything- oil, electricity and car - was approximately £450 and we’ve done a lot of insulation since, so I’m worried/wondering how adding the ashp (ignoring initial outlay) will affect this. If it saves cash for heating but needs a tariff that makes the car twice as expensive (currently IOG) that would be unfortunate.

SimonClarke Morning Simon. It's a big subject and everyone will have their own ideas.
I have an A2A heat pump which covers our heating through the winter very well in our two bedroom open plan bungalow. We moved in 3 years ago and had a new gas boiler put in way before I'd really thought about solar and battery which we put in 18 months ago. Since we put in the A2A heat pump at the same time as the solar, the gas combi boiler now only heats the water and we use around 6-7 kw of gas a day.
As for the A2A heat pump, of course we only use it in the winter, and uses up to 10kw per day in the coldest times and on all day, to just 2-3kw a day in spring and autumn having it on mornings and evenings. Our normal daily use in the summer is around 6kw a day in the summer, unless it's really hot when we wack on the A2A to cool us down which keeps the house nice and cool. As you can see, we're actually quite light power users compared to some, but my wife and I are both retired and at home quite a lot.
Flux worked very well for us last summer till October when we moved over to Cosy with fixed export, so we could import cheaply twice a day on lower prices and keep the battery fairly full.
Over the 12months from Jan to December, we had actually made over the summer enough money from export to cover all electric imports, all gas imports and all standing charges, plus we finished up with £125 profit effectively making us energy neutral. Whether we'll finish up ahead this year we'll have to wait and see, but obviously export tariffs are less and standing charges higher.
Just for information, we have a 5.46kw solar array(6 panels east,7 panels south), Gen1 5kw inverter, and a 9.5kw battery.

As for ASHPs, that would be a different kettle of fish. They do seem to use a great deal of power, depending how big the property is and the temperature people feel comfortable at, but in any event, you need a cheap tariff to make it worthwhile. As an outsider and from what I've read, most seem to use Agile with fixed export which seems to work well for them. Geoffrey is probably the best person to give you some tips as he has a large solar array, two inverters and 2 batteries as well as ASHP. I'm sure there are many others who will be happy to enlighten you too.
Good luck with your research.

SimonClarke size the battery so it is exercised throughout the year, not just for worst-case winter demand. If you have some thermal mass, such as underfloor heating in a concrete slab or a buffer tank, this lets you do a lot of your heating in the off-peak period, same with hot water. In cold snaps, you can also take advantage of low-cost daytime slots on IOG to recharge the battery and run the ASHP when charging your EV. We replaced oil with an ASHP in 2013 and have no regrets.

TimHutchings Morning Tim, we have a 3 bed bungalow 132sq m, (EPC yesterday!) and we were using 1600 litres of oil so about 16000kw ish and 3400kw electricity for the house and 2400 for the car (9/10k a year ). I think (too early to be sure) that we have cut the oil to 1000 litres. We run the heating like an ashp ie on full time and after various tests the cost difference is insignificant. Just radiators which would all be replaced ( old anyway built 1996), and microbore pipe. Fag packet calculations suggest a Vaillant 5kw ashp would work. Similar solar set up- 5 kw gen 1, 6.48 solar split 8 each east west, and a 9.5 battery. House is not open plan so probably more problematic for A2A but not insurmountable. I like the cooling idea but really not needed at the moment!

stevelewis the battery is about right for us at the moment so obviously an ashp would use way more in the cold. No underfloor and IOG has never offered a day time cheap rate! Again fag packet calculations mean at a cop of 4.5 ashp would be about £300 a year dearer than oil at 27p kw but probably come out about even with solar, battery and a better tariff.

SimonClarke Hi Simon, adding my 2p worth.

By way of background we have a large (extended) house with (now) 6 bedrooms over 3 floors; EPC C. We had an oil boiler but 2 years ago the oil tank started leaking and the current oil tank regulations meant we couldn’t really replace the existing tank so went for an ASHP (air to water). As you’ve said we gained a load of space in the garden and we’ve now got mains pressure hot water rather than gravity fed.

In hindsight I think our system was over-sized, the heat loss survey proposed a 16kW system but at the time there were no MCS accredited systems that size so we ended up with 2 9kW LG ThermaV air to water heat pumps. With a design flow temperature of 55 degrees (which is high for a heat pump) and most of the radiators replaced.

Then in January 2023 we had two GivEnergy 5kW hybrid inverters, a 9.5kW and a 5.2kW battery, and 10.4kW of solar panels fitted. We also have an older 4kW FIT array, making 44 panels in total (14.4kW).

Trying to be succinct and answering your questions, in the winter the heat pumps do use a lot of juice. We use about 14kW normal house load plus a winter average (November 23-March 24) of 28kW a day. On really cold days it can be as much as 60-80kW. In summer just on hot water its 1-2kW a day. We run the heat pump all the time in the winter with weather compensation, an indoor temperature of 20 degrees and an overnight temperature setback of 17.5. The house is comfortably warm all the time, its just the electricity consumption thats a bit ‘ouch’.

We were on Flux last summer and going into this winter I knew from previous year’s data that we would consume far more than the batteries could supply. I looked at all the tariff options and concluded that as our consumption was so high the cheapest would be agile and that has borne out in practice, its been much cheaper (about half the cost) to be on Agile vs Flux, Cosy or the standard rate. We use predbat to manage the battery based on predicted house load and solar generation; in the winter it generally charges the battery overnight, holds the SoC it during the day, then releases it from 4pm when the Agile rates are highest. As we have two inverters giving 5.2kW discharge this covers the draw from the heat pump and cooker etc reasonably well. Some peak rate import occurs but its very small amounts. In fact for most of this winter I only had the 5.2kW battery in operation which was not quite enough to cover the Agile peak period, but it took the worst off it.

Net electricity consumption (import-export) for this year: November £250 (ASHP 825kWh), Dec £194 (ASHP 850kWh), Jan £244 (1233kWh), Feb £91 (700kWh), Mar £16 (600kWh). In the summer we are net exporters so every day in April so far we have been in profit (-£77 so far).

Comparing to running costs of oil, its been about the same so I’ve been reasonably happy with that. For years 1 and 2 its cost just over £1400 each year for the ASHP to provide heating and hot water. Of course I can generate my own electricity unlike oil so net I expect to end up with an overall lower energy bill.

In terms of your personal experience SimonClarke as you have a low EPC that’ll help. If you have air to air it will consume less than an air to water system, but I don’t think they are as good for large houses and you’ll still need a method to heat your hot water (although air to air that can do hot water as well are starting to come on the market). Your energy profile during the day will change and unless you have lots of batteries already you are going to end up drawing from the grid in the day time. Extra batteries are probably not cost effective. Agile is not as cheap as IOG overnight but its typically in the 10-13p range so not massively more expensive. Depends how many EV miles you do.
I wouldn’t go into it with expecting the heat pump will save you energy unless you have a really old inefficient system already. I’m happy with getting a break-even consumption cost.

If I were doing it now the only thing I would change is to push for a much lower flow temperature. We had most of our radiators replaced with double panels but the design was (I believe) for too high a flow temp and thus needed a larger heat pump than we could have had.

geoffreycoan morning Geoffrey thanks for all the details! I would be happy to break even as I think the gains ( extra cupboard as I would attempt to put the hot water tank in the loft, water pressure and garden space plus of course being greener) are useful. When I have been attempting to work out what we might need using Heatpunk etc I’ve aimed for 40c and a cop of 4 as that should work ok. I’m retired and my wife will be next year but only works two days now so we are used to wanting the house warm all the time hence running the oil full time now (and in our last two houses). Agile starts to sound like the way to go. I just like being able to tell people my Tesla costs 2p a mile using IOG!

SimonClarke on IOG, cheap rate is 2230 to 0530 every day plus any time during the day that your car is charging under Octopus' control.

stevelewis should be 23.30 but yes I know but it doesn’t matter when I plug it in we never get extra outside of the standard times in the day. Plugged in last night and when it finally decided what it was doing - 3 different schedules- it did start an hour early at 22.30 which is very unusual and sometimes it runs later but never past 8am. So pretty useless times really and not much help with ashp.

SimonClarke If you're using an Ohme charger, plug in at 1pm and ask for a set charge amount by 5pm.

stevelewis it's a Hypervolt so I use the car - Tesla - but I must admit it is usually plugged in late afternoon or evening for 8am so I'll give it a try

SimonClarke I think the trick is specific to Ohme - for all other integrations, it's Octopus that does the scheduling, whereas they allow Ohme to do the scheduling for that integration, and I guess Ohme aren't quite aligned with Octopus on what are suitable times to charge. (There were rumours that Ohme were doing some gaming during the savings sessions, but no idea if that was ever substantiated.)

With Zappi I sometimes get 05:30 to 06:00, and once I got 08:00 to 08:30 + 09:00 to 09:30 on a Saturday morning (it was probably windy or something).

TimHutchings
Hi Tim, I had A2A fitted yesterday! What temp/fan speed do you generally run at to get best economical use?(sorry to hijack thread but I can’t find a way toDM)

Watcher Morning. I normally set the temp to 20c, as the it's warmer nearer the ceiling as heat rises. Room temperature normally stays then around 19-19.5c at sofa level which is comfortable for us.
Fan speed I usually set to auto as it will adjust the speed to whatever is necessary to keep the room at a steady temperature. Ocasionally in winter we move the setting for the vanes to move from side to side to spread the warmth more evenly, but mostly keep them straight ahead which then better heats the bedrooms and bathroom with our house layout.
Like all new toys, you have to experiment a bit to see what works best for you.

Watcher we also run at 20-20.5 Deg on most of the units. Fan on auto unless we wish to drop it to super quiet mode. We run the vanes up/down and side to side other than the kitchen due to close proximity of the fridge freezer. Works well.