Air Source Heat Pump: Electricity bills have tripled since having solar installed - any advice?

There is no consistency in those figures is there Julia? Huge relief tonight though, had a phone call from the Damien one of the installers. He told me to go with the changes I’ve made for a week. I am to ring him next week and if I am still not happy someone will come out to me. Can’t ask for more than that.

Here’s a comparison with my electricity use for the same period.

For us it’ll be mostly the heat pump; we also have a small electric heater going in the garage for a “short time”, an electric towel rail on occasionally, the usual kitchen things though rarely the oven recently. I had the heating on all night as a test until 28th March. Also I think the reading of 10kWh on 24th March is wrong - too low ! We were away 2nd - 4th April.

The air temperature has a noticeable effect on the amount electricity the hp uses, eg on the night of 23rd March it dropped to 5 degC and I had the heating running then.

So generally my use is less than yours, and I have the house at 22 degC. Yours ought to be lower too because your solar and battery should be giving you “free” electricity. That’s definitely something to question with the installers.

Good news that they’re able to send someone out. 

Here’s a comparison with my electricity use for the same period.

For us it’ll be mostly the heat pump; we also have a small electric heater going in the garage for a “short time”, an electric towel rail on occasionally, the usual kitchen things though rarely the oven recently. I had the heating on all night as a test until 28th March. Also I think the reading of 10kWh on 24th March is wrong - too low ! We were away 2nd - 4th April.

The air temperature has a noticeable effect on the amount electricity the hp uses, eg on the night of 23rd March it dropped to 5 degC and I had the heating running then.

So generally my use is less than yours, and I have the house at 22 degC. Yours ought to be lower too because your solar and battery should be giving you “free” electricity. That’s definitely something to question with the installers.

Good news that they’re able to send someone out. 

Gosh, that graph is so interesting Julia, we have been using a lot more energy than you. I spoke to the installer yesterday and told him I had turned all the rads on to 18 in the day and 15 through the night. He told me to lower it through the night as that is the time it is costing me so I lowered it to 12. Interestingly we used 2 kw yesterday day time with all those rads on but the reading this morning said we had used 12kw in total so 10 kw were used through the night. The house was much warmer but not quite warm enough so today I have turned the heating up to 21 and up till now (6.30 pm) we have used 2kw. I am happy with this as it works out having a warmer house for about £3 a day. I am going with this for a week or so but I think I will ask the installer to come as I have so many questions for them. It has definitely helped turning all the rads on as you suggested but because we are solar it isn’t as cheap for us to run them through the night as it is for you. I will see if turning them off at night will make a difference so that we only use 2kw all day. I have learned so much this last couple of weeks and it is all thanks to you, I’m very grateful.

Hmm. Not sure I agree that the heating would cost that much through the night. How are you controlling the times and temperature?

I I have a wifi hub that controls the temps in each room

Does that control the radiator valves ? What make is it ?

Hi @serennu How are you getting on ? Here’s a video of a Vaillant hp in a Welsh house (previously using solid fuel) showing how it should be done. When you see your installers you should get them to show you 1) the heat loss of your house and that your hp is correctly sized, 2) what the weather heat curve is set to and what flow temperatures that gives you, and 3) how to set the radiator controls so they don’t influence the Vaillant hp controls. 

In this example the owners bills have dropped significantly by having the hp.

Yes Julia, it controls each rad valve, it is a Honeywell

@serennu 

I thought I’d just summarise this thread to make sure I’ve got everything straight.

Can you read through all this and correct me if I’ve got anything wrong please.

You have a small 3 bedroom house in Powys, two occupants (“oldies”) with an ECO4 installation of an air source heat pump, solar and battery, installed last year, replacing the solid fuel central heating. You still have a log burner. The installers were Sprint Renewables, who also put in new radiators, plumbing and shower. Last summer you were still taking energy from the grid though you expected to generate and store sufficient for your use.

You’ve been through one winter and the last 3 months cost you £1150 which is triple your usual electricity bill. Importantly your house has not been warm enough and you have been supplementing the radiators with your log burner. The bills are not estimates: you do not have a smart meter but have sent an up-to-date reading recently. You are on the Simpler Energy tariff, ie a single rate over all 24 hours.

You have not felt confident enough to alter the settings on the new “Cape Canaveral” controls in the airing cupboard. Warm Wales (who I assume organised the installation) suggested SevernWye came to advise you but it transpired they knew nothing about your system so could not give any help at all.

You have 9 radiators though have not had them all switched on because of the large bills. You are using Honeywell wifi controls (part of the new installation?) to set the time and temperatures they run, eg two lounge rads 21 deg for 8 hours, bathroom rad 21 for 2 hours and one upstairs for 2 hours. You have a 139 litre hot water cylinder, set at 60 deg but you have since reduced that to 50 deg. You use the shower once or twice a day.

The solar inverter is a Sun Synk, (no obvious CT clamp though one should be present where the mains electricity enters the building ie close to your meter), you have now set up an online account with SunSynk, but need help to understand further.

The battery appears to be a Dyness, it is situated where it doesn’t have much space around for cooling.

The heat pump is a Vaillant VWL 105/6 A 230V S2R1 which is a 10kW unit.

The radiator controller has a Honeywell wifi hub and individual controls on each radiator valve.

Assistance from the installer recently has been: they agree with running all the radiators at 18 in the day, but suggest setting back to 12 at night. Your low daytime electricity use suggests that the solar was supplying the house. You still need a strategy for setting back at night, at the last comment you used 10 kW at night with rads set to 12 deg. You are now running the radiators at 21 deg in the day.

My recommendations:

The Vaillant has its own inbuilt control system for setting the temperature in the house. I am certain that you should not be controlling the radiators with the Honeywell wifi controls as that will use much more electricity. Your installer (or someone competent) should show you how to do this.

I think it’s quite possible that you have an oversized heat pump. You can check that with the documents you should have from your installer. If it is oversized then your installers should be made to replace it for a correctly sized one, an oversized unit means higher electricity bills.

Just had a very quick read through the thread. Very useful advice being given.

When is the water cylinder being reheated? Is this a constant reheat when the temperature drops below a certain value or is it set to a schedule to reheat at a certain time (perhaps overnight?)?

Is there a way of checking usage on the backup or immersion heaters to make sure these are not being overly used rather than the heat pump?