ASHP and electric tariff

[JohnMo]

In the process of installing the ASHP waiting for the weather to warm up a bit before I finish off.

 

So operating modes I can use, weather compensation - run 24/7 on normal price electric or a hotter WC curve (lower CoP but cheaper electric) to batch charge the UFH based on outside temperature but do the charge in a reduced cost tariff period of 7 hours at night.  The reduced tariff is 15p while the day time jumps from 34 to 49p, so from experience is a favourable night tariff worth it?

[ProDave]

In my well insulated house, the ASHP uses about 1/3 of the total electricity used in the house over the whole year, so being kicked onto a higher rate for all the other stuff (most of our use) would be a deal breaker for getting a little cheaper at off peak times.

[JohnMo]

Thanks for that, been going round in circles with this, with so many people talking about time of use tariffs.

[Conor]

We're on economy 7 overnight tariff. Approaching a full year and I've it setup to run only in this time. I'll take some meter readings and see how it's working out. 

 

However, I know most of our use is likes of the dishwasher and washer dryer. It's more of a challenge to used that stuff off peak than the heating. If you go down this route, you have to shift most of your usage to the off-peak time. Think about how this would work for you. If you've an electric car tho, no brainer.

[JoeBano]

Have you looked at octopus agile tariff? I’ll probably be switching to this in April when my octopus go comes to a end. Apparently for the last 30 days I would have averaged 29p/kWh that’s cheaper than the government cap. My heat pump is using around 15kWh a day for heating and hot water 1930s detached insulated to modern building standards. I’ve been following this forum for years got all my information on here to install my second hand grant aerona3 heat pump couldn’t have done it with you lot! 

[JohnMo]

23 minutes ago, JoeBano said:

octopus agile tariff?

Unfortunately our smart meter doesn't want to communicate, we have had several and they have all been the same. So cannot use a tariff that requires a smart meter.

[ReedRichards]

Wouldn't the best thing to do be to start with a standard tariff then experiment with different patterns of usage to see if they keep you warm enough?  Monitor your usage and if it looks like you could make use of an Economy 7 tariff then you can switch.  

[JoeBano]

I had a smart meter fitted with Scottish power never worked. I swapped to ovo energy they wouldn’t touch it then I swapped to octopus, they replaced the meter never had any issue since 

[m0deller]

Octopus Go Faster. 6hrs cheap 0130->0630. 12kW Vaillant ASHP

[JohnMo]

Is that just HP kWh or total kWh?

[JohnMo]

Update, after lots of messing about to get a smart meter working, went E7, but since this thread started I have a battery also. So currently 90%+ of the electric is coming from E7 and only a couple of kWh at full price, for whole house use including heating via an ASHP.

[PhilT]

52 minutes ago, JohnMo said:

Update, after lots of messing about to get a smart meter working, went E7, but since this thread started I have a battery also. So currently 90%+ of the electric is coming from E7 and only a couple of kWh at full price, for whole house use including heating via an ASHP.

makes sense around this time of year but may become more expensive in the depths of winter. You could compare tariffs - wait till it gets a bit colder, make a note of a day's conditions, usage and cost at your current E7 for reference, switch to standard variable and wait for a similar day's conditions and see how usage and cost compares with your reference E7 day. It may be closer than you think given nigh time CoP, battery charging losses etc.

Edited November 3, 2023 by PhilT

[JohnMo]

A quick update 27 October 2023 to today.

 

Including the last cold snap where we had temperatures down to -7, our total electric bill is on average 34.4% cheaper being on E7 compared to standard rate. To make these saving is only possible with the battery, it being charged on cheap rate.  Most the period our heat pump was running on WC 24/7. Had a couple of mild days and did night-time floor charging and the saving was 43%, with no day rate electric being used.

 

Comparison includes all heating, DHW heating and all other normal electricity usage.

 

Happy so far

[Ronny]

On 07/03/2023 at 18:38, JoeBano said:

Have you looked at octopus agile tariff? I’ll probably be switching to this in April when my octopus go comes to a end. Apparently for the last 30 days I would have averaged 29p/kWh that’s cheaper than the government cap. My heat pump is using around 15kWh a day for heating and hot water 1930s detached insulated to modern building standards. I’ve been following this forum for years got all my information on here to install my second hand grant aerona3 heat pump couldn’t have done it with you lot! 

I am on Octopus cosy, with heat pump, solar and 2 batteries. There is 3 different charges depending on time of use and i use about 3KWh a month on the very high charge so not worth bothering about. My actual bill for November / December was for a total of 838.7 KWh. The average  price i paid was 18.65 pence per KWh excl vat. Looking to add another 2 batteries so this will reduce the average price even more. I do not use the heat pump during the high rate between 16.00 and 19.00 hrs. I installed an  air con in the sitting room and the batteries carry the load of the house until after 19.00 hrs. I have given up looking at different tariffs as there does not appear to be any which would give any worthwhile savings. 

[joth]

On 18/12/2023 at 20:24, JohnMo said:

A quick update 27 October 2023 to today.

 

Including the last cold snap where we had temperatures down to -7, our total electric bill is on average 34.4% cheaper being on E7 compared to standard rate. To make these saving is only possible with the battery, it being charged on cheap rate.  Most the period our heat pump was running on WC 24/7. Had a couple of mild days and did night-time floor charging and the saving was 43%, with no day rate electric being used.

 

Comparison includes all heating, DHW heating and all other normal electricity usage.

 

Happy so far

For reference, how large is your battery and what's your typical daily usage?

 

We have 10kWh storage and about 18kWh per day consumption, plus Octopus Go only has 4 hour cheap rate. So works out better overall value to blast the ASHP at high temp for all those four hours, which generally is more than enough to meet our daily demand (heating + DHW) and the battery covers all the non ASHP usage (including 2x ppl working from home and all cooking).

With a larger battery:usage ratio I can see 24/7 ASHP with WC would be the next level of optimisation. But battery prices really don't justify it yet. 

[JohnMo]

Just compared last years December billing with this (used today's rates (pence) at last year's kWh. Last year gas and electric was £70 more expensive than this December is likely to be. This year we have a battery, more solar and ASHP. That reduction includes some high usage days where I was not using the ASHP optimally, plus we always heating the garden room (which we didn't have last year) to above 10 degs and some days up to 21 degs.

 

Taking into account the additional heating going to the summer house, we are closer to £90-100 cheaper than last December. So overall about 23% cheaper running the heat pump compared to gas.

 

 

Edited December 29, 2023 by JohnMo

[PhilT]

6 hours ago, JohnMo said:

Just compared last years December billing with this

Not sure about Scotland but down here in Buckinghamshire this December is very much milder than last December, so our total usage will be c. 800kWh compared to 1,119kWh last December, nearly 30% less, the heat pump obviously accounting for most of that.

[JohnMo]

1 hour ago, PhilT said:

Not sure about Scotland but down here in Buckinghamshire this December is very much milder than last December, so our total usage will be c. 800kWh compared to 1,119kWh last December, nearly 30% less, the heat pump obviously accounting for most of that.

Good weather down south, not so nice up here.

 

This years Dec average is up a couple of degrees (current average is +4), compared to +2 in 2022, but we still managed -9 at the beginning of the month. More rain, so less solar gain. Currently 1 deg with a high of 3 today.

[PhilT]

12 hours ago, JohnMo said:

Good weather down south, not so nice up here.

 

This years Dec average is up a couple of degrees (current average is +4), compared to +2 in 2022, but we still managed -9 at the beginning of the month. More rain, so less solar gain. Currently 1 deg with a high of 3 today.

Weather here this month has been shite, hardly any sun at all, wind, rain, dismal nearly all the time, but freakily mild. Solar panels will have generated c. 85kWh by the end of the month compared to 232kWh in Jan'23 just after they were installed. Average temps here +8 this Dec so far compared to -1 last Dec when we had two weeks of sub zero, including two nights of -12 minima! My ASHP energy used for heating only will be c. 520kWh this month compared to 837kWh last Dec.

[HughF]

Very mild in the south west too… 12 degrees the other day.

[SteamyTea]

11 hours ago, HughF said:

Very mild in the south west too… 12 degrees the other day.

I am quite high up, so a bit cooler.

 

This is until today.

 

 

And this is daylight hours.

 

 

 

 

 

[JohnMo]

On 03/11/2023 at 17:01, PhilT said:

makes sense around this time of year but may become more expensive in the depths of winter. You could compare tariffs - wait till it gets a bit colder, make a note of a day's conditions, usage and cost at your current E7 for reference, switch to standard variable and wait for a similar day's conditions and see how usage and cost compares with your reference E7 day. It may be closer than you think given nigh time CoP, battery charging losses etc.

Been charting my usage over the winter months, but have remained on E7 throughout. Looks like I loose about 1kWh per day during the charging process

 

During November I managed to utilise 80% of all usage, via the low tariff (16p) and the remaining 20% came from the higher tariff (35p) 

December we had 2 weeks at around -7 deg, but still managed to 72% at low rate

January was 74%

Last few days has all been low rate as the suns been out, and is charging the battery during the day

 

Have tried during the winter period, several operating regimes

• 24/7 running on WC,
• batch charging the floor, weather compensated flow temp
• and fixed flow temp running on a thermostat, to effectively batch charge over the 7 hours of E7 and as long as required in higher tariff period by utilising the battery.

From an energy (kWh) used per day perspective, the fixed flow temp on a thermostat option, seems to work out best for our house.  The fixed flow temp is set at 35, with heat pump rarely actually getting to that point, due to the mass (approx. 47 Tonnes) of floor to heat up, and by the end of the heating period the heat pump is producing around 33 degs (ish). No cycling of the heat pump (except defrosting), one single run per day of between 8 and 12 hrs (so far).  I do get a CoP impact, but not enough to worry about generally.

 

From a monthly cost perspective, when compared to gas I have been around £100 cheaper in Nov and £40 cheaper Dec and Jan. When compared kWh to kWh per day, on normal rate and E7 rate, I am saving between £60 and £100 per month during the heating season.

 

Pretty good day today - At midnight last night, I still had 40% battery charge.  -2 over night up to 7 degs during the day and the sun is out, but due to be -5 tonight.  This morning floor finished heating at 8.30am, cylinder at 50 degs at 1pm, battery fully charged again at 1.15pm (by PV generating around 4kW).  Currently hot water cylinder being topped up by diverter and heat pump running (forced override on the thermostat) to do an hour or two floor charging for free. Expect zero high rate electric today, same as yesterday. But on Thursday wet all day forecast so expect zero solar that day.

[Wil]

These shoulder seasons are great when the sun shines for the PV. Less so the rest of the time.

 

In November, I moved to Octopus Intelligent Go (pre-requisite compatible EV). Which gives 7.5p from 11.30pm to 5.30am, 29.5p the rest of the time. We absolutely rinse the 23.30 to 02.30 slot- Tesla batteries (20kWh) and car take around 40kWh between them if the car has been out and about. Actually do night time set forward on the ASHPs to run during cheap (20degC  target temp). Then set back at 5.30 (19degC). We load the dishwasher through the day and set it off over night. The same with the washing machine. Timed boost of the immersion from 04.30 to 05.30 to make sure the 300ltr tank is at around 56degrees which means we’ll get through to the evening on a normal days use.

 

We usually wake up to about 56kWh overnight usage, then if I can get 10kWh out of the solar I can go the whole day with no peak grid use and the occasional heat pump blip to keep the temp up.

 

The wind turbine appears to save about 10p per annum. It’s not in an ideal spot tbf.

 

Octopus appear to have balls’d up my billing (despite the smart meter) and apparently I only owe them £18 for December and January… considering the standing charge is around £14 a month I fear I’ve got a shock coming… either way, it’s way better than my previous Octopus flex economy 7 which was 16/34p and 45p standing.

 

Oh and the saver sessions are great too- just turn the HPs off and let the battery reserve take the slack for £8ish saving. Thank you.

[JohnMo]

2 hours ago, Wil said:

either way, it’s way better than my previous Octopus flex economy 7 which was 16/34p and 45p standing.

My issue is a smart meter doesn't work/commicate with the outside world, where we live, so can either have E7 or standard rate only.

[Wil]

4 hours ago, JohnMo said:

My issue is a smart meter doesn't work/commicate with the outside world, where we live, so can either have E7 or standard rate only.

 No external antenna that can be fitted to help it read? That was potentially an issue for us too, but harder getting a 3phase smart meter installed and then a suck-it-and-see if it works… jury still out but they let me switch…