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Savings - using Weather Compensation & Time of Use Tariffs

 
Air Source Heat Pumps (ASHPs)
Last Post by Tim441 1 year ago
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 Tim441
(@tim441)
Honorable Member Contributor
Joined: 4 years ago
Posts: 398
Topic starter 18/02/2025 4:41 pm   [#2123]

Looking back at last few years there are 2 clear savings that I've made that far exceed other savings from more minor tweaks.

1. Weather Compensation. This reduced my annual heat pump usage from just over 8000kwh/pa to 5800kwh/pa. Heat pump installed 2020. WC from end 2022.

2. Time of Use tariffs. I was slow to wake up to all the possibilities. Partly as my inverter is a slow 2.6kwh charge/discharge making it harder to maximise cheap slots.

Solar PV & Batteries added 2021

EV added 2023

Fixed/standard tariffs to end 2022

Octopus Tracker to end 2023 saved approx 25% vs standard tariffs

Octopus Agile to end 2024 saved nearly 50% vs standard tariffs by maximising cheap overnight slots & batteries. Agile poor since late 2024.

Octopus Intelligent Go has surprised me by offering a lot of cheap rate daytime slots. Perhaps making it possible to run around 8p average. Currently assuming a worse case 10p/kwh.

WITHOUT WEATHER COMPENSATION

annual total usage circa 14000kwh @ 24p = £3360

Annual heat pump usage circa 8000kwh @ 24p = £1920

WITH WEATHER COMPENSATION & ToU tariff

annual total usage circa 12000kwh @ 12p = £1440. Saving 57% / £1920

Annual heat pump usage circa 5800kwh @ 12p = £696. Saving 64% / £1224

2025 potential? I've assumed 10p average import cost

annual total usage circa 12000kwh @ 10p = £1200. Saving 64% / £2160

Annual heat pump usage circa 5800kwh @ 10p = £580. Saving 70% / £1340

PLUS by utilising IOG imports more I hope to increase my exports. Last year I exported approx 2700kwh earning £400. Perhaps £500 this year?


Listed Grade 2 building with large modern extension.
LG Therma V 16kw ASHP
Underfloor heating + Rads
8kw pv solar
3 x 8.2kw GivEnergy batteries
1 x GivEnergy Gen1 hybrid 5.0kw inverter
Manual changeover EPS
MG4 EV


   
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Ashp Weather compensation tou
 Old_Scientist
(@old_scientist)
Honorable Member Member
Joined: 2 years ago
Posts: 406
23/02/2025 1:16 pm  

I agree, using Weather Compensation will have a large effect on the efficiency of the heat pump and hopefully ensure the system is running flow temps as low as possible, which will make a big difference on efficiency.

With the ratio of electricity to gas prices hovering around 3.8, one needs to achieve a (S)COP of 3.8 to beak even on running costs if using the ofgem price cap tariffs. Reducing the overall import cost of electricity is essential. I'm currently on Cosy (with no battery) and achieve an average import cost of around 20p just by time shifting usage a little - setting back or turning off the heat pump at peak times, and bumping up the temp in the cheap slots to help compensate for the set back periods. This is a LESS efficient way to run the heat pump (slightly lower COP), but is more than offset by the half price electricity in the cheap slots. The important take home message here is the need to reduce your import costs. At 20p per kWh for electricity, I now only need a COP of 3.1 to break even with gas (or ~2.85 if you factor in that a gas boiler is not 100% efficient). If you are lucky enough to have some battery storage too, then further savings are possible.


Samsung 12kW gen6 ASHP with 50L volumiser and all new large radiators. 7.2kWp solar (south facing), Tesla PW3 (13.5kW)
Solar generation completely offsets ASHP usage annually. We no longer burn ~1600L of kerosene annually.


   
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 Tim441
(@tim441)
Honorable Member Contributor
Joined: 4 years ago
Posts: 398
Topic starter 23/02/2025 1:34 pm  

@old_scientist yes indeed.

The battery point is crucial. In years gone by batteries were typically seen as the best way to maximise use of PV solar production. However I would suggest it's much less important for that now we have export tariffs at 15p or more. Especially with most solar being produced in summer & shoulder months.

Batteries are now more important for maximising time of use tariffs and to that end helping with time shifting.

When I installed my solar & batteries in 2021 I thought it was to maximise use of own solar. Now its all about ToU tariffs.


Listed Grade 2 building with large modern extension.
LG Therma V 16kw ASHP
Underfloor heating + Rads
8kw pv solar
3 x 8.2kw GivEnergy batteries
1 x GivEnergy Gen1 hybrid 5.0kw inverter
Manual changeover EPS
MG4 EV


   
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