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Our journey through Octopus tariffs 2020-2025

Electricity, Tariffs, Monitoring & Providers

Last Post by Batpred 3 months ago

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Tim441

(@tim441)

Honorable Member Contributor

Joined: 3 years ago

Posts: 398

Topic starter 01/12/2025 11:33 am

Everyone will have a different setup, usage, needs etc but it still might help others to see our journey from oil heating to ashp that will likely see us import over 14500kWh and export around 7500kWh this year - at a net negative cost.

Background

Somerset based

Listed Grade 2 building with large modern extension. Approx 100sq m old building & 100 sq m modern, well insulated
LG Therma V 16kw ASHP Installed Aug 2020
Underfloor heating throughout downstairs + Rads Upstairs

Fixed flow first 2 years then changed to weather compensation in winter 2022. Reducing heat pump usage from circa 8000kWk/pa to 5800 - saving 27.5%

8.7kw pv solar (2.2kw on FIT 2015 south facing, 6.5kw installed 2021 on east facing, low pitch)
3 x 8.2kw GivEnergy batteries installed 2021
1 x GivEnergy Gen1 hybrid 5.0kw inverter. Important to note max charge/discharge rate 2.6kWh that limits ability to take full advantage of cheap charging etc.

Manual changeover EPS

MG4 EV From 2023

WonderWatt used to help manage imports and exports

Comparisons

Comparisons are not easy due to changes in usage as well as:

we did not record previous oil usage or cost. At a guess 2500litres/pa
Move to weather compensation ashp Dec 2022 from fixed flows
EV from 2023
2025 move to Intelligent Go meant batteries used more over summer to maximise cheap overnight imports and maximise exports

Rough numbers:

ASHP uses 5800kWh/pa
Solar prod 6500kWh/pa (7000kWh in exceptional 2025 and shading reduced)
Exports prior to 2025 ~2500kWh/pa
Exports 2025 ~7500kWh with forced emptying batteries. Income £1125 + FIT
Imports therefore changed a lot to include additional battery filling at night for forced exports in summer + EV etc
EV charging at home ~2500kWh/pa

Tariff journey

Fixed tariffs 2020 - Feb 2023
Tracker Feb 2023
Agile Mar 2024
Intelligent Go Jan 2025

Tracker averaged 16.15p - saving at least 20% vs standard/fixed tariffs
Agile averaged 12.03p - saving around 50% vs standard/fixed tariffs
Intelligent Go so far this year has surprisingly averaged 7.5p. Vast majority imported at cheap rates (overnight plus extra slots). Cost for full year likely to be ~£1100

Faff factor is important. Hence use of WonderWatt to capture cheap slots on IG. Also used it for Agile to help manage. Also helps manage exports to maximise without running batteries down too much.
At a guess oil would cost us ~£1500 pa now if still using.

So net import/export cost for us this year is roughly zero. Obviously capital costs need to be factored in.

Fwiw the heat loss calcs for heat pump suggested

27597 kWh of which 23800 was heating & 3800 hot water

Actual usage of 8000kWh on fixed flows might suggest average SCOP of just over 3? Our heat pump does not record SCOP

This topic was modified 3 months ago 3 times by Tim441

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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Judith

(@judith)

Honorable Member Member

Joined: 2 years ago

Posts: 489

01/12/2025 12:46 pm

That’s a great journey to read. We’ve all got different combinations of tech, purchased at different times. It clearly helps to have large roof areas pointing the right way!

2kW + Growatt & 4kW +Sunnyboy PV on south-facing roof Solar thermal. 9.5kWh Givenergy battery with AC3. MVHR. Vaillant 7kW ASHP (very pleased with SCOP 4.7) open system operating on WC

👍

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Tim441

(@tim441)

Honorable Member Contributor

Joined: 3 years ago

Posts: 398

Topic starter 01/12/2025 1:00 pm

@judith its interesting to see the 6.5kw array is at just 5deg pitch and facing east. I suspect they produce 90% or more of the production if they'd been optimal south facing on normal pitch. Luckily they're single storey high so i can clean them with brush and hose pipe. Dirt is therefore not an issue - if left uncleaned i suspect buildup of lichen and sahara dust etc would cause a problem over time.

The older array is south facing and around 40deg pitch

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Majordennisbloodnok

(@majordennisbloodnok)

Famed Member Moderator

Joined: 4 years ago

Posts: 1693

01/12/2025 1:20 pm

Posted by: @tim441

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...

Dirt is therefore not an issue - if left uncleaned i suspect buildup of lichen and sahara dust etc would cause a problem over time.

...

Now that would be a really interesting point to get clarified. I've never cleaned our panels and they're pretty much as clean now as they were when first installed, since the rain, sleet and snow do a pretty good job of cleaning for me. However, with your panels at just 5 degrees I can understand why there might theoretically be a difference.

105 m2 bungalow in South East England
Mitsubishi Ecodan 8.5 kW air source heat pump
18 x 360W solar panels
1 x 6 kW GroWatt battery and SPH5000 inverter
1 x Myenergi Zappi
1 x VW ID3
Raised beds for home-grown veg and chickens for eggs

"Semper in excretia; sumus solum profundum variat"

👍

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Tim441

(@tim441)

Honorable Member Contributor

Joined: 3 years ago

Posts: 398

Topic starter 01/12/2025 1:41 pm

I mentioned above

"2025 move to Intelligent Go meant batteries used more over summer to maximise cheap overnight imports and maximise exports"

A small reminder that there is a round trip loss caused by converting grid import to battery and re-export. I think most people suggest this is around 10%.

So with IOG imports at 7p+ vat and exported at 15p is still very worthwhile. Especially as i can do automatically for the most part. But of course will need to watch if export rates drop etc.