congratulations! 

my only question is why you've stayed with Cosy instead of Intelligent Go? With your battery and a bit more tweaking you may find IG cost effective.

We have ashp ... and battery. We run it 24x7 

our average cost of elec is around 8p - even with some higher rate usage

@tim441 very good question, and the reason is our limited BESS capacity of 13kW, which would not power the ASHP in the heating season during the day. A night-time tariff for EVs doesn't power our ASHP too well. We get 8hrs low rate with Cosy @ 3+3+2hrs. That allows us to recharge the BESS at 3000W max rate 3x each day sufficient to power the ASHP vs 6hrs overnight with EV tariff which would deplete our BESS mid-late morning, leaving us having to import at standard or peak rate to power the ASHP. Cosy is the better and most cost efficiency Octopus tariff for load shifting to 13kW BESS based on our load usage profile. I guess it's down to the size of the ASHP and what it consumes, in winter ours will chew through 3kWh.

Great job @allyfish 

I think it's an easy decision if you only have a heat pump or only have an EV, but combine the two (as will hopefully become more common) and the choice of tariff becomes less clear. I guess the choice will depend on which usage dominates.

Luckily there are plenty of excellent tools (such as https://timandkatsgreenwalk.co.uk) to help determine the optimum tariff and strategy.

Posted by: @old_scientist

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Luckily there are plenty of excellent tools (such as https://timandkatsgreenwalk.co.uk) /a> to help determine the optimum tariff and strategy.

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Thanks for that, @old_scientist. There are several threads historically where people have asked how my setup with Home Assistant and lots of automation combined with Octopus Agile compares with the more predictable tariffs and I haven't been able to give a truly accurate answer. Now, with that tool, I've been able to do just that.

Over the last year, we ended up paying Octopus £1,328.13. The tool above reckons the best tariff we could have gone for for the whole year is Intelligent Go, which would've cost us £1460.22. It also says that, by playing the tariff-switching game and bouncing about between Cosy and Intelligent Go, we could've got the annual cost down to £1237.68.

Net result, my setup is doing better than the tool's best tariff by £132.09, but we're paying a premium of £90.45 for not having the hassle of trying to switch tariffs multiple times a year.

Overall, I'm pretty happy with that and it finally gives a good idea of how Agile can compare with the other tariffs if you play with it. I hasten to add that this is based on a battery size of 6.5kWh which is now regarded as rather small, so I cannot comment on how a larger battery would improve or at least affect things.

Great journey @allyfish. Totally relate to your experience as we embarked on a similar journey at home ourselves.

Though I find the return on investment story also compelling. When I tell my friends and family that it costs less than £700 per annum to run a 200 square metre home including all electricity, heating and car, they are immediately interested.

On tariffs, we also have a smallish 13 kWh battery. Cosy was a great tariff when we started with just 6.5 kWh battery, but when doubled to 13 last May, Octopus Go is comparable to Cosy, other than some very cold days. So, except in January, other months Go beats Cosy, and I decided to stick to one tariff for the whole year. Having said that I am constantly looking out for tariff rates that I can switch to for saving more!

@allyfish 

Great to read how you managed it. 
My main suggestion would be to try to add more energy storage. When we get closer to removing gas, we will need to feel we can still cope with the odd power cut… 

@chandykris 
I agree, the savings when getting off fossil fuels do build up over time… we will soon be joining that group with the mix of ashp and ev and no obvious tariff to choose. In our case, the storage £/kwh is low enough so we should try to stay on overnight rates… 

@allyfish, a four year old as the catalyst for the whole journey is probably the best origin story on this forum, and probably more persuasive than anything the government has managed.

On the footnote… the scale of what’s happening in the world makes personal carbon savings feel almost absurd at times. I’ve written about it. Most importantly, most of us have done their bit.

@batpred Absolutely, the savings do build up over time. Also, not having to worry about energy prices is a huge bonus. Case in point being the recent price cap increases. While gas is going up nearly 25%, electricity is going up by a much smaller 5% or it could even be no increase for off-peak EV rates.

Last year we managed a net nil cost. Exceeding all my hopes/expectations.