Go, Octopus, Go!

One of the surprising things about Octopus, the UK company from whom we purchase our gas and electricity, is that, despite growing to the point where they handle about a quarter of UK households, they continue to innovate.

For a long time, we’ve been on the ‘Octopus Go’ tariff, which means that for the four hours starting from 00:30 each night, we get electricity at less than one-third of the cost of the rest of the day. We make good use of this, charging our home batteries to the point where, combined with our solar, we very seldom use any normal (i.e. peak-rate) power.

We also charge our car during this time, meaning that our ‘fuel’ costs are about 2p per mile, and one of my favourite statistics is that, since it cost me about £600 to replace our car tyres recently after 30,000 miles, we pay almost exactly the same per mile for fuel as we do for tyre rubber.

All of this may sound very impressive, green and economical… just don’t ask me how much I’ve spent to get to this point! Still, I find it very satisfying.

One of the purposes of this post, by the way, is to remind anyone else also on Octopus Go that, from today, the cheap period has been extended to five hours: from 00:30-05:30. So go and reprogram your cars, car chargers, home batteries or whatever now, before you forget! For those of us who have a standard 7kW home charger, that means 35kWh of cheap-rate power per day, which probably translates into about 100-150 miles, depending on your car.

But Octopus also have some interesting features aimed at balancing the load on the grid during times of peak supply or demand. They’ve tried a few variants, and the availability of any particular one will be rather dependent on your postcode, but here we do quite well, as a result, I think, of generating vast amounts of wind power off the East Anglian coast and not yet having all the cabling that’s needed to distribute it effectively to other parts of the country!

One of these schemes is called ‘Saving Sessions‘, where, at times of peak demand, you can get paid surprisingly high rates per kWh for using less than your normal amount of electricity. At first, I ignored this because we use so little daytime grid power anyway that I thought it would be pointless, until a friend pointed out that even if your usage is normally zero, you can be paid for negative usage; in other words, for exporting to the grid.

“Oh ho!”, thought I, “I can do that!” And so, after a bit of programming, my home automation system notices whenever a Saving Session is active and starts discharging my house battery (and any excess solar) to the grid. These sessions only happen in the winter, and not very frequently, but we still managed to export 40kWh between November and March, earning us about £100. Yes, they really do pay as much as £2.50/kWh for energy we might have bought the night before for 9p. On rare occasions even more.

And finally, there are Octopus Power-Ups. When they think supply is going to exceed demand, they need to absorb it, and so they will let you consume as much as you want for free. Since this is primarily down to the weather forecast predicting strong winds, or lots of sunshine, or both, you don’t get very much notice: typically an email the day before or even on the same day. I just plug the times into my system, and when the moment comes, my car starts charging, my batteries start charging, my hot water starts heating, and so on. It costs me nothing, Octopus probably make more money the more I use, and everyone is happy. (Except my envious friends who don’t live in one of the blessed postcodes!) The main challenge was that I had expended so much effort over many months trying to configure the house to draw as little as possible from the grid, and I now had to set all of the components to do precisely the opposite for a short time and then revert! Still, that’s what home automation is for!

Octopus is a large company now, and like all organisations on such a scale, does have plenty of problems too. They suddenly realised at one point in the past, for example, that they had been billing me for gas but not electricity for nearly a year, and I got a very large bill that month. Also, I had smart meters installed for both gas and electricity, and the gas one has never worked, so I still have to go and read it manually. To be fair, this is a technical problem suffered at a lot of UK households by most providers, who didn’t realise that providing the electricity meter with connectivity and assuming that the gas meter could relay its reports through it using Zigbee wasn’t going to work when, as is often the case, the meters are on opposite side of a brick or stone house filled with competing 2.4GHz signals!)

But, in general, I’m a happy customer, and I hope they continue to explore new and interesting ways to optimise supply and demand. Further innovations will, of course, require me to keep tweaking my code, but, hey, everyone needs a hobby!

My thanks to my pal Gareth Marlow, who has a similar set-up and whose Home Assistant configuration helped me make mine much better! Gareth has also done some great YouTube videos analysing the costs and savings resulting from his home solar/battery system; perhaps the best I’ve seen on that topic for UK enthusiasts. Recommended.

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Interesting stuff, thank you as always. I have enjoyed all your videos on the subject.

Out of curiosity and to help the solar/battery curious could you say how many KwH of electricity you use in a year? And how much without your car charging?

I still fear that the key sentence in your piece is ‘just don’t ask me how much I’ve spent to get to this point!

We use ~850KwH a year in a two adults, 3 bed detached, which cost us about £1050 for the last year. I am concerned that to get to the stage of paying for substantially less from the grid, I’d have to spend a substantial amount upfront, for which the payback period would be many years. We also don’t expect to be in our current house more than ten more years before downsizing and moving to a more urban setting.

I kind of feel I’d rather enjoy the money we’d have to invest at this point in our retirement, rather than have it drip fed back over the next 10-20 years.

Intellectually I’d love to be where you are, (we have a 45 degree due south facing roof) but every time I look into it, the numbers just don’t add up.

I have to make the point that the imbalance in cost between gas and electricity makes me even less keen on a heat pump and the massive upfront cost of that technology in a 1930s house. Gas is cheap enough to make it easy to say no at the moment.

And one more thing. Our smart gas meter is one metre away from the electricity meter in the same under stairs cupboard and still can’t talk to it. Shambolic technology.

And one more thing: we use ~3400KwH, copied the wrong number from my spreadsheet. Sorry. Cost figure correct.

Hi Jim –

Haha – yes, I thought your 850kWh/year was impressive! We use a lot more — I have a note that we used approx 850kWh/month before installing our system, but that did include car charging, which I think was around 1/3 of it. So I believe our consumption, without the car, was about twice yours – we have a bigger house, there are a few servers running all the time, and I work from home so am always here using more of it. (We don’t have electric heating — we looked into it, but, like you, decided it didn’t make sense, at least while our existing boiler was working so well.)

Even then, when the energy prices tripled a year and a half ago, if we hadn’t had the cheap-rate tariff, we would have started paying over £4000/year including car charging. If we assume a third of that was the car and was always charged on the cheap rate, we’d get closer to £3000, but still quite a lot of money.

Our installation was expensive: we got big batteries, big solar, and an in-roof, rather than on-roof, installation, plus I had specific requirements for handling power outages etc. As a rough approximation, it was 1/3 each for the batteries, the solar, and the installation. It was something we wanted to do, and saving money wasn’t the primary motivation. I expect it’ll take somewhere between 10 and 20 years to repay the investment, by which time we’ll almost certainly have moved house, so I hope the next buyers value it as much as I do, and price their offer accordingly!

But it’s also true to say that we could have gone for a much cheaper system which would have given many of the benefits and paid it off much more quickly, if our goals had been primarily financial.

In theory, I have all the data needed to calculate our usage now compared to before and do a proper comparison, but it’s complicated by a range of things like (a) Octopus’s confusion about our billing and (b) the fact that we now deliberately draw as much as we can from the grid sometimes: during the ‘Power Up’ sessions, we’re often pulling 17kW, for free, which is very pleasing but does mess up one’s statistics!

I do recommend Gareth’s videos, linked in the post, if you want a good analysis of what a more normal system can mean financially. This one, in particular, is worth watching: https://www.youtube.com/watch?v=ThjeN4B5IDY


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