UKH

We are just having more solar panels and a couple of batteries fitted and I’m struggling with the maze of different tariffs offered by Octopus. It seems likely to me that a tariff which allows the company to take power out of my batteries at a high price at peak demand (4pm -  7pm) should be worthwhile. I’ll call this tariff X for now. However, we tend to use quite a lot of power ourselves at that time - cooking dinner - so we could end up using net import (at peak time high prices). However, we have a large array of west facing panels with no trees or hills blocking the sun which in the summer half of the year are very productive (weather permitting) in late afternoon (which my experience here suggests is the sunniest part of the day on average). Octopus say it’s very simple to switch tariffs and this made me wonder about switching to tariff X when the clocks change in March and going back to a different tariff come the autumn equinox.

BTW we don’t have an EV yet or a heat pump.

Any comments or experience to share?

Nothing on specific tariffs, but switching is easy, either via email or X.

Only thing to keep an eye on is the available tariffs change fairly regularly, so you'd probably need to research which one suits best every time you want to change. 

Without EV or ASHP, the batteries aren't going to payback unless you can use them to massively shift the cost of your electricity. (I have ASHP, Solar PV and Thermal for 10 years, so speak from experience).

If you're not using much electricity right now, then it looks like the best option is the one where you charge your battery 2-5 am and discharge 4-7 pm. But even if you perfected that to a fine art you're looking at 30 yr + on the battery payback.

If it's not too late, I'd check first that you've not been tricked on the battery install. I really think it's niche use where battery can pay back. You'd probably spend less and get better payback on ASHP if you want to also improve your green creds.

If you're stuck with a battery, then Octopus Flux looks your best option. If you want to put more details about battery cost, size and your elec use then perhaps others can offer a more optimised solution.

We have solar plus battery, no ASHP yet but hopefully get one in before next winter.

I just assumed I would be able to force discharge to grid at peak times, but turns out that with the foxcloud battery system I got you can't do watch out for that. I've submitted an IOI for an integration to octopus.

We're on flux, and just set to charge the battery over night for the winter. Didn't actually look to see if one of the other tariffs might be more suitable until we get the heat pump or fire summer, but once we get the heat pump charging from grid pre peak and overnight should offer decent savings.

think you might have missed the point of the battery there. Its been installed becuase peak Solar generation does not coincide with peak use of electricity. Sensible then to store the solar power no matter how inefficient that process is so that you can use it later when its needed.

the best course of action imo is to get an EV or hybrid.  Given that you might have up to 60 KWh capacity in an EV you can store away all the energy generated in by the sun in the summer and use if for getting around. The ASHP doesn't need to be on generally when the sun is out so most if its use will be during the winter  when no solar is being generated. 

I have solar PV and a 13.5KWh battery. Currently i'm on Agile import (prices change every 30 minutes) and use Wonderwatt to charge the battery at the cheapest slots (usually overnight).  i then just run off battery  / solar through out the day and sell any excess solar back at the fixed 15p rate.  As long as the cost to buy cheap overnight is less than 15p, then it doesnt matter how sunny it is.  if it was pricey overnight for some reason, and predicted to be very sunny, i'd just charge less or not at all, and have my solar PV charge my battery during the day.

This may all change in summer as I'm considering switching to flux to get the best export rate at peak hours, but it does mean you loose the cheap import rates that i currently get on agile (average 8p since December)

Only sensible if the battery cost divided by differential value is favourable.

You can export from Octopus for 15p, it costs 28 p to import. You therefore get 13p value for what you can shift. If you have 7 kW battery you can shift max 7 * 13p. You can only really for that for about half the year. Hard to use 7 kW if no EV / electric heating but still that's about £160 / year of value. When I looked at batteries we were talking ~£5k for a battery which is 30 years payback.

That's the standalone economic argument, but there's also factors such as home storage reducing demand for spin up of fossil fuel power generation at peak times, and power outage resilience that people may want to consider.

These a fringe benefits used to promote battery purchase. If anyone has a workable configuration that provides a <8yr battery payback I would be interested. Since early 2023 the big change is the export rate of 15p and the decline in import cost. In 2022 you got maybe ~2.5p for deemed export vs 45p for import. Now you have 15p export and 28p import.

Anyone without HP or EV probably has low use. Maybe induction stove would give a high demand in the 4 - 7 pm range. Maybe 2 - 6 units depending on how gourmet you are.

If you have EV then you don't need a home battery, you need an EV tariff as they are cheaper than using your own PV + battery + import on wet/winter days.

If you have an ASHP, you can use your own PV a lot. In summer you get Export.

I took 2 years of data on my own house and looked to see what I could do to shift my export to consumption using a battery. Even under almost perfect conditions, and making use of a HP-friendly Octopus tarrif, I couldn't find a way to get a payback under 8 years.

Second hand info (I have panels but no battery, no EV) but I was talking to a friend at the weekend and he's on an incredibly generous Octopus tariff. They get invites to make use of cheap power at times, he was expecting it to be odd unsociable hours but they come fairly often. He can effectively charge his (2) cars, fill his batteries and then heat the house super cheap (all electric and floor heating). Car may be a prerequisite, not sure.

Cautionary note.  We live in the highlands and are with Octopus and have recently had solar installed but after waiting about two years and counting we are still unable to get Octopus to install a smart meter - without which you cannot take advantage of selling surplus or use the more detailed tariffs.  We are at the stage of a formal complaint - and word from Octopus is that they simply dont have any engineers and cannot give us a timeline - whether we must wait 10 weeks or 10 years and that lots of other people / areas are in the same situation.

Friends locally have got meters - from Octopus but say they dont work and the engineers say this is because the ' system ' is out of date.

Fringe benefits to you perhaps, we purchased our system to reduce our impact on the planet, not to save money.

I say fringe as I doubt either are really impactful.

1. Feed in devices have to deactivate on powercut for safety. You can't potentially make the supply live when it should be de-energised.

2. To reduce demand use of gas/coal takes a bigger move towards batteries than is happening, and would be more efficiently addressed with large hub batteries. Without the CO2 footprint of a battery, you can reduce demand impact by shifting your demand. Octopus have a tariff for this.

I took put the environment first 10 years ago when I bought a coal heated house, ignored the cheaper oil option and went solar and ASHP, with a then more expensive green tariff from Good Energy funding growth in renewable. The spare coal was buried in the garden.

I benefited from RHI and Feed In Tariff, but would still do it today. I wouldn't waste money on a battery before green heating and transport.

But as you've bought yours, how have you found your ability to shift usage. Care to share any figures on impact. I'd love to be wrong, and fine that a couple of powerwalls would make a difference.

I'm with octopus. ..charge batteries at night 7.5p/kWh between 2330 -0530. Then run the house during the day with them. If no solar during the day, my 3 x 3.2kw batteries last us till about 7pm. Then 29p till 2330..... 

Batteries were £1500 each fitted.

Obviously any solar helps, run the house, charge batteries, heat water and if all that is covered, then export at 15p.

Thanks for the info. And you can see how that supports the point. Without PV, using batteries to shift 9 kW by for net 21p / unit is a 6 year pay back. But that's assuming every day you use it in full. In which case you've done ~2000 cycles, which is 2/3 of the battery life. If you extend the saving for the other 3 years the return on your original £4.5K is a yearly impact of ~5.6% - you would beat that in a stocks and shares ISA.

You have solar PV - which also needs to payback. On what basis did you pay for that - because if you batteries are keeping things going until 7 pm, your solar is going all for export. But the tariff you have limits the export payment to 8p not 15p (othewise you could just charge at 7.5p and sell it back to them at 6 am presumably - https://octopus.energy/export-tariffs/ ). Which on a typical 3MWhr annual solar generation is a £200/year hit to your payback.

I'm not knocking the idea. You're definitley using more of your own PV in summer than I am with no battery. But you're paying to do it.

If you've got smart export (which you need to get more than deemed) you have the info to work out how much you made, how much you consumed, how much went into batteries to get shifted. How does your PV payback period look with your current setup, and how different would it be without the batteries.

I'm assuming you electricity use is low if you can do until 7 without more than 9 units. The standing charge becomes pretty annoying at that point. With such a lot in storage, can you not get a much better return using the agile pricing that can give free electricity?

You clearly do detail Philip, which I don't, so I'm sure you're right.

I do get 15p export and people certainly do send it back if they can during the day.

And when the panels are working fully, then the batteries are charged by them, so not incurring the 7.5p charging. And it heats my water. And charges my EV. 

I am glad it was already installed when we went through the craziness on energy prices a little while back. And it gives me peace of mind for the future if they start going up again.

And stocks and shares may go down as well as up.

Thanks for posting your calculations. 

If you get the sparky to put in a manual switchover you can run in island mode when the mains power is out.

I figured "be the change you want to see" and all that. Adding a battery does it's little bit to help reduce peak demand. It's easy enough to shift washing machine cycles and stuff but I like cooking at tea time.

Fair enough.

We need a new roof so it make sense to add the solar system first. Left the gas boiler in place while we work on insulation and air tightness but ASHP will be next.

To be honest, it's been pretty fire and forget for me so far (we only got it in August), but haven't used any peak grid since it went in. In the back end of the summer we weren't buying any electricity, at some point I started charging it overnight and in the depths of winter I had it charge before peak.

Planning on having a heat pump in by next winter, so at that point will charge it twice a day all winter.

Hopefully Octopus will release an integration for the foxcloud system at some point, then we can let them manage it for us, providing electricity to the grid at peak times and minimising our payback time.