New heat pump - should I go for Octopus Intelligent Flux or Octopus Cosy?

System

This discussion was created from comments split from: Electric only tariff for heat pumps.

beansfortea

My heat pump goes in next week. I already have solar and battery. Does anybody have a view on whether Octopus Intelligent Flux or Octopus Cosy would be my best choice of tariff?  I have heard that some people run on Cosy during the winter, when they are less likely to be exporting to the grid, but need more heat, and then switch to Intelligent Flux in the summer, when the heat pump is drawing less, but significant exports are possible. Last summer (with no heat pump) I was exporting more than I was consuming.

NedS

beansfortea said:

My heat pump goes in next week. I already have solar and battery. Does anybody have a view on whether Octopus Intelligent Flux or Octopus Cosy would be my best choice of tariff?  I have heard that some people run on Cosy during the winter, when they are less likely to be exporting to the grid, but need more heat, and then switch to Intelligent Flux in the summer, when the heat pump is drawing less, but significant exports are possible. Last summer (with no heat pump) I was exporting more than I was consuming.

I don't have batteries, but do have a heat pump and solar. I'm on Octopus Cosy, and at present my average import cost is ~20p per kWh, if that helps. With a battery, you should be able to significantly lower that as you'd be able to charge / discharge 3 times per day during the 3 cheap 12p periods.

I guess much would depend on the size of your battery and usage. If you have a small battery, then being able to cycle it 3 times per day may work well compared to charging on a cheap rate overnight tariff and then running out during the day.

I'd also recommend using the Octopus Compare App, which will analyse your smart meter data and compare tariffs for you, although any comparison is likely somewhat skewed by the fact your usage is hopefully optimised for the tariff you are on rather than the tariff you are comparing with.

Alnat1

@beansfortea My heat pump was installed week of 20th Jan. I switched to Cosy the week before install and it's working great for us with our small battery.

We heat the tank at 4am while also filling up the battery and then the heating kicks in at 21C at 4.30am after the overnight set back. The dishwasher often runs in this slot too. The house is up to heat and heat pump settling down to around 300-500Wh (I've no fancy gadgets to measure more accurately, can only see whole house use and guess) by 7am most days.

On a couple of dull, cold days the battery was empty before 1pm but this week, with a bit more power in the sun, it's been fine. We set temp down to 20C 4-7pm, 21C again 7-9.30pm, then 18C overnight. The battery has lasted until the 10pm slot most evenings, mostly depends how much we use cooking. Refill again 10-12. 

Last 7 days our average import is 18.34kWh a day, average price 13.57p

Hoping a bit of real life info helps you decide what could work for you. It's made us think that we might like a bit more battery storage before next winter but no rush, prices are still slipping down slowly.

Edit to add, we will possibly switch to the ordinary Flux tariff around mid to late March, Intelligent Flux wouldn't be my choice even if I had the right kit. I'm too much of a control freak to let Octopus decide when to import and export for me, I like to do that myself. What if they take all my battery power just when I want to do a big roast dinner, arghhhhh.

Nick_Dr1

How big is your battery compared with what the heat pump will use?

Ours chugs along at about 1kW electrical most of the day in the winter, with bursts higher for a few hours when its really cold. Our 7kWhr battery isn't quite big enough to supply normal house use and heat-pump (on Cosy) and definitely isn't on cold days. In the summer it will be fine as the heating is mostly off.

So there are two scenarios to consider
1) Winter. No solar and high heat pump usage - need a cheap tariff. Cosy works well if you can survive the expensive periods on battery, so battery size is important. Export price not important as you won't export anything meaningful, but you can get 15p flat rate. Cosy probably better.
2) Summer. Loads of solar, not much demand, export becomes significant. If you have a battery then this can be exploited to export in the high charge tariff periods if you are on one. Flux probably better.

Coupled with this is the cost of a suitably sizes battery - you can buy a lot of electricity for the cost of a battery or a battery upgrade if yours isn't big enough.
In my case on cosy, my average varies from about 12p a unit to 18p unit depending on how cold it is, compared with say 25p unit if I had no battery on a normal tariff. It takes a few years and probably some man maths to come to a reasonable pay back period. Of course this all depends on the price of electricity over the next few years.
If you have an EV, then significantly cheaper tariffs are available. But best use of tariffs to get the lowest average cost is the only real answer and for that you need personal data which you don't have yet!

PS Don't be shocked at the giant increase in electricity you will see. You have to offset the amount of gas/oil you are not using against this increase!

I'd probably do some estimates and take a best guess at a tariff (flux or cosy), run for a few months/year and then decide what needs to happen in terms of battery. I think in my case for example, I'm going to buy a bigger battery (15kWhr) and that should see me through cold days in the winter. Some will argue that batteries are a waste of money, but that ignores the entertainment value!

Oh and buy it on an interest free credit card and put the money in a savings account. Knocks a few percent off the overall bill!

NedS

Nick_Dr1 said:

How big is your battery compared with what the heat pump will use?

Ours chugs along at about 1kW electrical most of the day in the winter, with bursts higher for a few hours when its really cold. Our 7kWhr battery isn't quite big enough to supply normal house use and heat-pump (on Cosy) and definitely isn't on cold days. In the summer it will be fine as the heating is mostly off.

So there are two scenarios to consider
1) Winter. No solar and high heat pump usage - need a cheap tariff. Cosy works well if you can survive the expensive periods on battery, so battery size is important. Export price not important as you won't export anything meaningful, but you can get 15p flat rate. Cosy probably better.
2) Summer. Loads of solar, not much demand, export becomes significant. If you have a battery then this can be exploited to export in the high charge tariff periods if you are on one. Flux probably better.

Coupled with this is the cost of a suitably sizes battery - you can buy a lot of electricity for the cost of a battery or a battery upgrade if yours isn't big enough.
In my case on cosy, my average varies from about 12p a unit to 18p unit depending on how cold it is, compared with say 25p unit if I had no battery on a normal tariff. It takes a few years and probably some man maths to come to a reasonable pay back period. Of course this all depends on the price of electricity over the next few years.

To put this in context I have similar heat pump usage and am on Cosy but with no battery, and my average import price is ~20p, so at best the battery will save you 7p per kWh (versus no battery) if you can shift ALL your usage to the cheap 12.8p slots ranging to only 2p per kWh saving if you are only averaging 18p import.

Even at a 7p per kWh saving, my back of an envelope calculations show a battery will only break even over it's 10-12 year lifespan. For my usage I estimate it may save £400-500 per year and may cost £4-5k to install. It's really nice to have, but I don't see it as a decent capital investment at current prices, but that may change rapidly given how volatile electricity pricing currently is. The other thing that may massively change the equation is if the 15p SEG export rate for solar disappears, then storing and using excess solar rather than exporting it for next to nothing adds real value.

ed110220

Have you considered Octopus Go? I know Octopus promote it as a tariff for EV users, but I don't think it's strictly a requirement. I switched to it in late Dec last year despite not having an EV. I have 4.8 kW of PV and a 15 kWh battery. So far this year we have imported 631 kWh for £61.80 (not including standing charge) so average of 9.79p/kWh. We've exported 119 kWh for £17.90 so 15p/kWh.

Things to consider:

a) how much your battery can store. I run the dishwasher overnight on the off peak rate and that means we very rarely run out of battery power before the 00:30-05:30 off peak period starts. We don't have ASHP (yet) so I expect your consumption will be higher.

b) your inverter and battery max charge/discharge rate. Ours is 3 kW so it means if we draw more than that the balance comes from the grid, even if we have charge in the battery. By trying to avoid running high power devices at the same time we minimise that, but a little import outside the off peak period is inevitable (that's why our average import is 9.79p not the 8.55p off peak rate). This also determines your maximum nightly storage: 5 hours on Go for us is 15 kWh max.

TroubledTarts

NedS said:

Nick_Dr1 said:

How big is your battery compared with what the heat pump will use?

Ours chugs along at about 1kW electrical most of the day in the winter, with bursts higher for a few hours when its really cold. Our 7kWhr battery isn't quite big enough to supply normal house use and heat-pump (on Cosy) and definitely isn't on cold days. In the summer it will be fine as the heating is mostly off.

So there are two scenarios to consider
1) Winter. No solar and high heat pump usage - need a cheap tariff. Cosy works well if you can survive the expensive periods on battery, so battery size is important. Export price not important as you won't export anything meaningful, but you can get 15p flat rate. Cosy probably better.
2) Summer. Loads of solar, not much demand, export becomes significant. If you have a battery then this can be exploited to export in the high charge tariff periods if you are on one. Flux probably better.

Coupled with this is the cost of a suitably sizes battery - you can buy a lot of electricity for the cost of a battery or a battery upgrade if yours isn't big enough.
In my case on cosy, my average varies from about 12p a unit to 18p unit depending on how cold it is, compared with say 25p unit if I had no battery on a normal tariff. It takes a few years and probably some man maths to come to a reasonable pay back period. Of course this all depends on the price of electricity over the next few years.

To put this in context I have similar heat pump usage and am on Cosy but with no battery, and my average import price is ~20p, so at best the battery will save you 7p per kWh (versus no battery) if you can shift ALL your usage to the cheap 12.8p slots ranging to only 2p per kWh saving if you are only averaging 18p import.

Even at a 7p per kWh saving, my back of an envelope calculations show a battery will only break even over it's 10-12 year lifespan. For my usage I estimate it may save £400-500 per year and may cost £4-5k to install. It's really nice to have, but I don't see it as a decent capital investment at current prices, but that may change rapidly given how volatile electricity pricing currently is. The other thing that may massively change the equation is if the 15p SEG export rate for solar disappears, then storing and using excess solar rather than exporting it for next to nothing adds real value.

Similar to yourself we have a heat pump and we're considering a battery only install.

We have only been on Cosy since the 2nd Jan when Agile became too high and have averaged 17.6p kwh.

We were eyeing up the fogstar 15.5kwh for £2499 with an 8kwh inverter and then whatever is needed for install and charging them (I really don't know what we fully need) but I thought we could get that all in for £4k (is that realistic?)

Even so the saving on that usable 14kwh with losses might only be 5p perk kwh or 70p a day in the 6 months of winter/heating season so let's say 180 days that's £126 a year. We just can't get the calculations to add up to make it worth it.

ed110220

TroubledTarts said:

NedS said:

Nick_Dr1 said:

How big is your battery compared with what the heat pump will use?

Ours chugs along at about 1kW electrical most of the day in the winter, with bursts higher for a few hours when its really cold. Our 7kWhr battery isn't quite big enough to supply normal house use and heat-pump (on Cosy) and definitely isn't on cold days. In the summer it will be fine as the heating is mostly off.

So there are two scenarios to consider
1) Winter. No solar and high heat pump usage - need a cheap tariff. Cosy works well if you can survive the expensive periods on battery, so battery size is important. Export price not important as you won't export anything meaningful, but you can get 15p flat rate. Cosy probably better.
2) Summer. Loads of solar, not much demand, export becomes significant. If you have a battery then this can be exploited to export in the high charge tariff periods if you are on one. Flux probably better.

Coupled with this is the cost of a suitably sizes battery - you can buy a lot of electricity for the cost of a battery or a battery upgrade if yours isn't big enough.
In my case on cosy, my average varies from about 12p a unit to 18p unit depending on how cold it is, compared with say 25p unit if I had no battery on a normal tariff. It takes a few years and probably some man maths to come to a reasonable pay back period. Of course this all depends on the price of electricity over the next few years.

To put this in context I have similar heat pump usage and am on Cosy but with no battery, and my average import price is ~20p, so at best the battery will save you 7p per kWh (versus no battery) if you can shift ALL your usage to the cheap 12.8p slots ranging to only 2p per kWh saving if you are only averaging 18p import.

Even at a 7p per kWh saving, my back of an envelope calculations show a battery will only break even over it's 10-12 year lifespan. For my usage I estimate it may save £400-500 per year and may cost £4-5k to install. It's really nice to have, but I don't see it as a decent capital investment at current prices, but that may change rapidly given how volatile electricity pricing currently is. The other thing that may massively change the equation is if the 15p SEG export rate for solar disappears, then storing and using excess solar rather than exporting it for next to nothing adds real value.

Similar to yourself we have a heat pump and we're considering a battery only install.

We have only been on Cosy since the 2nd Jan when Agile became too high and have averaged 17.6p kwh.

We were eyeing up the fogstar 15.5kwh for £2499 with an 8kwh inverter and then whatever is needed for install and charging them (I really don't know what we fully need) but I thought we could get that all in for £4k (is that realistic?)

Even so the saving on that usable 14kwh with losses might only be 5p perk kwh or 70p a day in the 6 months of winter/heating season so let's say 180 days that's £126 a year. We just can't get the calculations to add up to make it worth it.

If you have a battery and can shift all your import to the 00:30 - 05:30 Octopus Go off peak period you'd be on ~8.5p/kWh.

QrizB

TroubledTarts said:

We were eyeing up the fogstar 15.5kwh for £2499 with an 8kwh inverter and then whatever is needed for install and charging them (I really don't know what we fully need) but I thought we could get that all in for £4k (is that realistic?)

If you don't mind 3 hours of careful DIY, the Fogstar kits are only £1500-ish.

https://www.fogstar.co.uk/collections/seplos-mason-kits

I built mine at the weekend. It was probably 1 hour of actual work and 2 hours of watching the video tutorial and double-checking everything before connecting anything up

But yes, all the kit shouldn't cost more than £4k (£3k if you build the battery yourself). Whoever installs it will also need to get the G99/G100 DNO authorisation.

Edit to add:

There was a guy (with an all-electric flat, E7 and storage heaters) who posted back in 2021 or early 22 that he'd had storage batteries fitted so he could run his flat from off-peak electricity during the daytime. I think he had 6kWh of battery.

It seemed a reasonable idea but the payback time (based on tariffs and battery prices then) was quite long, 10 years or so, and several forumites ridiculed him. Quite unfairly, to my mind.

Eventually the thread was deleted but I occasionally wonder how he's getting on. He'll have benefitted significantly over the EPG period, where there were E7 tariffs with nighttime electricity well below 10p/kWh despite the day rate being 40p or so. It would be good to hear back from him.

TroubledTarts

QrizB said:

TroubledTarts said:

We were eyeing up the fogstar 15.5kwh for £2499 with an 8kwh inverter and then whatever is needed for install and charging them (I really don't know what we fully need) but I thought we could get that all in for £4k (is that realistic?)

If you don't mind 3 hours of careful DIY, the Fogstar kits are only £1500-ish.

https://www.fogstar.co.uk/collections/seplos-mason-kits

I built mine at the weekend. It was probably 1 hour of actual work and 2 hours of watching the video tutorial and double-checking everything before connecting anything up

But yes, all the kit shouldn't cost more than £4k (£3k if you build the battery yourself). Whoever installs it will also need to get the G99/G100 DNO authorisation.

Edit to add:

There was a guy (with an all-electric flat, E7 and storage heaters) who posted back in 2021 or early 22 that he'd had storage batteries fitted so he could run his flat from off-peak electricity during the daytime. I think he had 6kWh of battery.

It seemed a reasonable idea but the payback time (based on tariffs and battery prices then) was quite long, 10 years or so, and several forumites ridiculed him. Quite unfairly, to my mind.

Eventually the thread was deleted but I occasionally wonder how he's getting on. He'll have benefitted significantly over the EPG period, where there were E7 tariffs with nighttime electricity well below 10p/kWh despite the day rate being 40p or so. It would be good to hear back from him.

That is super handy thanks I was a bit confused as to whether I could build this myself and to be honest even looking now what would 16 x 280Ah capacity be in kwh?.

If you have a link to the YouTube vids that would be great as I am all for saving some money.

Do I have to get DNO authorisation if I am just using the power and not exporting to the grid