Should we get more home battery capacity?

[Bam Bam]

We've got 9.5kwh of battery storage with our Givenergy system.

That has been fine until we've got our heat pump installed.

On cold winter days the battery seems to run out before getting round to the next cheap period.

I've obtained a quote from our installer as follows...

Extra battery
5.2kwh = £1904.17
9.5kwh = £2648.17

Pebbles is not convinced that it is worth getting more.

I think the pay off period will be about 10 years but that of course depends on tariffs and energy costs during that time.

Further advantages...

• Longevity: Additional battery would reduce the pressure on our existing battery and thus extend its life. It is currently doing around 1.5 cycles per day
• Backup capability: Extra battery would also make it more useful as a backup system since I'd keep more of a buffer in there.
• Environmental: Extra battery is helping the energy transition by shifting energy from low to high carbon times.

Export rate changes?
Octopus have today reduced their export payment rates (15p to 12p) and they will probably drop further.

However, the export rates will remain high in the evening peak.

Does this mean that...
1. Batteries will be more valuable as you can sell during the evening demand peak (for more) rather than the daytime
2. Batteries will be less valuable because you can't get as much arbitrage from filling up overnight and selling during the day.

Any thoughts?

 

[GaryMG4]

There was a report that HMRC was considering making income from arbitrage taxable.

 

[Giller]

We've got 9.5kwh of battery storage with our Givenergy system.

That has been fine until we've got our heat pump installed.

On cold winter days the battery seems to run out before getting round to the next cheap period.

I've obtained a quote from our installer as follows...

Extra battery
5.2kwh = £1904.17
9.5kwh = £2648.17

Pebbles is not convinced that it is worth getting more.

I think the pay off period will be about 10 years but that of course depends on tariffs and energy costs during that time.

Further advantages...

• Longevity: Additional battery would reduce the pressure on our existing battery and thus extend its life. It is currently doing around 1.5 cycles per day
• Backup capability: Extra battery would also make it more useful as a backup system since I'd keep more of a buffer in there.
• Environmental: Extra battery is helping the energy transition by shifting energy from low to high carbon times.

Export rate changes?
Octopus have today reduced their export payment rates (15p to 12p) and they will probably drop further.

However, the export rates will remain high in the evening peak.

Does this mean that...
1. Batteries will be more valuable as you can sell during the evening demand peak (for more) rather than the daytime
2. Batteries will be less valuable because you can't get as much arbitrage from filling up overnight and selling during the day.

Any thoughts?

Interesting. Solar and battery installed last May, 10.2 kWh battery fed from 12 panels through a 3.68 kWh inverter (max we can have in NI) and with off peak charging battery in winter months works well, but we don't have a heat pump.

Given your comments and everything I'd say go for it, just don't tell Pebbles I said that

 

[Bam Bam]

There was a report that HMRC was considering making income from arbitrage taxable.

Even if it is just credit on the account that you use at another time?

My understanding is that if you withdraw money from your energy provider then that is taxable income, though I haven't checked lately.

As things stand, we've just had our first bill in 11 months. £15.15.

Maybe with the heat pump now we will end up in credit over the full year, but I imagine we will break even at best.

 

[GaryMG4]

Even if it is just credit on the account that you use at another time?

Interesting point, as with most taxation it probably hasn't been thought through, I would imagine a credit is still benefit in kind. I had similar thoughts regarding me FiT payments, in a good year it could exceed the '£1000' limit although with 2 EVs the generation amount won't be above 120% of consumption so should be tax free but I wondered if I switched the FiT supervisor to Octopus and received credits whether it would count.

 

[Rolfe]

Seems to me one could make a good argument that any tax due should be able to be offset against the expenditure of installing the system.

 

[GaryMG4]

Seems to me one could make a good argument that any tax due should be able to be offset against the expenditure of installing the system.

Certainly would be the case if you were a business not sure there's anything in personal tax like that.

 

[Everest]

Certainly would be the case if you were a business not sure there's anything in personal tax like that.

Well, you can certainly offset costs for expenses for rental income or working from home, even if you're not a formal business - so if HMRC classify such income as taxable it would be logical that running expenses etc., even if not capital expenditure could be an allowable deduction. Caveat is .. not that everything HMRC do is 'logical' though!

 

[Everest]

Any thoughts?

I have a few Here's my 2p worth...

We've got 9.5kwh of battery storage with our Givenergy system
...
Extra battery
5.2kwh = £1904.17
9.5kwh = £2648.17
...
I think the pay off period will be about 10 years

As much as one always wants as much battery as possible and no-doubt, like me, you hate occasionally running out of charge before the next cheap rate, it's a law of diminishing returns. The issue for you, IMHO, is that you are somewhat tied into a proprietary system so the price of the battery, even the bigger (= cheaper per kWh) one means the payback is so long. It would be different if you could buy a 'generic' 48V LiFePO4 pack; for example the Fogstar 16kWh one for less than £2000.

A payback of 10 years is not that far off the expected life of a LiFePO4 home storage battery, where calendar ageing over 12-15 years is likely to be the limiting factor into its usefulness, rather than cycle count.

Longevity: Additional battery would reduce the pressure on our existing battery and thus extend its life. It is currently doing around 1.5 cycles per day

Is it that many over the whole year? I would have assumed that in the summer 6 months, then you'll be maybe be only using 30% per day = 1 cycle equivalent per 3 days. But, I've no experience of heat-pump usage and don't know what SOC Givenergy drop down to before stopping battery discharge.

Backup capability: Extra battery would also make it more useful as a backup system since I'd keep more of a buffer in there.

I guess you need to put a price on that? How many times over the last year have you had a power cut where your backup supply has become depleted before that romantic evening meal with Pebbles?

Environmental: Extra battery is helping the energy transition by shifting energy from low to high carbon times.

Again, what price do you put on that?

Batteries will be more valuable as you can sell during the evening demand peak (for more) rather than the daytime

True, but presumably that only applies if you are on Agile or Flux?

Overall, I'm with Pebbles... I'd say whilst it would be "nice-to-have" the financial numbers don't add up (*). Within 10 years there will be new storage technology (SIB for example), more HV battery systems, greater capacity. Who knows if GivEnergy will be around over that timescale, so if something goes belly up, you may not have the support available.

If you had the skills and inclination, I'd add a DIY battery to extend your existing system - but that requires electronics and software skills, so it's a very niche option.

(*) edited to add... it's a head or heart choice too - just like I won't buy new cars because they depreciate too much for me, some people like to have something new

 

[Archev]

I have a few Here's my 2p worth...


As much as one always wants as much battery as possible and no-doubt, like me, you hate occasionally running out of charge before the next cheap rate, it's a law of diminishing returns. The issue for you, IMHO, is that you are somewhat tied into a proprietary system so the price of the battery, even the bigger (= cheaper per kWh) one means the payback is so long. It would be different if you could buy a 'generic' 48V LiFePO4 pack; for example the Fogstar 16kWh one for less than £2000.

A payback of 10 years is not that far off the expected life of a LiFePO4 home storage battery, where calendar ageing over 12-15 years is likely to be the limiting factor into its usefulness, rather than cycle count.


Is it that many over the whole year? I would have assumed that in the summer 6 months, then you'll be maybe be only using 30% per day = 1 cycle equivalent per 3 days. But, I've no experience of heat-pump usage and don't know what SOC Givenergy drop down to before stopping battery discharge.


I guess you need to put a price on that? How many times over the last year have you had a power cut where you backup has become depleted before that romantic evening meal with Pebbles?


Again, what price do you put on that?


True, but presumably that only applies if you are on Agile or Flux?

Overall, I'm with Pebbles... I'd say whilst it would be "nice-to-have" the financial numbers don't add up (*). Within 10 years there will be new storage technology (SIB for example), more HV battery systems, greater capacity. Who knows if GivEnergy will be around over that timescale, so if something goes belly up, you may not have the support available.

If you had the skills and inclination, I'd add a DIY battery to extend your existing system - but that requires electronics and software skills, so it's a very niche option.

(*) edited to add... it's a head or heart choice too - just like I won't buy new cars because they depreciate too much for me, some people like to have something new

Thought provoking resume. And the only battery I work with is my Vtoman camping power pack which I use for cooking and some heating at home whilst I dream of a house battery

 

[Bam Bam]

I have a few Here's my 2p worth...

Very useful, thanks.

As much as one always wants as much battery as possible and no-doubt, like me, you hate occasionally running out of charge before the next cheap rate, it's a law of diminishing returns.

Absolutely. If it is once a year it isn't worth it.

The issue for you, IMHO, is that you are somewhat tied into a proprietary system so the price of the battery, even the bigger (= cheaper per kWh) one means the payback is so long. It would be different if you could buy a 'generic' 48V LiFePO4 pack; for example the Fogstar 16kWh one for less than £2000.

Yeah, people who have a bit more nous might be able to go for cheaper systems that are less 'plug and play' consumer friendly.

A payback of 10 years is not that far off the expected life of a LiFePO4 home storage battery, where calendar ageing over 12-15 years is likely to be the limiting factor into its usefulness, rather than cycle count.

Good point - what will last longer, the inverter or the battery?

Both are unknowns.

Is it that many over the whole year? I would have assumed that in the summer 6 months, then you'll be maybe be only using 30% per day = 1 cycle equivalent per 3 days. But, I've no experience of heat-pump usage and don't know what SOC Givenergy drop down to before stopping battery discharge.

Another good point. Depends how much we charge up and sell during the summer. Most of the time the batteries would be full otherwise since the heat pump will use very little energy in the Summer. Just heating the hot water.

I guess you need to put a price on that? How many times over the last year have you had a power cut where your backup supply has become depleted before that romantic evening meal with Pebbles?

It is thankfully very rare!

But we paid a few hundred quid to have the backup system installed in the first place so it seems to have had a value placed on it.

Again, what price do you put on that?

Energy transition is the key thing I think.

I would pay for that, and kind of have, but Pebbles is a bit more sensible.

True, but presumably that only applies if you are on Agile or Flux?

We go onto Intelligent Flux in the Winter. Don't really need extra battery for that, but we might get higher peak discharge rates if we had more capacity.

Overall, I'm with Pebbles... I'd say whilst it would be "nice-to-have" the financial numbers don't add up

I think the energy transition point is the big difference.

The extra battery wouldn't be a terrible financial choice but it probably wouldn't be a great one.

I'd rather put some money into that rather than having it sit in a bank account.

Overall Pebbles and I are both quite financially conservative and we also wouldn't buy a new car due to the depreciation!

 

[Everest]

The extra battery wouldn't be a terrible financial choice but it probably wouldn't be a great one.
I'd rather put some money into that rather than having it sit in a bank account.

Have you thought about more panels, rather than more battery? Panels are so cheap in comparison and IMHO would be a better use of all that money wasted in the bank earning little interest. The net effect is a better proposition IME. You can generate more, especially on dull overcast days. Like today... it's one of those bright but overcast days and we're generating between 4 and 6kW (admittedly with a lot of panels), but that's keeping the battery full until 5pm however much I try and use the washing machine and tumbler

 

[Bam Bam]

Have you thought about more panels, rather than more battery? Panels are so cheap in comparison and IMHO would be a better use of all that money wasted in the bank earning little interest. The net effect is a better proposition IME. You can generate more, especially on dull overcast days. Like today... it's one of those bright but overcast days and we're generating between 4 and 6kW (admittedly with a lot of panels), but that's keeping the battery full until 5pm however much I try and use the washing machine and tumbler

Yes, that was my first thought and that was the first quote I got. A bit of extra generation would save the battery from getting depleted during the day and it would last a bit longer.

Roof option
Unfortunately, it would be very difficult to add panels to our roof now (we've got 2 arrays of 8 so quite a lot, but could technically have squeezed another two on each side). The panels are no longer manufactured.

Garage option
Then we have the garage, which I'd love to put panels on, but the complication is that it is half ours and half owned by next door.

I actually got the neighbour's landlord to agree to let us put some on his side (which has a small amount of South facing) in return for giving him the option to take them over in the future at cost price. We could put a switch in their garage so they could take over the supply for the panels on their part of the garage.

Pebbles is worried that this means we don't have control over those panels and also that it might make matters very complicated if we came to sell the house (or they sold).

We could maybe fit three West-facing panels on our bit of garage. Handy, but expensive for the electrical work for such a small amount of generation.

South facing wall option
We could put four panels on our south facing wall. Would be good in the winter but not much good other times.

Fence/garden option
We have south facing fence (replaced a year or two ago after the old one blew down in a storm), which is set back slightly from the road with a pebbled verge. I considered putting panels up on the verge but that would be open to the street and so I don't know if that would be safe really or if the panels and things would just get stolen.

Or we could put them in the back garden but it would be heavily shaded (mostly by the house). Plus it would take up garden space in a prime location so I don't think that would be popular.

Conclusions?
All of these extra array options are very small (3 or 4 panels). But they would need a lot of electrical work (upgrade to add a consumer unit in the garage) to facilitate.

The panels themselves are very cheap but the other electrical costs mean that we would be paying something like £4k to get a small amount of extra generation.

I think it would be a small and fiddly job for an installer and so they are unlikely to quote competitively.

Again, I'd be willing to do these things for the sake of the energy transition, but Pebbles thinks it is a bad idea.

 

[T1 Terry]

Have you thought about using the EV as a second battery to get you over the shortfall till you reach the cheaper power availability ....
Sorry if someone has already posted about this idea, but the wife has said it's time for bed Yeah, but I can dream though

T1 Terry

 

[Everest]

Unfortunately, it would be very difficult to add panels to our roof now (we've got 2 arrays of 8 so quite a lot, but could technically have squeezed another two on each side). The panels are no longer manufactured.

Technically as in physically possible, with enough room before wall edge, or electrically as in VoC won't exceed inverter input limit with another panel in series? Presumably it was decided that 2 x 9 was not feasible in the first place, otherwise the original installers would have done that then for tiny incremental cost at the time. But, either way, unlikely worthwhile now for cost and complication of extra mounting brackets, scaffolding etc.

Pebbles is worried that this means we don't have control over those panels and also that it might make matters very complicated if we came to sell the house (or they sold).

I agree ^^^ listen to her

The panels themselves are very cheap but the other electrical costs mean that we would be paying something like £4k to get a small amount of extra generation.

Ouch. Glad I DIY!

Again, I'd be willing to do these things for the sake of the energy transition, but Pebbles thinks it is a bad idea.

As above, IMHO

 

[Bam Bam]

Technically as in physically possible,

Just economically. It is a push in terms of the closeness to the edge of the roof but just about do-able. In terms of voltage, 10 would work on a string, but it sounds like they would need to match the existing panels.

with enough room before wall edge, or electrically as in VoC won't exceed inverter input limit with another panel in series? Presumably it was decided that 2 x 9 was not feasible in the first place, otherwise the original installers would have done that then for tiny incremental cost at the time.

They didn't even consider doing that number. I had to force the installers to go up from the 12 they wanted to do to go up to 14 and then to 16 in the final version.

Another company suggested 20 panels but wanted to put in really expensive kit and their quote was well over twice the other companies.

But, either way, unlikely worthwhile now for cost and complication of extra mounting brackets, scaffolding etc.

Exactly, big scaffolding costs for a few extra panels isn't worth it.