Home Battery ??

LoopySnooker

Hi folks

Would really appreciate some opinions on whether it would be worth us getting some kind of battery storage for our household.

Currently on EON Next Drive, so 6.7p/kWh for 7 hours overnight. Our usage for the last 12 months has been 1350kWh cheap rate (inc EV charging) and 2000kWh day rate (approx 27p).

At the moment I’m struggling to justify a battery as the most we’re likely to save is around £400 per year based on eliminating the day rate. However, I’ve started reading about export tariffs and beginning to wonder if I’m missing something obvious. Solar PV is another consideration further down the line as we have a reasonable size south facing roof which used to have solar thermal on.

Many thanks in advance.

QrizB

I'd suggest that solar PV is a more useful first step than a home battery would be, with better financial returns.

Although if you live in an area that's prone to power cuts, and/or have medical equipment (or expensive tropical fish) that relies on electricity, a battery might offer other benefits besides a lower electricity bill.

Screwdriva

Even when combining your consumption, 3350 kWh per year isn't high enough to justify the upfront cost of a battery (unless you're planning on getting a heat pump in the near future or suffer from blackouts).

Solar PV on the other hand does make more sense as it typically has a better return on investment. Expect to spend around £5.5K for 10 X 500W bifacial panels and a 5kW SolarEdge inverter with 20 year warranty. Expect this system to generate ~4800kWh per year on a roof like yours (give or take 150kWh).

Assuming you export 2950 kWh of that at 16.5p per kWh = ~£485
Assuming you consume 1850kWh of that saving 27p per kWh = ~£500 saved

That's ~£985 per annum returned on a ~£5.5K spend or a 18% tax exempt return. Despite these numbers being very rough, safe to say no non-DIY type battery can deliver anything close to that.

EDIT: Well, not for the 200+ households I've helped with achieve Solar PV anyway.

Solarchaser

The first piece of advise i would give is to take each answer from a forum member as you would from Billy down the pub, which is not to say don't believe, as people post here to help each other out, but verify, and crucially, make sure the advice you take fits your situation best.

Each person here will give you advise based of their current route, or aspirational route, as with their calculations,  it's best for their circumstances, which is why it's the route they are following, myself included.

You are already on the 6.7p for 7 hours off peak, and Eon has a an export tarrif to match that which is 16.5p.

And so if you were to think of a very inefficient battery system, it would have a round trip losses of 20% leaving 80% recovered.
Most modern systems are much better than that, but for these types of calculations,  it's always better to be conservative. 

So if you bought 1 kwh at 6.7p, and then sold it at 16.5p, you make 9.8p, 80% of that to include the round trip losses = 7.84p "profit".
So let's say you are buying an inverter and battery system that does 3.5kw, and so over your 7 hours off off peak you can store a total of 24.5kwh each night (8942/year) and so by selling it back you can make £1.92 a day, or £701 a year

However, you already buy 2000kwh a year at 27p/kwh, and you would assume your battery is now going to cover the vast majority of that, so we take 2000kwh off the 8942kwh you are exporting a year
You are now only exporting 6942kwh and so £544 a year.
But since you are now not buying 2000kwh at 27p, you save an extra £540 a year

This is a total saving of £1084 per year.

To have 24.5kwh of battery to use, the cheapest way that I can verify works (as I'm personally using the same system for the last 18 months) is a fogstar kit:-
https://www.fogstar.co.uk/products/seplos-v4-kit-and-x16-envision-315ah-grade-b-bundle?variant=41838228242491&country=GB&currency=GBP&utm_medium=product_sync&utm_source=google&utm_content=sag_organic&utm_campaign=sag_organic&gad_source=1&gclid=CjwKCAjwzMi_BhACEiwAX4YZUADR3vZCGvruFFiOgpTTJXM5pXBRjFFl_KF6F1KChbL-1k_SngWn4BoCgaMQAvD_BwE

2 of these batteries would cost around £3120 and give you just about 24.5kwh useable from the battery

One of thse inverters would give you 70a or roughly 3.5kw charge and discharge 
https://callidus.shop/products/multiplus-48-5000-70-100-230v-ve-bus-pmp485021010?variant=40963633545269&country=GB&currency=GBP&utm_medium=product_sync&utm_source=google&utm_content=sag_organic&utm_campaign=sag_organic&tw_source=google&tw_adid=&tw_campaign=18270442965&dm_cam=18270442965&dm_grp=&dm_ad=&dm_net=adwords&dm_kw=&gad_source=1&gclid=CjwKCAjwzMi_BhACEiwAX4YZUFLeZNAGrHkS4j_gZhauiqZO09laWVYHqMWsarDNfeJj3U-2rBD0qxoCBMwQAvD_BwE

Let's say you spend £300 getting someone to wire it up, and you are around £4000 outlay, for over £1000 return or as screwdriva said in terms, a 25% tax free return.

Now you add screwdriva's deal to that and effectively all of your solar production becomes export and so you can add £792 on top of that, per year. (4800kwh at 16.5p)
Add a larger inverter and another 2 batteries and you have another £701/year, so a total of £2577 combined savings and profit, but obviously at this point you have laid out like £13.5k

The difference you have is that you are on EONs, and while the vast majority of export tarrifs are only available to MCS registered solar panel installs, EON will let you export from a battery system without solar, though I'd definitely advise having a chat to them first. 

michaels

Will your DNO approve a G99 without MCS?

Also I think your round trip profit calc is off - 1 kwh in costs 6.7p.  0.8kwh out after loss nets 16.5 x 0.8 = 13.2p, profit = 6.5p per kwh cycled each day

Solarchaser

Ahh good thinking Michaels. 
Dno, no idea, very much depends on the area I guess.

I personally would always go for solar as well as batteries, I was purely offering an opinion on whether batteries would work or not. 

I came back to this thread because at 2:30am when I can't get to sleep, random things pop into my head, and i realised I'd made 2 mistakes in my calculations/reasoning.
The first was that i forgot to include round trip losses in the house consumption,  and took the 2000kwh figure as a straight deduction,  oops.

The other was i took the charge rate as 100% all the time, but as we all know, batteries can slow down for the final few percent, meaning you can't get 3.5kw charge for 7 hours.

This made me check real figures with my real inverters and figured it was worth coming back and correcting.

I am on intelligent octopus, which is 6 hours off peak.
Theoretically I can charge 6x3.5kw so 21kw each night, but in reality it's only 20kwh, and I've checked over several months, it's pretty consistent on both inverters.
And discharge is between 17.8 and 18.3kwh, assumably linked to temperature on various days of both inverter and batteries.
So my real round trip efficiency is somewhere between 89% and 91.5%, so 89% is the logical number to take it think.

So instead of 24.5kw, we should take 23.3kwh, x 365 days is total consumption of 8617kwh at 6.7p is £571 spend
So we know that the round trip of 8617kwh will be x0.89 to get our true output which is 7669kwh

Since it's pure output we can take the 2000 assumed peak usage away which leaves only 5669kwh for export at 16.5p which comes to £935.
Taking away what you have spent to buy that electricity you are left with £364 plus the £540 you save on not buying peak electricity, so £904 not the £1084 i said previously, so only a 22% return on the assumed £4000 outlay.

Apologies for the flawed calculations. 

Worth saying this is for my system, using my inverters and my batteries, and so another system may perform better (or worse) as my inverters are 6 years old.

Same goes for solar.
If you are pure south facing and unshaded, you will generate the best figures for solar, but if you are not pure south facing and/or you suffer shading for part or all of the year, your figures will suffer also.

NedS

michaels said:

Will your DNO approve a G99 without MCS?

Chicken and Egg? You cannot install and connect the equipment to the grid without prior G99 approval, and MCS certification cannot be issued until after the installation has been completed.

Qyburn

NedS said:

michaels said:

Will your DNO approve a G99 without MCS?

Chicken and Egg? You cannot install and connect the equipment to the grid without prior G99 approval, and MCS certification cannot be issued until after the installation has been completed.

G99 you get an "Offer" which you accept before starting work. After installation you submit details to the DNO showing your installation complies with the "offer". If MCS certificate was part of the DNO's requirements then if would be supplied at that stage. 

Finally the DNO responds with confirmation that they are happy with its compliance. This is the bit the supplier needs to see to get export tariff in place.

michaels

Solarchaser said:

Ahh good thinking Michaels. 
Dno, no idea, very much depends on the area I guess.

I personally would always go for solar as well as batteries, I was purely offering an opinion on whether batteries would work or not. 

I came back to this thread because at 2:30am when I can't get to sleep, random things pop into my head, and i realised I'd made 2 mistakes in my calculations/reasoning.
The first was that i forgot to include round trip losses in the house consumption,  and took the 2000kwh figure as a straight deduction,  oops.

The other was i took the charge rate as 100% all the time, but as we all know, batteries can slow down for the final few percent, meaning you can't get 3.5kw charge for 7 hours.

This made me check real figures with my real inverters and figured it was worth coming back and correcting.

I am on intelligent octopus, which is 6 hours off peak.
Theoretically I can charge 6x3.5kw so 21kw each night, but in reality it's only 20kwh, and I've checked over several months, it's pretty consistent on both inverters.
And discharge is between 17.8 and 18.3kwh, assumably linked to temperature on various days of both inverter and batteries.
So my real round trip efficiency is somewhere between 89% and 91.5%, so 89% is the logical number to take it think.

So instead of 24.5kw, we should take 23.3kwh, x 365 days is total consumption of 8617kwh at 6.7p is £571 spend
So we know that the round trip of 8617kwh will be x0.89 to get our true output which is 7669kwh

Since it's pure output we can take the 2000 assumed peak usage away which leaves only 5669kwh for export at 16.5p which comes to £935.
Taking away what you have spent to buy that electricity you are left with £364 plus the £540 you save on not buying peak electricity, so £904 not the £1084 i said previously, so only a 22% return on the assumed £4000 outlay.

Apologies for the flawed calculations. 

Worth saying this is for my system, using my inverters and my batteries, and so another system may perform better (or worse) as my inverters are 6 years old.

Same goes for solar.
If you are pure south facing and unshaded, you will generate the best figures for solar, but if you are not pure south facing and/or you suffer shading for part or all of the year, your figures will suffer also.

89% is encouraging. 

Do you know if your batteries have suffered any loss of capacity?

My understanding is that the lifetime of LFP is all about throughput (cycles) whereas NCM is much more impacted by age (and specifically time spent at high or low charge levels)

Solarchaser

michaels said:

Solarchaser said:

Ahh good thinking Michaels. 
Dno, no idea, very much depends on the area I guess.

I personally would always go for solar as well as batteries, I was purely offering an opinion on whether batteries would work or not. 

I came back to this thread because at 2:30am when I can't get to sleep, random things pop into my head, and i realised I'd made 2 mistakes in my calculations/reasoning.
The first was that i forgot to include round trip losses in the house consumption,  and took the 2000kwh figure as a straight deduction,  oops.

The other was i took the charge rate as 100% all the time, but as we all know, batteries can slow down for the final few percent, meaning you can't get 3.5kw charge for 7 hours.

This made me check real figures with my real inverters and figured it was worth coming back and correcting.

I am on intelligent octopus, which is 6 hours off peak.
Theoretically I can charge 6x3.5kw so 21kw each night, but in reality it's only 20kwh, and I've checked over several months, it's pretty consistent on both inverters.
And discharge is between 17.8 and 18.3kwh, assumably linked to temperature on various days of both inverter and batteries.
So my real round trip efficiency is somewhere between 89% and 91.5%, so 89% is the logical number to take it think.

So instead of 24.5kw, we should take 23.3kwh, x 365 days is total consumption of 8617kwh at 6.7p is £571 spend
So we know that the round trip of 8617kwh will be x0.89 to get our true output which is 7669kwh

Since it's pure output we can take the 2000 assumed peak usage away which leaves only 5669kwh for export at 16.5p which comes to £935.
Taking away what you have spent to buy that electricity you are left with £364 plus the £540 you save on not buying peak electricity, so £904 not the £1084 i said previously, so only a 22% return on the assumed £4000 outlay.

Apologies for the flawed calculations. 

Worth saying this is for my system, using my inverters and my batteries, and so another system may perform better (or worse) as my inverters are 6 years old.

Same goes for solar.
If you are pure south facing and unshaded, you will generate the best figures for solar, but if you are not pure south facing and/or you suffer shading for part or all of the year, your figures will suffer also.

89% is encouraging. 

Do you know if your batteries have suffered any loss of capacity?

My understanding is that the lifetime of LFP is all about throughput (cycles) whereas NCM is much more impacted by age (and specifically time spent at high or low charge levels)

So far it looks like my 2 x 280ah kit, so 28kwh is delivering between 27.8 and 28.6kwh, and my 2x 305ah kit (through a single BMC) so 30.4kwh is delivering between 30.8 and 31.6kwh
and that is basically doing a calculation based on how much it's discharged that day in kwh divided by the percentage it's dropped.

I did the calculations there for 5 different days to get those figures.
Both have been running over a year, usually 100% to somewhere between 45% and 22% depending on the house load and how much export I've forced through.

I'm pretty darn happy with these fogstar batteries it has to be said.

NedS

Qyburn said:

NedS said:

michaels said:

Will your DNO approve a G99 without MCS?

Chicken and Egg? You cannot install and connect the equipment to the grid without prior G99 approval, and MCS certification cannot be issued until after the installation has been completed.

G99 you get an "Offer" which you accept before starting work. After installation you submit details to the DNO showing your installation complies with the "offer". If MCS certificate was part of the DNO's requirements then if would be supplied at that stage. 

Finally the DNO responds with confirmation that they are happy with its compliance. This is the bit the supplier needs to see to get export tariff in place.

 @Qyburn Thank you for clarifying the process