On-grid domestic battery storage

Exiled_Tyke · 14 March 2017 at 11:08PM

Martyn1981 wrote: »

Forgot to mention this, but I think it needs its own post as this is so important. That battery appears to come with a 6,000 cycle and 10yr warranty.

TBH, I'm making most of this up as I go along, trying to figure out what 'a good battery' is. My gut feeling is that the economics need to improve a lot, but regardless, we'll still need at least 10yrs to have any hope of making the investment viable, so I think 10yrs is a minimum, and 5,000+ cycles even better.

Looking at the CleanTechnica list, the cycles, warranties, life expectancies etc seem to vary not only in length but description too, so hopefully we'll see some sort of standardisation as the years progress.

So essentially you are speculating that this offer is still twice the price of what it needs to be to be worthwhile?

Martyn1981 · 15 March 2017 at 8:29AM

Exiled_Tyke wrote: »

So essentially you are speculating that this offer is still twice the price of what it needs to be to be worthwhile?

For me, yep. I think I could reduce import by about 900kWh pa, which would save me about £110, plus I could switch to a NSC tariff which would save me a bit more (after allowing for the higher leccy price), so perhaps £150, or £1,500 over 10 years.

Higher leccy users with enough export to make use of it would benefit more, and the batteries get proportionately cheaper as they get bigger.

Also need to ponder how leccy prices will rise, as that will help, if cycle warranty is 10,000, or 15-20yrs that makes a big difference, also time of day tariffs, as that recent idea of 5p/kWh through the night is probably cheaper than the cost of a battery, so I'd half my battery size and only focus on balancing during the day, and covering evening demand.

Genuinely don't know how to work this out. I can make a logical assumption for myself, based on generation, export and import and consumption patterns, but I'm not sure there is any kind of rule of thumb - we may all have to do some number crunching individually.

Are we having fun yet?

Exiled_Tyke · 15 March 2017 at 10:30AM

Martyn1981 wrote: »

For me, yep. I think I could reduce import by about 900kWh pa, which would save me about £110, plus I could switch to a NSC tariff which would save me a bit more (after allowing for the higher leccy price), so perhaps £150, or £1,500 over 10 years.

Higher leccy users with enough export to make use of it would benefit more, and the batteries get proportionately cheaper as they get bigger.

Also need to ponder how leccy prices will rise, as that will help, if cycle warranty is 10,000, or 15-20yrs that makes a big difference, also time of day tariffs, as that recent idea of 5p/kWh through the night is probably cheaper than the cost of a battery, so I'd half my battery size and only focus on balancing during the day, and covering evening demand.

Genuinely don't know how to work this out. I can make a logical assumption for myself, based on generation, export and import and consumption patterns, but I'm not sure there is any kind of rule of thumb - we may all have to do some number crunching individually.

Are we having fun yet?

Interesting. My approach is (may be far too) simplistic in just comparing the cost per Kwh of the stored electricity compared to current prices. Anything else means estimating inflation of electricity - which now admittedly looks significant in our new over-nuclear, non-renewable era. The only other check is that all the units (ie. cycles) will be used within the warranty of the battery. Variable pricing obviously makes it more complicated. I take it from the above that you are assuming that a decent system will allow you to choose when to pay for cheap import depending on some price factor? (This does make things more complicated though? - I need to decide whether to buy cheap electricity to top up the battery or hope the following morning will be sunny enough to to do it for me for fee before I need it). Do you know whether such systems are available here as suppliers are not yet charging domestic customers in this way?

Martyn1981 · 15 March 2017 at 1:38PM

Exiled_Tyke wrote: »

Do you know whether such systems are available here as suppliers are not yet charging domestic customers in this way?

I was thinking of this offering by Green Energy. It's not great as it has high standing charges, but it sets out an idea that may affect battery size.

It offers:
11pm - 6am 5p/kWh
6am - 11pm weekends 11p/kWh
6am - 7pm weekdays 11p/kWh
7pm -11pm weekdays 25p/kWh

At 5p/kWh at night there's no point using a battery as it may well cost more than 5p/kWh in costs (depreciation, wear and tear).

So you let the battery help balance out demand and supply during the daytime, then crucially cover the 7pm to 11pm slot. That way you are only buying leccy at 5p at night, and some leccy (minus PV gen) during the day at 11p.

According to my FF his system is programmable, so in the low generation months, he would tell it to full up on 5p leccy and not to discharge below XkWh's before 7pm - X being the amount of leccy he usually uses between 7pm and 11pm.

Obviously this is all theoretical ponderings, but it would remove my need to store leccy for the 11pm-6am period, and perhaps lower the necessity for daytime cover a bit too, keeping all focus on that peak period. I might only need 2kWh of useable storage, but I would also need to check what the discharge rate of the batt is as demand could hit peaks such as cooking.

Martyn1981 · 16 March 2017 at 12:27PM

Exiled_Tyke wrote: »

The price appears to be for a 3.3Kwh battery (which can discharge at 2.5Kw) together with an inverter (does this make is less efficient than systems which link into the existing inverter Marty?). Unfortunately I cannot find anything else out about the battery itself - crucially expected cycles. Still it looks like a step in the right direction.

Hello, hello. Here's an update.

Had a great chat with a 'very nice man' from EDF. Loads of info, and not a hard sell, quite the opposite, they are well aware that we are only touching the edge of viability.

First off, I can't have one. You have to have an import of 3,000kWhs or more. They don't believe it's viable at lower import levels, and mine's about 1,500kWhs after PV.

I think this is a very responsible approach, reminds me of all the advice I got from them when discussing how a PV extension would work, and each e-mail ended with something along the lines of ' .....but we really wouldn't recommend you get a WNW install ...."

Another minimum criteria is a 2.5kWp PV system due to the cost of the batts and reasonable returns.

They suggest payback would be 15yrs+ (10 year battery warranty) so again they are being very careful with their advice.

Next ..... AND VERY IMPORTANT ..... it's not a DC system as I assumed. The inverter is not a replacement for the PV inverter, it's the inverter to work with the batts. So it's totally separate to the PV, and is an AC system installed after the TGM.

The price is £3,999 for the inverter, batts, energy management tools and install/VAT.

This is a trial launch, they are being careful, and they do know it's a lot of money. They also said it was ok for me to post what we chatted about.

So an information update for the thread, but looks like we still have a few more years to wait.

silverwhistle · 16 March 2017 at 6:15PM

Only yesterday I received a hand-delivered card through the door for solar storage from a company called MOL-4.

As I buy in a fair bit less than Martyn I'm even less interested in storage at the moment (plus I already store some energy in an immersion tank..), but I'd be interested if anybody else has been contacted. They're based on the South coast (Fareham).

michaels · 17 March 2017 at 10:58AM

Martyn1981 wrote: »

Hello, hello. Here's an update.

Had a great chat with a 'very nice man' from EDF. Loads of info, and not a hard sell, quite the opposite, they are well aware that we are only touching the edge of viability.

First off, I can't have one. You have to have an import of 3,000kWhs or more. They don't believe it's viable at lower import levels, and mine's about 1,500kWhs after PV.

I think this is a very responsible approach, reminds me of all the advice I got from them when discussing how a PV extension would work, and each e-mail ended with something along the lines of ' .....but we really wouldn't recommend you get a WNW install ...."

Another minimum criteria is a 2.5kWp PV system due to the cost of the batts and reasonable returns.

They suggest payback would be 15yrs+ (10 year battery warranty) so again they are being very careful with their advice.

Next ..... AND VERY IMPORTANT ..... it's not a DC system as I assumed. The inverter is not a replacement for the PV inverter, it's the inverter to work with the batts. So it's totally separate to the PV, and is an AC system installed after the TGM.

The price is £3,999 for the inverter, batts, energy management tools and install/VAT.

This is a trial launch, they are being careful, and they do know it's a lot of money. They also said it was ok for me to post what we chatted about.

So an information update for the thread, but looks like we still have a few more years to wait.

I know you always do the maths and I am always too lazy to so....what size battery at what price would make sense to you? With this system with the battery after the gen meter can you also use it to transfer peak usage to E7 in low PV months?

Martyn1981 · 17 March 2017 at 12:28PM

michaels wrote: »

I know you always do the maths and I am always too lazy to so....what size battery at what price would make sense to you? With this system with the battery after the gen meter can you also use it to transfer peak usage to E7 in low PV months?

Not being evasive, but I can't work out if there is a simple rule regarding battery size, or if we'll all need to do our own calculations. I seem to recall that you have high import, so whenever generation is high then you'd probably get better returns than myself, assuming you have enough export too.

For myself, today (ignoring special tariffs or perhaps an EV in the future), I'd only need 4kWh useable, and I'd want to pay £1,500 or less, just to breakeven over 10yrs.

If the warranty period goes up, then that will help with returns, and if the battery lasted twice as long, then that would reduce its cost (per kWh stored and import avoided) by half, allowing for almost double the spend, but for now I'd only consider the amount of kWh's I could extract from the battery within the warranty period.

I hope this makes sense, but again I'm making it up as I go along, as I don't exactly know how to price a battery for domestic use.

One last thought, and this is way out there and for the future, but I wonder if a group of us got together, if that would help?

I'm thinking that an installer must be finding this hard work at the moment, but if they could order say 10 systems in one go, they'd get a discount, also they could allow a smaller mark up as it's not a one off, and even with geographical differences they'd still have a nice weeks work.

Whether or not this is possible I've no idea, and it might be a logistical nightmare, as we'd probably have to settle on a specific battery, or at least one make, with a range of sizes. Something to ponder over the next 2yrs+ perhaps?

shavy65 · 17 March 2017 at 12:36PM

Martyn1981 wrote: »

a specific battery, or at least one make, with a range of sizes.

Well I`m none the wiser. I`d be more than happy to let you decide for us Mart :cool:

Exiled_Tyke · 17 March 2017 at 3:54PM

Martyn1981 wrote: »

Not being evasive, but I can't work out if there is a simple rule regarding battery size, or if we'll all need to do our own calculations. I seem to recall that you have high import, so whenever generation is high then you'd probably get better returns than myself, assuming you have enough export too.

For myself, today (ignoring special tariffs or perhaps an EV in the future), I'd only need 4kWh useable, and I'd want to pay £1,500 or less, just to breakeven over 10yrs.

If the warranty period goes up, then that will help with returns, and if the battery lasted twice as long, then that would reduce its cost (per kWh stored and import avoided) by half, allowing for almost double the spend, but for now I'd only consider the amount of kWh's I could extract from the battery within the warranty period.

I hope this makes sense, but again I'm making it up as I go along, as I don't exactly know how to price a battery for domestic use.

One last thought, and this is way out there and for the future, but I wonder if a group of us got together, if that would help?

I'm thinking that an installer must be finding this hard work at the moment, but if they could order say 10 systems in one go, they'd get a discount, also they could allow a smaller mark up as it's not a one off, and even with geographical differences they'd still have a nice weeks work.

Whether or not this is possible I've no idea, and it might be a logistical nightmare, as we'd probably have to settle on a specific battery, or at least one make, with a range of sizes. Something to ponder over the next 2yrs+ perhaps?

Well I'd be up for it although like you I'm not overly optimistic that it would be viable. I'd be wanting something which made best use of my SolarEdge inverter.

On-grid domestic battery storage

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