On-grid domestic battery storage

zeupater wrote: »

Hi

Agree, I know a couple of people (and am aware of a number more from various sources!), who have been disappointed by their battery performance relative to supplier claims and have eventually been able to return their product for a full refund (took some time, but they have done it!), which supports a conclusion that many justification models are seriously flawed ...

I would rather expend my effort helping both suppliers & consumers understand the issues involved in employing erroneous logic at this early stage, than see seriously negative newspaper headlines concerning home storage in a few years time ...

In reality, I'd rather that the relevant industry associations, Ofgem, FCA etc sat down and agreed to commission a standardised assessment process & basic algorithm to be employed by all suppliers in correspondence with potential customers, particularly so at quotation stage, but that would either need to be driven by the industry now, or imposed by regulation later !

HTH
Z

Yep. To all that.

I'm more than happy to agree that cycles should exceed 6,000 going forward, and batts should last much more than 10yrs going forward, but I'm not going to suggest to anyone else that they trust me and invest £5k+ based on my beliefs. Not till we have more to go on.

For instance I used to say that folk should expect an inverter to fail during the first 10yrs, and cost ~£1k. Now I think that's less likely, will cost less, and can be insured against via extended warranties.

As explained (too many times (sorry)) I think for safety's sake we should omit inflation and cost of capital, so I thought I'd see what that would give us:

I'm going to go with the £6k and 10kWh (useable (I assume)) suggested, and the 2% capacity loss pa.

I'm also going to use E7 for one third of the cycles, and assume 32 days pa when no cycling occurs - partly to represent faults with the batt, faults with the PV, days in the sunnier months when weather is too poor to charge, and holidays etc & partly to fudge round numbers of 30yrs and 10,000 cycles.

In the first decade we get 333 days x 9kWh (90% capacity average) = 29,970kWh

In the second decade we get 333 days x 7kWh (70% capacity average) = 23,310kWh

In the third decade we get 333 days x 5kWh (50% capacity average) = 16,650kWh

So, that's a total of 69,930kWh's.

2/3rds or 46,620kWh's save us 15p/kWh = £6,993
1/3rd or 23,310kWh's save us 6.6p/kWh* = £1,538

Total = £8,531 and a saving of £2.5k over 30yrs

[*6.6p is the saving based on E7 at 7.5p, day rate at 15p, and batt efficiency losses meaning that 1.12kWh of E7 is needed for 1kWh of output.

However, is it worth bothering with E7, I doubt it at these battery costs since we have a batt cost of £6k/69,930kWh's = 8.58p/kWh which when added to the E7 purchase cost of 8.4p = 17p/kWh exceeding the saving of 15p/kWh day rate.

Better perhaps to protect the capacity of the batts.]

Would I do that - no.

Would I do it if I was certain that it would last 30yrs and 10k cycles - no.

Would I do it if I was certain that it would last 30yrs and 10k cycles and costs won't fall significantly over the next 5-10yrs - yes.

Would I recommend that other folk invest £6k to make £2.5k over 30yrs ......... nope!

Would it work for me, not today, the battery draw down in year 1 is 3,330kWh's and I import about 1,600-1,700kWh's pa, but in the future as I've mentioned on thread my demand may go up further thanks to an EV, and this will hopefully coincide with falling storage costs.

Lastly do I like the look of what is being offered by this company - yes. It's pretty much everything I would hope for, and I believe a reasonable price compared to elsewhere. Unfortunately the state (price) of the technology is too high today (no ones fault), and I fundamentally object to the use of inflation, especially high inflation rates over long time periods, to make something work. I'm funny like that!