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pbmasters

Can someone look at the figures to ensure the maths is right which, if so, should provide a warning to all who might be misled into non-existent returns through any subsidised power saving scheme?


I did the calculations below to see if I can make a proposition in a subsidised Home Electricity Battery Storage scheme trial fly as an investment. To help me do this I need to understand my generation potential, the storage potential and cost of electricity.


Annual Solar generation: 1071kWh (2016). I think this value will remain fairly constant for my Long/Lat., size of array and whilst the sun shines in the sky.

Daily generation & seasonal variation:
Lowest 0.20 kWh curve troughs between October to February
Average 2.97 kWh
Highest 7.01 kWh curve peaks April to August


Based on the average generation above my array generates:
2 kWh per day 33/52 = 63% of the time.
4 kWh per day 15/52 = 29% of the time.
∴ < 2 kWh per day 4/52 = 8% of the time.


So, assuming that ½ of that generated 1071kWh could be stored (and used) because it is not being used through the course of a day lit day = 535kWh.
Cost of buying a kWh unit of electricity from a provider = 0.1386p (average figure). Ignore standing charge as that is paid regardless.


535 kWh x 0.1386p = £74.15 per annum (or the amount per annum I am offsetting against capital outlay.)

• Provider 1 2kWh Lithium-ion - 2,585 + 20% VAT = £3102 (break even on capital outlay = 40 ½ years)
• Provider 1 4kWh Lithium-ion - 3,575 + 20% VAT = £4290 (break even on capital outlay = 57 ½ years)
• Provider 2 (assume installed 2 kWh system VAT incl.) = £3000 (break even on capital outlay = 40 ½ years)

This ignores other operational costs such as any power consumption a storage unit might need, the relative cost of not having the space to utilise for anything else, and guaranteed cycle values i.e. 4000 cycles = 11 years (less if lead/acid), which means that every 11 years or so I may need to change the batteries and disposal at further cost.


I’m have to say that because maths shows an unrealistic return within an abnormal amount of time, I could not waste money through either scheme. What is disappointing is the attraction to the scheme by the subsidy from a UK company, which might fool people into thinking they are doing the right thing (and noting £3-4000 invested properly over 40 years would show a much better and more immediate return).


Am I not seeing something here, as I cannot believe that any UK company might think they could operate a proposition to the public a 40 year break even?

NigeWick

pbmasters wrote: »

Am I not seeing something here, as I cannot believe that any UK company might think they could operate a proposition to the public a 40 year break even?

Without checking your figures, I do not think battery storage is cost effective for personal use at present. Battery prices are coming down rapidly and I am fairly sure there will be a cost benefit in the next two or three years.

That said, when I have got the cash I will be buying battery storage because I want to be electricity independent. Early adopters are willing to pay a premium for new "stuff" and it is their money that allows further development and eventually lower costs due to scale of production.

Cardew

Welcome to the forum.

Most of the discussion on solar PV and battery storage is in the 'Green and Ethical' section of the MSE forum.

There is no doubt that at the moment battery storage is not a practical(economic) proposition. However I would disagree with the last paragraph of your post. Some of the public are suckers for silver tongued salesmen playing the 'Green' card and quoting completely unrealistic figures.

System

To put this into its proper context, your maths are skewed by scale. If you are only generating 1071kWhs/year, then you must have a very small PV array. To make the maths work, a big array is needed because generation is most needed in Winter - not in the height of Summer. Your battery system also needs to be big enough to store enough power to cover days when there is no generation.

There are many schemes out there is maximise use of PV solar. few, if any, give a proper return on investment imho. That said, I do have an EV and I charge it off my roof whenever the sun is out. Total fuel costs for 2016 were £24 for Ecotricity charging plus 2 gallons of petrol for the REx.

Martyn1981

pbmasters wrote: »

Am I not seeing something here, as I cannot believe that any UK company might think they could operate a proposition to the public a 40 year break even?

Hiya and welcome.

I think your maths are correct, though of course it does depend on the prices and whether you can do better. I recently got an installed quote for 4kWh useable (8.8kWh LA) at £2.8k. But it needs to be nearly half that for it to become viable (for me).

Hengus is spot on about scale. The Tesla PWII has a useable 13.5kWh for an installed price of £6.2k, and for your generation I'd have thought the 1.2kWh Enphase batt would suit, which if proportionally priced would be about £550, but of course that's not realistic considering shipping, install etc etc.

You could contact your DNO and ask if they are carrying out any trials, to see if you can get a discounted batt, but that's a long shot.

Long story short, batts aren't there yet, but are improving faster than expected. Don't expect too much in the UK till maybe 2020, but Australia and some US states (with high leccy rates) are deploying more and more. Also Germany and Sweden are now subsidising domestic storage as it helps with peak demand, loads and prices.

If you want to learn more have a read of this thread.

On-grid domestic battery storage

All the best.

matelodave

What you've also missed in your calcs is how long your batteries will last.

It's highly unlikely that they'll last for the 40 years payback that you are expecting. I'd guess that 10 years would be a reasonable guess at present, so you need to factor in changing them at least twice during the 40 years.

Hopefully the price would come down a bit and the replacements might last a bit longer as battery technology evolves and you might even get something back by recyling the old ones.

Many years ago I was involved in designing solar powered telecom cabinets together with the arrays and back-up batteries for use in Jordan (where the sun shines a lot).

The size of the arrays and back-up batteries that were required to keep the equipment powered 24/7 were eye watering when you considered that that the sun doesn't shine at all at night and even in Jordan it's been known to snow. I think it will be a long time before they become viable in a domestic situation.