The Lemon Fool

Hello

I'm thinking about investing in a pair of these for home

https://www.tesla.com/en_GB/powerwall

Which should give me 28kWH of storage. I've got 4kWH of solar panels and also an electric car (a 24kWH leaf, otherwise I think one powerwall would cut it). Currently I charge the car from a 13amp socket, I've not bothered with the fast home charging, so the 5kWH continuous power supply should be enough to charge the car.

Has anyone any experience of this kind of large scale battery storage?

Check out navitron.org.uk/forum

They have an EV board and a board for storage.

Home battery storage is in the "pickle" stage at the moment. It isn't quite ready for mainstream, and with the product developing at a great rate. You have to be a "believer" to buy in now. Within a year or so, you will be able to buy more storage for the same money. It has already happened with Powerwall and Powerwall II.

Don't forget for 6 months of the year (or more), you aren't going to generate enough from your PV to run it outright. I have generated 180W one day this month from 3.7Kwp!

You may need to price up whether Economy 7 or something may be worthwhile, charging the car at night during the winter?

Meatyfool..

I am a believer - it's the environment I'm thinking of, not essentially the £ (I accept I'm unlikely to get my £ back on it). I think I'd be self sufficient for 7 months a year (I write down the power usage every month) and from mid March to late September.

Just interested in trying it really

I too have been recording my meter readings every month, for nigh on 10 years. If you don't measure, you can't see unexpected increases in consumption!

I wish I could jump now too, but I'm afraid I'm not one for the bleeding edge. Would like to see my summer excess going into batteries for use in the evening.

Research well. The "guarantee" that is provided for the batteries is not as comprehensive as seen at first glance.

Consider non-lithium options as well. I think flow batteries at the domestic level aren't quite there yet.

Meatyfool..

I have experience of this size and larger.

If you are planning to charge your home storage during the day from PV, then dump it into your EV storage overnight, then you have just doubled your charge/discharge losses and halved your cyclic life. Are you thinking this way because your car is away from home during the day, i.e. your circumstances force it on you ?

(by the way once you start to think through most practical use-cases you begin to realise the real issues in using 'surplus' EV storage for grid support purposes: there basically is no surplus as the peak grid demand in the evening coincides with the minimum point in the typical EV charge cycle ...)

The economics of home storage in the UK are dubious at present, indeed they are dubious everywhere that is connected to a stable grid and where normal economics applies. I have checked my own economics and they would not work - and I am a 90% spill to grid situation from my PV. Have you quantified your spill, as opposed to the deemed 50/50 ? My advice to myself is to wait as long as I can, and in the meantime put the money somewhere boring (not HUR ...).

regards, dspp

FredBloggs wrote:if you have more PV power than you're using, wouldn't it be better to heat your hot water with the surplus? Just another way of energy storage, but quite an efficient one?

If you have a water tank then a solar hot water panel on the roof is an efficient way to heat it, cutting out the middleman of PV electricity.

Friend of mine has such a panel alongside her solar PV.

FredBloggs wrote:if you have more PV power than you're using, wouldn't it be better to heat your hot water with the surplus? Just another way of energy storage, but quite an efficient one?

If I had a storage tank, but we've got a combi boiler.

wheypat wrote:I am a believer - it's the environment I'm thinking of, not essentially the £

The question is whether in 2028 you'll look back and wonder if the environment would have been better off with you having 11 years of battery X or 10 years with battery (X+y%). I'm not sure if we're quite there yet at the current rate of change - ie y is more than 9% per year at the moment.

wheypat wrote:If I had a storage tank, but we've got a combi boiler.

Err - use the electricity to hydrolyse water and blend in the resulting hydrogen to the gas supply to the combi boiler? Hythane is quite the thing these days... (for the avoidance of any doubt - I'm not being serious)

dspp wrote:basically is no surplus as the peak grid demand in the evening coincides with the minimum point in the typical EV charge cycle ...

It may be the minimum point of the cycle, but there may be plenty of juice left. Average mileage per car is about 8000 miles/year which averages out at 22 miles per day. That's about 4kWh in a Leaf, leaving you 20kWh left in the evening for peaking purposes from the basic 24kWh powerpack when it's new.

Admittedly there's a good argument that you don't want to be thrashing your car powerpack through a full power cycle every day given the current state of the art in powerpacks which should just about last the life of the car but not much more than 100-150,000 miles. But if Tesla can deliver on their promise of a million-mile powerpack, then it becomes a lot more attractive to use the leftover juice in the car for peaking purposes - after all, this is the most valuable electricity in the network.

H,

In my opinion the right way to use car battery packs is in a 2-stage lifecycle. Use the first x% of the cyclic duty in cars, then demount and install them in large-scale battery farms for the remaining y% of the cyclic duty. That way you roughly halve the cost of a new battery pack to the auto-world, and to the storage world. That's the biz-model I assume when I run my numbers. Decoupling like this seems to overcome most of the technical limitations at both the car end and the grid end, and don't require an awkward social ownership transition ("what do you mean you took the gas out of my tank - didn't you know I had to drive my wife to the maternity hospital at some point this week in a hurry").

regards, dspp

I like the idea, I think it's great but what puts me off is the speed of change/ improvement......what I buy today will almost definitely be out of date/ old technology in a year or two.

I have no wish to spend £6000 - £12000 on something that is likely to be superseded very very soon. Ill just let all those who like to get in early spend their money and road test the stuff.

Good luck