On-grid domestic battery storage

mmmmikey

JKenH wrote: »

It may not happen for a few years yet but as the take up of EVs and domestic batteries increases with attendant sophistication of charge management and time shifting there will presumably be more use of night time electricity and the cheap night rates may disappear.

I suspect that there will always be a differential to encourage night time use and it will more likely be a question of how much cheaper night time prices have to be than day time prices to level out demand. Having said that my own views is that there will be a healthy differential in the lifetime of a battery system bought now. Keep in mind there are a lot of folk that haven't even changed energy supplier and there are probably more people that don't know what a kWh than do, let alone really have their heads around what the energy hogs are in their household. The pace of change in the domestic market will be slow according to my own crystal ball. The same ball is also telling me that we're going to see some big incentives over the next few years to encourage us to switch to night time use. Be interesting to see how this pans out....

joefizz

Solarchaser wrote: »

Most of that I agree with completely Joe, however I think you missed my point about increasing the batteries in winter.... it was so I could buy e7 electric overnight and use it during the day to more than half my electricity cost.
Not that I thought they would be charged by the solar.

ahh, with you now!
I looked at the same for the batteries but I cant get E7 'on demand' as it were and would need to sign up for a year at a time over here. The yearly cost of the daily standing charge fee is about half to a third of what I pay in electricity per year so paying for import (albeit reduced from normal) for winter is cheaper than the fixed e7 fee for me. I usually dont use as much electricity in Dec/Jan than I do at other times.

Now if they allowed changing to E7 for a couple of months at a time... but I doubt that will ever happen!

mmmmikey

joefizz wrote: »

I import more when Im not at home on minimal load than I do when Im here working the battery to the fullest.

My solution to this has been to put my lawnmower battery charger on a timeswitch that comes on at 19:00 every day for 10 minutes - this draws enough in the first few minutes of being on to make the battery start delivery and there is sufficient hysterisis then to keep it going all night. Doing this has probably saved me as much as 50p over the last few months - haven't decided what I'm going to spend it on yet Who was it that mentioned monitoring OCD?

Picking up on a couple of comments above re: E7 and battery sizing....

On my E7 tarriff and with export metering I pay much the same for cheap overnight electricity as I will get when I move to export metering in a couple of months. This means I lose nothing by charging the battery fully overnight, as any spare solar export gets paid for instead of going into the battery. The only advantage of solar charging in this scenario is the ability to recharge the battery during the day to replace anything used when the sun goes behind a cloud, and on all but the darkest of winter days I'm more or less guaranteed to have a fully charged battery by the time the sun goes down and to last me through until 00:30 when E7 cheap rate starts. This means that there isn't really a big advantage to me for having a huge battery - it just needs to be big enough to meet my demand from sun down to E7 start.

On a similar note, anyone with export metering on a TOU tarriff such as Octopus Agile will be in the situation of significant diminishing returns. Very roughly, you'll be paying 25p per kWh for 3 peak hours an an average of 10p-ish for the rest of the day, meaning the return on the battery will be 20p-ish per kWh for 3 hours and 5p-ish per kWh for the rest of the day (i.e. the difference between the 25p you save and the 5p you'd otherwise get for export). So in this scenario, having a battery big enough to cover your usage for those 3 hours is probably all you need. Granted, adding capacity gets cheaper per kWh the more you buy, but when you set this against the redcued return I expect the economics will favour smaller battery installations (say 4-8 kWh?) if TOU tarriffs and export metering become the norm (as I expect they will).

A couple of caveats though. Firstly, if the battery isn't big enough it won't be able to drive the inverter for long at maximum output, even in a good state of charge (a point you have made, joefizz). And secondly a bigger battery would be expected to last longer (so there's an element of swings and roundabouts).

Yeti1980

Apologies if this has been covered before/elsewhere but has anyone investigated the Octopus Powerloop trial of V2G as an alternative to installing domestic batteries?

octopusev.com/powerloop

Exiled_Tyke

So I bit the bullet and splashed out on the Solax 6.3kW battery. The slightly (?) rash move was partly driven by the prospective increase in VAT to 20% although my installer has told me that there are quite legitimate ways to get round this. To get the reduced VAT I added a couple of panels with a microinverter (or to look at it another way I paid full price with VAT for the battery and got the panels free). I'm particularly pleased to be getting some East facing panels to give an early morning top up to the system.

The other justification is this: The battery is good for 6,000 cycles (hopefully). At 90% discharge that's 34,000 kWh. So at roughly £3,000 for the install I make that around 9p/kWh. Which is adequately less than what I am now paying per unit. Of course I appreciate that it's more complicated than that. 6,000 cycles will take a heck of long time to get through which could well be beyond the life of the kit. And of course lots of other uncertainties which I've ignored - like the price of leccy going up or down, battery deterioration etc..

My initial experience is very good. Over the last two weeks I've imported 2kWh which I'm very pleased about. The battery has a maximum discharge of 3.5kW and a recommended 2.5kW. It would be nice to know what level the 6,000 cycle life is based on - although I'm guessing nearer the 2,5kW. The installer has currently set maximum discharge at 2.9kW. They didn't seem unduly concerned about where it should be set. At this time of year it has only rarely discharged over 2kW so maybe this isn't something I should unduly worry about - presumably the slower discharges will keep the life up? Most of the time it's covering dips in PV production and covering a base load of around 200w during the night which shouldn't be doing too much damage?

Most days at the moment the battery is getting to almost full and only once (when we had a dinner party and put the dishwasher on at night) has it got down to 10% - although I reckon we only just started to import that night (the monitoring wasn't set up then so I'll never know!)

As others have mentioned my leccy habits have been tweaked but not massively. The obvious things are: still using appliances in the middle of the day to minimise battery use and having to import off the grid (for top up of 3kW appliances), not using more than one appliance at once and when I am in on my own still using the 1kW travel kettle to save battery consumption (and avoid 3kW consumption).

As others have again mentioned there's a nice warm feeling about being that little bit more self sufficient and using a lot more of what the PV produces and more importantly getting rid of the frustration of cloud creeping over just as the dishwasher starts its drying cycle. (I still like the idea discussed on these threads some time ago of having 'micro-batteries' just deal with peaks and troughs).

Monitoring of the system is pretty impressive too although the dashboards take a bit of getting used to as they are not intuitively laid out and labelled.

Well I hope that's of some interest to people and not too long winded. Of course if it is, you won't have got this far, nor thanked me so I'll realise soon enough .

Solarchaser

Enjoy being addicted to the app lol.

The 6000 cycles are complete cycles, so 10% to 100% and back to 10%.

The mini cycles of covering the heat cycle on the washing machine isn't registered as a cycle on the battery.

But if you think about the days where you wont have any solar for the batteries, or where you dont get the battery down to 10%, then you will be lu key to do 300 cycles in a year.... making them 20 year batteries

ASavvyBuyer

@Exiled Tyke. £3,000 for 6.3kW battery system + 600W of solar panels, all fully installed appears to be a good price. Who did you get to do the supply & install?

Zarch

ASavvyBuyer wrote: »

@Exiled Tyke. £3,000 for 6.3kW battery system + 600W of solar panels, all fully installed appears to be a good price. Who did you get to do the supply & install?

Yep, interested too in the model(s) of kit purchased, breakdown of prices and where from..... if you don't mind?

1961Nick

Solarchaser wrote: »

Enjoy being addicted to the app lol.

The 6000 cycles are complete cycles, so 10% to 100% and back to 10%.

The mini cycles of covering the heat cycle on the washing machine isn't registered as a cycle on the battery.

But if you think about the days where you wont have any solar for the batteries, or where you dont get the battery down to 10%, then you will be lu key to do 300 cycles in a year.... making them 20 year batteries

I've had batteries for 183 days & have recorded 122 cycles. Even with overnight charging in winter, that figure won't rise beyond 250 cycles pa. That should mean that at worst it'll take 16 years for the batteries to reduce to 80%.....easily solved by adding another battery.

Exiled_Tyke

Zarch wrote: »

Yep, interested too in the model(s) of kit purchased, breakdown of prices and where from..... if you don't mind?

Apologies for being unclear. It was £3k for the battery system. So the VAT would have been £600. The two new panels came to £700 which I was happy to pay as it avoided the 20% VAT rate on the battery.