On-grid domestic battery storage

JKenH

Coastalwatch wrote: »

Following on from Lightsource BP’s announcement of the signing of their PPA arrangement with Budweiser and Sonnen’s Virtual Power Plant supporting the grid in Germany has got me thinking about what would be the most useful(largest) size of battery that might accompany our system. As a minimum we should need 5 kWhs for daily overnight use in winter, then perhaps as a sensible maximum it could be as much as our system is capable of generating on any given day in the summer. This last year saw several days when output surpassed 60 kWhs. Given that we are made an allowance for the estimated 50% donated to the grid that we don’t use then it could be argued that a battery of around 30 kWh’s might not be a bad compromise.
At current storage costs, inconceivable, but in the fullness of time and with the benefit of grid smoothing payments(V2G etc) would it be out of the question?
I have to confess to hankering after larger rather than smaller as in winter time there is often two, three or more days without any measurable sunshine. So with a minimum 7 kWh’s daily required(not including hot water) then I can see 30 kWh’s disappearing quite quickly!


Can anyone make a case for going even larger?

No! I imagine on a very good day you can generate about 17kwh in winter but probably an average of say 9kwh might be more likely. You say you use a minimum of 7kwh daily so may have between 2 and 10kwh to spare but presumably on those good days you will also want to charge your EV. So realistically how many days in winter would it take to put 30kwh into your battery - 4 or 5 at least, more probably a week.

I wouldn’t go for a battery bigger than what you might realistically need for one day. The few consecutive dull days you will need several days storage might not be immediately preceded by consecutive sunny days. Are you planning to keep the battery pretty well topped up most of the time just for the few odd days you need 7kwh?

I would just plan on storing no more than enough to get you through from 3pm to 9 am the next morning as you would pretty well be guaranteed to use that every day but even then how many days could you generate enough for that in winter. In spring, summer and autumn you would use even less so why not base your requirement on the spring and summer usage when you know you will generate enough to fill the battery most days. With your system even on cloudy days you will probably cover your daylight base load all year round, the odd day or two a month excepted.



A 30kwh battery would potentially cost 3 or 4 times as much as a 7kwh one and those extra kWh would only be used a few days a year. The law of diminishing returns kicks in quickly as you go up in battery capacity.

Martyn1981

JKenH wrote: »

A 30kwh battery would potentially cost 3 or 4 times as much as a 7kwh one and those extra kWh would only be used a few days a year. The law of diminishing returns kicks in quickly as you go up in battery capacity.

I don't think we can understate how important that is, you are 100% spot on. For off-gridders they need to work to the worst days, with bigger batts and overcapacity of generation, and a back up gennie for extremely poor conditions. But for us on-grid, I think we only need to chase good days, and average bad days, then buy the difference in.

Not a defeatist attitude, just finding the right balance for the circumstances.

Where things might change going forward is the ability to store enough extra in the summer to keep an EV charged, or the ability to earn money selling to the grid at peak times. But I guess we have to see how all this rolls out, and despite my impatience, I think the delay is well timed as rising supply, falling prices, EV deployments and the market experimenting with home-to-grid are all coming along nicely ...... early 2020's perhaps? :think:

Martyn1981

Coastalwatch wrote: »

At current storage costs, inconceivable, but in the fullness of time and with the benefit of grid smoothing payments(V2G etc) would it be out of the question?

I have to confess to hankering after larger rather than smaller as in winter time there is often two, three or more days without any measurable sunshine. So with a minimum 7 kWh’s daily required(not including hot water) then I can see 30 kWh’s disappearing quite quickly!

Just spitballing here, more fun and jest, but ....... looking at say the Tesla Powerwall II at 13.5kWh, a lot of the cost is the ancillary kit, packaging, and install, not so much the battery itself. So if they made a bigger PW III say, then you might get a lot more storage, for only a small increase in total installed price.

Is this likely, possibly not, I haven't heard any such thing about the Powerwall, but a few days back they did announce their MegaPack, a massive batt, approx 12x the capacity of the PowerPack, at 2.7MWh.

So you never know ...... but don't hold your breath.

Coastalwatch

A 30kwh battery would potentially cost 3 or 4 times as much as a 7kwh one and those extra kWh would only be used a few days a year. The law of diminishing returns kicks in quickly as you go up in battery capacity.

Martyn1981 wrote: »

Is this likely, possibly not, I haven't heard any such thing about the Powerwall, but a few days back they did announce their MegaPack, a massive batt, approx 12x the capacity of the PowerPack, at 2.7MWh.

So you never know ...... but don't hold your breath.

Thanks both. I guess we have two schools of thought, one being the actual minimum to get us through overnight and no doubt the least expensive currently but then when bringing grid balancing into play it perhaps opens out to a wider debate. I wonder if at some point the Megapack would offer a reasonable payback given that with a smart Grid it would be available to store and then discharge as and when required. This being more likely the case as renewables play a more prominent role in the generation process. Certainly interesting times. 2.7MWh, that's almost a summers worth of surplus generation! Just think, the grid would have access to the bulk and even the small percentage remaining would be more than ample for home use!


Dreaming again!:)

Coastalwatch

The drive to make Lithium Ion battery manufacturing simpler and less expensive continues in Japan judging by the announcement below.

Japanese names invest to scale up 24M's semi solid 'next gen' battery tech.

24M, a start-up angling to disrupt the already-disruptive lithium-ion battery industry with the design and production of semi-solid lithium cells, has raised US$21.8 million in a Series D funding round.
The company, founded by MIT materials scientist Yet-Ming Chiang, is developing “ultra-low cost” batteries for a range of energy storage applications, based on manufacturing processes and designs that it claims eliminate some of the most costly or painstaking steps of mainstream lithium battery making today.

Providing battery longevity and degradation are not affected, then making the process simpler should not only result in more affordable prices but at increased production rates also!
I wonder if the home storage market is in their sights as well. Hope for us yet Mart!
https://www.energy-storage.news/news/japanese-solar-names-invest-to-scale-up-24ms-semi-solid-next-gen-battery-te

pile-o-stone

Coastalwatch wrote: »

Thanks both. I guess we have two schools of thought, one being the actual minimum to get us through overnight

My own thoughts of what I'd want from a battery would be to aim to be completely off grid during the summer months and to be completely off peak cost electricity at all other times.

I'd therefore be looking to size my battery to match our maximum daily electricity usage, which I guess is around 21st December, minus whatever we use during the E7 generation period. This would give me the maximum peak cost electricity that we consume.

I'd then be able to charge up the battery on E7 in winter and run the house all day on low cost electricity. In Summer, the battery would charge from solar. Spring and Autumn would have a mixture of both.

Maximising our solar self consumption and reducing/eliminating consumption of peak cost energy would give the 'best bang for our buck'. Grid balancing isn't going to pay, not unless you're talking about large scale industrial installations. It seems a complete waste of money to me for on-grid households to install a larger battery than your maximum daily usage.

Exiled_Tyke

pile-o-stone wrote: »

I'd therefore be looking to size my battery to match our maximum daily electricity usage, which I guess is around 21st December, minus whatever we use during the E7 generation period. This would give me the maximum peak cost electricity that we consume.
usage.

This then gets me thinking. Could we ever get to the time when E7, Batteries and ASHP could be the cheapest form of winter heating? Now my storage requirement has just gone by a few multiples!

Coastalwatch

Exiled_Tyke wrote: »

This then gets me thinking. Could we ever get to the time when E7, Batteries and ASHP could be the cheapest form of winter heating? Now my storage requirement has just gone by a few multiples!

Thanks ET, you've got me at it now! On that basis for us to cover one day in mid winter together with normal domestic demand, we now have two ASHP's and an EV. We have had quite a mild January and on the coldest day the HP's consumed near enough 10kWh, the EV averages 8kWh/day and there's around 7kWh for other domestic consumption. But wait, that doesn't include a hot water tank planned for installation in the spring so that may add another 5kWh's. That totals 30kWh's! And we've still some supplementary gas heating and hob to transfer across at some point.
I think I'd better stop just there!

Martyn1981

Coastalwatch wrote: »

Thanks ET, you've got me at it now! On that basis for us to cover one day in mid winter together with normal domestic demand, we now have two ASHP's and an EV. We have had quite a mild January and on the coldest day the HP's consumed near enough 10kWh, the EV averages 8kWh/day and there's around 7kWh for other domestic consumption. But wait, that doesn't include a hot water tank planned for installation in the spring so that may add another 5kWh's. That totals 30kWh's! And we've still some supplementary gas heating and hob to transfer across at some point.
I think I'd better stop just there!

Is that a daily total, or an 'outside of E7' total?

If the EV, and water can be done by E7, and some of the heating too, then the batt 'only' has to meet the daytime leccy consumption, let's say 5 of the 7, and the daytime ASHP. Maybe that helps a bit?

But, with colder weather needing more heating, and reducing the COP too, I think the numbers are still against you for the worst months.

pile-o-stone

For those with ASHP, perhaps an alternative differential tariff would be better?

Economy 10 has the following off-peak timings (though these can differ slightly depending on your region / supplier):

12.00am - 5.00am
1.00pm - 4.00pm
8.00pm - 10.00pm

https://sse.co.uk/help/electric-heating/economy-10

You could charge your batteries, EV and run the ASHP using grid energy during the above times and also charge up your battery for use outside those times.

The main drawback with differential tariffs like Econ 7/ Econ 10 is the higher cost of peak electricity, where the energy companies claw back the savings you made during the off peak periods. With a correctly sized battery you can reduce the peak energy periods to practically nothing.

Some lifestyle changes would have to be made because the peak output from batteries is much lower than the grid - so you'd have to avoid running two or more high wattage devices at once - like boiling a kettle, running an electric oven and hoovering up all at the same time, but this is manageable, especially on the Economy 10 package where you have reasonable off peak daytime periods to run the washing machine, hoover up, cook with electricity.

Other techniques could be to fit more energy efficient white goods and also use low energy alternatives, such a boiler tap (like qooker) that keeps a reservoir of hot water in a vacuum flask, where the heat is maintained by much lower wattage than a standard 3kw kettle element. Batch cooking food during off-peak electricity periods and warming it up in a low energy microwave, etc.

Fitting a lot of insulation would obviously help with reducing energy costs. With an insulated and reasonably air tight house, you could probably get away with only running the ASHP during the economy 10 off peak periods.