@diverted-energy I have to disagree with you there. I have a 5kwh battery and 5kw heat pump. It saves me loads coupled with my solar. Total energy bills for me over the year including charging my EV £40 per month. I have thought about adding another 5kwh module but I can't make the numbers add up.I would need to get the second module sub £1000 to make it even considerable.

While intuitively it sounds nice the be able to run your heat pump purely on battery power the financial reality is that a smaller battery with minimal grid usage in winter is more cost effective.

Posted by: @tim441

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I have no faith that our government (of any colour this century) or NESO have done enough or are in sufficient control to ensure supply.

Then Tim, may I suggest that you too ask to be included in the membership of your Regional Energy Strategic Plan organisation?

The RESPs are only just getting started. They've each held a couple of online briefing sessions, and are beginning to learn what needs addressing.

Have a look at this presentation on RESPs issued by DESNZ.
Helpfully, it gives the direct email addresses for the Manager of each RESP on the last page.

That's probably a mistake, as the public is meant to use the generic email address box.RESP@neso.energy
so I suggest everyone reading this discussion downloads a copy of that PDF and keeps it to hand!

Once the RESPs have elected Councillors within their membership, they will have more clout.
Under the provisions of the Energy Act (Nov'23), it is the RESPs who hold NESO to account.

Each has to form a Strategic Board by 2027 and will shape energy strategy for the future in their geographical area.
It is widely understood that they will also be given the remit for transport strategy and planning.

@bontwoody maybe you need the calculator I use.

Strange that after fitting the first, most I deal with add a second and a third.

Something also to filling up with 7p at night and flushing out at 15p during the day.

Then there's running AC or Heat Pumps, cooking and all the other things high energy users want.

Calculations may not work for you but seems I'm very busy installing batteries here and across Europe, so some calculations add up.

Charging/ discharging at a 5kwh's C Rating many times per day, how long before its done its cycle lifetime?

My installations run at 0.1 to 0.2C, not 0.5C most systems I've taken out were running.

Our 65kwh run one cycle every 3 to 5 days.. not 4x times per day.

Although you disagree - there's more to a battery than capacity when accounting for lifetime.

@transparent many thanks for this. I'll take a proper look and chase our Local Authority - if nothing else!

Posted by: @diverted-energy

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@old_scientist totally agree but 5kwh battery is a complete waste of money.

Taking away the Inverter requirements, 20-100% and you're left with 3kwh.

I install large capacity batteries and 15kwh should be the minimum considering we are electrifying our lives.

At least twice daily consumption in battery capacity for 1) longevity due to better C rates, 2) lower cycle count and 3) more night energy stored for daytime heating.

The number of installations I end up ripping out expensive Inverters and batteries to swap for a cheaper very capable Solis with 15kwh to 65kwh batteries.

End users quickly realise they gave been overcharged and mis-sold a tiny battery when reality kicks in.

3.6kwh max nighttime power and low capacity.

@diverted-energy I totally agree, but a regulated minimum would at least be a starting point and if it achieved nothing other than reducing export of solar during the middle part of the day and reduced dependence on the grid at peak times, it would serve it's purpose of helping to stabilise the grid. In an ideal world, house builders would specify a modular stackable system that the buyer could choose to upgrade at the point of purchase, in much the same way they may choose a premium kitchen finish and floor coverings.

Once you can get something regulated in principle in planning, then you can figure out the finer details of minimum amounts of solar & battery per new build property, but that would likely depend on why it was regulated in the first place - was it to minimise the impact of the new build development on the local grid or was it to allow new build home owners to fully benefit from all the latest green tech and live off grid with zero bills.

@diverted-energy I think perhaps our different viewpoints may come from the level of energy use. My battery is rarely depleted except in winter and once it is I use the grid.

Most modern houses will have a heat loss less than my old one and so should easily fit within a 5kw heat pump category.

At the end of the day my usage is documented not modelled and it's a trivial exercise to calculate the effects of another battery module and it's ROI

@bontwoody Totally agree. Even without a heat pump, if a 5 kWh battery helps storing the PV power generated during the daytime in spring, summer and autumn, and avoid using the grid in the evenings, it would be worth it. Modern batteries have a high DoD, so.if you could make use of 4.5 kWh each day during those 9 months, that could save you like £350 per annum.

I primarily doubled my battery storage to avoid cycling and prolonging the battery life. Even otherwise, the battery is going to be like 70% capacity after 10 years, so should get the money back. Also, this acts as an insurance against higher peak prices as power can be stored at off peak rates, but for that one would need an EV tariff.

@chandykris That matches my figures pretty closely, I reckon I save about a £1 per day on using electricity on the overnight tariff plus you have the difficult to quantify advantage of the battery picking up the slack when the sun goes in.

Ive set limits on my DOD from 5% to 95% to help the battery longevity but primarily that was why I was looking at another module too. I keep scanning ebay for a bargain.

My battery is DC coupled not AC so I think that helps with the inverter losses mentioned in the original post.

It's windy down South today, which means our electricity is dirty and expensive because most of the wind turbines are elsewhere.

@bontwoody Maybe one for @editor to consider whether a second hand battery shop on the forum might be worth it!

Jokes apart, totally with you on the financial viability aspect. We got lucky as Growatt had discontinued the GBLI6532 model, so we got hold of one of the last remaining batteries from a wholesaler (actually thanks to our installer who managed to track it down) for a reasonable price. Had it been the original price we paid minus the inverter cost, it would not have stacked up financially.

Interesting article on Interconnectors...
https://www.telegraph.co.uk/gift/a552809abbf2e670

If Interconnectors stopped for any reason (political...energy demand in other countries.. or even Russia cutting them?)... we don't seem to have any backup or alternative to outages?

@tim441 Puts even more reason behind any proposal to have battery back-up in one’s system doesn’t it? Anyone else seen the ‘press release’ on their Tesla app about the one millionth Powerwall having been manufactured on the June 2nd. 2025? Regards, Toodles.