Add another battery or not?

Is there a point in adding another battery to the system? I have 3.28 kW PV with a 5kW hybrid inverter and 8.2 battery.

marcingu3 do you use the full battery capacity in summer or winter? If not then it's probably not worth it as it won't get cycled enough

Theoretically, if the sun is out, charging the battery will take 4 hrs - more or less. We need to charge a car - 8/9 kW few times a week, run the house etc. -so it is on edge big time. However, for everyone, winter is a different story - I cannot see both being charged by the sun.

On this other recent channel post I shared a spreadsheet I put together to work out the payback of different battery and charging scenarios.
https://community.givenergy.cloud/d/2113-what-can-i-pair-with-a-95-kwh-battery

But very roughly, another 8.2kW battery will save you £0.34p x 8.2 = £2.79 every time you fill it up (excluding charging/discharging losses).
The battery costs circa £3,200, so you will need £3,200 / £2.79 = 1,147 full charge/discharge cycles to recoup the initial outlay.

Depending on the assumptions you make about how many months a year you will get that much solar, and that you can use it all overnight, you are looking at a payback of 3+ years.

marcingu3 If you can charge 8.2kWh battery in about 4 hours, it sounds like you probably generate enough power to charge EV entirely from solar (roughly 4kWh per day on average) ? What's your typical daily house usage ? And what tariff are you on ?

Newbie here, so please be kind !
6.4Kwp PV, H5.0 G2 Inverter, 9.5KWh G2 battery, Eddi immersion diverter and EV car in the East of England

Thank you Geoffrey for your useful spreadsheet - it makes me wonder if an Octopus Flux export tariff would reduce those payback periods quite a bit !

I would love a "spare" 9.5Wh battery to force discharge to the grid between 4pm and 7pm paying me 36.58p a unit ...

4kw + 5.2kwh battery here... considering adding another battery too. On good days with a near perfect south facing and unshaded roof, we've been generating well over 24kwh a day... average house use is between 10-14kwh, really heavy use days we've hit 19kwh once or twice... when using washer and tumble dryer at least twice, plus dishwasher and cooking plenty on electric.

With solar powering the house until around 7pm on a good day and the battery starting to assist perhaps from between 6-7.... if I have an early night as I have most of this week because exhausted from work... the battery has been lasting into the early hours of the morning.

Adding a second 5.2kwh battery should see the house powered for a whole 24hrs on good days... best we've had so far was 2 days away over Easter, with great generation and a fully charged battery powering the house until after 6am the next day. Only drawing from the grid between 6:15 and 7:40 before solar was enough to cover the house at idle. By the time we got home around 8pm with a takeaway so didn't have to cook.. and off to bed by 10pm as knackered... the battery again lasted until around 3am.

Total cost for that 48hr period was 41p (not inc VAT or standing charge)

A 2nd battery is going to cost in the region of £2600 as we'll have to pay VAT on it... I could added a couple more panels to get the vat knocked off... but the cost of the panels/scaffolding/installation is greater than the VAT on another battery.

At the moment, we are still on a fixed rate tariff until Sept, so only paying 15.93p per unit and 21.9p standing charge.

We've actually got a credit of £1230 on the account... and Eon just emailed us a bill saying they're INCREASING the DD to 84... f*ckwits at Eon can't get anything right at all. They screwed up the move and are still screwing up the transfer of the solar & fit payments from the old house to the new owners.

Anomnomnomaly the cost of the panels/scaffolding/installation is greater than the VAT on another battery
You could order the extra panels and either not install them, or prop them up in the garden? Unfortunately the other thing you may well come across is a minimum order quantity on solar panels. After working out what I thought was the maximum panels on my roof (28x 390w new panels to fit alongside the existing 16x 250w FIT array) and the company coming and doing an installation survey, as they were being put up I realised I could have got another 2 panels on the garage roof and maybe 4 in portrait across the front. But it just wasn't worth it, and would have to start the whole DNO approval again.

Anomnomnomaly average house use is between 10-14kwh
Sounds like an extra battery would be beneficial to you. We have an air source heat pump which alone consumes circa 20kW a day so our usage varies between 30 and 65kW a day but about 2/3 of it is now coming from solar and the battery. We've only managed one day so far (9th through to 10th April) where the battery ran the house overnight. As it gets milder and the heating is used less I'm predicting we'll be self-sufficient for most of the summer.

Data from this week:

marcingu3

That's not (at this time of year) particularly promising. Only 4kW exported this week.

Here for comparison is my generation graph for this week. I have 10.4kW of solar, 2x Get 1 Hybrid inverters and a 9.5 and a 5.2kW battery.

My PV array is 3.28 kW, three times less than yours - 46 kWh of generation. I just want to run home as much from the solar generation and battery - not really interested in exporting to the grid.

marcingu3 I just want to run home as much from the solar generation and battery - not really interested in exporting to the grid

Me too, it's all about saving £ on the electricity bill. We also have a 4kW FIT array installed 4 years ago which gives us about £500 of 'deemed export' payments which we would forgo if we moved to SEG export payments. According to my GE app I've exported 148kW so far this year, or at 34p/kW, about £50 if I had saved it in a battery. I'll do the math when we have a full year of data, but I'm still not thinking getting another battery is going to pay for me even though I would rather capture and use the electricity than sell it back at a rubbish SEG rate.

The "4kW exported this week" comment was referring to the fact that so far this week you've not had a lot of excess solar that would justify a second battery. Obviously this will increase as we get into longer summer days, but just thinking about the payback that's all.

geoffreycoan

We've had days where we've imported 1-2kwh from the grid. Yesterday was a good day, Generated about 19kwh, used 7kwh on the house, charged the battery and sent 8kwh to the grid.

Sun lasted well into the evening, powering the house until well after 7pm... We had an early night and went to bed to watch a movie. So house was kinda on idle from 8pm and battery lasted until 2am. Total import for day was 2.29kwh

Some days are costing pennies now... not counting VAT or standing charge... But we're still on a fixed tariff until Sept, so protected... Gonna be a shock this winter I think.

I was on a fixed budget for this install, had to be under 10k... and prices had been rocketing last year before we had it fitted in Jan. What should have been a 5kw and 8kwh battery... was a 4kw + 5.2kwh battery. Neighbour had their installed Jan last year and got 4.4kw+10kwh for just over 7k, ours cost just over 9k.

Anomnomnomaly Yesterday was a good day for us as well, we only imported 3.8kW with the batteries lasting until 10pm. So far we’ve only had one day where the batteries lasted through the night as we have an air source heat pump which can use 10-20+ kW a day. As the days get longer and the heating is on less I’m expecting self sufficiency for most of the summer.

I thought with the expense of the scaffolding I might as well maximise the investment and put as many panels on as could be fitted. We already had 16 in the FIT array on the back so most of the 28 new panels went on the front (East facing) with just 6 fitting in gaps at the back. We paid £14.5k for the panels, 2x inverters and a 5.2 battery, and then I bought a 9.5 battery separately for another £4k.
The batteries are so expensive.

Our 1 year fix ran out in February this year and I kick myself now for not originally going with a 2 year fix from Scottish Power, which at the time would have cost about £100 more for the first year. Never expected the rates to rise so much.

geoffreycoan Yeah ASHP will seriously drain batteries. Also max power draw exceeding the inverter AC output will force you into grid import when you need the most heating (winter).

With the government "planned" ban of Gas Boilers in 2030, I think it is now, it's about time we saw some joined up thinking by the government to require the DNO's to streamline the entire process so that they automatically permit 5/8kw+ inverters with Export Limitation. Also ensuring regulations for house builders are changed to ensure that all new builds MUST have Solar PV and 3 phase electricity installed by default. This would make a small difference on the limited new housing stock being built.

It also makes little sense to me that you require DNO permission for an ASHP over 3.68kw to be installed where I can easily convert my hob from Gas to an Electric Induction Hob that has anywhere from 4kw to 9kw power requirements.

I just found out that the development where our house was built had "Bore and Grout" - essentially they bore holes and fill with concrete due to mining. At the same time the developer could have drilled a bore hole for communal pipework for GSHP installs.......

All equipment is expensive primarily due to demand worsened by increased transport costs. Batteries are particularly affected due to the massive drive to electrify in China. Until we have manufacturing capabilities directly in the UK we will always be subject to the vagaries of those factors.

The only, small, light on the horizon is that in the second half of the year energy prices are being forecast to drop. Gas wholesale is more than half of what it was in November 2022. When, or if, we will see those price drops will be decided by Ofgen in July 23.

dragon2905 ASHP will seriously drain batteries. Also max power draw exceeding the inverter AC output will force you into grid import when you need the most heating (winter).

You make a good point about the ASHP exceeding the max current output of the inverter output; I hadn’t thought about that.
Looking through my daily graphs since the end of March (which is when the batteries were balanced across the two inverters), it’s actually been OK so far. With two inverters you’d hope there would be a doubling of potential AC battery output but I guess the plant setup doesn’t work like that.
In practice the highest draw I can see was 4kW and 2.9kW was supplied from the panels and the battery, only drawing 1.1kW from the grid. Most of the time the batteries and solar produce all bar 0.5kW of the power the house and ASHP needed.

dragon2905 It also makes little sense to me that you require DNO permission for an ASHP over 3.68kw to be installed

We have two 9kW ASHP’s installed as the heat loss calc couldn’t be met from a single MCS approved ASHP (I think we needed 14kW from memory). I’m pretty sure there wasn’t a DNO approval; there isn’t one in the paperwork handed over to me and the system was installed a couple of weeks after I signed the contract. I waited months for the DNO approval for the solar panels and then another month for a second approval to put in the second battery. Both the ASHP and the solar were done by the same installer. You can put a beefy electric shower in that draws more than my heat pumps!

dragon2905 At the same time the developer could have drilled a bore hole for communal pipework for GSHP installs.......

As you say short sighted thinking. I’d say it’s worse than that, we need house builders to put in communal heating systems and move away from the fixation of individual houses having their own boiler. Would be much more cost effective. Ideally GSHP as well considering they’re already digging the site for foundations, roads etc.

geoffreycoan there wasn’t a DNO approval

As you say, adding an electric shower could exceed the demand of an ASHP, so DNO approval wouldn't make sense.
However, from memory, putting solar panels on your roof is a permitted development (unless you're in a conservation area or the building is listed), unless you already have an ASHP and installing an ASHP is a permitted development unless you already have solar panels. There must be a reason why you can do either as a permitted development but doing both requires planning permission. I get that ASHP can become a noise nuisance for neighbours if not installed sympthetically but what the planning regulation thinking is to require planning input when adding one when you have the other is beyond me.

geoffreycoan
If new houses were built to passivhaus standards then pretty much a big TV in the lounge will do a lot of the heating.
Trouble is this needs a mind shift in HMGov regulations which are woefully lacking, a mind shift in builders to construct to these standards - recognizing that building things right should not cost more.

https://www.passivhaustrust.org.uk/what_is_passivhaus.php

SteveCook If new houses were built to passivhaus standards then pretty much a big TV in the lounge will do a lot of the heating.

Yeah agree, for all the government talk about the energy crisis there is precious little being done about insulation and reducing demand.
I just finished watching Guy Martin’s “Power series” that was on TV recently that looked at how power is generated and transmitted. Worth watching. The wave energy was perhaps the most interesting new th8ng to me. But he sums up at the end by saying we all need to use less energy.

Tim putting solar panels on your roof is a permitted development (unless you're in a conservation area or the building is listed)

This got me curious as to what the planning rules are so I went to have a look. As long as your house is not listed, within the grounds of a scheduled monument, or in a conservation area:

• Solar installations are permitted development https://www.planningportal.co.uk/permission/common-projects/solar-panels/planning-permission-solar-equipment-mounted-on-a-house-or-a-block-of-flats-or-on-a-building

• Air source heat pumps are permitted development https://www.planningportal.co.uk/permission/common-projects/heat-pumps/planning-permission-air-source-heat-pump
  Must use an MCS installer, equipment be 1m from the boundary, it’s the first installation, not on a pitched roof, and there isn’t a wind turbine

• Wind turbines are permitted development https://www.planningportal.co.uk/permission/common-projects/wind-turbines/planning-permission-building-mounted-wind-turbines
  Similar to ASHP, MCS installer, first installation only and there can’t be a ASHP already on the property

geoffreycoan funny that he says we all need to use less energy and Gov are pushing us to BEVs which will make us use more!

geoffreycoan I wonder if the issue is with wind turbines and ASHPs causing a noise nuisance? Solar doesn't (usually) make any noise, so contrary to what I thought, doesn't affect an ASHP installation.

Pretty sure (??) Tim is correct about ASHP requiring DNO approval if you already have solar but things are constantly moving.

Still as I said you could have solar and install a 10kw Electric Shower plus a upto 9k Induction Hob so why exactly do we need DNO approval for ASHP at all???

The passivhaus standards would be great. But in reality thats "wishing on a dream". I mean current cavity wall standards are something like 0.3u value (that's from memory). Typical Double glazed windows are around 1.6u Value. So your walls transfer less heat than your windows. Changing from Double to Triple glazing increases, glazing, costs by about 20% (but of course that would reduce slightly due to economies of scale). That would result in approx a reduction to 0.7u value.

Its also a requirement that new builds (unless passive house standard) have to have trickle vents installed. If you open our trickle vents the wind literally blows the downstairs curtains out (each curtain is 78" x 54" weighs maybe 3-4kg??).

Even when they do a leak test on new build homes they tape up the trickle vents and around the doors and letterbox opening................

But then it's still not (at least I think) a requirement that developers have to install Solar Panels on roofs..

Here's another great tidbit. New Gas Boiler installs have to comply with "Boiler Plus" along with future service requirements that plumbers improve, where possible, the system performance. BUT that ONLY applies to Combi boilers NOT Regular/Heat Only or System boilers...........

Steps down off rant horse