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Is a battery worth it with plug-in solar?

See what a battery adds to an 800 W kit in your home: how much more of your solar you use, what that saves, and how long the battery takes to pay for itself. Add a cheap overnight rate to see what charging from the grid adds.

a year used at home with a 2 kWh battery, Birmingham: +348 kWh
more saved a year on the price cap: £89
quickest payback of the batteries in stock: 4.7 years

Photo: Sergio Martins / Unsplash

1Where will the panels go?

Solar data for Birmingham.

South

The best direction for solar.

2Is someone home in the day?

Daytime use takes solar first. The battery only gets what’s left.

3How much do you use after dark?

From sunset to bedtime, plus overnight standby. A smart meter app shows it. On a time-of-use tariff, count only the hours outside the cheap rate.

Use after dark 3 kWh a day

We start at 3 kWh, our assumption for a typical home.

Kit panel size 890 Wp

Most 800 W kits have 800–1,000 Wp of panels.

4The battery

Pick one we track, or enter your own figures.

Usable capacity 1.6 kWh

Battery price

Electrician’s fee

Batteries aren’t plug-in products under GB rules. Add your electrician’s quote.

5Your tariff

Unit rate (p/kWh)

Export rate (p/kWh)

Most plug-in kits don’t get paid for export.

Cheap overnight rate: charge the battery from the grid too

A 1.6 kWh battery pays for itself in

4.7

years, on £399

£87

more a year

+341

kWh of solar used at home

237

full cycles a year

Your kit, with and without the battery
Measure	Without	With
Solar used at home	467 kWh	808 kWh
Sent to the grid	386 kWh	7 kWh
Saving a year	£119	£207

Over 10 years the battery adds about £798.

How full it gets from solar, month by month

Fills on an average day in 4 months of the year.

Fills on an average dayPart full

Share of a 1.6 kWh battery filled from solar on an average day
Month	Filled from solar
Jan	19% of 1.6 kWh
Feb	38% of 1.6 kWh
Mar	67% of 1.6 kWh
Apr	100% of 1.6 kWh
May	100% of 1.6 kWh
Jun	100% of 1.6 kWh
Jul	100% of 1.6 kWh
Aug	86% of 1.6 kWh
Sep	76% of 1.6 kWh
Oct	42% of 1.6 kWh
Nov	28% of 1.6 kWh
Dec	20% of 1.6 kWh

Solar from PVGIS for West Midlands; a 90% round trip and 2% capacity fade a year are our assumptions. Batteries need an electrician: what the rules say.

Before you buy

A battery isn’t a plug-in product

The GB plug-in solar rules cover panels and an inverter of up to 800 W, not storage. Every battery below needs an electrician to install it and tell your network operator, so add their fee to the price.

The law

SI 2026/848 defines a plug-in microgenerator as one that isn’t designed to import from your home’s wiring to store energy for later. A battery that charges from the socket doesn’t qualify.

The product specification

The DESNZ Interim Product Specification (§1) leaves out “plug-in battery systems” and “plug-in solar PV devices integrated with battery systems”.

The regulator

Ofgem says plug-in electricity storage devices “will therefore remain prohibited from being sold, supplied, or used in the UK” as plug-in devices. What that means for you.

Worked example · today’s prices

What each battery we track would add

Added to an 890 Wp kit facing south at 30° in Birmingham, with someone home some of the day and 3 kWh used after dark. Without a battery the kit makes 853 kWh a year and 467 kWh is used at home, saving £119 at the West Midlands price cap of 25.60p.

Battery	Usable	Price today	Extra solar used	Extra a year	Cycles a year	Payback	Buy
Indevolt BK1600 Plug-in Home BatteryIndevoltIn stockElectrician install	1.64 kWh	£399£244/kWh	344 kWh	£88	234	4.7 years	Buy ↗Indevolt
Zendure SolarFlow 2400 AC+ZendureIn stockElectrician install	2.40 kWh	£899£375/kWh	348 kWh	£89	161	11 years	Buy ↗Zendure UK
Zendure SolarFlow 2400 ProZendureIn stockElectrician install	2.40 kWh	£1,099£458/kWh	348 kWh	£89	161	14 years	Buy ↗Zendure UK
Thunder Vault 1.92 kWh Plug-In Home BatteryThunder EnergyIn stockElectrician install	1.92 kWh	£1,049.99£547/kWh	348 kWh	£89	201	13 years	Buy ↗Thunder Energy

Payback is the battery price alone, before an electrician’s fee, with 2% capacity fade a year. Prices are the best in-stock offer, or the last price we saw if none is in stock. All are marked Electrician install because no battery is covered by the plug-in rules. We don’t have a usable capacity from the maker yet for EcoFlow STREAM Ultra X, EcoFlow STREAM Ultra Pro, EcoFlow STREAM AC Pro, EcoFlow STREAM AC, EcoFlow STREAM Series Solar Battery, Zendure SolarFlow 3680 Mix AC+, Zendure SolarFlow 3680 Mix Pro, Indevolt PowerFlex 2000, Indevolt SolidFlex 2000, Indevolt SolidFlex 3000 Hybrid Pro, Jackery SolarVault 3 Pro Max, Jackery SolarVault 3 Pro Max AC, so they’re left out.

Kits sold with a battery

These come as one package, so the payback is for the whole kit, panels included, in the same home in Birmingham.

Kit	Panels	Battery	Price today	Saving a year	Payback	Buy
Thunder Bolt Plus 460W Kit with BatteryThunder EnergyIn stockElectrician install	460 Wp	1.92 kWh	£1,549.99	£111	14 years	Buy ↗Thunder Energy
Thunder Bolt Plus 920W Kit with BatteryThunder EnergyIn stockElectrician install	920 Wp	1.92 kWh	£1,749.99	£215	8.3 years	Buy ↗Thunder Energy

Bigger isn’t better

Each extra kWh earns less

The same 890 Wp kit and home in Birmingham. A plug-in kit has only so much spare solar, and only in summer. Past a couple of kWh, the extra capacity sits empty most of the year. Want the right size for your home? Try the battery size tool.

Usable capacity	Extra solar used	Extra a year	Months it fills	Cycles a year	Saving per kWh of battery
0.5 kWh	153 kWh	£39	9 of 12	339	£78 a year
1 kWh	257 kWh	£66	7 of 12	285	£66 a year
1.5 kWh	330 kWh	£84	4 of 12	244	£56 a year
2 kWh	348 kWh	£89	0 of 12	193	£44 a year
3 kWh	348 kWh	£89	0 of 12	129	£30 a year
5 kWh	348 kWh	£89	0 of 12	77	£18 a year

Solar from PVGIS 5.3; West Midlands unit rate 25.60p (Ofgem price cap, October to December 2026). 3 kWh after dark is our assumption, as are the 90% round trip and the average day in each month. Ten years of a 2 kWh battery’s extra saving comes to about £814.

How we work it out

Where a battery’s saving comes from

Spare solar. We split each month’s output from PVGIS into what your home uses as it’s made and what’s left over, using the same model as the calculator, with the 800 W output cap.
Into the battery. On an average day of each month the battery takes the spare, up to its usable capacity, and never more than you use after dark.
Out in the evening. 90% of what goes in comes back out. Each kWh saves your unit rate, less any export payment the spare would have earned.
Cheap overnight top-up (optional). On a time-of-use tariff the battery fills overnight with whatever the next day’s sun won’t provide, when the peak rate is worth more than the cheap rate after losses.

When it pays

Who a battery suits

Out all day, busy evenings. More of the kit’s output is spare, and you use it after dark.
A cheap overnight rate. The battery earns in winter too, when the sun can’t fill it.

It suits you less if you’re home all day: the kit’s output is mostly used as it’s made, so there’s little left to store. For a kit without a battery, see is plug-in solar worth it.

Batteries and plug-in solar: questions

Is a battery worth it with plug-in solar?

Usually not on payback alone. With an 890 Wp kit facing south in Birmingham, a 2 kWh battery stores about 348 kWh a year that would otherwise go to the grid, worth about £89 a year at the 25.60p price cap rate. The quickest payback among the batteries we track in stock is 4.7 years (Indevolt BK1600 Plug-in Home Battery at £399), before any electrician's fee. It pays back faster if you're out all day and use a lot in the evening, or if you also charge it on a cheap overnight rate.

Can I plug a battery into a socket with my plug-in solar kit?

No. The GB plug-in rules don't cover batteries, whether built into the kit or plugged in separately. The DESNZ product specification leaves out plug-in battery systems and kits integrated with them, and Ofgem says plug-in storage devices remain prohibited. A battery needs an electrician to install it as a fixed installation and notify your network operator.

How much extra solar does a battery let me use?

In our worked example (an 890 Wp kit facing south in Birmingham, someone home some of the day), the kit makes about 853 kWh a year and 467 kWh is used as it's made. A 2 kWh battery adds about 348 kWh, taking the share used at home from 55% to 95%.

How many cycles a year will the battery do?

On solar alone, a 2 kWh battery in our example does about 193 full cycles a year: nearly one a day in summer, very little in winter. Charging it on a cheap overnight rate as well can take it close to 365.

Does a time-of-use tariff make a battery pay back faster?

Often, yes. On a tariff with a cheap overnight rate, the battery can top up overnight in the months the sun won't fill it, and you use that energy at the peak rate instead. Each kWh saves the gap between the two rates, less 10% lost in charging. Turn on "Cheap overnight rate" in the tool and enter your tariff's rates.

What does the payback leave out?

The electrician's fee (add your quote in the tool), any standby power the battery draws, and replacement. We assume an average day in each month, one charge and one discharge a day, a 90% round trip and 2% of capacity lost a year. On dull days the battery stores less than our average and on bright days it fills sooner.

Sources

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