A Scottish year, day by day
PVGIS gives month-by-month output for each place (PVGIS 5.3). Dividing by the days in each month gives an average daily figure for a 4 kW system at the best angle, set against Ofgem's typical household use of 2,500 kWh a year, about 6.8 kWh a day (Ofgem).
| Month | Dundee (945 kWh/kW a year) | Lerwick (765 kWh/kW a year) |
|---|---|---|
| Jan | 4.1 | 1.5 |
| Feb | 7.1 | 4.0 |
| Mar | 11.0 | 8.3 |
| Apr | 14.9 | 13.1 |
| May | 15.7 | 15.5 |
| Jun | 15.1 | 14.8 |
| Jul | 15.0 | 13.4 |
| Aug | 13.4 | 12.1 |
| Sep | 11.5 | 8.9 |
| Oct | 7.7 | 5.2 |
| Nov | 5.3 | 2.3 |
| Dec | 3.1 | 1.0 |
From spring to late summer the panels make more than a typical home uses each day, and much of it while people are out. That surplus is what a battery stores. In the darkest months output falls below daily use, everything is used as it is made, and a battery bought only for winter would sit nearly empty.
Choosing a size
The battery should match the evening use you want to cover and the summer surplus available to fill it. For most homes both are a few kWh, which is why the examples here use 5 to 10 kWh. Smart-meter data shows how much your home uses after dark; that is the best guide. A bigger battery adds cost, and it can also push the combined system past the G98 limit.
Some households charge their battery from the grid overnight on a cheaper tariff, which gives it a job in winter too. Whether that pays depends on your tariff, so check the rates on offer from your own supplier.
What size buyers are choosing
The same DESNZ release counts the batteries behind its prices. Its 2025/26 sample holds 16,270 batteries under 6 kWh, 14,457 from 6 to 11 kWh and 12,176 from 11 to 30 kWh (DESNZ). The biggest band is growing fastest: by our arithmetic it made up about 21% of the sample in 2024/25 and 28% in 2025/26, and the average battery in the latest year held about 9.6 kWh.
Hold that average against the table above before copying it. In Lerwick, 4 kW of panels averages 1.0 kWh a day in December, so a battery of that size filled only by the roof would sit almost empty all winter; even in Dundee's best month the array's daily output is shared between what the house uses at once and what is left to store. A large battery is far more likely to be used in full where the household also charges it overnight from the grid.
What batteries cost
DESNZ publishes installed prices for batteries fitted to existing homes, using the MCS database (DESNZ). For 2025/26:
| Size band | Median per kWh | Example (our arithmetic) |
|---|---|---|
| Under 6 kWh | £1,300 | 5 kWh: about £6,500 |
| 6 to 11 kWh | £890 | 10 kWh: about £8,900 |
| 11 to 30 kWh | £630 | 15 kWh: about £9,450 |
The figures are Great Britain-wide; DESNZ does not split battery prices by region. Installed batteries carry 0% VAT until 31 March 2027 (HMRC). Home Energy Scotland stopped funding energy storage for applicants sent a link after 6 June 2024 (HES terms), so for most households the full price applies; our funding page covers the exceptions.
The grid connection
Scotland's two network operators, SP Energy Networks in the centre and south and SSEN in the north, apply the national connection rules (SSEN). Under G98, equipment up to 16 amps per phase, 3.68 kW on a single-phase supply, is connected by the installer and notified afterwards. A battery's inverter counts towards that limit, so solar plus a battery can need a G99 application before connection, unless the export is limited. Our connections guide explains both routes.
Where it goes
A battery needs a safe, ventilated spot that is not on an escape route, and the installer should follow the industry's fire-safety guidance on siting. Detached houses, 23.9% of Scottish households (Census 2022), usually have a garage or utility room. Tenement flats are harder: the common stair is an escape route and the title deeds may restrict changes, so talk to the other owners first, as our page on tenements and flats explains.
Adding a battery to existing panels
If your panels went up first, you are far from alone. Home Energy Scotland alone funded 3,368 solar PV measures in 2023–24 and 1,319 in 2024–25 (Heat in Buildings progress report 2026), but households who now want storage cannot go back to it: its funding for energy storage ended for applicants sent a link after 6 June 2024. HMRC's zero VAT rate does reach a battery retrofitted to existing panels, from 1 February 2024 until 31 March 2027, after which the rate reverts to 5% (HMRC).
Two questions decide how a retrofit is wired. Can the existing inverter take a battery directly, or will the battery need its own inverter on the AC side? And how old is it? The Energy Saving Trust expects an inverter to last around 12 years (Energy Saving Trust), so on an older system it can make sense to replace it with a hybrid unit at the same visit. Either way, the inverters together count towards the G98 limit described above.
Questions for a battery quote
- Usable capacity in kWh, not only the nominal figure, and the battery inverter's power in kW.
- The location, with confirmation that the siting follows PAS 63100:2024, the BSI specification for fire protection of battery systems in homes, which covers dwellings up to 200 m² (BSI).
- Grid charging: whether it can charge overnight from the grid, and who sets the schedule.
- The connection: G98 or G99, and who deals with SP Energy Networks or SSEN.
- The warranty: how many years, and any cap on the energy the battery can put through.
- A separate battery price, so you can set it against the DESNZ medians; our cost page shows how to check panels and battery line by line, and the installer guide covers the checks on the firm itself.