Estimated annual generation per kWp, south-facing, by mounting angle (Surrey)
Without the hype
Is Balcony Solar Worth It?
Energy
The UK government has announced balcony solar will be legal and available in shops soon, so I thought: is it actually worth it? The only way to really answer that is to look at my historical energy usage and how much the solar panel will generate. Fortunately, this isn’t particularly difficult. But before I do…
Updated October 2026: plug-in solar went on sale in the UK on 27 August 2026. I’ve added real kit prices and paybacks, what a battery would add, and my calculator is now at solar.johnewbank.co.uk for anyone who wants to run their own numbers.
The UK government has announced balcony solar will be legal and available in shops soon, so I thought: is it actually worth it? The only way to really answer that is to look at my historical energy usage and how much the solar panel will generate. Fortunately, this isn’t particularly difficult. But before I do that, I’m going to explain some assumptions I made and a bit more about what balcony solar is.
What balcony solar is
It is a plug-in solar system that can connect to a standard socket without an electrician or grid notification. It is just solar panels connected to an inverter, connected to your plug socket. I’ve heard that it might be limited to around 800W, but this number hasn’t been confirmed. (Update, October 2026: it is now confirmed. A plug-in system can feed in at most 800 W, and kits are designed around that limit.) I would have thought it would make sense to limit to a higher figure, such as the peak output of two standard panels, currently around 1000W.
Unlike a rooftop installation, where an installer handles the angle and orientation, balcony solar is largely a DIY decision. You can mount a panel flat, tilted, or vertical – against a fence, on a balcony rail, or fixed to a south-facing wall. The angle matters more than most people expect.
For my location, the optimal tilt is roughly 35° from horizontal, facing due south. A vertical south-facing panel loses about 30% of its annual yield compared to that optimum. A flat horizontal panel loses less.
Mounting angle matters more than most people realise. A vertical south-facing panel generates around 28% less annually than one at the optimal 35° tilt — but for a fence or balcony rail installation, it’s often the only practical option.
Daily generation per kWp through the year, south-facing, by mounting angle (kWh, 7-day average)
The vertical mount’s flatter seasonal curve is less disadvantageous in winter, when the sun sits low in the sky. The tradeoff is a notably weaker summer. Drawn in October 2026 from Open-Meteo’s irradiance data, because PVGIS, which the March charts used, is currently refusing requests; its yearly totals are within 3% of the figures above.
How you mount yours will depend on your balcony. If you’re mounting on a south-facing balcony rail, vertical is probably your only practical option, and it’s still worth doing. If you have a flat roof or garden, tilt it.
I would mount mine at the optimal 35°.
I’m only looking at facing directly south
The property I am at faces directly south, as does the balcony. Consequently, I’m going to face the solar panels south. If your property faces a different direction, then you would have to consider how that would vary your output.
How the Calculator Works
To work out whether a panel would actually save money, I pulled a full year of half-hourly electricity consumption data from the Octopus API – 17,500 data points covering every 30-minute slot through 2025. I then used PVGIS, the EU’s solar irradiance database, to generate a typical hourly generation profile for my location in Surrey based on 2021–2023 weather data, scaled to 1kWp installed capacity. From what I understand, the peak output of balcony solar is limited to 800 watts, but I don’t know if that is the inverter max or something else. So I have assumed it will be sold with 485W panels, which roughly rounds up to 1kW. So generation might be a bit over, but it’s good enough.
For the calculations, I looked at the electricity consumption for my previous year and the potential solar generation. I ignored batteries and exports, as I wanted to make it as simple as possible. I only offset my true consumption for each half-hour period.
There is no simulated load shifting, no battery, and no export, only self consumption.
My saving from having a 1kW array
Saving = (self-consumed kWh × import rate)
My import rate is 23.35p and is fixed for the next year, so the saving is simply
619.3 kWh x 23.5p Annual saving: £145.54
Generations and savings by Month
| Month | Consumption (kWh) | Generation (kWh) | Self consumed (kWh) | Saving (£) |
|---|---|---|---|---|
| January | 176.4 | 41.4 | 30.9 | 7.3 |
| February | 159.9 | 58.1 | 38.6 | 9.1 |
| March | 189.1 | 83.6 | 57.1 | 13.4 |
| April | 137.9 | 119.4 | 55.2 | 13.0 |
| May | 140.7 | 121.6 | 63.7 | 15.0 |
| June | 171.0 | 129.5 | 78.7 | 18.5 |
| July | 139.8 | 122.7 | 60.0 | 14.1 |
| August | 125.2 | 115.0 | 53.4 | 12.5 |
| September | 218.4 | 91.0 | 70.5 | 16.6 |
| October | 210.1 | 72.2 | 50.0 | 11.8 |
| November | 244.5 | 46.3 | 37.9 | 8.9 |
| December | 253.8 | 25.4 | 23.3 | 5.5 |
| Total | 2,167.0 | 1,026.2 | 619.3 | 145.5 |
Monthly breakdown — consumption, generation, self-consumed
For my usage pattern, a 1kWp south-facing 35° array generates 1026 kWh annually in this location. Of that, roughly 619 kWh gets self-consumed and around 400kWh is wasted. At 23.5p/kWh import and 0p/kWh export, that works out to about £145.5/year in savings.
Monthly generation from 1 kWp at 35°, south: used at home and not used (kWh)
The lighter portion of each bar is generation that can’t be used in the moment and gets exported at around 5p/kWh rather than displacing grid electricity at 23.5p. Summer months have the largest gap between what’s generated and what’s actually useful.
Payback
A reasonable balcony solar kit — 800W panels and microinverter, are said to cost around £400. At £146/year in savings, the simple payback is just over three years. For a single panel this is quite compelling, particularly since the system requires no maintenance, no installer, and can be taken with you if you move.
Cumulative saving against a £400 kit, at £145.54 a year
At £145 in annual savings, a £400 system pays for itself in under three years — after which it’s pure saving for the remaining life of the panel, typically 25+ years.
Considering there is no attempt in my usage to load shift towards periods of high solar generation. The payback period Is impressively short. Obviously this would vary depending on what tariff you are on, but considering what could happen to electricity prices this winter, I believe a year long fix with a £25 exit fee, is a good bet.
The broader point here is that balcony solar makes a lot of sense. The payback is potentially very rapid, though this depends how much solar is installed over the coming year and whether or not the grid is oversupplied! Perhaps the payback won’t be very good if everyone gets it.
Update: real kits, October 2026
Plug-in solar has been on sale since 27 August 2026, and prices are now real rather than “said to cost”. Octopus Energy sells two bundles, each with a microinverter and a plug-in cable: a single 460 W panel for £450 and two 460 W panels for £650. A price tracker of other retailers lists kits from about £340 for a single panel to around £1,000 for the largest.
I re-ran my 2025 usage through the same calculation as my calculator, with each kit’s output capped at 800 W. The cap barely matters: after losses, two 460 W panels peak at about 813 W and go over 800 W for only 7 hours across three years of weather data.
| Kit | Price | Generated kWh/yr | Used at home kWh/yr | Saving, no export | Payback, years | Saving with Outgoing | Payback, years |
|---|---|---|---|---|---|---|---|
| Octopus single-panel bundle (460 W) | £450 | 470 | 382 | £100 | 4.5 | £111 | 4.0 |
| Octopus dual-panel bundle (920 W of panels) | £650 | 941 | 592 | £156 | 4.2 | £198 | 3.3 |
These use the current price cap of 26.32p/kWh. At my fixed 23.5p, the dual-panel bundle saves about £139 a year and pays back in 4.7 years.
Simple payback for my usage, at 26.32p/kWh
Two things have changed since March:
- Export can now be paid, but only for Octopus’s own kits. If you buy the bundle from Octopus and Octopus supplies your electricity, you can join Outgoing Octopus, currently 12p/kWh (variable). You need a smart meter, and the kit has to be registered with the ENA and approved by your network operator first. Kits bought elsewhere can’t go on an Octopus export tariff. For the two-panel bundle, about 37% of what it generates goes back to the grid, so that payment cuts the payback from about 4.2 to 3.3 years.
- Kits cost more than the £400 I assumed for two panels. The single panel is cheaper but generates half as much, and because more of its output is used at home, its payback ends up similar.
If you want to try this with your own usage, the calculator at solar.johnewbank.co.uk pulls your half-hourly data from your Octopus account and lets you change the size, angle, direction and tariff. If you’re switching to Octopus, my referral link gets you £50 credit.
What about a battery?
A battery isn’t allowed with a plug-in kit at the moment. The regulations that made plug-in solar legal define a plug-in device as one that is “not designed to import electrical energy … for the purpose of storing energy for later supply”, and the product specification requires kits to warn against using them with a battery. A battery would have to be a conventional installation, by an electrician. So treat this as a what-if, in case the rules change.
I modelled a battery that charges only from surplus solar and covers the home’s use when the panels can’t. That is the best a battery can do on a flat tariff. It uses the same assumptions as my calculator: 90% charging efficiency, 10% of the capacity kept in reserve, and charging and discharging limited to 800 W, as on plug-in-scale batteries.
Annual saving with a battery, by battery size (at 26.32p/kWh)
| Battery (dual-panel bundle) | Saving a year | Extra from the battery | Most it could cost to pay back in 10 years | Extra, with Outgoing | Most it could cost, with Outgoing |
|---|---|---|---|---|---|
| 1 kWh | £208 | +£52 | £525 | +£26 | £259 |
| 2 kWh | £222 | +£66 | £661 | +£33 | £326 |
| 3 kWh | £227 | +£71 | £712 | +£35 | £351 |
| 5 kWh | £231 | +£75 | £752 | +£37 | £371 |
- With one panel, a battery adds little: about £21 a year whatever its size, because a single panel rarely makes more than the house is using.
- With two panels, most of the gain comes from the first kilowatt-hour or two. A 1 kWh battery adds about £52 a year and 2 kWh about £66, but going from 2 to 5 kWh adds only £9 more.
- Being paid for exports makes a battery worth much less. On Outgoing Octopus, the surplus already earns 12p, so a 2 kWh battery adds only about £33 a year.
To pay for itself within ten years alongside the two-panel kit, a 2 kWh battery would have to cost under about £661 installed, or £326 if you’re being paid for exports. Until batteries are allowed with plug-in kits, the free way to capture more of the solar is to use it as it’s generated: run the washing machine and dishwasher during the day, as in the next section.
What If I could use all the energy I generated.
As a thought experiment, it’s worth asking what the numbers look like if I was able to use everything I generated, for a 1kW array it wouldn’t be challenging to self-consume more, by running the washing machine and dishwasher during the day, cooking things in the oven during the day, etc. I wouldn’t be able to use it all, but more of it.
Monthly saving from 1 kWp: actual, and if every kWh generated were used at home (£)
The gap between the two bars is essentially the value a battery would capture. At ~£96/year it would make the case for shifting daytime loads like dishwashers and washing machines into solar hours.
| Month | Generated (kWh) | Self-consumed (kWh) | Actual saving (£) | Perfect saving (£) |
|---|---|---|---|---|
| January | 41.4 | 30.9 | 7.3 | 9.7 |
| February | 58.1 | 38.6 | 9.1 | 13.6 |
| March | 83.6 | 57.1 | 13.4 | 19.6 |
| April | 119.4 | 55.2 | 13.0 | 28.1 |
| May | 121.6 | 63.7 | 15.0 | 28.6 |
| June | 129.5 | 78.7 | 18.5 | 30.4 |
| July | 122.7 | 60.0 | 14.1 | 28.8 |
| August | 115.0 | 53.4 | 12.5 | 27.0 |
| September | 91.0 | 70.5 | 16.6 | 21.4 |
| October | 72.2 | 50.0 | 11.8 | 17.0 |
| November | 46.3 | 37.9 | 8.9 | 10.9 |
| December | 25.4 | 23.3 | 5.5 | 6.0 |
| Total | 1,026.2 | 619.3 | 145.5 | 241.2 |
- Actual annual saving: £145.54
- Perfect self-consumption saving: £241.16
- Gap (battery opportunity): £95.62
At 1,026 kWh generated annually, full self-consumption would save around £241/year at 23.5p/kWh. Against the actual figure of £145, that’s a gap of roughly £96. Payback in the theoretical case would drop to under two years.
What about Octopus Agile pricing? (draft) – will check again.
I’ve had a request or two about what would happen if I was on agile and whether vertical solar would make any difference. For AGILE-24-04-03 C (which I believe is London)
This is for a current price cap and historical agile prices, this is a somewhat flawed analysis. I fixed my price this year as I anticipate that prices will rise this winter. If they do then Agile prices will likely rise at times too. So using agile prices from 2025 to 2026 might be misleading.
| Setup | Agile Tariff | Price Cap Tariff |
|---|---|---|
| Total Cost: No solar | £416.59 | £509.24 |
| Savings: Vertical panels | £88.92 | £121.61 |
| Savings: Optimal incline (35°) | £107.77 | £145.54 |
| Total Cost: Vertical panels | £327.67 | £387.63 |
| Total Cost: Optimal incline (35°) | £308.82 | £363.70 |
The usage figures in this article come from our Octopus Energy account, pulled half-hourly through the Octopus Home Mini and the Octopus API. If you’re thinking of switching, my Octopus Energy referral link gets you £50 credit once the switch completes.