Solar panels for a shed or garden office in the UK

A shed or garden office is a common first solar project in the UK: a small building, a roof that catches the sun, and often no power cable. This guide shows how to size a system for one, step by step, and is honest about the British winter. No electrical background needed.

The short version

• List what you will run and for how long. Watts times hours gives watt-hours, the energy you use in a day.
• A panel in Bristol gives about four times as much energy on an average June day as on an average December day; in Edinburgh, nearly six times.
• A summer-only shed is easy to power. A year-round garden office needs two to four times the panels for the same work.
• Electric heating is out of reach for a small solar system in winter. If you need heat, keep or add a mains connection.
• Lithium (LiFePO4) batteries must not be charged below 0 °C, and some datasheets set 5 °C. A cold shed needs a plan for that.
• A new mains circuit to a shed is notifiable work under Part P of the Building Regulations in England. Panels on a shed roof are usually permitted development, within limits.

Step 1: List what you will power

Multiply each item's power in watts (W) by the hours it runs, and add them up. The answer is in watt-hours (Wh), the energy you use per day. Think of water: watts are how fast it leaves the tap, watt-hours how much ends up in the bucket. A 50 W laptop used for 8 hours uses 400 Wh.

Typical power ratings from the Centre for Sustainable Energy, a UK energy charity, which notes that the real figure depends on the model (CSE):

• Laptop 50 W, desktop computer 140 W, broadband router 10 W, fridge 150 W.
• Electric heater 2,500 W, oil-filled radiator 2,000 W, kettle 3,000 W.

For lights, LED bulbs are the obvious choice: the Energy Saving Trust says they match halogen bulbs for brightness while using about 80 % less electricity (Energy Saving Trust).

Your own appliance's rating is on its label or charger; a plug-in energy monitor measures what it really draws over a day. Note two numbers per item: watts (for the inverter, the box that turns battery power into mains-style power) and watt-hours per day (for the panels and battery).

Step 2: Be honest about when you will use it

This step decides almost everything, because UK winter days are short and the sun is low.

Here is what 1,000 W (1 kW) of panels, tilted 30 degrees and facing south, gives on an average day, according to the European Commission's PVGIS solar calculator, using satellite records from 2005 to 2023 and its standard 14 % allowance for losses in cables, dirt and ageing (PVGIS Bristol, PVGIS Edinburgh):

• Bristol: about 4.17 kWh a day in June, 3.13 in September, 1.42 in November and 1.02 in December.
• Edinburgh: about 3.75 kWh a day in June, 2.69 in September, 1.18 in November and 0.66 in December.

For a single 100 W panel, that is about 417 Wh on an average June day in Bristol and about 102 Wh in December: roughly four times less. In Edinburgh it is about 375 Wh against 66 Wh: nearly six times less. (Our calculation from the PVGIS figures.)

So a shed used from April to September and an office used all year are very different projects, even in the same garden. More places: solar in each UK region. How watts become energy: watts, watt-hours and sun hours.

Step 3: Heating, the kettle and when to keep the mains

An electric heater at 2,500 W running for 4 hours uses 10,000 Wh (10 kWh) in a day. To make that from the sun on an average December day in Bristol, you would need about 10 kWh / 1.02 kWh per kW = roughly 10 kW of panels (our calculation), far more than a shed roof holds, before even counting the battery.

A kettle uses little energy in a day, but at 3,000 W it needs an inverter that can deliver 3,000 W at once, far bigger than a laptop and lights need. Three sensible set-ups follow:

• Solar only, summer use: lights, laptop, phone charging. A modest system covers April to September.
• Solar plus mains: a proper mains supply for heating and heavy loads, solar for the rest. The honest answer for a heated, year-round office.
• Solar plus a backup charger: solar most of the year, a mains charger or generator to top up the battery in the darkest weeks.

Linking a solar system with your home's mains wiring is a job for a qualified electrician, and feeding power into the home or grid has its own rules (plug-in solar rules in the UK).

Step 4: Panels, battery, controller and inverter

Panels. A first estimate is your daily need divided by what 1 kW gives on an average day in your darkest month. But many days are worse than average and dull weather comes in runs, so real sizing checks years of daily weather for how often the battery would run empty. PVGIS's free off-grid mode does a simple version and reports the share of days the battery hit its lower limit (PVGIS user manual). Steeper panels catch more of the low winter sun.

Battery. It carries energy into the evening and through dull days. Draining it completely shortens its life: the PVGIS manual uses a 40 % cut-off for lead-acid and suggests about 20 % for lithium. PVGIS's off-grid mode assumes the system delivers 67 % of what the panels could make, which its manual says may be conservative. More in how big a solar battery do you need.

Charge controller. It sits between panels and battery and stops overcharging. Its limits are the most current it delivers and the highest panel voltage it accepts; panel voltage rises in the cold, so check against your coldest morning (MPPT vs PWM).

Inverter. Batteries store direct current (DC); mains appliances need alternating current (AC), like your house sockets. The inverter translates. Size it for everything running at once, plus extra for motors such as a fridge, which draw a burst when they start. With only 12-volt lights and USB chargers you may not need one.

Step 5: Batteries in a cold shed

In the PVGIS hourly records from 2005 to 2023, the air dropped below 0 °C at some point on about 36 days a year in Bristol and about 41 days a year in Edinburgh, with lows of about -9 °C and -11 °C (our count from the PVGIS hourly series; these are area averages, and a shed on a frost-prone plot can be colder).

That matters because lithium batteries must not be charged in the cold. Charging a lithium cell below freezing can plate metallic lithium onto one of its electrodes, and the damage is permanent (Grepow). Among the lithium iron phosphate (LiFePO4) batteries we have checked for our UK catalogue, the makers' datasheets set the lowest charging temperature at 0 °C for four and at 5 °C for the other six. A cold winter morning in a shed can be below both.

Your options: a battery with a built-in heater; a controller and battery management system (the battery's protective electronics) that refuse to charge in the cold; a spot that stays above the limit; or using the system only from spring to autumn.

Also follow the battery maker's instructions on where it may be installed, spacing and ventilation. The wiring rulebook BS 7671 gained a new chapter on stationary batteries in Amendment 4, published in April 2026 (IET). Our article LiFePO4 batteries in cold weather goes deeper.

Step 6: Part P, BS 7671 and when you need an electrician

Part P of the Building Regulations covers electrical safety in homes in England. Its official guidance, Approved Document P (2013 edition), says it applies to outbuildings such as sheds, detached garages and domestic greenhouses, and to things like garden lighting and pond pumps (GOV.UK).

Some work is notifiable: building control must be told and the work certified. Approved Document P lists three kinds:

• installing a new circuit;
• replacing a consumer unit (the fuse box);
• adding to or changing circuits in a "special location", the space around a bath or shower.

So a new mains cable from your house to a garden office is a new circuit, and notifiable. It is done by an electrician registered with a "competent person scheme", who self-certifies it, or checked through building control or a registered third-party certifier.

What about a shed powered only by its own solar panels, with no link to the house? The legal wording of Part P limits it to buildings and gardens whose electricity comes "from a source located within or shared with a dwelling". A fully separate solar system may therefore fall outside it, but we found no official guidance saying so directly, so ask your local building control. Either way, badly built wiring can still start a fire.

Approved Document P is for England; Wales, Scotland and Northern Ireland have their own rules.

BS 7671, the IET Wiring Regulations, is the British standard for safe wiring that electricians work to, and Approved Document P says new work should follow it. The current version is BS 7671:2018 with Amendment 4:2026; the IET said the previous version would be withdrawn six months after Amendment 4 was published (IET).

Our advice: use a qualified electrician for any new mains circuit, any link between the solar system and the house wiring, any fixed battery installation, and anything you are unsure of.

Step 7: Do I need planning permission?

Often not. The Planning Portal sets out England's "permitted development" rules, which changed on 27 August 2026. The change has a transition until the end of 26 August 2027: until then you may follow either the old or the new rules (Planning Portal, on buildings).

Panels on a shed or other building in your garden. On a pitched roof, panels should not go above the highest part of the roof (not counting a chimney) and should stand out no more than 200 mm from the roof slope. On a flat roof, the highest part of the panels can be no more than 600 mm above the highest part of the roof. Panels must not go on a building within the grounds of a listed building or on a scheduled monument. In national parks, Areas of Outstanding Natural Beauty, the Broads, conservation areas and World Heritage Sites, a flat-roof installation needs prior approval from the council.

Panels on a frame on the ground ("stand-alone"). Under the new rules for a house, the array can be no bigger than 9 square metres, and its height is limited to 1 metre within 5 metres of the boundary in front of the house, 2 metres elsewhere within 5 metres of the boundary, and 4 metres in other cases, with extra limits in conservation areas and World Heritage Sites, and prior approval needed within 5 metres of the boundary on the protected land listed above. Under the old rules: at least 5 metres from the boundary, no higher than 4 metres, at most 9 square metres (3 m by 3 m), and only the first stand-alone installation counted (Planning Portal, stand-alone).

Either way, place equipment to limit its effect on how things look, and remove it when no longer needed. Leaseholders may need their landlord's permission. Wales, Scotland and Northern Ireland have their own rules; if in doubt, ask your council.

A worked example: a garden office in Bristol

Our calculation from the figures above; an illustration, not a design for your garden.

The day, without heating:

• Laptop, 50 W for 8 hours: 400 Wh.
• Wi-Fi extender, about 10 W for 8 hours (CSE's figure for a router): 80 Wh.
• Two LED lights at 9 W for 4 hours (our assumption; check the packaging): 72 Wh.
• Phone charging, 10 W for 2 hours (our assumption): 20 Wh.

Total: 572 Wh a day. We round up to 600 Wh.

Summer use (April to September). We put 400 W of panels tilted at 30 degrees, a 2,400 Wh lithium battery with a 20 % cut-off and 600 Wh a day into the PVGIS off-grid calculator for Bristol. From April to September, the battery reached its lower limit on fewer than 1 day in 100. But in March it did on about 4 days in 100, in November on 47 in 100, and in December on 86 in 100 (PVGIS off-grid run).

All-year use. With 1,000 W of panels tilted steeply at 60 degrees and a 3,000 Wh battery, it still ran short on about 5 days in 100 in December and 3 in 100 in January (PVGIS). With 1,500 W and a 4,800 Wh battery, no month ran short in the records (PVGIS). That is almost four times the panels and twice the battery of the summer system, for the same 600 Wh a day. PVGIS does not count cold-charging limits or snow, so real winters are harder still.

The rest. With a 12-volt battery, 400 W of panels means up to about 400 / 12 = 33 amps of charging current; 1,500 W would mean about 125 amps; a 24 or 48 volt battery halves or quarters that. The loads above add up to under 100 W at any moment, so a small inverter is enough, unless you want the kettle.

What to check before you buy

1. Write your load list: watts and watt-hours per day.
2. Pick your months and find the darkest one.
3. Decide how heating and heavy loads will be powered.
4. Check the controller's current rating against your panels at your battery voltage, and its voltage limit against a frosty morning.
5. Check the inverter's continuous and start-up power against your loads.
6. Check the battery's lowest charging temperature, and whether it has a heater.
7. Plan cable sizes and DC-rated fuses (solar cable size and fuses).
8. Check the planning limits for where the panels go.
9. If any mains wiring is involved, book a registered electrician.

What can go wrong

• A summer-sized system in winter. It works in June and is flat by November.
• Charging a frozen battery. Without a heater or a low-temperature cut-off, a lithium battery can be damaged for good.
• Cold panel voltage above the controller's limit on a bright, frosty morning.
• A heater on the battery. A 2,500 W heater would empty a 2,400 Wh battery in under an hour (our calculation), if the inverter could supply it at all.
• Thin cables and missing fuses. Low-voltage systems carry high currents, and a cable that is too thin heats up.

Questions people ask

Can solar run a garden office all year? For lights, a laptop and a router, yes, with enough panels and battery. For electric heating, not realistically; keep or add a mains supply.

Is a portable power station enough? For a summer shed with light use it can be: power station or DIY system.

How our quiz sizes a shed or garden office

Choose "Cabin, shed or tiny house" and enter your postcode. The quiz runs a day-by-day energy balance over many years of PVGIS satellite weather for your 5 km area, with panel temperature, losses, battery limits, cold charging and snow. It gives three options: Minimum (no shortfall on 90 % of days in your season), Medium (97 %) and With margin (99.5 %), each a parts list checked for compatibility. If the winter sun in your area cannot do the job with the space you have, the result says so and suggests a hybrid, such as mains or a backup charger, instead of ever more panels.

Size my shed system. For the full method, see how we size systems, and for any term you met here, the solar glossary.

Our results and guides are estimates and do not replace advice from a qualified electrician.