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Solar Generator Sizing Calculator (UK)

Size a portable solar generator for UK camping, caravanning and power-cut backup. Calculate battery Wh, inverter W and solar panel W with UK sun-hour data.

Solar Generator Sizing Calculator

Daily energy (Wh)
360 Wh
Battery capacity (Wh)
889 Wh
Inverter continuous (W)
1,500 W
Solar input (W)
402 W

How to use this calculator

The UK solar generator calculator above converts a load profile into the three figures every portable power station spec sheet quotes: battery capacity in Wh, inverter continuous power in W, and solar panel input in W. Enter your average load, daily runtime, peak surge load and UK peak sun hours — outputs recalculate instantly.

  1. Average load (W) — sum the running wattage of everything running at once. A laptop runs 50 W, a 12 V compressor fridge 50–80 W, LED lighting 5 W per bulb, a CPAP 30–60 W.
  2. Runtime per day (h) — actual run-time, not 24 h. A fridge cycles about 8 of 24 hours; CPAP runs the 8 hours you sleep.
  3. Days of autonomy — UK weather is rarely sunny for two consecutive days outside July–August. Plan on 2 days minimum, 3 in winter or for prepping.
  4. Peak surge load (W) — the largest single load. A 1,000 W kettle, 1,500 W hair dryer, fridge compressor start 1,500–2,000 W. The calculator multiplies by 1.25 to size the inverter.
  5. Peak sun hours — UK annual averages from PVGIS / Met Office: 2.6 for England/Wales, 2.3 for Scotland, 2.4 for Northern Ireland. Winter (Nov–Feb) drops to 0.8–1.5 across the country.

How the math works

Three first-principles formulas:

Daily energy:

daily_Wh = avg_W × hours

Battery capacity (Wh):

battery_Wh = daily_Wh × autonomy / (DoD × inverter_eff)

For 60 W × 6 h × 2 days at 90% DoD and 90% inverter efficiency: 720 / 0.81 = 889 Wh. Round up to the nearest commercial size — 1,000 Wh class units (Jackery Explorer 1000 v2, EcoFlow Delta 2, Bluetti AC70) are the UK sweet spot.

Inverter continuous (W):

inverter_W = peak_W × 1.25

Solar input (W):

solar_W = battery_Wh / (PSH × charge_eff)

At UK average 2.6 PSH and 85% MPPT charge: 889 / 2.21 = 402 W of panel input. Plan a 400 W folding array (e.g. four 100 W panels or two 200 W).

What a solar generator costs in the UK (Q1 2026)

Pricing from Jackery UK, EcoFlow UK, Bluetti UK, Anker SOLIX UK and Argos / Halfords portable power categories:

Use caseBattery WhInverter WSolar input WTotal kit
Weekend camping (phone + lights + CPAP)300–500600–1,000100–200£350–650
Caravan / campervan (12 V fridge + appliances)500–1,2001,000–1,800200–400£600–1,400
Power-cut essentials (fridge-freezer + lights + router)1,000–2,0001,800–2,400300–500£1,200–2,500
Whole-home critical loads (fridge + central-heating pump + boiler controls)3,000–5,0003,000–5,000800–1,200£2,800–5,500
Off-grid expandable (modular battery packs)6,000–15,0004,000–7,2001,200–2,800£5,500–15,000

VAT note: portable plug-and-play units are billed at 20% VAT. Fixed solar + battery installations via an MCS-certified installer qualify for 0% VAT under Schedule 8 Group 23 until 31 March 2027.

Where most UK solar generator buyers under-size

Three patterns from the UK Caravan and Motorhome Club, Camper UK and EcoFlow UK community forums:

  1. Sizing on running wattage, ignoring surge. A 1,000 W inverter handles a 700 W kettle but trips on a fridge compressor start. UK fridge-freezers commonly hit 1,500–2,000 W surge.
  2. Solar input sized for Spanish PSH, not British. A 200 W folding panel that fully recharges a 1 kWh unit on the Costa del Sol covers about 40% of that in a UK November.
  3. Mixing chemistries. LiFePO₄ packs (current Jackery v2, EcoFlow Delta 2/Pro, Bluetti AC range) tolerate 3,000–6,000 cycles at 90% DoD. Older NMC-based units cycle 500–1,000 times. For daily UK off-grid use, LiFePO₄ is the right pick.

Pair this with the off-grid system calculator, battery bank calculator, and campervan solar calculator

This calculator gives the headline three numbers for a portable solar generator. The off-grid calculator scales the same logic to a fixed cabin or summer house. The battery bank calculator drills into amp-hour capacity at 12 V / 24 V / 48 V for DIY builds. The campervan calculator picks roof-mount panel wattage for caravan and motorhome installs.

Sources

Frequently asked questions

What size solar generator do I need for caravanning in the UK?
For a weekend caravan or campervan trip running a 12 V compressor fridge, LED lighting, phone charging and a CPAP — about 60 W average for 6 hours/day plus a 1,000 W kettle in short bursts — you need roughly a 700–1,000 Wh battery, a 1,500 W continuous inverter, and a 200 W folding panel. UK peak sun hours average 2.6 (Met Office / PVGIS), so larger solar input is needed than in southern Europe.
Will a solar generator power my fridge during a UK power cut?
A typical UK A-rated 240 V fridge-freezer draws 80–120 W running and cycles about 8 hours/day — 700–1,000 Wh/day. With one day of autonomy and a 90% LiFePO₄ depth-of-discharge that becomes a 900–1,200 Wh unit. Compressor surge can hit 1,500–2,000 W, so you need a 2,000 W continuous inverter. Realistic UK options: EcoFlow Delta 2, Bluetti AC180, Jackery Explorer 2000 v2.
How much solar panel do I need to recharge a portable power station in the UK?
Take battery Wh ÷ (PSH × charge efficiency). A 1,000 Wh unit in a 2.6 PSH UK climate at 85% MPPT efficiency needs 1,000 / (2.6 × 0.85) = 453 W of panel — so plan on a 400–500 W folding array. In winter (PSH drops to 1.0–1.5 across most of England, Scotland and Wales), recharge from solar alone is unreliable; mains top-up via a 240 V charger is part of the plan.
Do solar generators qualify for the 0% VAT relief on energy-saving materials?
HMRC's 0% VAT on energy-saving materials (in force until 31 March 2027 under Schedule 8 Group 23) covers solar PV panels and battery storage when supplied and installed in a residential dwelling. A portable solar generator that's plug-and-play and not installed by a registered contractor does NOT qualify — it's taxed at standard 20% VAT. Fixed solar + battery installations through an MCS-certified installer do qualify, including standalone battery retrofits since 1 February 2024.
Solar generator vs petrol generator — which works better in the UK?
A 2 kWh solar generator runs an A-rated fridge plus LED lighting plus phones silently for about 16 hours — fine for most UK power cuts, which average under 50 minutes/year (Ofgem CI data). Petrol generators are limited by the noise restrictions in most UK residential areas (Control of Pollution Act 1974 working hours) and need carburettor maintenance and stored fuel that degrades. For typical UK backup use, a 1.5–2 kWh solar generator covers 95% of real-world outages.

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