How Much Power Do I Need?
The UK Energy Calculator 2026
Not sure how much battery or solar you actually need? This free calculator works out your daily power usage, recommends the right size system and shows you exactly what to buy – all based on your real appliances and UK sun hours.
Pick your location and whether you want solar
Tick the appliances you want to run and set your daily usage
Hit Calculate – we’ll show you three ways to power your setup with live prices
New journeys coming soon – check if your existing kit is up to the job, and calculate whether you’re within your campsite hook-up limit.
Gemshore Power Guide
How Much Power Do I Need?
Tell us where you are and what you want to run - we will show you exactly what to buy.
What do you want to do?
I need to buy kit Calculate what I need and show me what to buy
I have a battery Will my existing kit cope with what I need?
Campsite hookup Am I within my site's amp limit?
Step 1 - Where are you?
At Home Garden, shed, home backup
Camper / Caravan / Boat Any mobile or marine setup
Other Off-Grid Cabin, remote location
Step 2 - When and how?
Yes - include solar Panels charge the battery during daylight
No - battery only Charge from mains or vehicle only
Used to estimate daily solar generation for your location
Step 3 - What do you want to run?
Tap a category to expand it, then tick the appliances you want to run and set your daily usage.
Fridge cold-start warning: A fridge or freezer starting from warm draws 3 to 5x its running wattage for 10 to 30 minutes. This is NOT in the Wh calculation but your inverter must handle this startup surge. Always check peak/surge ratings before buying.
Loading appliances...
Step 4 - How long do you need power for?
One Night
Weekend
A Week
or enter days: days
Your Power Estimate
Daily Usage - Wh per day
Solar Generation - Wh/day estimated
Net Daily Deficit - Wh from battery
Battery Needed - Wh recommended
Daily Energy Balance
Total daily consumption-
Estimated solar generation-
Net deficit (battery must cover)-
Device Breakdown
| Appliance | Watts | Daily Use | Duty Cycle | Wh/day |
|---|
What Should You Buy?
Based on your daily usage of - Wh, here are three ways to power your setup.
Duty Cycles
12V compressor fridge: 35% duty cycle (runs approx 8.4h/24h at temperature)AC fridge-freezer: 30% duty cycle
Water pump: fixed 0.5h/day
CPAP: fixed 8h/night
ECO mode fridge: 40% consumption reduction applied
All other devices: user-set hours per day
Solar Generation
South-facing UK mount at 35 degrees - average UK location.Scotland typically 10 to 15% less. Southern England 5 to 10% more.
20% system efficiency loss applied (cable, MPPT and inverter losses).
Battery Sizing
Net daily deficit x 1.25 safety margin divided by 0.8 depth of discharge (LiFePO4).Minimum 500Wh regardless of result.
Startup Surge
Fridge cold-start draws 3 to 5x running watts for 10 to 30 mins.Flagged as a warning - NOT added to the Wh total.
Always verify your inverter peak rating covers startup surge before buying.
Important - Please Read Before Purchasing This calculator provides estimates based on typical UK conditions and average device specs. Real-world consumption varies with temperature, battery age, usage patterns and weather. Always verify compatibility of every product before purchasing - confirm solar panel voltage matches your MPPT controller, inverter surge rating covers appliance startup, and battery chemistry is supported by your controller. Gemshore accepts no liability for purchasing decisions made on these estimates. When in doubt, consult a qualified electrician or solar installer.
Duty Cycles
- 12V DC compressor fridge: 35% duty cycle - runs approximately 8.4 hours per 24 hours at temperature
- AC fridge-freezer: 30% duty cycle
- ECO mode fridge: 40% consumption reduction applied on top of duty cycle
- Water pump: Fixed 0.5 hours per day
- CPAP machine: Fixed 8 hours per night
- All other devices: User-set hours per day multiplied by wattage
- Kettle: Calculated at 5 minutes per boil
- Microwave / air fryer: Calculated at 15 minutes per use
Solar Generation
- Based on a south-facing UK panel mounted at 35 degrees - average UK location
- Scotland is typically 10 to 15% less. Southern England is typically 5 to 10% more
- 20% system efficiency loss applied to account for cable losses, MPPT inefficiency and inverter losses
- Monthly sun hours used: Jan 1.0h, Feb 1.5h, Mar 2.5h, Apr 3.5h, May 4.3h, Jun 4.8h, Jul 4.6h, Aug 4.2h, Sep 3.1h, Oct 1.9h, Nov 1.1h, Dec 0.8h
Battery Sizing
- Net daily deficit multiplied by 1.25 safety margin, divided by 0.8 depth of discharge (LiFePO4)
- Minimum recommended battery size is 500Wh regardless of calculated result
- For battery-only setups (no solar), full daily load multiplied by number of days is used as the base figure
Startup Surge
- Fridge cold-start draws 3 to 5x its running wattage for 10 to 30 minutes
- This is flagged as a warning but is NOT added to the Wh total
- Always verify your inverter's peak/surge rating covers appliance startup before buying
What We Have Not Included
- Washing machines and dishwashers have been deliberately excluded - these high-draw appliances (1,500-3,000W continuous, with significant startup surge) require a more detailed assessment of your full system including cable sizing, fuse ratings and inverter capacity. If you need to run white goods off-grid, we recommend consulting a qualified installer.
- Electric heating and immersion heaters - these are extremely high draw and rarely practical off-grid
- EV charging - this requires a dedicated off-grid system design
Important - Please Read Before Purchasing This calculator provides estimates based on typical UK conditions and average device specifications. Real-world consumption varies with temperature, battery age, usage patterns and weather. Always verify compatibility of every product before purchasing - confirm solar panel voltage matches your MPPT controller input range, your inverter surge rating covers appliance startup, and battery chemistry is supported by your charge controller. Gemshore accepts no liability for purchasing decisions made on the basis of these estimates. When in doubt, consult a qualified electrician or solar installer.
Off-grid power systems in the UK have grown significantly in recent years, driven by falling battery costs and improving solar technology. According to the Solar Trade Association, the UK solar market continues to expand with more homeowners, campers and self-builders exploring battery storage as a practical and affordable alternative to grid connection. With the right sizing, a well-designed system will reliably power everything from a weekend campervan to a full garden office setup.
The UK Government published its UK Solar Roadmap in June 2025, setting out ambitious targets for solar deployment and signalling long-term support for small-scale and domestic installations. Whether you are powering a campervan, garden shed or preparing for home backup, getting your battery and solar sizing right from the start saves money, avoids an underpowered system and gives you genuine energy independence.
Frequently Asked Questions
For a typical camping weekend with LED lights, phone charging and a laptop you'll need around 300-500Wh. Add a 12V compressor fridge and that rises to 800-1200Wh. The calculator above will give you an exact figure based on your actual appliances. As a rule of thumb, always buy 20-25% more capacity than you think you need to account for battery ageing and cold weather. Read our full battery guide.
Most portable power stations will comfortably run phones, laptops, tablets, LED lights, a CPAP machine and a small TV. Mid-range stations (500-1000Wh) can also handle a travel kettle, mini fridge and drone chargers. Larger stations (2000Wh+) can run a microwave, induction hob or even a hair dryer for short bursts. Check the wattage of your appliances against the station's continuous output rating before buying. Read our full power stations guide.
In the UK, a 200W panel generates roughly 400-960Wh per day depending on the month - from as little as 160Wh in December to over 900Wh in June. For a typical campervan or garden setup, 200-400W of panels paired with a 100Ah LiFePO4 battery covers most daily needs from spring through autumn. The calculator above factors in UK sun hours by month to give you a precise recommendation. Read our full solar panels guide.
Currently, connecting plug-in solar panels directly to a ring main socket is not legal in the UK - the BS EN 62109 product standard has not yet been published (expected July 2026) and DNO notification via G98 is required for any grid-tied generation. However, using plug-in solar panels to charge a battery or power station directly is completely legal and requires no notification. This is the off-grid approach we recommend on Gemshore. Read our full plug-in solar regulations guide.
LiFePO4 (lithium iron phosphate) is safer, lasts far longer (3,000-6,000 cycles vs 500-1,000 for standard lithium-ion) and performs better in cold temperatures. Standard lithium-ion is more energy-dense so it's used in portable power stations where size matters. For a fixed battery bank in a campervan, shed or home backup setup, LiFePO4 is almost always the right choice. Read our full solar batteries guide.
Yes, for most appliances. Modified sine wave inverters are cheaper but can damage sensitive electronics like laptops, CPAP machines, some fridges and anything with a variable speed motor. Pure sine wave inverters produce the same clean power as the mains grid and are safe for all appliances. The price difference is small - always buy pure sine wave. Read our full inverters guide.