How Much Solar Do I Need? PV Panel Size Calculator (UK)
If you’re trying to work out what size off grid solar panels you need for your campervan, motorhome, shed, boat, tiny home, or off grid setup, this guide will help you calculate it quickly. Sunlight in the UK varies a lot between seasons, so choosing the right solar size is important to avoid running out of power, especially in winter.
Below, we explain how to estimate the correct solar panel size and provide a simple UK based solar calculator you can use instantly.
How Our Solar Calculator Works
Our calculator is based on typical UK sunlight hours assuming that:
- On average during the UK summer months, you’ll get up to 5 hours of direct sunlight per day.
- On average during the UK winter months, you’ll get up to 1 hour of direct sunlight per day.
When you enter your daily energy usage in Wh, the calculator will display the minimum solar panel size (peak power rating) required in winter and summer. This gives you a realistic expectation of how much solar you need to go completely off grid.
Our UK Solar Panel Size Calculator
How Much Solar Do I Need?
Tip: Use our power usage calculate to quickly determine your Daily Energy Usage.
How to Calculate Solar Panel Size Manually (UK)
If you prefer to do everything on paper the math behind our calculator is simple, below is the formula the calculator uses:
Example
If you use 500Wh per day:
- In Summer: 500 Wh ÷ 5 sun hours ≈ 100W of solar
- In Winter: 500 Wh ÷ 1 sun hour ≈ 500W of solar
This shows why most UK setups need much more solar than you might expect since the winter output can be up to 5 x lower due to the shorter daylight and unpredictable weather conditions.
Typical Solar Needs for UK Off Grid Users
Here are rough guidelines based on common appliances:
Light Usage (200 to 400Wh/day)
- Phone charging
- LED lights
- Small fans
- Occasional laptop use
Recommended solar: 100W to 400W depending on season
Medium Usage (500 to 1,200Wh/day)
- Laptop
- Water pump
- Router
- Diesel heater
- 12V fridge
Recommended solar: 300W to 800W
High Usage (1,500+ Wh/day)
- 12V fridge
- TV
- Tools
- Coffee maker
- Microwave (short run time)
Recommended solar: 600W+
Why UK Solar Needs Are Higher in Winter
Many online solar calculators use US sun hours, which can be 3 to 6 hours even in winter.
In the UK:
- Cloud cover is higher
- The sun sits lower
- Days are shorter
- Panels rarely output full rated power
This is why we use realistic figures (5h summer, 1h winter) so you never end up undersized.
What If You Don’t Have Space for Enough Solar?
If roof space is limited, here are alternatives:
- Add a battery charger for mains hookup
- Use a DC DC charger to charge from your vehicle
- Add portable folding solar panels
- Reduce daily energy usage
These help you stay powered even if your roof area can’t support a large array.
Choosing the Right Solar Panels
When picking panels for a van or off grid system, focus on:
- Panel efficiency
- Available roof space
- Your winter energy needs
- Voltage compatibility with your charge controller
- Rigid vs. flexible panels
Rigid monocrystalline panels usually offer the best long term reliability in the UK.
Conclusion
Knowing how much solar you need is the most important step in building an off grid electrical system. Use the calculator above to get an instant estimate for the size of panels you may need based on typical UK conditions.
If you would like to read more on the topic, check out our guide: how much electricity do solar panels generate
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