How Many Watts Do You Actually Need?
This is the #1 question we get asked. Whether you're powering a camping setup, a garden lighting system, or a home backup solution, the answer depends on three things: what you're powering, how long you need it to run, and how much sun you get.
This guide walks you through the calculation step by step — no engineering degree required.
The Solar Wattage Formula
Here's the core formula:
Watts Needed = (Daily Watt-Hours Required) ÷ (Peak Sun Hours per Day)
Let's break that down.
Step 1: Calculate Your Daily Watt-Hours
List every device you want to power and how long you'll run it each day:
| Device | Watts | Hours/Day | Watt-Hours/Day |
|---|---|---|---|
| LED garden lights (x6) | 5W each = 30W | 8 hrs | 240 Wh |
| Phone charging | 10W | 2 hrs | 20 Wh |
| Laptop | 45W | 4 hrs | 180 Wh |
| Mini fridge | 60W | 24 hrs | 1,440 Wh |
Add up your total daily watt-hours. For the example above: 240 + 20 + 180 + 1,440 = 1,880 Wh/day.
Step 2: Find Your Peak Sun Hours
Peak sun hours vary by location and season. Here are typical averages:
| Location | Summer (hrs/day) | Winter (hrs/day) |
|---|---|---|
| Southern Europe / Middle East | 7–8 | 4–5 |
| UK / Northern Europe | 5–6 | 1.5–2.5 |
| US (South) | 6–7 | 4–5 |
| US (North) | 5–6 | 2–3 |
| Australia | 7–8 | 5–6 |
Always size for your worst-case season (winter) to ensure year-round reliability.
Step 3: Apply the Formula
Using our example (1,880 Wh/day) in the UK in winter (2 peak sun hours):
1,880 Wh ÷ 2 hours = 940W of solar panels needed
Add a 25% buffer for inefficiency losses (wiring, inverter, temperature): 940W × 1.25 = ~1,175W. Round up to the nearest panel size.
Quick Reference: Common Use Cases
| Use Case | Recommended Panel Wattage | Battery Capacity |
|---|---|---|
| Garden lighting only | 20–50W | 20–50Ah |
| Weekend camping | 100–200W | 100–200Ah |
| Full-time van/RV living | 400–600W | 200–400Ah |
| Off-grid cabin | 1,000–2,000W | 400–800Ah |
| Home backup (essentials) | 2,000–4,000W | 800Ah+ |
What About Solar Lights Specifically?
Built-in solar garden lights have their panels and batteries pre-matched by the manufacturer. For these, you don't need to do wattage calculations — just check:
- Panel size (larger = faster charge)
- Battery capacity in mAh (higher = longer runtime)
- Lumen output (brightness)
- IP rating (weather resistance)
Browse our solar garden lights — all specs are listed on every product page.
Need a Standalone Solar Panel?
If you're building a custom solar setup for camping, off-grid power, or home backup, browse our solar panel range. We stock panels from 20W to 400W+ with free worldwide shipping.
Not sure which panel is right for your setup? Contact us and we'll help you spec it out.
