Solar panel yield calculator
Calculate how much energy your boat solar panels will generate each day and month.
Related tools
UK summer average ≈ 4–5 h | UK winter average ≈ 1–2 h | Mediterranean ≈ 6–7 h
Worked example
Two 200W panels on a UK summer passage (4 peak sun hours, 80% system efficiency):
- Total array: 2 × 200W = 400 Wp
- Daily yield: 400 × 4h × 80% = 1,280 Wh (1.28 kWh)
- Monthly yield: 1,280 × 30 ÷ 1,000 = 38.4 kWh
- A 100Ah / 12V battery (1,200 Wh) would receive 1.1× its capacity per day — enough to stay in balance with moderate loads
Try 2 panels / 200W / 4h / 80% above to verify.
What is a peak sun hour?
A peak sun hour (PSH) is one hour of sunlight at an irradiance of 1,000 W/m² — the standard test condition for solar panels. A panel rated at 200W will produce 200 Wh in one peak sun hour at 100% efficiency.
In practice, UK coastal and inland sites average 2.5–5 PSH depending on season. The sun hours slider above uses rough UK averages — adjust it for your actual conditions or location.
Daily yield (Wh) = Total Wp × Peak sun hours × System efficiency
UK average peak sun hours by month
These are approximate values for UK coastal locations. Southern Europe gets 30–60% more.
System efficiency explained
No solar system runs at 100% efficiency. Losses come from:
- MPPT controller: typically 93–97% efficient
- Wiring losses: 2–5% depending on cable size and run length
- Panel temperature: panels lose ~0.4% output per °C above 25°C
- Shading and soiling: rigging shadows, bird droppings, salt haze
80% is a realistic all-in figure for a well-installed marine system with an MPPT controller. A PWM controller is typically 70–75%.
Frequently asked questions
How much solar do I need for a liveaboard?
A typical liveaboard uses 100–200 Ah/day (1,200–2,400 Wh). At 4 peak sun hours and 80% efficiency, you need roughly 375–750 Wp of panels to break even. Most cruising liveaboards run 400–800 Wp. Use the battery capacity calculator to size your bank first, then size solar to match your daily consumption.
Should I use MPPT or PWM?
MPPT (Maximum Power Point Tracking) controllers are significantly more efficient — typically 93–97% vs 70–75% for PWM. On a boat where panel space is limited, an MPPT controller can give you 20–30% more usable energy from the same panels. The extra cost is almost always worth it.
Can I mix different panels?
You can, but it's not ideal. Mixing panels of different wattage or type in series reduces the array output to that of the weakest panel. If mixing is unavoidable, wire them in separate parallel strings to an MPPT controller.
Why does my actual output seem lower than calculated?
Common causes: the panels are shaded by rigging or sails during part of the day; the panels are mounted flat rather than tilted toward the sun; the controller is PWM rather than MPPT; or conditions are overcast. Winter output in the UK is genuinely low — budget for shore power or generator charging from October to March.