Solar panels convert daylight into DC electrical power, helping recharge the leisure battery and extend the amount of time you can spend off-grid. Most modern leisure solar panels use monocrystalline cells, which offer good efficiency from a relatively compact panel area.
Works with daylight Generates power whenever there is usable light available. Output varies with season, weather, time of day and shading.
Helps extend time off-grid Replenishes battery power and offsets your daily usage, allowing for extended time off-grid.
Panels can be linked together Multiple panels can be connected to create a larger solar array and increase your overall charging capability.
Charges through a solar regulator Solar panels are designed to work with a solar regulator, rather than being connected directly to the leisure battery.
Key benefits
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Free, silent charging from daylight
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Extends time off-grid without needing hook-up
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Reduces reliance on the alternator and mains charger
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Low maintenance, with no moving parts
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Works automatically once installed
Things to be aware of
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Output varies with season, weather and time of day
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Shading, even partial, can reduce output significantly
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The regulator must be matched to the panels and battery
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Available roof space limits how much solar can be fitted
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Unlikely to fully replace other charging in winter
Solar Panels
Rigid and flexible panels, voltage and cell types
Rigid Solar Panels
Key Benefits
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Strong and durable construction
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Better airflow underneath when mounted on brackets
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Can run cooler in hot conditions
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Well suited to long-term permanent installations
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Easier to remove or replace if needed
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Available in a wide range of sizes and wattages
Things to be aware of
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Heavier than flexible panels
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Higher profile on the roof
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Requires brackets or a suitable mounting system
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Needs enough roof space for the frame and mounts
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Positioning of brackets and cable entry still matters
Flexible Solar Panels
Key Benefits
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Lightweight and low profile
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Useful where roof weight needs to be kept down
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Can follow gentle roof curves
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Often simple to install by bonding to the roof
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Good option where roof space is awkward or limited
Things to be aware of
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Less airflow underneath can mean more heat build-up
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Higher temperatures can reduce output
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Usually less durable over the long term than rigid panels
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Bonded panels can be harder to remove or replace
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They are flexible, not foldable
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Roof preparation is important before bonding
Why does my solar panel show 18–22V when charging a 12V battery?
A 12V solar panel does not actually produce only 12V. A typical panel designed for a 12V battery system operates at around 18V and can show an open-circuit voltage of approximately 21–23V. This higher voltage is needed so the regulator has enough headroom to charge a 12V battery, which may require around 14V or more while charging.
Solar panel ~18–22V (typical for 12V systems)
Solar regulator Converts and controls the power
Leisure battery Correct charging voltage (around 14V)
Note: "12V solar panel" describes the battery system it is designed to work with, not the exact voltage produced by the panel.
Monocrystalline Cells
Most leisure solar panels are made from monocrystalline silicon cells. These are made from a single crystal structure, which makes them highly efficient and well suited to the limited space available on campervan and motorhome roofs.
Key takeaway
Solar panels harvest energy rather than store it. Adding more panel capacity gives the system more opportunity to replace the energy being used, helping the leisure battery last longer between other charging sources.
Solar Panels: What Affects Solar Output
How season, weather and time of day affect the power your solar panels can produce
Time of Day
30–50%
80–100%
40–70%
Solar output is usually lower in the morning and late afternoon, and highest around midday when the sun is at its highest.
Seasons
10–30%
80–100%
40–70%
Winter has a lower sun and shorter days, reducing solar potential. Summer has a higher sun and longer days, giving the best charging conditions.
Weather
10–50%
90–100%
50–80%
Cloud, poor weather, shade, dirt and fallen leaves can all reduce the light reaching the panel. Less light means less power.
KEY POINT: Solar output is not determined by one factor alone. Season sets the overall potential, the time of day affects the position and angle of the sun, and weather or shade determines how much of that sunlight actually reaches the panel. These factors work together, which is why the same solar panel can produce very different amounts of power throughout the day and year.
Percentage figures are indicative only and show typical output compared with ideal conditions.
Solar Regulators: PWM vs MPPT
Every solar panel needs a regulator to safely manage the power going into the leisure battery.
PWM Solar Regulator
MPPT Solar Regulator
What is it?
A simple, low-cost option that reduces the panel voltage to suit the battery. This means some available solar energy can be lost, so PWM is best suited to small, basic systems.
What is it?
A more efficient option that converts excess panel voltage into additional charging current, helping extract more energy from the same panels. It is better suited to larger systems and modern battery setups, including lithium.
Key benefits
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Lower cost
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Simple and reliable
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Suitable for smaller solar setups
Key benefits
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Extracts more energy from the same panels than PWM
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Compatible with all battery types, including lithium
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Ideal for larger or multi-panel systems
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Multi-stage charging: bulk, absorption and float
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Adjusts automatically to changing light conditions throughout the day
Things to be aware of
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Does not make efficient use of available solar power
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Panel and battery voltages need to be suitably matched
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Less suitable as the solar array becomes larger
Things to be aware of
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More expensive than PWM
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Must be correctly sized for the solar array
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Charging settings must suit the battery type
Best suited to: Small, simple solar installations.
Best suited to: Most modern campervan and off-grid solar installations.
Choosing the correct regulator
The regulator must be matched to both the solar array and the battery. Check the total panel wattage, voltage and current, then make sure the regulator can safely handle the complete array and has the correct charging profile for the battery type.
Choosing the Right Solar Setup
Bring the battery, daily usage, solar panels and regulator together
1
How much power do you use?
Work out the approximate energy used each day by the fridge, lights, pumps, charging, fans and other equipment.
2
How much can your battery store?
Battery capacity determines how much energy you have available before it needs recharging.
3
How much do you want solar to replace?
The more of your daily usage you can recover from solar, the longer you can remain off-grid.
4
How much solar can you fit?
Consider available roof space, rigid or flexible panels, shading and whether multiple panels are required.
5
Choose the correct regulator
Make sure the regulator can safely handle the total panel wattage, voltage and current, and has the correct charging profile for the battery.
Example
This example shows how the different parts of a solar setup work together.
Daily usage
600Wh per day
For example: fridge, lights, pump, charging, fans and other 12V equipment.
Battery
100Ah (12V) ≈ 1,200Wh nominal capacity
This is the total energy available before the battery needs recharging.
Solar array
200–300W (for this example)
A larger solar array gives more opportunity to replace daily usage, but actual charging will vary depending on conditions.
Solar regulator
MPPT
Must be correctly sized for the total panel wattage, voltage and current, and compatible with the battery type.
Output depends on
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Time of day
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Season
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Weather
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Shading
Remember
Solar does not have to replace all of the energy you use to be worthwhile. Even partially replacing your daily usage can significantly extend the amount of time you can stay off-grid.
Key point
A good solar setup is not simply the biggest panel you can fit. It is a balanced system matched to how much power you use, how much energy your battery can store, the solar available to you, and a regulator capable of safely managing the complete array.
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