Owner guides
What size solar panel do I need for my motorhome guide?
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Solar power is a fantastic option for motorhomes. Solar panels aren’t just about charging your leisure battery and starter battery – they’re a clean, green and efficient way to generate power, allowing you to go off-grid for longer!
But like many aspects of a motorhome conversion, the information and vast range of products on the solar panel market can be overwhelming. If you’re unclear on questions like “What solar panel types are available?” and “What size solar panel do I need for my motorhome?”, read on for our expert lowdown. We’ve explained the main terms relating to solar panels, how to calculate your energy needs, solar panel types such as rigid or folding, and how to choose a solar panel.
Solar panel terms explained
Simply put, a motorhome solar panel uses energy from sunlight to charge the 12v leisure battery, and often the 12v engine or starter battery. Power is generated by the solar panel, stored in the battery, and used by the electrical items you want to run off your solar power system.Rosie (below) is one of our motorhomes for hire that use solar power for off-grid adventures.
The three main terms you need to be familiar with here are watts, amps and voltage.
Watts
A watt is a unit of electricity used to measure power, by measuring the amount of energy released in an electrical system. Solar panels are rated in watts (w): for example, 100 or 200, up to 360w – the higher the wattage, the higher the amount of power the solar panel can generate. Watt hours are the amount of time a device can be powered by an electrical system.
You don’t necessarily need high-wattage solar panels: as thissolar power reckoner from Select Solar shows, a 60w system can power a small motorhome’s lights, TV, water pump and radio for about two hours per day. If you do want to opt for something higher, this120w solar battery charger kit should power bigger items like TVs and fridges.
(For electrical appliances, the higher the watt, the more electricity the appliance will consume. Most appliances have wattage displayed – thiselectric whisk, for example, is 120w, while thiselectric pancake maker has a wattage of 1200.)
Amps
An amp (a) or ampere measures electric current flowing through an electrical system to a device. This is then rated in amp hours (AmpHrs or Ah), which shows how long the system will be able to power electrical items. The120w solar battery charger kit mentioned above should produce about 84Ah per day.
The leisure battery in your motorhome will have a capacity in Ah. We recommend a200Ah battery for bigger vehicles, which on 130w solar systems should generate power for lights, water pump, TV and 240V appliances for up to three hours a day year round.
Voltage
Voltage is the pressure used in an electrical circuit’s power source. It pushes current through a conducting loop, which allows the current to power an appliance. Motorhome solar panels will use a voltage of 12, as this is the voltage of the leisure battery.
12v leisure batteries, from £89.99
What size solar panel do I need for my motorhome?
It’s not so much the size of the solar panel needed for your motorhome, but the wattage/watt hours that each panel generates for your leisure battery. This also means that it doesn’t matter whether you install one 100-watt solar panel or five 20-watt ones, as the overall wattage will be the same.
Here’s what you need to consider when thinking about solar panel wattage and choosing a motorhome solar panel. And for another solar-powered motorhome available for hire on Camplify, check outHannah above!
How much energy your leisure battery can store
Energy produced by your solar panel needs to be stored in the leisure battery, so you can’t decide on solar panel size or wattage without knowing your battery’s energy storage capacity of your leisure battery. As above, this will have a capacity in Ah or amp hours – the higher the Ah, the more energy the battery can store. Look for as high an Ah as possible for your motorhome’s size and weight, such as the 200Ah battery featured above.
Your daily energy usage
Knowing how much energy you’re likely to consume, on average, every day is your vital next step. For example, there’s no point setting up a 30w solar power system if you’re likely to use electrical appliances for several hours a day.
The simplest way to figure this out is to take your motorhome out for a trip with a fully charged battery and see how long it lasts with normal use of your electrical appliances, in other words, how many watt hours each appliance will use. (Don’t skimp here – you want to calculate normal usage.) Once you know how much energy your fully charged battery will use for, e.g., two days, you can then move on to the final step.
Tip – look for 12v electrical items to conserve as much energy as possible. Ourbest 12v TVs for motorhomes guide has you covered for your essential entertainment item!)
How much energy your solar panel can generate
Use the Ah from your battery plus the info from your daily energy usage calculations to calculate the amount of energy your solar panel can generate.
Let’s say your battery is 110Ah (amp hours) and it’s lasted for a two-day trip; that means you need an average of 55Ah per day to power your appliances. So you’ll need a solar panel that can generate 55Ah per day, like this80w model from Towtal.
If you want to know the daily energy usage for your motorhome without taking it out on the road, you can check the wattage for each appliance and then convert your total into amp hours. So:
Appliance 1 – 24 watts per hour (wph); appliance will be in use for four hours: 24 x 4 = 96
Appliance 2 – 20 watts per hour (wph); appliance will be in use for two hours: 20 x 2 = 40
Appliance 3 – 30 watts per hour (wph); appliance will be in use for three hours: 30 x 3 = 90
Watt hours per day = 226
As we said above, watt hours are the amount of time a device can be powered by an electrical system, whereas amp hours show how long the system will be able to power electrical items as a whole. So you need to convert your watt hours per day into overall amp hours:
Wh/V= Ah – watt hours divided by voltage = amp hours
In the example above, 226 watt hours divided by 12 volts = 18.33 amp hours. Rounding up, you’ll need a solar panel system generating 20Ah per day.
Solar panel types for your motorhome
There are three main types of solar panels available – rigid, flexible or folding. All three suit road vehicles like caravans and motorhomes; whichever is used, they’re a simple and green way to power a motorhome, like Teo, above.
Rigid frame solar panels
Rigid frame solar panels or fixed solar panels are as they sound – solar panels which fit into an unmovable frame. The frame is then mounted on the vehicle roof in a permanent installation. This only works with fully flat surfaces, so isn’t suitable for curves or contours.
As the frame is fixed, these types of panels are tough and durable, and as they’re permanently installed can just be fixed and left. They’re a good option if you’re renting your motorhome out and solar power is one of the motorhome’s selling points, as a renter won’t have to do anything to keep the system going.
Flexible solar panels
Again designed how they sound, flexible solar panels have leeway in how they can be mounted. Also available in semi-flexible, they’re bonded to a roof using adhesive, or to a junction box panel mounted to the rear. They’re lighter and more versatile than rigid frame panels.
Semi-flexible solar panel with rear junction box, £249
Folding solar panels
The most versatile and cost-effective of the three, folding or briefcase solar panels are the best option if you don’t want to attach a panel permanently to your motorhome. As they’re portable, you can place them in direct sunlight even if you’re parked in the shade, and turn them throughout the day to get the maximum sunlight possible.
One drawback of this type of panel is storage space, as it has to be kept in the motorhome when not in use. It’s also not recommended to leave the panel outside while you’re not in the motorhome, due to the risk of theft – this means you can’t charge your battery while you’re out and about.
120w folding solar panel with controller, from £289
Discover the best solar panels for motorhomes in the UK !
Install solar panels on your motorhome
Once you know what type of solar panel best suits your needs, it’s time to buy and install it. Ourmotorhome electrics guide gives an overview of what you need to do.
Remember you can always hire a motorhome with solar power to try it out for yourself before buying! Holli-Camper, above, is available to hire in Cornwall.
Earn extra income from your motorhome
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