Demystifying Caravan & Motorhome Solar Panels

Much has been said about the virtues of solar power. It's a clean, renewable, and dependable source of energy for homes of every kind, even those on wheels. That's right; they do make caravan and motorhome solar panels, and they're not nearly as bulky, complicated or unsightly as the contraptions people lay on their roof tiles.

So, if you're thinking about going green, why not harness the sun's power? These new-fangled gadgets should supply your motorhome or caravan with a decent amount of electricity. In fact, you could become entirely self-sufficient with only a few powerful motorhome and caravan solar panels. Just imagine: you could travel across the world and stop wherever you please. No need to worry about hooking up to the mains, keeping the motor running, refuelling the generator, or budgeting for diesel.

Home Vs. Motorhome Solar Panels
What makes motorhome solar panels different? The principle is virtually the same – converting light to electricity -, though caravan and motorhome solar panels do have their quirks. A solar system basically consists of panels, batteries, and a charge controller. The solar panels contain photovoltaic solar cells, which essentially produce electricity. The batteries store this energy and the controller regulates the output.

When it comes to motorhome solar panels, the size and layout usually depends on budget. These, along with the type of solar cells and the quality of the build will influence the output. For a home solar PV system, the layout, size, and output will generally also depend on the angle of the roof and how it's positioned against the sun.

Likewise, for touring enthusiasts, the battery bank will be a matter of personal requirement. Caravan owners generally opt for 12V battery banks, but tourers that need more flexibility may opt for pairs of 12V batteries assembled into 24V DC battery banks. By comparison, domestic PV arrays can go as high as 600V.

Finding the Right Caravan Solar Panels
To find out if you can achieve complete autonomy with motorhome or caravan solar panels, you should first assess your every-day power needs. Go through all your electrical devices and their wattage. Include your water pump, fridge, TV, heater, cooker, kettle, lamp, as well as any chargers you use regularly. Estimate how much you use them per day. Multiply the wattage with the number of hours for every device and calculate your total daily usage.

You'll probably find that you use under 1,000Wh per day. So, you may only need one or two ultra-high efficiency 100W panels, which should produce about 600Wh each. But bear in mind that cheaper versions with polycrystalline cells tend to produce less than monocrystalline cells. Also, your standard polycrystalline cells tend to yield only about half of what the most efficient sunpower cells produce on a cloudy day.

So, to find the number of panels you need, it's best to factor in the number of hours of sunshine per day and a realistic output per panel. For example, if you expect your 100W panel to capture sunlight for about 5 hours per day with an efficiency of 70%, then your panel should yield 100W x 5 hrs x 0.7 efficiency = 350Wh of output. In other words, you'd need two panels to cover 700Wh worth of usage, and three if you're likely to go over 1,000Wh per day.

Telling Motorhome Solar Panels Apart
How do you know that you're getting your money's worth? One clue is in the colour. There used to be three types of solar panels. But then low-efficiency and environment-friendly amorphous silicon cells like the ones used in school calculators stopped being used as much in domestic photovoltaic arrays.

This leaves monocrystalline and polycrystalline cells. The first are generally black, like the Zamp solar panels we stock at Leisureshopdirect. They're very powerful, with an output of up to 160Wh and an efficiency of nearly 80%. A single panel yields about 640W after 5 hours of exposure to the sun. It comes with an aluminium rail system that enables you to easily mount it where you want. You simply fit it on the frame and plug it in to start enjoying your devices. With toughened glass and anti-reflective coating, your panel will capture as much sun power as currently possible.

Polycrystalline cells like the ones in the Vision Plus 40W system, which are usually of a navy or dark blue colour, weigh less and they yield less. You'd need four of these to match the output of a single Zamp panel like the one above. The advantage is that they're much cheaper, and you can buy add-on panels whenever your budget allows it. Also, you only need to fit the master panel, securing your cable with glands and connecting them to the charge controller. Any add-on panels you buy later are simply glued onto the roof with no drilling or special assembly.

Controllers for Motorhome Solar Panels
Solar systems like the Vision Plus Master kit come with a controller, but most caravan solar panels don't. To find the right size controller, first add the 'short circuit current' value of your existing and future panels, and then use the total in amps (A) to find a controller with matching current values. You'll then choose between PWM and MPPT controllers with this amperage.

A PWM (Pulse Width Modulation) controller is cheaper, but it loses some power when it converts the 17V from the panel to the 12V of the battery. An MPPT (Maximum Power Point Tracking) controller enables the panels and the batteries to be linked regardless of their voltage, but only if the panels have a higher voltage than the batteries.

MPPT controllers are ideal for 24V solar systems with ultra-high efficiency panels because they yield 10% to 15% more charge. They also tend to be more sophisticated, some with remote panels, built-in displays, and even the option to split the charge between the starter battery and the leisure battery.

Batteries for Motorhome and Caravan Solar Panels
Now that your panels and controller are sorted, you should turn your attention to batteries. They should be leisure or deep cycle batteries. It goes without saying that you should never use standard car batteries on your solar systems. Adding 240V batteries can only be done with inverters connected onto the batteries.

As a rule of thumb, you need batteries large enough to last you at least two days without going below 50% of charge, even with no solar input. An assembly of two 110Ah batteries connected in 'parallel'(230Ah in total) should be more than enough for a caravan using 700Wh worth of electricity per day. Calculate your daily usage multiplied by the number of days. Then divide by the residual charge and the voltage of your devices. That's 700Wh*2days/0.5*12V, which gives you 233.33 Ah.

As you can see, hoping to go green entirely may be unrealistic for most home-owners. But as for motorhome enthusiasts, it's much easier to go off-grid. To find out if motorhome solar panels could cut your touring costs, browse our growing collection of solar panels and accessories at Leisureshopdirect.