Solar panels have become a very common accessory on a 4WD, especially if you travel off grid on a regular basis. Technology improvements have allowed us to take a fridge, inverter and even a coffee machine or microwave and power it almost entirely off a good battery system and solar panel.
A lot of people use portable solar panels, which work OK, but we much rather have a permanent system that runs by itself, that we never have to touch. Even light weight solar blankets still have to be set up, packed away and you risk some low life walking past and tucking them under their arm as they walk off.
For us, the ultimate setup is a solar panel (or several) bolted to your 4WD that produces more than enough power to keep your battery healthy even over periods where you aren’t driving, or its overcast. If you aren’t sure of whether to go for fixed or portable solar panels, we have a post covering it in detail.
Picking the right size solar panel
The correct way to size your solar panel is to work out your consumption, and then go backwards. You know how much you are going to need each day, how many hours of usable sun there is and then you can get the right size panel.
If you are just running a fridge, some lights and a small inverter on the odd occasion, you’ll get away with a 120 – 150W solar panel. However, my recommendation is a 200W panel if you are going to bolt it permanently, as bigger is better when it comes to solar, and it gives you some wiggle room for when you don’t drive around, or if its cloudy.
Make sure you get the size panel that you order. I’m so tired of reading of people who’ve bought solar panels from eBay and found they don’t perform. The large majority of panels being sold on eBay are not sized correctly for their rated advertising, and people are paying for a 200W panel and getting a 160W, or paying for a 160W and getting a 120. You can read more about this here – eBay solar panels; how to avoid getting ripped off.
Matching the solar panel to the battery
Just as important as the solar panel is the battery, and the charging system that you are going to use. Some people say 1 amp hour of battery for every 2 watts of solar, and I reckon this is overkill. I would go more down the path of 1.3 – 1.6 watts of solar per amp hour of battery.
One thing to think about here is the usable capacity. A normal 100 amp hour deep cycle battery is only really good for 50 amp hours of usable capacity before you start to dramatically reduce their life span. If you go down the lithium path you have a lot more usable capacity. A 100 aH lithium generally has about 80 aH of usable capacity.
Another thing to remember is a fixed panel will never generate as much power as a portable one that you physically move around, to follow the sun. Oversizing it on this point alone is quite important.
In our Dmax, we run a 150 aH deep cycle battery, coupled to a 200W solar panel bolted to the canopy, and this kills everything we throw at it.
How do you mount the solar panel?
There are lots of ways to mount solar panels. You can buy specific corner brackets made of plastic that screw into the solar panel, and then bolt onto a roof rack. The most common way though, is to mount a solar panel is to bolt it straight to the roof racks.
Alternatively, a lot of people are buying the flexible panels that are much lighter, and just gluing them down to the roof of the vehicle, or spacing it out with some corflute material to reduce the temperatures of the panel.
On our 200W panel, I installed extra bits of aluminium flat bar along the length of the panel as it was flexing quite a bit, and I thought it would shatter off road due to this. I also mounted it on four pieces of industrial rubber, to absorb some of the shocks off road and keep the panel in good condition.
Panel location and angle
Where you mount the panel is really personal preference based on how much room you have up top, and what you can attach it to. We like to balance a 4WD’s weight, so bear this in mind when you install it. Also, panels aren’t exactly the strongest things in the world and they don’t like regular, constant shade. If you plan on putting items on top, make sure they are somewhat soft, and flexible, and don’t apply too much weight to the panel!
It’s common to see solar panels put on an angle right at the front of the vehicle, to create a bit of a wind deflector for the roof rack behind, a roof top tent, or even a caravan/camper trailer. This does work quite well, and many people report fuel consumption savings by doing so.
Another great option is to have them hinged, so you have the ability to lift and lower the panels as the sun rolls overhead. I have seen them removable too, so if you get to camp for some time and don’t want to park your vehicle in the sun you can pull the panel (s) off and make them portable.
Our panel is mounted flat on the light weight aluminium roof racks, and as we never use them for anything else it works perfectly fine.
Cable run and connections
This section is going to depend hugely on your vehicle, and how its set up. For Utes, you can usually punch through the canopy roof, or underneath, or in via the usual cable run. Ours runs through a gland in the roof, down the front of the canopy and into the electrical box.
I have seen people run them down inside snorkels, or just on the outside, and into the engine bay. I’ve also seen them run to the rear of a vehicle, and inside the rear door, or through the rear light grommets. Ultimately, you want the cabling to be sized correctly for the power and cable run, to be secure and not rub against anything, and to look as neat as possible.
Regulating the panel
Your solar panel needs to feed through a regulator, which controls the charging of the battery. On the cheapest end of the scale you’ll get away with a PWM regulator for $20 – $60, and then the pricing goes up to a good MPPT regulator, and then DCDC battery chargers with solar input.
If you run your solar straight to the battery without a regulator, it will destroy the battery almost immediately. For us, we run it through a Projecta DCDC, but we also have a backup PWM regulator should this fail. In the past we’ve run a quality Victron MPPT on the camper trailer, and were very happy with it.
The better your regulator, the more you will get from your panels. Don’t make the mistake of expecting amazing performance from a cheap regulator.
Your regulator should be as close as possible to the batteries, and suit the panels that you are using in terms of voltage and current. Some regulators will accept up to 100V, and many will not go over 24V. This means that not all panels suit all regulators, and you’ll have to do some research to get it right.
A permanent solar setup is great
If you get a permanent solar setup right, its set and forget. The only times you need to worry about it is if you are parked up in the shade for some time, and then you either need to move your vehicle, go for a drive (to charge it) or set up a portable panel.
We’ve found this to be very rare, and under normal conditions we don’t even look at the permanent setup; it just does its thing without any intervention.