Understanding how solar panels work will help you tailor-make your solar setup to suit your needs. Here’s everything you need to know about solar panels.
Getting your solar panel setup bang on is vital to being able to tour and stay ‘off-grid’… As long as you have water and food to last, power is the next most crucial ingredient to extended stays in the bush. Understanding how your solar panels work will help you get the most out of your setup. To help with this yarn, we spoke with the boffins at Redarc.
How do solar panels work?
Solar, or photovoltaic (photo = light; voltaic = voltage/electricity) panels, whether monocrystalline, polycrystalline, or amorphous all work in essentially the same way. Energy and light from the sun knocks electrons loose from silicon atoms (the most common construction material used) on the top side of the cell to the bottom, creating an overbalance on the bottom of electrons. The only way those electrons can get back to the other side, is via the positive wire, through your battery (charging it on the way through), and back up the negative wire to the panel. Throughout the process nothing is used up; the electrons continue to travel around the circuit, equalising themselves out as more are knocked through, charging your batteries as they go.
Understanding panel efficiency
Panel efficiency boils down to how much electricity you can extract from a panel of a given size. Clear direct sunlight overhead supplies around 1000 watts per square metre. A good quality solar panel will run at around 16-17 per cent efficiency, meaning a one-square-metre panel, in direct, clear sunshine, will generate approximately 160-170 watts of energy. Cheaper panels will often generate less than that, but we’ll talk more about that below.
However, it goes beyond watts per square metre, and for those of us trying to reduce weight from our four-wheel drives, another way to look at it is watts per kilogram. Where the amorphous cells, like those used in some solar blankets, really shine is in their weight difference. Your average alloy framed monocrystalline or polycrystalline panel that you can bolt to the roof or unfold and face to the sun would be likely to generate approximately 10 watts for every kilogram. When you put that against the amorphous panels, they will generate upwards of 25 watts per kilogram. From a weight perspective, amorphous panels are much more efficient, however do command a premium in price.
Size of Shadow
Further to the efficiency of the panels, is what is known as the ‘Size of Shadow’. The amount of power generated by a solar panel is proportional to how much sunlight is shining on it. Therefore, the bigger the shadow the panel makes on the ground behind it, the more energy it will generate – a panel at 45 degrees to the sun (with a smaller shadow than at 90 degrees), will not generate as much as a panel perpendicular to the sun. To get specific, at 45 degrees, it will generate 70 per cent as much power (Cos 45 degrees = 0.7). This also does not consider reflected sunlight off the glass or dirty panels, which reduces efficiency further again.
Where you can maximise the size of shadow, is if you’re setting up a foldable panel, position it so the shadow it makes on the ground behind it is as large as possible. You will achieve this by ensuring it is perpendicular, or at right angles to the sun. In so far as shade over the panel is concerned, having the panel in full direct sunshine is critical. Ten per cent shading over a monocrystalline panel will reduce the energy generated to near zero, whereas the same shade over an amorphous panel will still reduce the output, but not as much.
Regulated or unregulated panel
When utilising your solar set-up with a dual input BCDC charger, you will need to run the panel directly into the BCDC charger, without using a regulator. All of REDARC’s BCDC dual input chargers have a built-in MPPT solar regulator, so like any regulator, it requires an unregulated panel on its input. Should you attempt to connect a regulated panel into a BCDC dual input charger, it’s likely the BCDC solar input won’t even turn on. If your panel has an inbuilt regulator that you can’t bypass, you will need to connect the panel directly to your battery, or alternator/main battery input on your charger.
How much solar power do I need?
There are many calculators out there to help you work out how much input you’ll need, for example REDARC has one at https://www.redarc.com.au/calculator/solar. Within the calculator there are different examples of appliances you may own to tally up your power requirements, from fridges to stereos, and LED lighting. There are also apps available for iOS and Android devices that will help calculate your solar requirements.
The simple rule of solar is ‘You need a battery big enough to supply all your electrical needs when the sun is not shining and enough solar panels to replace all that (plus an extra 20 per cent) when the sun IS shining’. An even simpler rule is ‘You can’t have too much solar’. It’s also worth considering where you’re touring, as different areas of Australia receive different amounts of sunlight per day; ensure you are taking sunlight hours per day into account; it will be shorter in mountainous country, and in winter.
Are cheap panels just as good?
Simply put, no. Why would you choose a brand name, like REDARC, over no-name, cheapy, ‘eBay’ panels?
- The panels will output rated power or better – not just claim arbitrary numbers to sound the best;
- They use only the highest efficiency ‘A’ grade cells, meaning maximum cell size with minimum imperfections – not from the ‘factory seconds bin’;
- The portable black blankets use top-of-the-range SunPower cells;
- They utilise genuine industry standard Anderson plug connections; and
- They have first-class tech support, and a massive network of installers and technicians to help out with anything you need, or any issue you’re having.
As with everything, the poor man pays twice, and when you’re looking to get off-grid for weeks at a time, you really don’t want to have to run your 4X4 for a few hours every day to stop the fridge falling over and wiping out your food.
This article originally appeared in Issue 37 of Pat Callinan’s 4X4 Adventures.