There have been significant advancements in solar technology in the past ten years and at last solar recharging is a practical and non cost-prohibitive method of charging batteries in the bush.
The reason solar has earned a bad reputation is because so many products are sold that simply do not live up to the claims made by those who sell them and the ignorant buyer who gets taken for a ride.
Consider the following:
• Do you want a solar system to lengthen your stay in a camping spot without having to start the engine to charge the batteries?
• Do you want to add 25% on your time there, double your time or stay indefinitely?
• If you want to add 25% to your time, you need to supplement 25% of your power consumption.
• If you want to double your time there, then you require a minimum of 50% of the current drawn to be replaced.
• If you want to stay indefinitely, then your solar system must recover more than 100% of the current drawn.
A simple exercise
For example if you are running a 40-litre Engel and two lights, you need to measure the average current consumption over a 24 hour period. If that’s too much stress to measure then try this: How long can you stay at one place without charging batteries? Let’s say it’s three days drawing current from one, 100 amp battery. This means that over one day 33,3 amps is consumed (100 divided by three days). To add one more day you need to add 33,3 amps to the battery and you must do it within three days.
Let’s say you want to double your stay. If your consumption is 33,3 amps per day, then you must put back half of that, 16.65 amps in each 24-hour period. In effect you are halving the current consumption and doubling your stay. In the same way, if you want to stay indefinitely your system must replace 101% of the current drawn – a little over 33,3 amps each 24-hours.
The solar experts will probably balk at this and what I am about to write, because it is too simplistic. I say, ‘So what!’. It’s my experience that solar experts are the opposite – too technical and often make claims that are relevant in the laboratory but are meaningless to 4×4 drivers like you and I who are looking for a simple solution to a technical problem. They may say, ‘There is no simple solution’. Nonsense.
Let’s take a 60-watt cell. This is a common medium-sized solar panel. 60-watts means that at the point that the sun is at its highest, and at the moment when it is shining directly at the panel it will, on a good day, when the panel is brand new, produce 60-watts, if you’re lucky. 60-watts translates into 5-amps at 12-volts. The time that panel will spend delivering 5-amps, if it gets there at all is probably, on average, never. It will more than likely top out at 4,5 amps. All the other time the current delivered will be less, far less.
The angle at which the sun strikes a panel reduces the output current significantly, even if it’s just a couple of degrees. So, a 60-watt panel is actually a 28.5-watt panel. Why? With eight hours of sunlight, the first and last two hours the oblique angle means that the panel is only running at an average of 15 watts. That means that for four hours out of the eight it produces just 1.25 amps-per-hour, a total of 5 amps. For the other four hours it produces an average of 3.5 amps per hour, totaling 14 amps. Add this to the 5 amps and the panel is producing 19 amps. That means that with just one 60 watt panel, that delivers 228 watts. Over the eight hours of sunlight the panel delivers 28.5 watts, replacing over half of the current I use over a 24-hour period.
So you see with this example based on what happens at my campsite on a sunny day, this surely gives you comfort that with a simple solar set-up such as I have, solar recharging is possible without spending a fortune. Fact is that I have worked a 60-watt Solarex crystalline panel for over twelve years and have had much joy and success with it.
Types of solar panels
Solar experts will talk about crystalline and amorphous panels and the advantages of both as well as voltage regulators and other devices. I will leave the details of these to them. For most 4×4 users this is not of any real consequence. What does matter is the amount of current they will generate in the environment in which we play and the cost-per watt.
Strapped to a roof rack, placed on the ground, leaned against a tree or bush with a few wires run down to a regulator and onto the battery system. As long as the meat stays frozen and the drinks are icy, that’s all that really matters. My advice: Keep it simple.
Solar panels and their performance claims:
• Look for panels with good low-light claims.
• Ratings must be measured above 13,8-volts. Some panels
boasting high yields boost their figures by lowering the voltage
to 12-volts or lower. Don’t be fooled; a 12-volt battery at 12-volts
is a flat battery! A healthy battery under load should never fall below 12-volts.
• Look at the ratio of current per cost. E.g. For every unit of currency spent I get X units of current (amps or watts).
• Beware of cheap Chinese trash. So many badly made panels stop working soon after delivery as they are unable to take the vibrations from being mounted on a vehicle. They are also far less efficient.
Solar panels come in rigid and flexible types. Flexible units are more robust and practical for 4×4 use, but they are costly and inefficient for their size. Rigid panels are almost twice as efficient size for size, but are bulky and must be loaded flat on a roof rack and tied down very firmly. If they flex, even a little bit, they will break.
Fitting solar panels:
• Forget about making fancy mounts so that the panel can slide out from a rack or trailer because the angle at which the sun strikes a panel reduces the output current significantly. ‘Clever’ mounts are not clever at all, because a vehicle or trailer cannot be easily moved to follow the sun. Rather have the panel/s loose, so that they can be leaned against a chair or tent, and then moved from time to time to keep them perpendicular to the moving sun.
• Electric cables must be heavy copper. Hand joins, bad connectors and thin cables will severely reduce efficiency. This is VERY important. This may not seem necessary because amperage is low, but it seems as if solar systems are very sensitive to this, probably because of the long distances from panel to battery.
• Advanced electronics available to help the solar panel deliver more current more efficiently are a nice to have but not a must have. For years I have run heavy cable from the panel, via a diode, to the battery. I can measure the battery voltage and can measure the current the panel is delivering. Without fancy electronics I achieve much. With electronics I can achieve more, but do I really want it?
• It is better to spend the money on heavy cables and the best connectors one can find.
• If the solar system has the potential to over-charge the batteries, a regulator is essential. Should you choose the simplest set-up, disconnect the panels at night or fit a diode in the circuit to prevent reverse flow during the hours of darkness.
Regulators. Do I really need one?
Yes. But some regulators just prevent over-charging and some also manage the higher voltage produced by the panel and efficiently drop it to a voltage suitable for the battery. If this latter thing is done inefficiently, then the solar system can loose vital charging amperage. Don’t skimp on the regulator as you might as well skimp on the panels as well.