4x4 PROFESSOR
Sunlight gives life to both plant and animal, and without it we would definitely spend less time on the beach. But the sun can also drive the electric gadgets in your vehicle – here’s how to get your free electricity.
It’s almost impossible to imagine an overland trip without a fridge/freezer in the back of your rig, but this device requires a dual-battery system – and its charge will run out if you camp for several days without driving anywhere.
You will therefore need to make a plan if you’re dug in on a sheltered beach somewhere along the West Coast, or in the Kalahari under a lonely tree where there is no external power source to top up your battery. One solution would be a portable generator, but they’re noisy and take up valuable storage space. A better alternative is a solar panel, because the sun is an ideal source of energy here in the southern parts of our continent.
We chatted to two solar specialists: Battery & Outdoor King in Pretoria, and 4x4Direct in Cape Town. 4x4Direct showed us what the devices look like, while Battery & Outdoor King explained how the technology works.
Don’t just jump in your bakkie to go and buy panels. First make a list of all the electrical and electronic devices you want to take with you on your epic journey. Will it only be a fridge/freezer and camp light, or are you taking along the hair dryer, power drill, and satellite TV? Write down the power consumption of each appliance – a 220 V hair dryer uses up to 2 000 W, for example, and the battery charger of a cordless drill, 60 W. The next step is to convert the Watt to Ampère by dividing the Watt by the Volt. Ampère is the unit used to determine how many batteries and solar panels are needed. The calculations will reveal that a hair dryer draws 9 A and a cordless drill 0,2 A. By the way, a typical fridge/freezer uses between 2 and 6 A, depending on how hard it works.
Take this list of your power requirements as well as your budget to a solar-power specialist like Battery & Outdoor King; they can help you decide on the best solar-panel system for you.
Black or blue?
There are currently three types of solar panels on the market: monochrystalline, polycrystalline, and amorphous panels.
The former is usually dark in colour – almost black – while polycrystalline panels usually have a blue sheen. Because amorphous panels are less efficient and their popularity is declining, we’re not going to bother discussing them here.
A monochrystalline panel consists of thousands of cells, each containing a single silicon crystal, while a polycrystalline panel’s cells consist of crystal shards with different orientations fused together. According to Battery & Outdoor King, monochrystalline panels are more efficient and can convert 20-22% of sunlight into electricity – compared to the 13-16% of polycrystalline panels. Monochrystalline panels are, of course, also more expensive and currently still relatively scarce – it will take some time before they are commonly available. Monochrystalline panels also work in moderate shade – obviously they generate less electricity in such conditions – while polycrystalline panels don’t perform nearly as well in low light. 4x4Direct says polycrystalline panels have a small advantage when sunlight falls at an oblique angle on the panel, because then the crystal shards and their different orientations capture a little more light than a single crystal can.
Floppy or rigid?
Rigid glass panels mounted in aluminium frames are durable and reliable. They are, however, relatively heavy and bulky. Flexible panels, on the other hand, don’t weigh nearly as much and are particularly suitable for attaching to a curved surface. Make sure you choose a reputable brand, because many flexible panels are cheap unreliable knockoffs.
The gate keeper
The next device after the solar panel is the charge controller, and here you have one of two options: a PWM and an MPPT charge controller. These acronyms stand for pulse width modulator and maximum power point tracking, respectively. A PWM controller will cost you significantly less than an MPPT controller, but according to Battery & Outdoor King, it only transfers about 70% of the energy captured by the solar panels to the battery. In contrast, an MPPT controller gives 95-98% of the panel’s charge to the battery.
When asked if a controller could overcharge a battery and thus damage it, Battery & Outdoor King’s answer was: “Yes, definitely”. Make sure you buy the type of controller that cuts off the current as soon as the battery is full – not all charge controllers have this feature. According to 4x4Direct, fuses are extremely important in a solar panel system. They suggest you splice in a fuse near the positive pole of the solar panel, charge regulator, and battery. This is apparently particularly important if you also want to wire your vehicle’s alternator up to the charge controller.
Battery & Outdoor King agrees, but add that if you use the correct cabling with the appropriate copper core thickness in the first place – and send the direct current through a decent charge controller that can nullify spikes in the current – then putting fuses on the wiring is of lesser importance.
Some charge controllers, known as hybrid controllers, not only accept power from the sun and your bakkie’s alternator but also from a portable generator and the national grid.
Storing power
The third component in a solar-panel system is the battery. There are many types of batteries, including sealed, flooded, valve regulated, traction, and lead crystal batteries. We focus here only on the four most popular: silver-calcium, AGM, gel, and lithium.
A silver-calcium battery is the cheapest and can withstand high temperatures. Its disadvantage is that it needs more Volts to stay healthy, which means you need to fit a special type of charge controller specifically designed for silver-calcium batteries. This battery lasts about six years.
An AGM battery – it stands for absorbed glass mat – has been the most popular deep-cycle battery for many years. Fibreglass mats between the battery cells’ respective plates and absorb acids – this prolongs the battery’s life and prevents leaks. An AGM battery that’s treated properly should last between 7 and 10 years.
A gel battery’s performance is only slightly better than that of an AGM battery, but it lasts 10-12 years. As the name suggests, the battery acid in a gel battery is not free-flowing but rather suspended in a gel that prevents the acid and electrolytes from separating and accumulating in layers (called stratification), which in turn weakens the battery’s power supply.
According to Battery & Outdoor King, there is nothing bad to say about a lithium battery other than its price. They cost upward of R8 000, but compared to a lead-acid battery, a lithium battery is 50% lighter and holds about 60% more charge.
Does that mean the lithium battery is the best then? It depends on how often you tour. If you only travel to the Bushveld on long weekends, we suggest you save your money and get a silvercalcium battery. A better choice, however, would be the AGM or gel battery, but then you must mount it far away from your vehicle’s engine because they don’t like the heat.
If you are a full-time adventurer who can barely remember what a mailbox or doormat looks like, we suggest you consider a lithium battery. It weighs the least, takes up the least amount of space, and is particularly suitable for powering energy-intensive devices – plus it charges faster. With enough lithium batteries, you cannot only take a hair dryer along but also an air conditioner and a washing machine. To do that, however, you will have to purchase a fourth component: an inverter to change the
12 V current to 220 V. A fridge/freezer and camp light don’t require an inverter, as they get power directly from the battery.
Battery & Outdoor King recommends using the largest possible battery for your solar-panel system. Not only does this extend battery life, but it also provides extra capacity on cloudy days when solar power is low.
Loose or fitted?
Should you bolt solar panels on your rig’s roof or leave them loose so you can set them up on the ground? It’s a personal choice. Not everyone likes to stack panels every morning only to put them away in the evening, but, bear in mind, the sun shines directly from above only once a day, and that’s also only in the summer months. So, if you bolt them to the roof, you will rarely achieve optimal energy – though you can compensate for this by installing more, or larger, panels than you actually need.
Some people like to park their vehicle in the shade and place the panel in the sun with an extension cord leading to the battery system. This setup, however, takes up packing space, and if the extension cord is long, you will experience voltage drop, which means that you will have to use a thicker (and more expensive) cable that not only weighs more, but takes up even more packing space.
Battery & Outdoor King devised a clever solution by fitting a slide between the vehicle’s roof and the roof rack in which you stow the panels.
Sun chasers who keep their panels facing the sun all day long, use an empty toilet paper roll, holding one end against the glass while the other open end faces the sun. Once the roll casts a shadow, it’s time to reposition the panel.
Series or parallel?
Two or more panels wired in parallel offer the advantage that, should one fail, the other will continue to supply power. The disadvantage is that you must use thicker cables because the Ampère is doubled by a parallel connection, while the Voltage remains unchanged.
You can use thinner wire to connect two panels in series, as the Ampère remains the same, while the Voltage doubles. Unfortunately, you will lose all power if one of the panels fail. Battery & Outdoor King prefers series, because they believe the benefits far outweigh the single downside.
Final question...
How many panels and batteries do I need, and which brand’s charge controller should I get?
The answer to the first question is easy: as much as you can fit. Battery & Outdoor King says a Victron 25 Ah super-cycle AGM or 140 Ah Discover dry-cell battery connected via a good quality MPPT charge controller to two 100 W solar panels in series, is a winning recipe for someone who wants to camp for a few weeks with a larger fridge/freezer, even when the sun hides behind the clouds for a few days. Those with two fridge/ freezers should look at two 180 W panels with multiple batteries.
We’re going to highlight a single brand when it comes to charge controllers, but do buy the best MPPT charge regulator you can afford. The kind that connects with an app on your phone or tablet via Bluetooth works great, as that gives you insight of your solar-panel system, and allows you to control every aspect of it.
If the hair dryer and TV must come along, you will need to add more lithium batteries and an inverter, but for that you will need to first talk to a specialist and then your bank manager...