Choosing a Solar Panel for the A'vanA 1 square metre panel is fairly large. The power ratings of those offered as options with the A'van are of the order of 20 Watt (small panel) or 50 Watt (larger panel). This works out at around 16 Watts useable maximum output for the smaller panel and 40 Watts for the larger panel. 20 Watt Solar Panel on an A'van Sportliner In addition to the panel (or panels), an appropriate solar panel charge regulator is necessary to avoid overcharging of the battery. This is wired between the panel(s) and the battery. Manufacturers of some of the smaller panels claim their products do not need a regulator, but in practice, these might not fully charge the battery as the panel output voltage drops to the point where it might be less than the battery voltage when the panel gets hot. The optimum size of a solar panel depends upon why you need it. If it is required only to keep the battery charge topped up when the A'van is stored between trips, then a small 20 Watt panel (suitably located) would be quite adequate. It would just need to make up for the inevitable gradual loss of battery charge that occurs when not used, even though you do not have anything switched ON. To reliably keep topping up your battery when camping where there is no 240V mains supply however, requires a more powerful (bigger) panel, the size being dependent on how much charge you drain from the battery each day. Determining the minimum size (or Watts) panel required under these circumstances does involve some (but not much!) mathematics. Solar panels are rated in Watts, whereas battery charge current is in Amperes (Amps). Batteries are rated by their voltage (usually 12 Volts in an A'van), and capacity in Ampere Hours, i.e. the number of hours a fully charged battery can deliver a given current. A "deep cycle" lead-acid battery as might be fitted in an A'van could have a 120-Ampere Hour (Ah) rating. When fully charged, such a battery could be expected to supply one Amp for 120 hours or two Amps for 60 hours etc. (For much higher currents however, this relationship does not hold, the hours decreasing significantly from this relationship as the current increases). The magic formula which ties Watts, Volts and Amps together is "Watts = Volts times Amps" (W = V x A). Using the above formula, a 20 Watt, 12 Volt bulb consumes a steady 1.7 Amps (20 / 12 = 1.7). Two such 20 Watt bulbs on for three hours a day will consume 10.2 Ampere Hours of charge from the battery. As battery charging is not 100% efficient, i.e. 10.2 ampere hours of charge will not increase the charge retained in the battery by quite this much, then to make up for this, your panel would need to generate typically 12 Ampere hours a day. A 50-watt panel at 80% efficiency (due to the charge regulator) would, in full sun, be generating at the most just over three Amps (50 x 80 /100 / 12 = 3.3 Amps). Full sun for around four hours would replace what you used the previous night. In practice the orientation to the sun and clouds will mean it will take up the best part of the day to keep the battery fully charged... in which case, unless you have atrocious weather, with this size panel you could keep on camping for ever! More lights (particularly if you leave the step light on) and maybe a car radio in the van running off the van battery will of course call for a bigger panel or longer exposure to full sun. Replacing the incandescent light bulbs with equivalent brightness LED bulbs will use less current, in which case your battery charge will last longer. Another consideration is where to located the panel. For maximum charging, the panel needs to directly face the sun. If you have the panel on the roof of your A'van and you have parked in the shade... guess what... charging from your solar panel could be minimal! For this reason, many travellers prefer to have portable panels which they can best position to catch the sun. The amount of charge generated from an A'van roof located panel whilst travelling is also likely to be small. Collapsible 80watt Solar Panel, with Regulator & Carry Bag Whether the panel is on the van roof or portable, it will of course need to be wired (via a charge regulator) to the battery. For a roof installation the wiring could pass through a sealed hole on the roof behind the panel, thence to the battery location inside the van. For the portable situation however, a weatherproof two (or more) pin connector could be fitted through the floor of the van in the battery compartment near the side so the cable from the panel can be plugged in from the underside without too much bending down. Fit the regulator in the battery compartment rather than outside, as it will be weatherproof in there.
Should you intend buying solar panel(s) for your existing A'van, the A'van agent might be a good starting point,
but there is an internet website called CaravansPlus (www.caravansPlus.com.au) which lists a wide range of panels
and appropriate regulators.
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