Solar power systems for your caravan
By utilising solar power efficiently, you can invite a little ray of sunshine into your world on even the greyest days.
We all live for the sun but how do we convert it into an efficient 12V solar system? Finding the right solar setup can be a hot topic for debate so, here, we’re going to shed some light on solar power and how to make it work for you.
Basically, solar panels convert sunlight to electrical energy (electricity). Solar energy is then regulated by a solar regulator and stored in a deep-cycle battery. 12V DC electrical appliances can be run off the battery while an inverter will be needed for 240V AC appliances.
Utilising a solar system efficiently is a mathematical science – but you don’t have to be Archimedes for the numbers to stack up.
WHY USE SOLAR POWER?
Firstly, because it’s clean. Many Australians use generators or simply start up their car and charge batteries from the alternator for energy when they’re off the grid. Both methods are noisy, produce fumes and are not environmentally friendly. With solar, there is no noise, no fumes, and it is environmentally sustainable.
Secondly, it’s free. Generators and solar have upfront equipment costs but while generators consume fuel, solar costs nothing to run.
Thirdly, it’s maintenance free. Generators need to be refuelled and serviced but a well-designed solar system works autonomously. The solar regulator will take care of the battery and deep-cycle batteries are fully sealed and maintenance-free.
However, solar should be thought of more as an optional accessory or attachment to a complete power supply system, rather than a solution in itself. The integral component in any energy system is the battery and all other energy management equipment, such as inverters and battery chargers, work closely with the battery. A solar system is an energy source for the battery, serving as an alternative to traditional sources such as alternators and generators.
GETTING SET UP
There really is no typical solar setup, especially with RV systems, as the number of accessories and the style of camping changes dramatically from camper to camper. Many RVs run inverters, 12V TVs and some have 12V fridges while others run gas.
Industry stalwart Alan Johnson from Victoria’s Piranha Offroad Products said a typical RV solar system would comprise panels (rated in watts), a regulator (to control volts to battery), a battery (to store energy), and a monitor (to check on power stored).
"To calculate what size panels and batteries you need, you have to establish what the system is going to run – including lights, water pump, fridge, inverter, TV, radio and computer," Johnson said.
"Things you probably should not attempt to run include an oven, toaster, stove, microwave, hair dryer, air-conditioner and washing machine, and any items with a heating element that use very high amounts of power."
You need to consider the amp hour capacity you require, the DC charging system and the period of time you’ll be without mains power. To add up your total power consumption (amps) for an average day, you simply divide the wattage of each item by 12 then multiply that amount by the number of hours the device is going to run and add them all up. We are lucky enough these days that most vans run LED lighting which draws very little power, so that won’t be a huge consideration.
TYPES OF PANELS
There is perennial discussion among campers about specific solar panels being more effective than others (i.e., flexible or folding, fixed or portable, monocrystalline or polycrystalline). In a nutshell, the crystal formation of a mono cell has a higher efficiency, while the crystal formation in a poly cell (often notable due its changes in colour) is more tolerant of changing light conditions and angles throughout the day.
Overall, the best composition in a long-term camping environment is often a poly panel, whereas a mono panel may be more suitable if you will just be stopping for shorter periods and setting up the panel in the middle of the day.
Flexible-style panels, typically with an aluminium or poly back and often seen fixed to the roof, are not as efficient as traditional glass-mounted panels for a number of reasons but they are a necessary compromise for people who have height and space restrictions.
MONITORING YOUR SETUP
RV enthusiasts often query how inverters, battery management systems, and regulators/controllers fit into the solar equation.
Quite simply, inverters convert power from 12V to 240V so you can run devices reliant on domestic power supply without mains power connected. The most common appliances run on an inverter include laptops and digital camera chargers. Discerning the size of your inverter will require you to take in a number of considerations including the load created on your battery bank, which is critical.
Johnson said many inverters are not particularly efficient with losses of 25 per cent being common.
"If a device, like a TV, can run on 12V DC or 240V AC, it is far more efficient to use 12V DC," he said. "Inverters are rated as constant watts and peak watts, meaning an inverter rated at 600W could be 1200W at peak lasting a few seconds, so we should be aware of what we need at the continuous rating. The peak rating activates the device from the OFF position."
Invariably, there is confusion as to how much power is required when running an inverter. This is ruled by Ohm’s Law of watts divided by volts equals amps. This can be confusing, with many devices rated in watts and others in amps. But the following should help – a 100W globe divided by 240V equals 0.41A AC; and a 100W globe divided by 12V equals 8.3A DC.
Battery management systems (BMS) can vary from an elaborate system designed to charge your battery bank from 12V to 240V and/or solar, through to a simple 12V DC charger. A BMS is one of the critical items that will determine how long your batteries will last. A basic battery management device connects your auxiliary battery (or caravan battery) to your main battery and ensures that the charges from the alternator will apply to the main battery and will not be shared with the auxiliary battery until the main battery is fully charged. It protects the voltage of your main battery so you can start up your car every single time even if you have heavy load on your auxiliary battery.
An upmarket battery management device will accept charges from power sources other than the alternator, such as 240V AC power from the grid, a generator or 12V/24V DC power from solar. Multiple sources can be connected to the battery simultaneously and it will choose the best charging method intelligently. This comes in handy for campers with multiple power sources. On the other hand, these upmarket battery management devices can be costly and they usually come with a limited solar input allowance, sometime as small as 200W. So make sure you choose one large enough for your solar system, prior to purchase.
PITFALLS TO AVOID
The biggest risks to solar power are cycling the batteries too much, using undersized cable and improper storage. Always keep your system above 50 per cent capacity and always isolate the auxiliary battery when in storage to prevent discharge. And keep it on a 240V charger!
Another common mistake is buying a 24V panel for a 12V system. Make sure to check with retailers about the voltage of the panel.
Most solar regulator/controllers are designed for AGM batteries. If you are using gel or lithium batteries, make sure your controller can provide the charging profiles for gel and lithium batteries.
The full feature appeared in Caravan World #548 February 2016. Subscribe today for the latest caravan reviews and news every month!