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This article is the second in a series. If you have not read Calculating How Big Your Battery Needs To Be, I suggest you read it first, as it explains a lot about batteries and how they should be set up. There is already a lot of information out there, but our articles are directly related to RVs and the Australian situation. This article explains how to get more from your batteries by either supplementing the charging with solar or going for a complete solar system.
Not everyone who reads this needs a full system, so I will cover the basics first.
Above: Glass solar panels have been around the longest and offer the best solution in household and commercial installations.
Above: For mobile applications the semi-flexible panels offer some advantages, but generally at a more expensive price.
Above: Folding panels in both glass and flexible are very popular with campers, mainly because they can be moved around to catch the most sunlight.
A solar panel is a grouping together of individual solar cells to produce an electric current. The electric current leaves the solar panel and goes through a solar regulator, then into a battery. While you can run a 12V appliance or light directly from some solar regulators, a more basic setup connects everything to the battery.
Above: A single panel generates around 17 to 19 volts. The solar regulator then reduces that voltage to a suitable charging voltage for your battery.
Multiple panels and batteries can be connected to a single regulator, but that will be discussed later.
A solar panel is made from solar cells. Different solar cells can produce a different number of watts from a given surface area. This is particularly important for the limited mounting surfaces available on a caravan or motorhome.
As detailed above, the cells can be bonded to glass or a semi-flexible base. The temperature of the panel surface can affect the output also. This is a reason given to support the use of raised glass panels. While I have not tested the difference in output in identical circumstances, I chose a flexible panel due to the weight reduction, durability, and ease of cleaning. The cost was only marginally more after the price of mounting brackets was added to the glass panel cost.
Fixed panels are extremely convenient and more secure from theft compared to portable panels. Portable panels allow for maximising solar capture by locating and pointing the panels directly at the sun. Theft of portable panels can be an issue, particularly if leaving the campsite unattended. You also need to allow storage space for portable panels that are packed up and not operating during travel.
A panel that can be fitted to a roof during travel and only removed when setting up in a shaded position is also a real option.
The specifications of a solar panel will indicate the output voltage and output wattage. Solar panels can be joined together to give additional wattage output at the same voltage.
Remembering from above, a solar regulator controls the voltage that comes from the solar panel to what the battery needs to charge correctly.
The solar regulator will have a specification for the maximum number of amps it can accept from the solar panel or panels. Adding the total number of amps from multiple connected panels will give the minimum sized regulator you need. Don't skimp on this, as many people decide to increase panel numbers or size after a while. Another reason not to cut it too fine is that solar panels can actually exceed the quoted output in ideal conditions, especially in full sunshine but cold ambient temperature.
Another important consideration is whether the solar regulator can vary the output to maximise the battery charging like a multi-stage battery charger. This allows faster battery charging at the beginning and float charging to get the battery up to 100%.
Many caravan solar systems now use MPPT regulators, while some smaller or older systems use PWM regulators. The important checks are still the same: the regulator must suit the panel voltage, panel current, battery voltage and battery chemistry. If you are joining panels in series, check the regulator's maximum input voltage carefully before connecting anything.
Some other features that a solar regulator may have are:
Some solar panels come with MC4 connectors, which allow for easy waterproof wiring. We also sell the easy to add connectors. There are adapters available that permit joining two cables to one. These provide an easy way to add any number of panels to the one set of wires, and a useful junction for testing if a fault occurs.
Many people install solar panels by cutting the connectors off and soldering, but troubleshooting problems is easier with the connectors in place.
The instructions that come with the solar regulator will identify the wire thickness required depending on your distances, but RV applications commonly use 6mm square UV stabilised wire connecting your solar panels to a solar regulator. The same thickness wire can connect the regulator to the first battery.
Voltage drop matters on long runs. If the panel is a long way from the regulator, or the regulator is a long way from the battery, check the regulator instructions and use a cable size suitable for the total current and cable length. If in doubt, use an auto electrician rather than guessing.
When connecting batteries together, you are advised to use premade battery leads available through automotive parts suppliers. If you have a large inverter, say 2000W, you would also connect it with battery leads to the battery bank.
Many people love their first solar panel and the free power they get, so they decide to upgrade. It is an easy upgrade if you have the space.
Above: 2 panels or more can be connected in parallel, positive to positive, resulting in the same voltage but double the watts. Also, 2 or more batteries can be connected together in parallel to double the storage capacity. Having 2 or more batteries allows larger inverters to provide 240V for equipment like microwaves.
An example installation may have 4 x 100 watt panels that produce (4 x 5.5) 22 amps. This is within the capability of a 30 amp regulator and will give a healthy charge to your battery bank.
If you are adding a new panel to an existing system, check that the regulator can accept the extra current and that the new panel is suitable to connect with the existing panels. Panels connected in parallel should be matched sensibly, and panels connected in series must stay within the regulator's input voltage limit.
Solar and battery wiring can carry high current. Use suitable fuses or circuit breakers close to the battery on positive battery feeds, and follow the fuse and cable instructions supplied with the regulator, DC-DC charger, inverter and battery equipment. Do not connect unfused wiring directly to the battery and leave it unprotected through the caravan.
Some modern DC-DC chargers include a solar input. In that setup, the panel wiring normally goes to the DC-DC charger rather than to a separate solar regulator. Do not run a regulated solar output into another charger unless that equipment specifically says it is designed for that connection.
It is common for a battery to be connected to a solar regulator and a 240V battery charger at the same time, provided both chargers are suitable for the battery and installed correctly. If the caravan has a battery management system, follow that system's manual rather than bypassing it.
Portable solar panels with their own regulator are usually connected directly to the battery or to a dedicated regulated solar input. Do not assume a rear 12V socket or Anderson plug charges the caravan battery unless you know how it is wired.
Any 240V caravan wiring, changeover switching, inverter connection to fixed outlets, earthing or mains inlet work should be handled by a licensed electrician. Never back-feed an inverter into the caravan's 240V inlet unless a compliant changeover system has been installed for that purpose.
Above: This diagram represents a more comprehensive 12V/240V system that is very functional and would meet the requirements of most caravans and motorhomes.
Warning: Do not connect your battery charger to this 240V outlet. Specialised switching is required to input the 240V back into your 240V circuit.
For more information on how many panels and how many batteries you need, see Calculating How Big Your Battery Needs To Be.
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