Disclaimer: This article is designed to provide helpful information on the subject discussed and does not aim to provide an authorized guide for the installation or maintenance of photovoltaic systems. Before starting, it is recommended to seek advice from a photovoltaic retailer or a professional installer in order to obtain the support needed.
In camping and caravanning sector, great attention should be paid to energy requirements because electric and electronic equipment on board needs continuous power supply. For this reason, it is foundamental to be equiped with a photovaltaic system that guarantees energy self-sufficiency even in case of longer periods of isolation from conventional electric sources.
In this guide, we will follow the installation step-by-step and give you some advice to autonomously install a photovoltaic system on your motorhome.
In order to chose how to build your photovoltaic system, it is necessary to take into consideration the amount of space at disposal and the daily energy requirements of your vehicle. This can be done by simply adding up the power absorbed by the equipment on board the vehicle (lights, battery charger, TV, fridge, etc.). Remember to pay attention to the current type required. Usually camper equipment requires absorption of direct current. In this case, service battery is sufficient for the storage of energy. On the contrary, an inverter will be necessary if the equipment requires absorption of alternating current. At this point, you can buy all the components necessary for the FV system from a specialized retailer, such as:
Solar charge controller for the charging management of the batteries (see article for further information);
Batteries (lead, gel or AGM) (see article for further information);
Inverter for the fruition of direct current (see article for further information);
Cables, cable glands and connectors (see article for further information);
Diodes and fuses for the safety of the fundamental components of the system (see article for further information).
The choice of the components listed should be based not only on obvious budget considerations and on the compatibility of the components but also on the possible future expansion or updating of the FV system.
We advise you to read all linked articles about the above-mentioned topics in order to achieve a better understanding of this guide.
Once you have planned the system and you have purchased all the needed components, you can start the installation. We would recommend to place all the elements of the system in their position first and then to begin connecting the equipment following the instructions given together with the installation manual of panels and solar charger controllers.
Concerning the electrical connection, it is advisable to follow accurately the instructions given in the manuals because different charge controllers can require different installation procedures on the base of their functions (some require to connect first batteries and then the panel others vice versa).
The first stage to installing solar panels consists in mounting the module on the chosen surface, usually the roof of your motorhome or van. According to your needs and the space at disposal, you can install your panel in different ways: you can paste it directly on the roof of the vehicle, fix it using brackets or fix it using pre-existing structures, as roof racks. Pasting is the cheapest and quickest way to install a panel, however, it has a relevant disadvantage: removing the panel in the future will be complicated and will cause inevitable damage to the surface of the vehicle. On the contrary, fixing it through brackets or roof racks will give you the opportunity to keep panels separate from the roof of your vehicle avoiding damages and keeping, at the same time, its aerodynamic properties. Nevertheless, it is important to remember that robustness and cohesion between panel and surface are fundamental in order to avoid mechanical stress during motion. Do remember to cover the panel with a dark cloth or some cardboard for your safety and the preservation of the panel during installation.
You will need first to place the brackets and the panel on the roof and draw with a pencil the exact position of the components. Then, you can drill small holes in the brackets and in the aluminum side of the panel. We advise you to do it on the ground so that, after having fixed the brackets, you can install the panel without needing to drill the panel on the roof of your vehicle. When holes are done, lay out the brackets and paste them on the pre-determined place using a silicone sealant (see suggested product). This product needs to rest for about an hour to harden. It is recommended to place the panel on the brackets without fastening the screws so that you can use the load of the panel to facilitate the adhesion of the brackets to the surface. After about an hour, you can fasten the screws through the holes previously made.
Although simple, this step can lead to dangerous consequences if carried out in the wrong way. In order to let the cables pass from the outside to the inside (where the charge controller is set), it is necessary to drill a hole into the roof of your vehicle. We recommend to use a cable gland like this to ensure permeability to your vehicle. Concerning the brackets, you will need to draw the position of the junction box (it should be fixed in a position allowing an easy passage of the cables in the cabin, possibly near the solar charge controller).
WARNING: panels are usually equipped with MC4 cable terminals that do not fit cable glands due to their size. Therefore, we recommend to take them off and connect cables in the cable gland using a terminal board.
This will allow you to fit the cables of the panel directly in the cable gland and then, once inside the cabin, to connect them through terminal board to the cables reaching the solar charge controller. In this way, it will be easy to isolate the connection and to protect it from water or possible breaking.
After having drawn the exact position of the cable gland, you can drill the roof of your vehicle, connect cables and finally paste the cable gland on the roof. In this case too, it is advisable to let the silicon sealant rest and, if possible, to put a load on it to let it adhere to the roof.
Cables must be properly dimensioned to the amperage produced by panels in order to avoid voltage drop higher than 1%. We recommend to use cables with 4mmq section for short-circuit currents exceeding 4 amperes to cover overall lengths inferior than 8 meters. For higher amperages or longer distances, we advise 6mmq section cables. In order to calculate the necessary cable section, you can also use some online tools, like myelectrical.com. Concerning the type of cables to be used to connect the system, the market offers some flexible and handy “solar cables” equipped with a fire-resistant sheath that protects them against UV rays.
The solar charge controller should be placed so that he can receive output cables from the solar panel, input cables to the batteries and possible paralleling connectors (they are necessary if you want to charge service and engine battery simultaneously). Furthermore, if not included in the solar charge controller, it will be advisable to install a remote display in a visible position that will allow you to check all the electrical data of your FV system.
Basic solar charge controller models usually have one input terminal (for the connection of the solar panel) and two output terminals, one for the batteries and the other for little loads (e.g. a light bulb). Do not connect heavy loads to this terminal because they would cause the blockage of the charge controller. Do remember to take always in consideration the characteristics written in the product manuals. Dual battery solar charge controllers – for example RegDuo EpSolar with PWM technology or WRM 15 dual battery Western CO – have also a 4th terminal that gives the possibility to connect a second battery (usually the engine battery). The display on the regulator will allow you to check all information concerning panels (watt and ampere output) and batteries (charge levels). If the solar charge controller is not equipped with a display, it is possible to buy it separately. Regarding the choice of the solar charge controller, this article can help in understanding which are the main differences among existing models.
The procedures to connect panels to the solar charge controller vary according to the number of panels installed. For this reason, we decided to explain separately the case concerning one solar panel and the case concerning two (or more) solar panels (see point 1 for a single panel, point 2 for two or more panels).
If you have decided to install only one solar panel, it will not be difficult to connect it to the solar charge controller. Firstly, you should pass the cable in the cabin. In order to do this, you only need to drill a little hole on the roof, as previously explained, and then insert the cable in the cable gland and fix it on the hole. Once inside, cables can be connected to the solar charge controller through the proper terminal. Most probably, the cables of the panel will not be long enough and you will need an extension. In order to preserve the safety of the system, we advise to connect cables to extensions through MC4 connectors (90% of solar panels are already equipped with them) or through a standard terminal board.
If you decided to install two panels , connection will be slightly more complicated because you will have to join the cables of the panels before connecting them to the solar charge controller. This can be done safely by means of splitter or paralleling MC4 connectors.
Concerning negative cables, you will only have to connect them to the two male input terminals of the connectors, leaving the female output terminal free for the connecting cable of the regulator. The same procedure should be applied for positive cables (in this case connector will have two female input terminals and one male output terminal).
In this case, however, you should install also some schottky blocking diodes before adding the connector. Diodes serve the purpose to avoid the circulation of abnormal currents within a string of parallel modules where there is a difference of tension and so to prevent damages due to current return. Two types of diodes are essentially used in photovoltaic domain. The basic version is cheaper but its installation requires specific technical equipment and good skills in electronics.
If you have no experience in this field, it is recommended to use DCM4 connectors with integrated diode that are more expensive but also more user-friendly. After having terminated the parallel connections, you can connect cables to the proper input terminal on the solar charge controller. If your system is composed of more than two panels, the connection procedure is the same, only the type of connector changes.
Batteries are usually positioned in a compartment inside the vehicle sheltered from possible water infiltrations and provided with holes for the passage of cables connected to the regulator. Since the highest amperage is to be found in the cables connecting batteries to solar charge controller, this compartment should be as close as possible to the regulator in order to reduce the length of the cable and reduce voltage drop.
After having positioned the batteries in the chosen compartment, you can connect output cables to the solar charge controller. Pay attention to connect positive and negative poles correctly. At this stage, we highly recommend to add fuses to positive cables. Fuses act as circuit breakers and, thanks to their breaking capacity, they prevent high return current from damaging the solar charge controller. If you have more batteries, you should interconnect them so that they are recognized by the regulator as a single battery block.
If the electronic or electrical equipment of your motorhome requires the absorption of direct current (12V), your FV system is complete. On the contrary, if some devices require absorption of alternating current (220V), you will need an inverter (see article for further information on different types of inverters). The inverter should be connected to the output cables of your batteries (pay attention to positive and negative poles) and will then furnish energy directly to your electronic or electrical devices.
Once the wiring stage terminated, it’s good practice to check the output of your FV system by comparing the electrical data given by the solar charge controller with the data measured – through a current clamp or a voltmeter – directly on the cables outgoing the panels and ingoing the batteries. If you use the current clamp, you will only have to register the value given by the negative pole when this is connected to the solar charge controller and batteries are (partially) charged. On the contrary, if you want to measure the voltage, you will only need to check it at the end of panel cables with the voltmeter (where cables connect to the terminal board of the regulator).
As to maintenance of the panels, it does not require big efforts. It is sufficient to clean their surface using non-abrasive products in order to keep the highest efficiency. You can do this procedure occasionally, when you also check the battery status.
If all components of your FV system have been connected correctly, you are now ready to produce and stock green energy from the sun!
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