In the following, I would like to share some simple DIY installation tips and tricks so that you can start using solar energy. Keep in mind that a solar energy system will not only keep your batteries charged but when coupled with and inverter, it can be used for onboard appliance and electronics usage.
Generally marine batteries discharge 1% of their capacity daily based on climate conditions. Like a car, if you don’t start your boat on a regular basis, the battery will go dead. Ideally, you want to maintain a “trickling” charge on the battery. A marine 100-amp battery would require a solar power system capable of 1-amp per day output.
Solar power is rated in watts so to calculate amperage output simply divide the wattage rating of the solar panels by 15. For example a typical 5 watt panel will give you .33 amps a day (5 divided by 15 = 0.33).
Because the highest rating output occurs when the sun is directly overhead, you can expect an average rated output approximately 5 hours a day. So, a 5 watt panel would give you 1.65 amp hours (5 x 0.33).
When you sit down and design a solar system for your boat use 3.5 watts per 100-amp hours of battery capacity. But don’t forget to take into account cloudy days as well as running essential systems such as heaters and bilge pumps.
Make sure that you have at minimum, 33 photovoltaic (PV) cells regardless of the size of your marine solar panel(s). Fewer than this will result in the batteries not sufficiently charging. If you are cruising in areas where there seems to be more cloudy days than cloudless ones (the Pacific NW in the winter), you may want to go with thinner filmed panels versus crystalline as thin filmed panels generally are more efficient in low light conditions.
You generally want to mount the marine solar panels in an area which has the most direct sunlight taking into account being able to angle the panels as the boat changes orientation. Ideally, the best mounting point for installation would be at the highest point which for sailboats would be on the main mast and for powerboaters generally on the radar arch. I have seen however, many deck-mounted installations which are okay but keep in mind that the panels produce heat so leave some clearance beneath the panels to allow for heat dissipation.
When installing and wiring the system together it is essential to use marine grade hardware and wire. Without the ability to include diagrams in this article I will try to paint as vivid and simple a “picture” as I can:
The positive (+) terminal from your marine solar panel(s) will connect to the positive post on the battery and the negative (-) terminal will connect to the negative battery post. I have to note here that panels which have a max output of 1% of the battery power do not require a voltage regulator however, I would certainly advise installing one to give you a sense of security if you leave your boat unattended for any length of time.
DIY Solar Panels and Windmills Building Guides
Earth 4 Energy - Make your own solar panels or wind turbine. More info here
Home Made Power Plant - There are some other guides for DIY wind and solar generators, but all of those that I've read don't get into the same details. More info here