Solar panels convert sunlight into electricity. Their power output depends on many things like sun radiation strength, angle of the solar panels, their type and age.
Unlike wind turbines, they have no moving parts, they produce no noise during operation and can be positioned more closely to the passengers and onboard equipment. They operate during the day, but during the night, they produce no electricity.
Very often, solar panels are combined with wind turbine(s) using the same Maximum Power Point Tracking (MPPT) charging controller.
There are several things to consider when buying solar panel, some of them are:
- power output of solar panel in 'ideal conditions' is given in watts (W) and for marine applications, solar panels range from just few watts to large panels providing hundreds of watts. Very often, value of the nominal voltage is provided (for example 12V, 18V, etc.), but good solar panels must come with MPPT controllers - these controllers enable solar panels to charge the battery even under low light conditions by converting just few volts provided by solar panel to battery voltage (12V, 24V etc). Also, such controllers protect battery from overcharging and protect solar panels from over-current and similar 'surge' conditions. Not to mention that many models enable connecting both solar panels and wind turbines to the boat's electric system, significantly simplifying the design.
- rigid, semi-flexible and flexible solar panels - to ease the installation on irregular surfaces, some solar panels can be bent, up to the certain point. Curvature depends on the model, but it ranges from just 5-10 degrees to 30 or even more degrees. If the panel is bent more than that, it can be damaged - these panels are not rigid, they are flexible and they bend, but they can't be rolled like pancakes or anything similar! Such flexible solar panels enables the installation of solar panels without rigid aluminum (carbon fiber, plastic etc.) frames directly to the boat's vertical or horizontal surfaces, without ruining the boat's contours. Even better, some flexible solar panels come with extra durable surfaces, enabling one to (gently) walk over them and since there are not void between such solar panels and the boat, they are very wind resistant (if installed properly). But good flexible and durable solar panels can cost more than rigid solar panels.
Rigid solar panels require sturdy frames, which can increase the price and the weight of the solar panel. However, it is much easier to remove and repair rigid solar panel bolted or fixed with the screws to the boat/yacht than flexible solar panel glued to the boat :)
- physical dimensions are height and width and sometimes depth. Weight of the solar panel is also important, especially for smaller boats. Physical dimensions and construction of the solar panel dictate the positioning of the panels on the boat. It is much easier to position and install several smaller and flexible solar panels than one large, rigid solar panel. However, larger solar panels are cheaper per produced watt.
- durability and warranty conditions - marine solar panels must survive and operate in very corrosive environment for years and even decades. Although they are built to last, they also depend very much on the actual position on the boat and quality of installation. They must be able to resist salt water, rain, wind, various impacts over the years etc. Warranty conditions vary from model to model and from manufacturer to manufacturer, but in general one should expect 1 to 5-year material and workmanship warranty.
Warranty conditions are void, if one, for example, drops 50 pounds anchor on the solar panel ... :)
Which solar panel or system to choose? This is not an easy question to answer, but first measure your boat where you plan on installing solar panels and check your wiring and energy requirements - if you have just GPS, depth meter and LED navigation lights to worry about, and you have a good, main deep cycle marine battery and you use your main engine every day for at least an hour, while being off-shore, then there is no need for large investments.
However, if you like to spend days without using main engine(s) and you have large number of devices and appliances (various radios, laptops, refrigerators, smart phones, even AC unit etc), then you need large solar panel(s) combined with marine wind turbine(s) and probably a power generator, just in case.
Long story short - write on the paper what you actually need and required power and time of operation. Then you will have a good starting point to choose right solar panel or solar panel/wind turbine combo, that will serve you well for years!