Breakdown of a simple solar power system

A solar power system comprises a number of components. Firstly, the solar panels themselves convert sunlight into direct current (DC) electricity. However, this is not necessarily in a useful form - the voltage output of a panel varies with the sun energy striking it, and at any moment you can only draw as much power as the panel is producing, which at night is nothing.

So most installations store the power produced in batteries, from where it can be used at will. A charge controller is normally used to prevent the batteries being overcharged, although if the solar panel is small relative to the battery bank capacity it isn't really necessary. At night power can leak back from the batteries and be lost through the solar panel, so a diode (a sort of one-way valve for electricity) is generally installed in the charging circuit to prevent this. Often this will be built into the panel itself.

Finally the electricity is used. Most lights and appliances on residential boats, yachts and caravans are designed to run off 12V (or occasionally 24V) direct current, and these can be wired straight to the battery bank. Where 240V alternating current is needed for household appliances, power tools and the like, an inverter is needed to convert the direct current from the batteries into alternating current.

An alternative to using batteries to store the energy is to connect the solar installation to the national grid. When the panels are not producing enough power (eg at night), power can be drawn from the grid instead - and on a hot sunny day when they are producing lots of power the excess electricity can be sold back to the electricity generating companies and fed into the national grid. This is not simple however - the waveform of the power being produced has to be matched very carefully to that of the national grid. Invertors capable of doing this job tend to be a little more expensive than those for off grid installations.