Photovoltaic Modules
When choosing photovoltaic modules for your gridless system, it is important to look at price, technology, how they adhere to the ceiling or shelf, voltage and current specifications, UL listed and warranty. The most typical type of module has a voltage that integrates easily with the organized configurations of interconnected inverters. The non-networked market can even take advantage of these common modules by using Maximum Power Point Tracking (MPPT), a charge controller that can reduce field voltage to the minimum voltage of a bank battery. There are still some modules on the market that are nominal 12V, made to directly charge 12, 24 and 48V bank batteries through a non-reducing charge controller, but they are becoming hard to find and are typically more expensive.
Proper sizing arrangement is crucial in designs without a network. It ensures that the loads you need to run will have power and that the battery can be fully recharged after a period of no sun. To size an array you will need to know the STC watt modules, the daily average of the maximum hours of the sun in the worst month and the amount of energy the load consumes. An arrangement needs to produce as much as the average daily consumes and be able to recharge the batteries to recover after cloudy periods. Whenever possible make the arrangement larger to account for the inclement weather. Most designers even specify a generator to accommodate during periods of low sunshine, whereupon the need to enlarge the arrangement in the future is removed.
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