Off-grid (stand-alone) PV systems are often applied in isolated places where conventional supply from the electricity grid is unavailable or available at a cost that is unreasonable. Examples for such an application are remote cabins & homes, telecom stations, industrial camps, isolate scientific research stations, traffic signs, water pumping stations, and many more situations- the opportunities to apply solar electric technologies are endless.
Careful consideration of the loads (fridges, tv, radio equipment, pumps,etc) is critical in off-grid system design. It requires a careful analysis of the many variables that if not put into a final equation could lead to unsatisfactory performance and premature failure. Under most circumstances, the first step is to list the power requirements of the appliance you intend on operating and determine the average daily hours each will use. This is expressed in a unit of energy -kilowatt hour (KWh).
A unit of energy is the same whether it is derived from alternating current (AC) or direct current (DC). A critical load analysis is the energy consumed by each appliance, with the ultimate goal of determining the total average daily energy consumed by all loads in the home. A word of caution here, you may find your loads start getting high when including many resistive loads, i.e., heaters, stove tops and toaster ovens. This daily consumption value is then used to design a battery bank large enough to provide enough energy for the day and additional days of autonomy. Appliances that can be plugged into a standard wall outlet are AC. For off-grid homes with full-time occupancy, the benefits of AC appliances typically outweigh the benefits of DC appliances.
Conventional appliances are readily available, and they run at higher voltages, so you can use smaller, standard AC wiring in your household. In certain applications, such as a system for a small cabin, an RV, or a boat, the greater efficiency created by eliminating the inverter. For example, a solar system for a boat or small cabin may run 12 VDC lights, a radio, a TV, and a refrigerator directly from the battery to avoid the need for an inverter.
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