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How do renewable energy power systems work?
Solar photovoltaic arrays and wind or hydro turbines convert sun or kinetic energy into direct current (DC) electricity. DC electricity is what is stored in batteries. Solar PV, wind, or hydro electric systems may be designed for 12 volt DC, 24 volt DC, or 48 volt DC.
To use the electricity generated by solar, wind, or hydro, it is either stored in batteries or fed into the grid.
For off-grid or battery based systems the DC power is stored in deep cycle lead-acid batteries or other high-performance batteries using a charge controller which controls the flow of power to the battery. To prevent battery damage from overcharging, the charge controller automatically cuts back or stops the charge when batteries become full. There may also be a meter to show the status of the charging process. Batteries will allow the user to draw power from storage, even during sunless, windless, or waterless periods. Power can be drawn slowly by light loads or quickly by heavy loads. The batteries can instantly supply large surges of stored electricity as needed to start or run heavy power appliances that the solar panels or hydro or wind system alone could not power. Typically, 2 to 12 square feet of batteries weighing 200 to 1000 pounds are enclosed in a battery box with a vent pipe to outside. The size of the battery bank depends on the characteristics of the system including surge power requirements and the amount of reserve power needed, because lead-acid batteries need to be frequently 100% fully charged (equalized) to remain in good condition. They should never be drawn completely down to empty. Because of these needs, to get the most years from your batteries requires some supervision/maintenance by the owner.
Most household appliances require AC power. However, DC appliances can be very energy efficient. Sometimes a small solar electric RV, boat, or cabin may use only DC wiring and appliances. Where AC power and appliances are needed, an inverter is used to convert the 12, 24, or 48 volt DC current from the battery into 120 volt AC current, the same as standard utility power for standard household lights, outlets, and appliances. Most solar homes use primarily 120 volt AC produced by the inverter. After conversion to AC, power from the inverter connects into the circuit breaker box of the house in place of utility lines. The house breaker box routes power to lights, appliances, and outlets of the house. Inverters for home power come in ratings from 50 to 5500 watts and are sized for the maximum combined load to be sustained.
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