This is the power control panel that acts as an interface between the solar cells, batteries, and home electrical circuits. Our photovoltaic array produces 48 VDC electricity, our storage battery is 48 VDC, and most conventional appliances require 120/240 VAC electricity. The power panel enables a smooth flow of energy from wherever it is produced to wherever it is most needed.
The charge controller is the interface between the photovoltaic array and batteries. It ensures the batteries remain in a “topped off” state, ready to supply backup during a power failure. If the charge controller senses the batteries are full, electricity is diverted to the inverter for use in-house or sale to the utility company..
The heart of the system is an OutBack GS4048A inverter. It interconverts the DC and AC electricity, and its computer performs all necessary functions automatically. It may look imposing, but it runs itself with little need for human intervention. When the commercial power grid goes down, as it often does during our monsoon season, the inverter kicks in within microseconds … and my PC keeps purring along without so much as a flicker.
Our electrical system is “grid intertied.” This means we can use commercially generated electricity if we want, and save the batteries for power outages. We use the grid at night, while the solar cells sleep, and purchase this electricity at off-peak rates. During the day we use mostly solar electricity, avoiding the peak rates. On a sunny day when not using much electricity, we can produce more than we use. This “spins our electric meter backwards”, generating credits that are applied to our electric bill.
The sub-panel is a standard 8-circuit breaker panel that connects critical house circuits to the inverter. By connecting only critical loads, we extend our backup time significantly. The inverter can output a total of 4000 watts AC, but if we used the batteries at that rate they’d be totally drained in a few hours. Running only critical loads (refrigerator, microwave, fans, lights, communication, and security systems) we extend our backup power to at least three days — longer if the Sun is shining. Very few grid power outages last longer than that.