Grid-connected systems provide what many people consider to be the best of both worlds: clean renewable energy when it's available and a steady, reliable source of grid power when it's not.
Owning a grid-connected solar electric system is like having your own private power plant operating silently on your roof or in your pasture. When the sun shines, the wind blows, or the creek flows, the system's inverter “pushes back” against the utility with as much force as your PV array or other generating source can provide. Any loads in the house will be supplied first, slowing down the utility meter. If the production exceeds consumption, the surplus power is “pushed” out of the main electrical panel, backwards through the meter, back through the transformer and off to the neighbors!
Compared to a battery system, the grid is a virtually unlimited electricity storage medium with 100% conversion efficiency. You don't have to worry about fully recharging your batteries early in the day and then “wasting” the extra power you're generating. By spinning your meter backwards you can effectively “bank” your solar-generated kilowatt hours (kWh) and use them later at night or during cloudy periods. This arrangement is called “net-metering.” In San Juan County, about 30 of the 11,000 OPALCO members have net-metered solar PV installations.
System Sizing and Load Calculation
While off-grid systems need to be sized to handle peak daily loads, grid-connected systems can be sized for the home's annual consumption. This means that you can use a smaller PV array than you would otherwise need. You're also saved the expense of batteries.