A grid tied or utility-interactive system is a PV system that operates in parallel with and is connected to the electric utility grid. These systems are the simplest and least expensive PV systems that produce AC power because they require the fewest components and do not use batteries. The primary component in a grid tied system is the inverter, which directly interfaces to the array and the electric utility network and converts DC output from an array to AC power that is synchronous with the utility grid. Grid tied systems are modular, so large systems can be designed as several smaller systems with individual inverters and then connected together.
Grid tied systems make a bidirectional interface with the utility at the distribution panel or electrical service entrance. When the PV system does not produce enough power to meet the system loads, additional power is imported from the utility. If there is an excess of PV power, the excess is fed back (exported) to the grid.
Net Metering. If the PV system uses net metering, the utility electricity meter runs backwards when power is exported from the PV system to the utility. Net metering is a metering arrangement where any excess energy exported to the utility is subtracted from the amount of energy imported from it. Using this system, energy supplied to the utility from a PV system is credited to the customer and the credit is used when the PV array does not produce energy (at night).
With recent legislation, it is now possible to get straight KWh (KiloWatt Hour) to KWh credit from Rocky Mountain Power. This works out very well for systems that produce excess power during the summer months but require supplemental power from the utility during the winter months. If the PV system and loads are perfectly balanced for annual energy production and demand, the result is a net energy bill of zero.
