Frequently Asked Questions

If you have a grid-tie renewable power system in the state of Washington, you have not one, but two power meters! Why? What does each measure?

Net metering is the difference between the electrical energy in kilowatt-hours (kWh) that has been delivered from the utility to the customer and the excess energy that has been received by the utility from the customer. The amount of excess energy the customer sends back to the utility is equivalent to the total amount of renewable energy generated, minus the amount of renewable energy that is used by the customer.

Digital net meters record the energy delivered to the customer separately from the energy received by the utility. Any energy received by the utility is credited on the customer's bill. The most significant benefit reflected in the power bill from net metering is in offset energy delivered that the customer does not need to buy, because much of the renewable energy is used as it's produced. The excess 'net' energy received by the utility and credited on the power bill is typically a small value.

Production metering is the total AC electrical energy output of the customer's renewable energy system, before any of the energy is used by the customer. Production metering is the basis for WA state incentive payments administered by the utility (for PSE, the Renewable Energy Advantage Program, or REAP). The production meter reading is also the basis for Green Tag (Renewable Energy Credit) sales.

Battery-less renewable energy systems should only record the amount of energy delivered by the system to the customer's electrical panel. Battery-based renewable energy systems will sometimes use grid energy to charge the batteries (such as following a sustained grid outage). Thus, the production meters for battery-based systems will record the amount of energy delivered from the utility, as well as the amount received by the utility from the renewable energy system.