Net Metering / Grid-tied

Utility Meter with Instruction Placard

Net metering is the state rule that allows utility customers to backfeed their electric meters.  If you are already connected to the utility and you are considering the addition of wind or solar power then you will also need to become familiar with your state’s net metering rule. Net metering in West Virginia and Virginia allows customer generators – folks with wind or solar – to gain a credit for any electricity that they put back on the grid.  Net metering encourages a network of small power plants.

 Small Grid-tied PV System

No batteries are required since the utility grid acts like a big battery which stores power during excess production. These grid-tied renewable energy systems do not need to be sized to meet the full load of the home or business. Instead, these can be sized to meet a portion of the annual load while grid power may be used to supply the remainder.

Grid-tied systems work in concert with the utility to produce clean power. The piece of equipment that makes this cooperation possible is the “grid synchronous inverter”. A inverter coverts DC power to common AC power. The grid synchronous inverter will analyze the signal from the power company (volts/hertz) and mimic its AC output to match. That makes the commingling of electrons seamless – your refrigerator won’t know if it is being powered by utility power or homegrown electrons!

Synchronicity with the utility’s signal can be a drawback at times when the utility experiences an interruption in service.  Outages cause the inverter to stop producing power.  This keeps the lineman from being shocked while they are making repairs. It also keeps you from making or using the power that you would normally be producing.

So what if you want to make and use power in the event of an outage? In this case you need to install a “grid-tied system with battery backup”. These systems are more expensive than a simple grid-tie setup. The added cost is caused by the addition of batteries and some extra wiring and electronics. An inverter with an automatic transfer switch must be used to allow the house to swiftly disengage from the utility and begin drawing battery power. As a source of backup power these systems are much quieter than a generator; the transfer time is almost unnoticeable (unlike a standby generator which has to crank up before it begins to feed power to the house), and the batteries will allow continued use of the power from solar or wind.