Often this question comes up about rooftop solar, what happens when the panels produce more electricity than the household uses?
In an off-the-grid wilderness home, the panels charge battery banks to full charge and then shut off. This stored energy is then used to power the house at night when no sun is shining.
Most of us will be using a grid-tied solar system meaning we are still connected to the grid. Electricity from the grid can still power our homes on cloudy days and excess power from our solar panels can flow to the grid.
With grid-tied systems, a new electrical meter will be installed at your home by the utility. These are called “net meters” and can measure electricity flow in both directions – in and out of your home.
Electricity coming in will be purchased from the utility and electricity flowing out will be sold to the utility. The rates are set by the utility and state governments. The best arrangement is a 1-to-1 exchange. Each kW of power you buy costs the same as the ones you sell.
More typically the utility will take out some distribution costs and pay you less for the power you sell to them, so your best deal is to use as much electricity you can while it’s being generated. For example, run your dryer or mow your lawn with an electric lawn mower when the sun is shining.
At the end of the month, if you generate more electricity than you use, the utility will give you credits for the next month. So during the summer, you can generate credits to be used in the poorly solar-producing winter months.
In my state of New Hampshire, the utility will cut the homeowner a check in March if there is a positive balance.
One of the most enticing incentives for going solar is net metering. Essentially, net metering is a process in which you can earn money for the excess electricity that your solar panels create but your home does not use. This excess energy is sent to the power grid, and is then used to power other homes or businesses.
Battery Storage
Besides sending excess electricity back to the grid for credit, adding a battery such as the Tesla PowerWall to your system is another way to capture excess power. In my system, the 14 kWh Tesla PowerWall II gets charged up first, before any power is sent to the grid.
On a nice sunny day, the PowerWall is charged up by noon, and then excess power is sent to the grid for credit. The PowerWall then discharges at night while also holding some reserve for emergency power outages.
EV Storage
With a bi-directional EV (electrical vehicle), the car can act as storage for excess energy. Use your solar to charge up your car and then if needed send power from your car to your house.
Net Meter Installation
Installing the net meter is the last step in what could be months of anticipation of throwing on the switch for your solar array. The utility might take up to two weeks to come and install your net meter after receiving word from the solar company that everything has been inspected and ready to go.
The actual net meter installation is a five-minute procedure. The old meter pops out like an electric plug and then the new net meter pops in.
Warning: Don’t be tempted to turn on your solar array before the net meter is installed. The old meter can not measure direction of electricity flow so you will end up PAYING FOR THE ELECTRICITY YOU ARE PRODUCING! Yikes! You don’t want that. Be patient and wait for the net meter to be installed.