Unlike your current electric meter, which only measures how much electricity you consume, a net meter tracks how much electricity you produce and how much you use. At the end of the month, the bill is calculated based on the net consumption. If you use more electricity than your panels generate, you pay the difference. If you generate more electricity than you use, Eversource credits you the difference (and that credit carries over month to month).
What does this look like in practice? Have a look at my September electricity bill. What it shows is that in the first full month we had solar, we generated 2237 kWh more than we used. As a result, Eversource credited us $404.16 for the month. That credit is the amount of excess production multiplied by the retail rate of electricity (minus a small fraction). Keep in mind, our array is large, because we have an all-electric house (including our heating system)!
A net metering credit carries over month to month until your consumption begins to exceed your generation. For us, that happened on our November bill. We used 111 kWh more than we produced. Our electricity bill that month was $26.83. But instead of paying Eversource, Eversource drew on our net metering credit from the summer. In fact, the credit we built up over the summer was large enough to cover our electricity bill in December, January, and February too! Then in March, our solar production once again exceeded our consumption.
You can see net metering in action on this annotated utility bill. And if you have questions about how solar and net metering work, email us at firstname.lastname@example.org.