Solar production and home usage rarely match hour by hour. Net metering describes one way eligible exported electricity can be handled by the utility billing system, but it is not a promise that every exported kilowatt-hour receives the same value.
The basic idea
Solar electricity generally serves the home’s immediate loads first. When production is lower than usage, the home can draw from the grid. When production is higher than usage, excess electricity may flow through the meter toward the grid and may create credits under the applicable rules.
At night or during low production, the home draws electricity from the grid.
When production exceeds usage
At a moment when a system is producing more than the home is using, the balance may flow outward through the meter. If the facility qualifies, the utility can apply net-metering credits under the applicable rules. Credit value, expiration, allocation, and account treatment are not the same for every facility.
When usage exceeds production
At night, during weather events, or whenever the home’s demand is greater than the system’s output, the home can draw from the grid. A yearly production estimate can be useful for planning, but the bills are shaped by the timing of production and usage as well as the applicable billing structure.
How credits generally appear
A utility bill may show energy delivered to the home, energy sent to the grid, and credits or charges handled under the account’s rules. Ask for an example bill or written explanation for the utility and system being proposed. Do not assume a calculator or sales presentation uses the same treatment.
Utility and interconnection considerations
To use the state program, the customer must be served by Eversource, National Grid, or Unitil, and the facility must complete interconnection and meet the electric company’s requirements and Massachusetts rules. A cap allocation through MassACA may be required. The program also sets different size and facility rules, including a general 60 kW threshold for certain facilities and separate limits for solar, wind, and anaerobic-digestion facilities. Most home systems are much smaller, but the installer should document which rule applies.
Source: Mass.gov net-metering eligibility and Mass.gov net-metering guide.
Why system sizing matters
A larger system can produce more energy but may also change the project cost, eligibility, export profile, and financing. The best system size is not automatically the largest roof can hold. Compare expected production with actual usage, site limits, equipment, and the rules that apply.
Net metering versus battery storage
Net metering is a utility billing concept. A battery is physical equipment that can store energy and potentially support later use or backup. A battery may reduce some exports by shifting energy to another time, but it also adds cost and operational considerations. They should be evaluated as related but distinct choices.
Net metering FAQ
What is net metering?
Massachusetts net metering lets an eligible generating facility send excess electricity to the grid and receive credits under the applicable utility billing rules. The system must be interconnected and meet the electric company’s requirements. The credit value and account treatment depend on the project and facility type.
Which utilities are covered by Massachusetts net-metering rules?
Eversource, National Grid, and Unitil customers may qualify for the state program. Customers of municipal electric companies are not eligible for that state program and should ask their municipal utility whether it offers a separate program.
Do exported kilowatt-hours always receive full retail value?
No. Massachusetts credit treatment depends on the facility and account. The value is based on the electric company’s basic service rate, and a customer whose competitive supplier bills supply directly may not be able to use credits against that separate supply bill.
Do I need a cap allocation?
Possibly. A facility may need to apply for a cap allocation through the Massachusetts System of Assurance of Net Metering Eligibility. The answer depends on system type, size, interconnection date, and the rules that apply to the facility.
What happens when my home uses more electricity than the panels produce?
The home can draw electricity from the grid, with the meter recording the flow under the utility’s billing process. How credits and charges appear depends on the account and applicable rules.
Does net metering work during a power outage?
Net metering is not the same thing as backup power. A standard grid-tied system generally shuts off during an outage unless it includes properly configured backup equipment.