How it works

  • Solar panels convert sunlight into direct current (DC) electricity.
  • Electricity is sent to the inverter, where it is converted from DC electricity to alternating current (AC) electricity.
  • The AC electricity is sent to the electrical panel, where it can be moved through the home’s electric circuitry for use.
  • Your home’s electrical panel will automatically draw additional power from the utility if the solar system is unable to meet the building’s electrical demand. If the solar electric system is producing more electricity than needed, the electrical panel will send excess electricity to the utility grid through a net meter.
  • Solar electric systems have few moving parts and are designed to produce electricity for at least 20 years.

Components of a solar electric system

Solar electricity

When sunlight strikes the semiconductor material inside a solar cell, it frees electrons to form an electric current in the cell. This process converts sunlight directly into electricity. The more intense the sunlight striking the cell, the greater the amount of electricity produced. Solar cells are aggregated together to form a panel or a module. A solar array generally includes several panels wired together to achieve the desired system size. While the electricity output of the solar electric panels will slowly reduce over time, the panel manufacturer production warranty typically guarantees that by year 20, the panels will still produce at least 80% of the electricity originally produced when first installed.


Solar electric panels produce direct current (DC) power. An inverter is used to convert the DC power to alternating current (AC), the type of power supplied by electric utilities in the United States. Typically, the inverter is located near where the electric service from the local utility enters the house (close to the electrical panel). Alternatively, micro-inverters may be individually placed directly behind each panel, converting the electricity from DC to AC at the panel level. In grid-connected systems, inverters are designed to shut off automatically in the event of a power outage. This is an important safety precaution for utility workers, as the solar electric system will not restart until power has been restored to the grid. Typical inverter warranties average around 10 years for central inverters, and 25 years for micro-inverters. Central inverters usually need to be replaced once during the life of the solar electric system.

External shut-off

Massachusetts utilities require solar electric systems to have an external shut-off, often called a “disconnect,” so the power company can shut down the system when workers are fixing the power lines.


A net meter is a bidirectional meter that spins backwards when the system is producing more electricity than what is being consumed on site, and will spin forward when energy is being used from the electric grid. A second, separate meter is also required to exclusively track cumulative production from the solar electric system for the purpose of receiving the SMART incentive.

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