Net Metering in Massachusetts: How Credits Work for Solar Owners

Net metering is the billing mechanism that determines how Massachusetts electric customers with solar installations are compensated for the surplus electricity their systems send to the grid. The program is governed by the Massachusetts Department of Public Utilities (DPU) and administered through the state's regulated electric distribution companies, including Eversource, National Grid, and Unitil. Understanding how credits are calculated, carried forward, and eventually reconciled directly affects the financial return on any residential or commercial solar investment in the Commonwealth.

• Definition and Scope
• Core Mechanics or Structure
• Causal Relationships or Drivers
• Classification Boundaries
• Tradeoffs and Tensions
• Common Misconceptions
• Checklist or Steps
• Reference Table or Matrix

Definition and Scope

Net metering, as defined under Massachusetts General Laws Chapter 164, Section 138 (M.G.L. c.164 §138), is a billing arrangement that allows customers who generate electricity from a qualifying renewable energy system to receive a credit on their utility bill for any excess generation delivered to the distribution grid. The credit offsets the customer's consumption charges in subsequent billing periods.

Scope of this page: This page addresses net metering rules applicable to Massachusetts electric customers served by investor-owned utilities (Eversource Energy, National Grid, and Unitil) regulated by the DPU. Municipal light plant (MLP) territories — serving roughly 41 municipalities across the Commonwealth — operate under separate enabling authority and are not required to offer identical net metering terms. Federal net metering policy does not exist at the national level; the regulatory framework described here is entirely state-law-based. Interstate or off-grid configurations fall outside this page's coverage.

For a broader orientation to how solar generation connects to utility infrastructure, the Massachusetts Solar Energy Systems conceptual overview provides foundational context.

Core Mechanics or Structure

The Billing Cycle and Credit Calculation

Under Massachusetts net metering rules, a customer's meter tracks two flows: electricity consumed from the grid and electricity exported to the grid. The utility bills the net difference. When export exceeds import during a billing period, the resulting surplus is converted into a kilowatt-hour (kWh) credit applied to future bills.

The credit rate for Class I net metering (residential and small commercial systems up to 10 kilowatts [kW] for residential or up to 25 kW for commercial) is set at the full retail rate — meaning the customer receives credit at the same per-kWh price they would pay to purchase electricity. This retail-rate compensation is the defining economic feature that distinguishes net metering from the lower-value SMART program tariff payments.

Class II net metering covers systems between 10 kW and 60 kW. Class III covers systems between 60 kW and 2 megawatts (MW). For Class II and Class III systems, the applicable credit rate is calculated differently and may reflect a slightly lower tariff depending on the utility and rate schedule.

Credits accumulate in a kilowatt-hour bank on the customer's account and are carried forward month to month. At the end of each 12-month reconciliation period (the "annualization period"), any remaining unused credits are compensated at the utility's avoided-cost rate — a value substantially below the retail rate. This end-of-year settlement is a structural feature that incentivizes right-sizing a solar system to match annual consumption rather than dramatically over-generating.

Billing Line Items Affected

Net metering credits offset the energy supply charge and, in some utility tariff structures, a portion of the distribution charge. Fixed monthly customer charges, demand charges (where applicable), and certain grid access fees are generally not offset by net metering credits. Understanding which line items are affected is essential for accurate payback modeling.

Causal Relationships or Drivers

Legislative Mandates and Capacity Caps

The structure of Massachusetts net metering flows directly from legislative action. The Green Communities Act of 2008 (M.G.L. c.169) established net metering as a statutory right for qualifying customers and set initial aggregate capacity caps. Subsequent legislation — including An Act Relative to Solar Energy (2016) and the Next Generation Roadmap Act (2021) — lifted and restructured those caps, at various points raising the private-sector cap to 7% of a utility's 2014 peak load and the public-sector cap to 8%.

When caps are reached, the DPU has historically issued emergency cap-lift orders or new rules to accommodate growth. The Massachusetts Clean Energy Center (MassCEC) tracks statewide solar capacity and communicates with the DPU on cap status.

Grid Export and Interconnection Linkage

A customer cannot receive net metering credits without a completed interconnection agreement with the serving utility. The interconnection process (utility interconnection process in Massachusetts) gates the start of credit accrual. Delays in interconnection approval directly delay when a system begins generating bankable credits.

Rate Design as a Driver

Retail electricity rates in Massachusetts rank among the highest in the contiguous United States, with residential rates from Eversource and National Grid consistently exceeding the national average (U.S. Energy Information Administration, Electric Power Monthly). Higher retail rates amplify the financial value of retail-rate net metering credits, making the program particularly impactful in the Commonwealth relative to states with lower electricity costs.

Classification Boundaries

Massachusetts net metering distinguishes three customer classes based on system capacity, and two sector categories based on ownership type:

By System Size:
- Class I: Residential ≤ 10 kW; Non-residential ≤ 25 kW
- Class II: 25 kW < system ≤ 60 kW
- Class III: 60 kW < system ≤ 2,000 kW (2 MW)

By Sector for Cap Purposes:
- Private sector: Privately owned residential and commercial systems
- Public sector: Government, municipal, and nonprofit-owned systems

Virtual net metering — a distinct but related mechanism — allows a single generating facility to allocate credits across multiple accounts at different locations. This is the mechanism underlying community shared solar in Massachusetts, where subscribers to a remote solar array receive bill credits even though the panels are not on their property.

The regulatory context for Massachusetts solar energy systems provides statutory and DPU rulemaking history relevant to how these classifications have evolved.

Tradeoffs and Tensions

Retail-Rate Compensation vs. Cost Shift Arguments

The most contested element of Massachusetts net metering policy is whether retail-rate compensation for Class I customers constitutes a cross-subsidy — meaning non-solar customers bear a portion of grid fixed costs that solar customers avoid through bill offsets. Utility companies have repeatedly filed testimony with the DPU arguing that net metering erodes the revenue base needed to maintain grid infrastructure. Advocates counter that distributed solar generation delivers grid services (voltage support, peak shaving, transmission loss reduction) that justify full retail compensation.

This tension has produced DPU proceedings examining whether a "value of solar" tariff framework should replace simple retail-rate crediting. As of the most recent DPU dockets on this subject, Massachusetts has not moved to a value-of-solar replacement — but the debate continues to shape legislative deliberation.

Annual Settlement Asymmetry

The 12-month annualization creates an asymmetry: credits accumulated during high-production summer months are worth their full retail value when used against winter bills, but any surplus remaining at year-end is settled at avoided-cost rates — which can be 50% to 75% below retail rates depending on the utility and the year. This asymmetry penalizes systems sized to maximize annual generation without regard to load matching.

Class III Viability and Compensation Rates

For larger commercial systems in Class III, the credit structure under DPU rate schedules may not match the economic return available through the Massachusetts SMART Program, which offers a fixed per-kWh incentive tariff. Project developers frequently model both programs to determine which produces superior economics for a given system size and location, and some systems are eligible for both programs simultaneously.

Common Misconceptions

Misconception 1: Net metering credits are paid in cash.
Credits are applied as a billing offset — a reduction in future charges — not as a monetary payment. Unused credits at the end of the annualization period that are compensated at avoided-cost rates generate a small monetary credit on the account, but routine month-to-month credits are non-cash billing adjustments.

Misconception 2: Solar owners pay nothing for electricity.
Fixed monthly charges, distribution access fees, and any consumption that exceeds net metering credits are still billed normally. Net metering reduces variable energy charges, not all utility costs.

Misconception 3: Net metering applies everywhere in Massachusetts equally.
The 41 municipalities served by municipal light plants (MLPs) are not governed by DPU net metering rules. Each MLP sets its own terms. Some MLPs offer net metering with comparable retail-rate credits; others offer lower rates or impose lower capacity limits. Customers in MLP territory must review their specific municipal utility's tariff.

Misconception 4: Credits never expire.
Credits carry forward indefinitely within a 12-month cycle, but at the annualization date, unused excess is settled at avoided-cost — it does not roll into the next 12-month period at full retail value.

Misconception 5: Any solar system automatically qualifies.
A system must pass inspection under the State Electrical Code (527 CMR 12.00) and receive utility interconnection approval before credits begin accruing. Permits and inspections are prerequisites, not formalities — a system generating without interconnection approval is not eligible for net metering credits and may create grid safety issues governed by IEEE Standard 1547 for distributed energy resource interconnection.

Checklist or Steps

The following sequence describes the stages a Massachusetts customer's account passes through to receive net metering credits. This is a structural description of the process, not advisory guidance.

1. Solar system permitting — Local building and electrical permits are obtained under 780 CMR (State Building Code) and 527 CMR 12.00 (State Electrical Code).
2. Local electrical inspection — The local electrical inspector approves the installation; the Certificate of Inspection is issued.
3. Utility interconnection application — The customer or installer submits an interconnection application to the serving distribution company under DPU-approved Interconnection Standards.
4. Utility technical review — The utility conducts a feasibility review. Systems under 25 kW on circuits with available capacity typically qualify for simplified "fast-track" review.
5. Net metering service agreement execution — The utility issues and both parties execute a net metering service agreement specifying credit class and rate.
6. Bidirectional meter installation — The utility installs or programs a net meter (or a two-register meter) capable of recording both import and export.
7. Permission to Operate (PTO) issued — The utility issues PTO, authorizing the system to energize and begin export.
8. First billing cycle with credits — The customer's first utility bill reflecting net metering credits appears after the initial full billing cycle post-PTO.
9. Annual reconciliation — At the end of the 12-month annualization period, unused surplus credits are settled at the utility's avoided-cost rate.

For a broader overview of the Massachusetts solar installation and program framework, the Massachusetts Solar Authority home page provides a navigational index of related topics.

Reference Table or Matrix

Net Metering Credit Comparison by Customer Class

Key Credit Value Determinants

References

• Massachusetts General Laws Chapter 164, Section 138 – Net Metering
• Massachusetts Department of Public Utilities (DPU)
• Green Communities Act, M.G.L. c.169 (2008)
• Massachusetts Clean Energy Center (MassCEC)
• U.S. Energy Information Administration – Electric Power Monthly
• 527 CMR 12.00 – Massachusetts Electrical Code
• 780 CMR – Massachusetts State Building Code
• IEEE Standard 1547 – Interconnection and Interoperability of Distributed Energy Resources
• Eversource Energy – Net Metering Tariff Information
• National Grid Massachusetts – Net Metering