How Net Metering Works in Massachusetts, Solar Bill Credits Explained

Net metering is the mechanism that turns the solar power your roof sends back to the grid into a credit on your electric bill. In Massachusetts, when your panels produce more than the house is using, the extra kilowatt-hours flow to your utility, and your utility credits your account at very close to the full retail price you'd otherwise pay for those same kilowatt-hours. That credit is what makes a daytime-heavy solar array pay for the kilowatt-hours you pull back at night.

People mix this up with the SMART program constantly. They're two different things, paid two different ways. SMART pays you a separate cash incentive for producing solar. Net metering credits you for the power you export. You get both, and they stack. This guide is about the net metering half, how the credit is calculated, whether it expires, the caps that almost never bite a homeowner, and the one thing that quietly disqualifies about 40 Massachusetts towns from the whole arrangement.

What net metering actually is in Massachusetts

Net metering is a billing arrangement run by your electric utility, not a check from the state. Your meter tracks energy flowing both ways. When the house draws from the grid, you're billed. When the array pushes power back, you bank a net metering credit that offsets future bills. Over a sunny month the two net out, hence "net" metering.

It is set in state law and overseen by the Department of Public Utilities (DPU) under the net metering statute (M.G.L. c. 164, §§ 138–140) and the regulation 220 CMR 18.00. That matters for one reason that trips people up: the statute binds the three investor-owned utilities , Eversource, National Grid, and Unitil, and nobody else. More on the towns that fall outside it below.

How the net metering credit is valued

A Class I solar net metering credit in Massachusetts equals 100% of your net excess kilowatt-hours multiplied by the sum of four of your utility's per-kWh charges: the basic service (supply) charge, the distribution charge, the transmission charge, and the transition charge (220 CMR 18.04). That's nearly your full retail rate, the credit covers both the supply side and most of the delivery side of the bill, which is why solar economics in Massachusetts hold up.

That "almost full retail" point is the part installers compress into "1-to-1." It's close, but the credit is built from a specific stack of charges, not a flat multiplier:

Bill component	Counted in the credit?
Basic service / supply (kWh)	Yes
Distribution (kWh)	Yes
Transmission (kWh)	Yes
Transition (kWh)	Yes
Fixed monthly customer charge	No, you pay it regardless

The fixed customer charge is the catch worth naming: net metering can zero out your usage charges, but the flat monthly connection fee stays. Even a homeowner who exports more than they use still gets a small bill.

For scale, the average Massachusetts residential retail electricity price was 30.21 cents per kWh in March 2026 (U.S. Energy Information Administration). Your net metering credit tracks most of that number, so every exported kilowatt-hour is worth real money, far more than the wholesale rate a power plant would get for the same electron.

Net metering vs. SMART, the two halves of the math

Both apply to the same array. Net metering credits your exported power on your bill; SMART pays a separate per-kWh incentive for everything your system generates. Here's the split:

	Net metering	SMART
What it pays for	kWh you export to the grid	every kWh the system generates
Who pays	your utility (bill credit)	the state program via the utilities (cash)
Value	~retail rate (four-charge sum)	a fixed block rate, set at enrollment
Duration	as long as you net meter	10 years
MLP towns	not covered	not covered

We don't re-derive the SMART block rates here, that's its own beast. See the Massachusetts SMART program blocks explained for the production-incentive side, and the full sticker-price picture in solar installation cost in Massachusetts.

Class I, II, or III, which one is your house?

Massachusetts sorts net metering facilities into three classes by size. Nearly every home is Class I.

Class	Size	Typical owner
Class I	up to 60 kW	residential rooftop, small commercial
Class II	over 60 kW to 1 MW (solar/wind/ag)	larger commercial, farms
Class III	over 1 MW to 2 MW (solar/wind/ag)	utility-scale, big institutions

A normal 5–12 kW home array sits comfortably inside Class I, which is the class that earns the full four-charge retail-style credit. You don't pick your class; your nameplate capacity decides it.

Do net metering credits expire? What happens to leftover credit

Net metering credits in Massachusetts carry forward month to month indefinitely, they don't expire at year-end the way some states' do (220 CMR 18.00). A New England array overproduces in June and underproduces in December, so the credits you bank over a Massachusetts summer are designed to carry you through the dark months. Sizing a system to roughly match your annual usage lets the surplus and deficit cancel across the year.

The reason most installers size to about 100% of annual usage rather than oversizing: a banked credit is worth its full value only while you have usage to apply it against. There's no advantage to building a permanent credit pile you never draw down. Match your consumption and the credits do their job.

The net metering caps, and why they rarely matter to you

Massachusetts limits how much net metering capacity each utility carries. The aggregate cap is 7% of the distribution company's highest historical peak load for private facilities and 8% for public (municipal and governmental) facilities (220 CMR 18.07). Those caps occasionally make headlines for large commercial projects, but a homeowner almost never runs into them, because small systems are exempt from the count entirely.

The DPU raised the cap-exemption threshold from 10 kW to 25 kW, so facilities of 25 kW-AC or less net meter without securing a cap allocation at all (Mass.gov DPU; MassACA). Private systems larger than 25 kW that serve on-site load are also exempt if their interconnection agreement is dated on or after January 1, 2021. In plain terms: your house-sized array doesn't have to fight for a slot. The cap is a commercial-scale concern.

The year-25 cliff most people never hear about

A Class I solar facility earns the full retail-style net metering credit for 25 years from interconnection authorization, after which the credit drops to the average monthly ISO-New England clearing price, the wholesale market rate (220 CMR 18.04). That's a steep haircut from the retail-grade credit, but it lands well past the typical payback window and past most panel warranties, so it rarely changes the buying decision. It's just worth knowing the retail-rate credit isn't literally forever.

MLP towns: why net metering may not apply to you

The Massachusetts net metering statute binds only the investor-owned utilities, Eversource, National Grid, and Unitil. If your electricity comes from one of the roughly 40 Municipal Light Plant (MLP) towns , Belmont, Concord, Reading, Wellesley, Hingham, Norwood, Taunton, Peabody, Holyoke, and the rest, the state net metering rules don't apply to you. Your town utility sets its own solar buy-back policy.

Some MLPs run genuinely good programs; others credit exports at a rate well below retail, which lengthens payback. There's no statewide rule , you have to read your specific MLP's solar policy. The same towns are also excluded from Mass Save, which we cover in MLP towns and the no-Mass-Save problem. If you're weighing a shared-array subscription instead of rooftop, group net metering credits are how community solar in Massachusetts distributes value, and those credits also flow only through the investor-owned utilities.

Before you get a rooftop quote, confirm which utility serves your address. A solar contractor who quotes you full-retail net metering revenue while you're on an MLP is quoting a number that doesn't exist for your house. Browse vetted installers on the solar installation hub.

FAQ

Is Massachusetts net metering 1-to-1? Effectively close. A Class I solar credit equals 100% of your net excess kWh times the sum of four utility charges, supply, distribution, transmission, and transition (220 CMR 18.04). That's nearly the full retail rate, but the flat monthly customer charge is never offset, so it's not a perfect 1-to-1 on the total bill.

Do my solar credits expire at the end of the year? No. Massachusetts net metering credits carry forward month to month indefinitely. Summer surplus is meant to bank against winter shortfall.

What's the difference between net metering and SMART? Net metering credits the power you export to the grid, on your utility bill, at roughly retail value. SMART is a separate state incentive that pays a fixed per-kWh rate on everything your system generates for 10 years. You get both, and they stack.

Does net metering apply if I live in a municipal-light-plant town? No. The state net metering statute covers only Eversource, National Grid, and Unitil. About 40 MLP towns set their own solar buy-back policies, which range from good to well below retail. Check your town utility.

Is there a size cap on my home solar system for net metering? Functionally no for a house. Systems of 25 kW-AC or less are exempt from the aggregate net metering cap, and a typical home array is far smaller. The 7% (private) and 8% (public) caps apply to large commercial and public projects, not rooftops.

How much is a net metering credit worth per kilowatt-hour? It tracks your utility's retail charges rather than a fixed published number. For scale, the average Massachusetts residential retail price was 30.21 cents per kWh in March 2026 (EIA); your credit covers most of that. For your exact value, ask your installer to run it against your current utility tariff.