Massachusetts Guide

Massachusetts Commercial Solar Interconnection: A 2026 Guide

Ferrius Energy · 2026-09-24 · 13 min read · Last reviewed September 2026

In Massachusetts, the utility interconnection process often takes longer than building the solar system. For a commercial owner facing a federal placed-in-service deadline, it is the part of the schedule that deserves the most attention and gets the least.

The short answer

Commercial solar in Massachusetts interconnects under each utility's DPU-approved Standards for Interconnection of Distributed Generation tariff, through one of three paths: Simplified (inverter systems of 25 kW or less on lightly loaded circuits, 25 business days maximum), Expedited (systems that pass the utility's screens, 45 to 65 business days), or Standard (everything else, 135 business days or more, with 200 or more for complex projects). Projects in a congested area may be pulled into a group study, and in some areas pay a per-kW Capital Investment Project fee. Timelines stop whenever the utility is waiting on the customer, and utility construction comes after all of this.

The rules: one model tariff, three utilities

Interconnection of distributed generation in Massachusetts is regulated by the Department of Public Utilities. Each investor-owned distribution company files its own Standards for Interconnection of Distributed Generation tariff, built from a common model tariff the DPU oversees. The three companies are NSTAR Electric d/b/a Eversource Energy, Massachusetts Electric d/b/a National Grid, and Fitchburg Gas and Electric Light d/b/a Unitil. Municipal light plants set their own rules and are outside this guide.

Before a system operates in parallel with the grid, the owner must have an executed Interconnection Service Agreement and a written Authorization to Connect from the utility. Every new generating source, regardless of ownership or technology, has to apply and pay the applicable fee.

The tariff changed in 2026. The Interconnection Implementation Review Group, a stakeholder body established by the DPU, filed proposed revisions in March 2025, and the DPU opened D.P.U. 25-48 to review them. According to the Commonwealth's interconnection page, the DPU approved revised interconnection tariffs for all three utilities in April 2026. Eversource's current tariff, M.D.P.U. No. 55G, took effect August 20, 2026. The figures in this guide are taken from that tariff; National Grid and Unitil tariffs follow the same model but should be checked directly.

Simplified, Expedited, and Standard

The tariff defines three paths. Which one a project takes depends on size, equipment, the type of distribution circuit, and whether it passes a series of technical screens.

Simplified

For listed inverter-based facilities of 25 kW or less on single-phase or three-phase secondary service, on a radial circuit where aggregate generation is less than 15 percent of the feeder's annual peak load. Raising this threshold from 15 kW to 25 kW was one of the consensus changes in D.P.U. 25-48. Few commercial systems fit here, but small carports and pilot installations can.

Expedited

For listed facilities on radial circuits that pass the utility's initial screens. The utility runs the full screening methodology and may do internal studies at no extra charge. If the project fails a screen, it goes to Supplemental Review or to the Standard Process. Even a project that passes every screen can still require minor system modifications, which are identified and priced in the Interconnection Service Agreement.

Standard

For everything that does not qualify for Simplified or Expedited, and for all facilities on area network systems, which are common in dense downtown areas. The Standard Process includes an initial review and, where needed, an impact study and a detailed study, paid at actual cost. Owners who know their project will not pass Expedited screens can go straight to Standard.

Pre-Application Report. Any facility of 250 kW or more must request and receive a Pre-Application Report before filing an Expedited or Standard application. Smaller projects may request one. It is the cheapest early look at what the circuit can take, and it should be done before design is frozen.

Timelines

Maximum utility time frames and fees

The tariff sets maximum time frames for each utility step, measured in utility business days. They are ceilings for the utility's own work, not a promise of a total schedule: the clock stops whenever the utility is waiting on information from the customer or an affected system operator, and utility construction of any system modifications happens afterward on a schedule set by mutual agreement.

Maximum utility time frames and application fees, Eversource M.D.P.U. No. 55G (effective August 20, 2026). Business days. Confirm the current tariff for your utility.
Path	Total maximum days	Application fee	Study costs
Simplified	25 (30 if Screen 5 fails)	$100 up to 3 kW, $300 above	None
Expedited	45 (65 with Supplemental Review)	$4.50/kW, $300 minimum, $7,500 maximum	Supplemental Review up to 30 engineering hours at $150/hr ($4,500 maximum)
Standard	135 (160 if the application started in Expedited)	$4.50/kW, $300 minimum, $7,500 maximum	Impact and detailed studies at actual cost
Standard, complex projects	200 or more, as determined by required system modifications	$4.50/kW, $300 minimum, $7,500 maximum	Actual cost

Two other points matter for larger projects. ISO New England requires its own system impact study for facilities, or groups of facilities, of 5 MW or more, and may require one above 1 MW; the tariff time frames pause during that study. And for Expedited and Standard projects, if construction does not begin within twelve months of signing the Interconnection Service Agreement, the utility may require further action under the tariff, so the ISA date starts its own clock.

Group studies

Where several applications land in the same part of the grid, studying them one at a time produces a queue in which each project waits for the one ahead and may be assigned the upgrades that the next project also needs. The DPU's answer, first established in D.P.U. 17-164, is the group study.

Under the current tariff, the utility may form a group whenever it receives more than one Expedited or Standard application in a common study area. The mechanics, all in business days:

Group window. The utility accepts completed applications in the area for up to 40 days after the first group notification. An application not deemed complete within the window is left out.
Scoping meeting. Held within 20 days of the window closing or the required reviews finishing, whichever is later.
Commitment. Members have 10 days after scoping to confirm they are proceeding, or the application is deemed withdrawn. Members then have 5 days to opt into an Extended Group Study, which requires unanimous consent and produces a tighter cost estimate of plus or minus 15 percent.
Agreement and payment. The utility issues the group study agreement within 15 days; members have 15 days to sign and pay. The study does not start until everyone has paid.
Study duration. 100 days for three or fewer applications totaling 10 MW or less with estimated modifications under $1.5 million; 125 days for up to five applications and 25 MW; 160 days for anything larger or with $1.5 million or more of modifications.

Group membership creates shared risk. If a member drops out and the study must be revised, the remaining members pay for the restudy and any increase in common system modification costs, and payments from a departing member are non-refundable. Project changes and time frame extensions that affect other members generally need group consent.

Group study exemption

The 2026 tariff adds a path out for smaller projects. An Expedited project that passes all initial screens and needs no material system modifications may be treated as exempt and proceed on its own, though it still pays any applicable common fees, including approved CIP fees, and the utility can move it back into the group for engineering or reliability reasons. For a well-sited commercial rooftop system, this exemption can be the difference between months and a year or more.

Capital Investment Projects and long-term planning

Group studies solve the sequencing problem but not the cost problem. When a substation or a line needs a multimillion-dollar upgrade to host more solar, the first projects in line can be asked to pay for capacity that later projects will use. The DPU's response was the Provisional System Planning Program, established in D.P.U. 20-75-B.

Under the provisional program, a utility can propose a Capital Investment Project for an area with heavy interconnection demand. If the DPU approves it, interconnecting customers pay a pro-rata CIP fee per kW rather than the full cost of the upgrade, and ratepayers fund a portion through a reconciling charge recovered over 20 years. The framework applies where upgrades result in a cost to interconnecting customers of $500 per kW or less. Fees apply to facilities over 25 kW.

The fees are material. National Grid's Provisional System Planning tariff, effective March 28, 2025, sets fees for four CIPs in central and western Massachusetts:

National Grid CIP fees under M.D.P.U. No. 1577, per kW of facility export capacity, each plus or minus 25 percent.
Capital Investment Project	Fee per kW
Gardner to Winchendon	$327.09
Monson, Palmer, Longmeadow (East)	$432.70
Spencer to Rutland	$558.47
Barre to Athol	$617.71

On a 1 MW AC project, a $432.70 per kW fee is roughly $430,000, before any project-specific upgrades. Eversource has its own CIPs, and additional CIP petitions have been docketed at the DPU. If your site is in or near a CIP area, the fee belongs in the pro forma from the first draft.

Status in 2026: confirm before relying on it

The provisional program was designed as a bridge. The utilities have proposed a permanent Long-Term System Planning Process, filed under their Electric Sector Modernization Plans, which would introduce a Proactive Hosting Capacity fee. That proposal is pending as D.P.U. 25-20, which was still listed as an open docket at the end of June 2026. A separate joint petition to add a Common System Modification Fee to the model tariff, D.P.U. 26-57, was also open. We could not confirm a final order in either as of this writing. Confirm the current status with your utility and the DPU file room before assuming which cost framework applies to your project.

Eversource, National Grid, and Unitil

All three utilities follow the same model tariff, time frames, and fee structure, but the experience differs in practice.

Eversource publishes separate hosting capacity maps for its eastern and western territories and posts information on its distribution group studies.
National Grid publishes interconnection documents and its System Data Portal hosting capacity map online. Its four CIPs above are all in its territory.
Unitil serves a small territory around Fitchburg. It filed its own revised interconnection tariff under D.P.U. 25-48 in 2026 and publishes a hosting capacity map.

Each utility reports interconnection data to the Commonwealth monthly and hosts regular interconnection workshops. The practical differences are in queue depth on the specific feeder and substation serving your site, which the hosting capacity maps and a Pre-Application Report will tell you more about than any general comparison. Two buildings a mile apart can face very different outcomes.

Interconnection and the 2027 tax deadline

Under Section 48E, solar facilities that began construction on or before July 4, 2026 are not subject to the 2027 placed-in-service deadline (subject to continuity rules). Facilities beginning construction after July 4, 2026 must be placed in service by December 31, 2027.

For a project starting now, that deadline runs straight through the process above. A Standard Process project with a 135 business day maximum study period, followed by utility construction of system modifications, can consume most of the remaining window before a single module goes on the roof. A project pulled into a group study can lose more. That is why the interconnection application is the first task on our schedule, not a paperwork step after design. Our Section 48E guide explains the credit rules in detail; confirm your position with a tax adviser.

What owners can do

Check the hosting capacity map first. It is free and it tells you whether your feeder is constrained before you spend on design.
Request a Pre-Application Report early. Required at 250 kW and above, useful below it.
Size to the grid, not just the roof. Where export capacity is limited, an export-limited design or a smaller AC rating can move a project from Standard to Expedited, or make it eligible for the group study exemption. Storage can also reduce export at peak.
Submit a complete application. The completeness review is 10 business days, and an incomplete application restarts the clock and can cost a place in a group window.
Answer utility requests fast. Every day the utility waits on the customer is a day added to the schedule and not counted against the utility.
Budget for fees and upgrades separately. Carry application fees, study costs, any CIP fee, and a system modification allowance as distinct lines.
Avoid late design changes. A change the utility deems significant sends the project to the back of the queue with a new application.
Watch the ISA clock. Plan to start construction within twelve months of signing.

We handle interconnection applications and utility coordination as part of our commercial solar work in Massachusetts, and we look at hosting capacity before a layout is drawn. If you want an early read on a specific site, send us the address and a recent utility bill.

Key takeaway. In Massachusetts, interconnection is a schedule risk and a cost risk at the same time. Know your path, know whether you are near a CIP or a group study, and start the utility process before design is final.

Published 2026-09-24 by Ferrius Energy LLC, a commercial solar EPC headquartered in Saugus, Massachusetts. Tariff figures are from Eversource M.D.P.U. No. 55G and National Grid M.D.P.U. No. 1577 as published at the time of writing. Tariffs, CIP fees, and DPU proceedings change; confirm current terms with your utility and the DPU.

Sources

NSTAR Electric d/b/a Eversource Energy, Standards for Interconnection of Distributed Generation, M.D.P.U. No. 55G. eversource.com
Massachusetts Electric d/b/a National Grid, Provisional System Planning Program tariff, M.D.P.U. No. 1577. nationalgridus.com
Commonwealth of Massachusetts, Utility Interconnection in Massachusetts. mass.gov
Massachusetts DPU, D.P.U. 25-48 Hearing Officer Memorandum. mass.gov
Massachusetts DPU, presentation on interconnection cost allocation (i2X, October 2025). lbl.gov
Unitil, Fitchburg Gas and Electric Light Company Open Dockets as of June 29, 2026. unitil.com
Eversource, Distribution Group Studies (Massachusetts). eversource.com
26 U.S.C. Section 48E, Clean Electricity Investment Credit. uscode.house.gov

Questions

Frequently asked questions

How long does commercial solar interconnection take in Massachusetts?

The tariff sets maximum utility time frames of 45 business days for Expedited projects (65 with Supplemental Review), 135 for Standard projects, and 200 or more for complex projects. Group studies add 100 to 160 business days. The clock stops while the utility waits on the customer, and utility construction of any upgrades comes afterward, so total time to Permission to Operate is usually longer.

What does it cost to apply for interconnection in Massachusetts?

Under Eversource's current tariff, Expedited and Standard applications cost $4.50 per kW with a $300 minimum and $7,500 maximum. Supplemental Review is up to 30 engineering hours at $150 per hour, and impact and detailed studies are billed at actual cost. System modifications and any Capital Investment Project fee are additional.

What is a CIP fee in Massachusetts?

A Capital Investment Project fee is a per-kW charge paid by distributed generation over 25 kW in an area where the DPU has approved a shared grid upgrade under the Provisional System Planning Program. National Grid's four approved CIPs carry fees from $327.09 to $617.71 per kW, each plus or minus 25 percent. A permanent long-term planning framework is pending at the DPU, so confirm current status with your utility.

Can my project avoid a group study?

Possibly. Under the 2026 tariff, an Expedited project that passes all initial screens and needs no material system modifications may be exempt and proceed independently, though it still pays applicable common fees such as CIP fees. Sizing the AC output or limiting export to fit the circuit can help a project qualify.

Do I need a Pre-Application Report?

Yes if the facility is 250 kW or larger: the tariff requires one before an Expedited or Standard application. Below 250 kW it is optional but useful, because it shows circuit conditions before the design is finalized.

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