Massachusetts DOER issues second-round RFP for 1,000 MW of mid-duration BESS

Massachusetts's Department of Energy Resources (DOER) and the state's three electric distribution companies (EDCs) issued a request for proposals on 31 July 2026 for 1,000 MW of mid-duration battery energy storage systems - the second tranche in a staggered programme that must deliver 5,000 MW of storage capacity by 31 July 2030^[1].

What the RFP covers

The solicitation, issued jointly by DOER and the EDCs, includes a separate 250 MW-300 MW procurement target for distribution-level projects alongside the primary 1,000 MW of mid-duration BESS^[1]. Mid-duration is defined under the programme as systems capable of discharging at full rated capacity for between four and ten hours. Individual project bids must fall between 40 MW and 1,000 MW nameplate capacity, and all projects must interconnect to ISO-NE.

The three EDCs participating in the RFP are Eversource, National Grid and Unitil^[1]. Together they will be the counterparties to any long-term contracts that result from the solicitation.

Where this sits in the 5 GW programme

The procurement is the second of four scheduled rounds under Section 83E of Chapter 239 of the Acts of 2024, the comprehensive energy bill signed by Governor Maura Healey in November 2024^[1]. The law mandates that Massachusetts procure 5,000 MW of energy storage by 31 July 2030, with the capacity split across:

• 3,500 MW of mid-duration storage (four to ten hours)
• 750 MW of long-duration storage (ten to 24 hours)
• 750 MW of additional storage, subject to commercial availability at reasonable cost

The staggered schedule runs: 1,500 MW by 31 July 2025 (Round I), 1,000 MW by 31 July 2026 (Round II), 1,000 MW by 31 July 2027 (Round III), and the remainder by 31 July 2030.

Round I outcome and pending approvals

Round I closed with DOER selecting 1,268 MW across four projects in December 2025: Trimount ESS (700 MW, Jupiter Power), Energizar (250 MW, FlatIron Energy), Salt Cod (168 MW, FlatIron Energy), and River Mill Storage (Rhynland Energy). The EDCs filed long-term contracts for three of those projects with the Massachusetts Department of Public Utilities (DPU) on 2 July 2026, with DPU approval still pending.

The Round I process was not without friction. Contract negotiations ran past their original March 2026 target date, with the EDCs and counterparties ultimately targeting execution by May 2026 before the DPU filing. That slippage is a reference point for developers bidding into Round II.

What to watch

The DPU must approve the Round II RFP before bids can be formally evaluated - a procedural step that added roughly two months to the Round I timeline. Developers will be watching whether the distribution-level tranche (250-300 MW) attracts a separate bid pool or competes directly with the bulk transmission projects. The Round I experience also showed that the state will select above its headline target when the project pipeline supports it: 1,268 MW was awarded against a 1,500 MW ask. Whether Round II produces a similar overshoot depends on how many shovel-ready projects have progressed through ISO-NE interconnection studies since last year's solicitation closed.