Interconnection (of Solar and Battery Energy Storage) and Net Metering

Interconnection

Note: Within the WMLP's service territory, customers cannot purchase or buy the solar energy output (e.g., on a $ per kWh basis) from installer- or other third party-owned systems (i.e., through power purchase agreements or "PPAs").  Customers can either purchase outright or lease a solar system (e.g., not based on the solar energy output) and use its energy output.

1. Review the process and requirements for interconnecting a power-generating facility (e.g., solar and battery energy storage) in the WMLP's Policy on Interconnection with Distributed Generation (this document also contains the application forms).
   1. The WMLP requires that the utility meter be (re)located, if not already, outside of the house or building in a location accessible by WMLP and Fire Department personnel.  The AC disconnect and if applicable, solar production meter, must also be located outside of the house or building in close proximity to the utility meter.
2.  Complete and submit the appropriate Interconnection Application and Agreement to the WMLP's Infrastructure Engineer, Alvaro Sosa at asosa@wellesleyma.gov and Assistant Director, Chris Chan at cchan@wellesleyma.gov. Please also submit site and rooftop plans showing the locations of the solar panels/modules, inverters, AC disconnect, utility and solar production meters, electrical service panels, and per unit module, per unit inverter, and total system design capacities (kW-DC and kW-AC); electrical one-line diagram; and equipment specification or cut sheets.
   1. Simplified Process application: For an inverter-based facility with a power rating of 10 kW-AC or less on a single-phase circuit or 25 kW-AC or less on a three-phase circuit
   2. Standard Process application: For a facility that does not qualify under the Simplified Process
3. If the facility is or includes battery storage, complete and submit the Backup Supplemental Form for Battery Storage
   1. For co-located solar and battery storage facilities, the combined design peak/maximum power outputs (kW-AC) of both the solar inverter(s) and battery inverter(s) govern whether the facility should fall under the Simplified or Standard process and is eligible for net metering.
   2. Subject to WMLP review and approval, battery storage systems can generally charge from and export to the grid.  However, DC-coupled solar and battery storage systems (i.e., that share a common inverter) may not be able to charge from the grid, particularly if the customer is participating in the WMLP's solar rebate program.
   3. The battery storage system must be able to automatically disconnect from the grid in the event of an outage.
4. Upon approval of your Interconnection Application, the WMLP will issue an Approval to Install.
5. For information on the WMLP's solar rebate program, please visit the WMLP's Go Solar webpage.
   1. Residential and small general service customer-owned (not leased) systems are eligible for the rebate.
   2. Rebate applications should be submitted after receiving our Approval to Install but before commencing installation.
6. After completing installation, the facility shall NOT be placed in service (i.e., shall be left off):
   1. Schedule final building and electrical permit inspections with the Town's Building Department.
   2. Schedule a witness test/inspection with the WMLP.
7. After successful witness testing, the WMLP will issue an Authorization to Operate.

Net Metering

• For solar system installations that are granted Approval to Operate by the WMLP after July 8, 2024, the WMLP provides residential and small general service customers a bill credit for excess solar generation exported to its system at the wholesale electric supply rate (see the WMLP's Solar Net Metering Rate Schedule SP-1), provided the system has a nameplate capacity equal to or less than 15 kW-alternating current (AC).
• For solar system installations that were granted Approval to Operate before July 8, 2024, the WMLP provides residential customers a bill credit for excess solar generation exported to its system at full-retail value, provided the system has a nameplate capacity equal to or less than 25 kW-AC.