Solar and battery interconnection rules in Maine

Size bands and what each one obliges

The screens that decide it

• Inverter based and at or below the 1 MW insurance floor Limit 1000 kW.

  Maine publishes a full insurance table and the floor is generous for solar: an inverter based facility of 1 MW or less needs none. For a non inverter machine the floor is far lower, with none required only at or below 50 kW, then $500,000 above 50 kW to 500 kW, $1,000,000 above 500 kW to 2 MW, $2,000,000 above 2 MW to 5 MW and $3,000,000 above 5 MW.

• Export capacity under 65 percent of the shared secondary transformer rating 65 percent of service transformer rating, a figure only the utility holds.

  Maine uses 65 percent of the transformer nameplate rating on a shared secondary, measured on export capacity. That is materially more permissive than the flat 20 kilovolt-amp limits used in several other states.

• Export capacity under 15 percent of line section annual peak load 15 percent of line section peak load, a figure only the utility holds.

  Measured at the substation, and the numerator is export capacity rather than nameplate, so an export limited design is measured on the limited figure. The utility may apply the screen at every automatic sectionalizing device upstream of the facility including the substation breaker, which means passing at one point is not enough.

Ask the utility this, before you sell it

1. What is the line section minimum load and minimum daytime load, and what percentage of it would this facility represent? Maine requires the utility to disclose all three on a screen failure where available, which is a better starting point than most states give.
2. What is the export capacity of this design as you will record it? Maine measures the screens on export capacity and the insurance and review level on generating capacity, so an export limited system is measured two different ways at once.
3. Is this address served by a consumer owned utility or a cooperative? Unlike most states these rules reach them, because the definition turns on operating a transmission and distribution plant rather than on ownership.

Worth knowing before you quote

Maine bars a utility from requiring an applicant to install additional controls including a utility accessible disconnect switch, to perform or pay for additional tests, or to buy additional liability insurance beyond the published table. That disconnect prohibition is a direct contrast with Wyoming and Arkansas, which mandate one. Level 3 is the non export track for generators not greater than 10 MW and is not a size band, with a fee of $100 plus $3 per kW. There is a dedicated energy storage section requiring a standard form describing the configuration, and a dedicated export control section listing the acceptable methods. Timelines run in business days: five to completeness, ten to screen results, ten for an additional review estimate, forty five for an impact study or thirty where a feasibility study was done, and ten to issue an agreement. No aggregate cap appears in the chapter.