Maine has seen a surge in proposed community solar farms, but they are encountering a serious obstacle: an aging grid that requires expensive upgrades to connect more sources of power to New England homes and businesses, putting the state’s clean energy transition at risk.

Maine passed legislation in 2019 to boost community solar development with generous fossil-fuel based incentives for developers and a billing program that allows customers to offset their electric bills.

Formerly net energy billing was reserved for smaller projects, such as rooftop solar, but under this legislation it was expanded to larger projects generating up to 5 megawatts.

Developers flocked to the state from across New England and the country to build community solar farms that customers can subscribe to in order to save on their electricity bill. But first developers have to get approval from Maine’s utilities — Versant Power and Central Maine Power — to connect to the grid.

Interconnection is the process by which electricity generated by solar arrays and other types of renewable energy is added to the network of power lines. The developers must pay to upgrade these distribution systems or else withdraw projects that become too expensive or unfeasible.

Over the last four years, 482 solar projects asked Maine’s two biggest utilities to connect to the grid but eventually withdrew their requests, according to data provided by the utilities.

Solar projects might withdraw their requests to connect to the grid for a number of reasons, and some may even relocate and request for interconnection again. But often they withdraw because it’s too expensive to upgrade distribution lines and systems.

The state has ambitious climate goals and aims to be powered by 80 percent clean energy by 2030. But with more than 785 community solar projects in various stages of development — in addition to other initiatives to eliminate carbon emissions such as by encouraging the use of electric vehicles and heat pumps — developers, utilities and transmission experts said an antiquated grid is posing a significant challenge in transitioning the state’s power sources to renewable energy.

“We have a serious problem, and this is an unfortunate byproduct of the net-energy policy that wasn’t fully understood or vetted, because we didn’t know how many projects would come forward,” said Bill Harwood, the Maine public advocate, who represents customers. “The grid wasn’t designed to take on that much generation.”

How much more capacity is needed?

“The grid would need to be expanded probably as much as three to four times the size of the current system to facilitate the clean energy transition,” said Richard Silkman, an expert on the regulation of utilities, the founder of GridSolar LLC and a founding partner of Competitive Energy Services, an energy consultancy.

There are relatively few locations to accommodate solar projects, and many are trying to connect near each other, which poses a technical challenge, Harwood said. Overloading the grid beyond its capacity could result in short circuits compromising the safety of the grid and the public, according to utilities.

Bartlett said an ideal community solar program would offer developers incentives to target sites on the grid that have more capacity and provide the most benefit. Currently, developers don’t always know ahead of time if a location is going to be feasible.

Utilities and transmission experts say that the distribution system’s smaller poles and wires cannot handle a two-way power flow and that it was originally designed for energy to only flow one way: from the generators to the rest of the system. But electricity produced by community solar farms joins a system where power is already flowing.

In a letter to the Maine Legislature in February 2021, Central Maine Power said the large volume of power on the distribution system requires new engineering designs and investments to accommodate “a potential reversal of that traditional one-way power flow.” It also notified developers in 2021 that many solar projects were leading to technical problems at substations and could result in expensive upgrades that developers would have to pay for.

In comparison, Maine’s smaller, consumer-owned utilities have restricted the total size of all the projects they connect. Their overall limit is 100 kilowatts to avoid overloading their systems.

The utility currently has 25 solar projects producing less than 100 kilowatts connected to its system.

Community solar projects under the initial community solar program defined by the Maine Legislature were meant to generate up to 5 megawatts each. Lawmakers later changed the program to reduce the size of these projects to just under 2 megawatts. The new rules may also have led some developers to withdraw their connection requests to modify their projects to meet the new project limit, Long said.

Smaller, distribution-level projects, such as community solar farms, only require approval to connect to the grid from the larger utilities, Versant Power or Central Maine Power. But larger, utility-scale solar and other renewable energy projects typically require approval to connect from the grid operator, ISO-New England, which has seen an increase in withdrawals over about the last decade.

From 2015 to 2021, 26 utility-scale power projects based in Maine were approved to connect to the ISO-New England grid, and 82 withdrew, based on national interconnection queue data compiled and analyzed by the Berkeley Lab in California. In the preceding seven years, from 2008 to 2014, 50 were approved to connect, and 46 withdrew.

Even for larger projects, such as utility-scale solar and wind farms, developers are responsible for the costs of upgrading and connecting their projects to the system, according to Kakley.

While some argue that developers shouldn’t have to bear the entire cost of upgrading grid infrastructure to connect projects, others point out that they are already receiving government-funded incentives to do so.