An ambitious state solar energy program has reached its goal four years ahead of schedule, leaving questions about whether some projects on the Vineyard still in development will remain eligible to take full advantage of the program.

Last week the state Department of Energy Resources announced that the commonwealth has received applications for 400 megawatts in solar projects, with an additional 550 megawatts under review. In response to a surge in applications, the department of energy is expecting to adopt emergency regulations to expand the program, including projects still under development. The regulations are expected to be completed by the end of the month.

Edgartown, Tisbury, West Tisbury and Chilmark all have projects in various stages of completion under the state-sponsored solar energy program.

The program creates market-based incentives through tax credits for residential, commercial, public and nonprofit groups to develop solar photovoltaic arrays across the state. The program was launched in 2010 to help meet Gov. Deval Patrick’s goal of developing 250 megawatts of solar energy by 2017.

The governor announced last month that 250 megawatts had already been installed across the state,  creating a “snowball effect” of applications.

“Applications . . . accelerated tremendously in April and May,” Dwayne Breger, director of the renewable energy division for the department of energy, said Monday. “We had to inform the industry that we did receive 400 megawatts of administratively completed applications and we needed to establish new rules with regard to how DOER would finish out the existing program and at the same time, how we are gong to bring a new program in.”

The state is also establishing new guidelines for a second round of the program, expected to begin sometime in 2014. The new round of incentives will work toward Governor Patrick’s goal of generating 1,600 megawatts of solar energy across the state by 2020.

“This extremely fast growth is not sustainable and we will be addressing that in the next phase of the program,” Mr. Breger said. “So while this is all good, we do need to be mindful that in the next phase of the program needs to be a bit more managed.”

The proposed emergency regulations require projects greater than 100 kilowatts to provide an interconnection service agreement with a local utility by June 7. The state has compiled a list according to application submission date; projects submitted after the 400-megawatt threshold was reached have been placed on a waiting list until the department of energy expands the program.

“We’re supporting projects that are real and can be installed quickly and are well into development,” Mr. Breger said.

Both Edgartown and Tisbury do not meet the test of having their projects applications ready before the 400 megawatts were completed,  but may still get in under the wire because they have interconnection service agreements with the power company Nstar. West Tisbury did have its application approved before the 400 megawatt threshold was met. Chilmark had not submitted an application yet for their projects.

The Edgartown solar array will be located at Katama Farm and near the town well off Edgewood Drive. The Tisbury solar array will go up on the town-owned former landfill site near the town park and ride. Both projects are estimated to produce 1.2 megawatts each. Aquinnah has a project that was built by the local energy cooperative Vineyard Power and completed early this year at its former town landfill.

In the wake of the state’s announcement, the Cape and Vineyard Electric Cooperative, which is overseeing the Edgartown, West Tisbury and Tisbury projects, is expediting its building permit process. CVEC project manager Ron Collins was on the Vineyard Monday to secure building permits for Edgartown and Tisbury.

Mr. Collins said the cooperative has received all necessary permits and has an interconnection service agreement with Nstar. “It’s one more attribute to show the state that the project is shovel ready,” he said. “We still believe they are very viable projects but want to take the next step in expediting the building permits to demonstrate our readiness to do work.”

The West Tisbury project at the capped landfill is planned for 883 kilowatts. Mr. Collins said he did not know the current status of the West Tisbury project.

Chilmark is also exploring building a solar array at the town landfill, a project approved by voters at the annual town meeting in April 2011. At the selectmen’s meeting last week, Vineyard Power president Richard Andre urged the board to issue a request for proposals as soon as possible.

About a year and a half ago a Chilmark resident pledged $1 million toward a Vineyard Power-sponsored 175-kilowatt project, Mr. Andre said.

“The real message is the time to act is now for the town of Chilmark and to issue an RFP if you want to participate,” he told the selectmen last week.

This story has been changed from an earlier version to correct the fact West Tisbury did complete its application in time to qualify for the tax credit.