Rhode Island’s solar industry is having growing pains as a popular incentive program has been halted after reaching its annual limit.

To the surprise of solar installers and their customers, the Renewable Energy Growth Program, or REG, was abruptly halted last week.

“This is slowing down our business as the REG was the preferred option for homeowners,” said Doug Sabetti, owner of North Kingstown-based Newport Solar.

Other installers, such as RGS Energy, notified customers who signed up for REG that they would have to wait until next spring for new solar panels.

“This is very disappointing for you. It is very disappointing for us as we will bear the cost of keeping our construction crews employed until April,” RGS Energy wrote in an email to customers.

REG offers fixed pricing for a fixed term for new residential and commercial solar installations. The residential, or small-solar program, is popular with solar installers and was recently extended by the General Assembly until 2029. It’s promoted through the discount Solarize program and due to its success other states have copied the program.

For the first time since it began in 2015 — it was a slightly different incentive between 2011 and 2014 — REG maxed out its allocation for the year. The program is administered by National Grid and the annual 40-megawatt allocation, divided over four enrollment windows, will open next March or April.

Solar installers were unaware that REG was reaching its limit and were caught off guard by the news that the program was halted. They are also dismayed that the legislation didn’t increase the annual 40-megawatt allowance.

National Grid told ecoRI News that it can’t be blamed for the shortfall, as the state Distributed Generation Contracts Board (DG board) sets the annual caps. A member of the DG board told ecoRI News that the cap limit is a positive development.

“We on the DG board fully expect that some megawatt allocations will be over subscribed while others may be undersubscribed,” DG board chair Kenneth Payne said.

Nations Grid said REG has been popular, with more than 900 solar projects approved in 2017.

Payne and the state Office of Energy Resources (OER) said a portion of unsubscribed megawatts from the commercial REG program may be available for the oversubscribed residential program. But installers believe it won’t meet demand.

OER is also encouraging installers to offer customers grants from the state Renewable Energy Fund. The grants typically cover up to 25 percent of the cost of a new solar array, up to about $8,000. The federal 30 percent tax credit is also still available.