A six-member House and Senate committee is trying to hammer out a compromise version of the bill.
It proposes changing the state's net metering program that allows electric customers and municipalities to sell excess solar power they generate back to the grid for credit.
Electric companies currently pay a retail rate for the energy. A proposed change would let them pay a much lower wholesale rate.
Democratic Newton Mayor Setti Warren says the change could wipe out most of the $4 million the city hopes to save over 20 years by leasing 13 municipal sites to a solar developer.