A state Department of Public Utilities decision this week on Eversource’s requested rate hike may be good news for electric customers in the western Massachusetts communities, but it’s too early to tell exactly how good.

Although the DPU’s 814-page decision called for about a 30 percent reduction in the $34.7 million increase sought by the company for its western Massachusetts division, it delayed until late December its ruling on the rate design that will take effect on Jan. 1

That means it’s not simply a matter of assuming the $11.64 monthly increase that had been expected for the typical 550-killowatt residential customer will be cut by one-third, said company spokeswoman Priscilla Ress.

Instead, she said, the company will be submitting next week estimated bill impacts based on the ruling, and the DPU will rule at the end of the month on how Eversource’s increase should be allocated across all customers in eastern and western Massachusetts.

Also left undecided until then is whether the DPU will allow a proposed Monthly Minimum Reliability Contribution for solar customers. This plan came under attack by many who attended a series of public hearings, including one in Greenfield in April as devaluing energy efficiency. Eversource argued it would require those residential customers with solar-electric panels to pay their “fair share” for maintenance of its distribution equipment.

The rate case, originally filed last January, was revised in June in response to criticism that western Massachusetts customers were bearing an unfair share of the rate request — which the company had originally justified on the greater number of miles of infrastructure in the more sparsely populated portion of its territory. The revised case proposed to increase western Massachusetts rates to generate an additional $34.7 million, or about a 27 percent increase over current revenues — in two phases, effective next Jan. 1 and on Jan.1, 2019. In response to having its base revenue request cut by $10.6 million, Ress said Friday, “We’re disappointed with the deep cuts the DPU made to our rate request because we feel we provided sufficient and detailed documentation to support the total increase we requested.

“We’re pleased, though, that the DPU agreed with our plan to begin implementing measures that support building the electric grid of the future,” she added, “including electric vehicle charging station infrastructure and an energy storage pilot program that will assist the commonwealth in meeting its greenhouse gas emission reduction targets.”

The DPU’s decision allowed $45 million in investments to accelerate development of electric vehicle infrastructure to support growth of electric vehicle use in Massachusetts and approved a “Performance Based Ratemaking mechanism” to encourage the company to “find cost-reducing efficiencies, improve resiliency and customer satisfaction, make investments in advanced clean energy technologies, and reduce greenhouse gas emissions. In its second order, the DPU will also decide about the Monthly Minimum Reliability Contribution for solar customers.

Under the decision, Eversource is precluded from filing another rate case until 2022.