The suit was filed by the town of Barnstable, businesses, residents and the Alliance to Protect Nantucket Sound.
It states Nstar’s contract to buy electricity from Cape Wind at three times the price of out-of-state green energy providers violates federal law and would put an unfair burden on ratepayers.
The Nstar 129MW PPA was stipulated by the Massachusetts PUC when the utility was seeking to merge with Northeast Utilties. Cape Wind has another PPA with National Grid.
The suit against Massachusetts regulators, Nstar and Cape Wind said the State discriminated against out-of-state electricity companies despite their lower costs.
They argue Massachusetts regulators exceeded their authority in setting wholesale rates for the contract, an action, they argue, that is reserved for the Federal Energy Regulatory Commission. It also states Nstar’s customers’ electricity bills will increase by nearly $1 billion over the lifetime of the contract.
This is one of several lawsuits against Cape Wind. It is facing four challenges of the environmental approval it received from the Department of the Interior, which were consolidated into one proceeding before the US district court in Washington DC.
An appeal has also been lodged against the Federal Aviation Administration's determination of no hazard from the project, the fourth such ruling the project has received since 2002.
The project has been on the drawing board for 12 years. In December, Cape Wind and Siemens finalised a deal that will see the German turbine maker supply 101 of its 3.6MW turbines with an option to add another 29 units. Siemens said installation and commissioning is expected for 2016.