NextEra Energy Inc., the company looking to buy Hawaiian Electric Industries for $4.3 billion, is assisting HEI on the utility’s renewable-energy plan at no charge, which has raised concern among at least two groups involved in the sale’s review.

In a document submitted to the Public Utilities Commission on Thursday, Florida-based NextEra said it will be assisting Hawaiian Electric Co. with its Power Supply Improvement Plans, 15-year renewable-energy plans the utility is required to file with the state.

“NextEra Energy has provided assistance and support to the Hawaiian Electric Companies, in a collaborative manner, with regard to technical and energy resource planning-related matters relevant to this PSIP review proceeding,” said Douglas Codiga, counsel for NextEra Energy Hawaii, in the document.

Rob Gould, spokesman for NextEra, said HECO is not paying for the collaboration from NextEra.

The two companies are separate entities until the sale closes, and the Public Utilities Commission must approve the sale before it can close. The PUC will resume hearings on the sale next month and is expected to make a decision later this year.

“It appears that NextEra Energy has, and continues to be, actively involved in the HECO Cos.’ energy resource planning,” said Nathan Nelson, general counsel for Hawaii Gas. NextEra is helping HEI with long-range plans “despite contradicting statements that it cannot undertake comprehensive resource planning until after the close of the merger,” Nelson added.

>> Draw up a 15-year plan.

>> Draft utility’s petroleum contracts.

>> Decide on liquefied natural gas sourcing.

>> Update designs for an emissions test plan.

If NextEra is assisting HEI in long-range planning, it makes it harder to evaluate the difference between the two companies’ vision of the future, said Henry Curtis, executive director of the environmental group Life of the Land.

“It is concerning from the point of view that the question for the merger proceeding is how will NextEra improve on the HECO plan,” Curtis said. “But if they write it together they have the same plan.”

NextEra has also advised HECO on recent fuel agreements. In a filing with the PUC on July 31, HECO told state regulators it has a consulting agreement with NextEra Energy to provide input on the utility’s petroleum request for proposals, liquefied natural gas sourcing and designs for an emissions test plan. The filing did not say whether HEI would pay NextEra for the assistance.

HEI entered into a merger agreement that covers HEI’s actions prior to the close of the sale. According to the agreement, HEI must get consent from NextEra prior to signing new contracts that would bind NextEra if it takes over the company and prior to buying or selling any asset worth more than $50 million.

HEI has had trouble winning the PUC’s approval of its long-range plan for renewable energy. The PUC sent HECO back to the drawing board in November for its “repeated failures to properly plan” a path to lower electrical rates using renewable energy in the utility’s Power Supply Improvement Plan.

HECO filed a plan in August 2014 laying out the utilities goals for 2030, which included lowering residential customer bills by “more than 20 percent,” getting 65 percent of its energy from renewable sources, using liquefied natural gas as a bridge fuel and tripling rooftop solar.

In NextEra’s latest filing the company said it “looks forward to continuing to work collaboratively with the Hawaiian Electric Companies to … advance the utilities’ resource planning efforts.”

Groups involved in the review said that NextEra’s collaboration with HECO on its long-range plan is odd given that NextEra hasn’t revealed much about its own plans for the utility.

NextEra has often declined to give detailed information about its plans, saying it can’t until the sale closes, said Isaac Moriwake, an attorney representing the Sierra Club of Hawaii. “I think they have a pretty substantial idea, which is why they are paying $4.3 billion,” Moriwake said.

Hearings about NextEra’s purchase of HEI will resume Feb. 1 and be held through Feb. 10. The hearings at the Neal S. Blaisdell Center will be open to the public.