The Bob Brown Foundation has demanded the government answer the $3.5 billion question about Marinus Link: who will pay for it?
The Bass Strait interconnector received a multimillion boost in the federal budget this week to help advance the design and approval phase.
But BBF director Christine Milne said the announcement failed to "answer the fundamental question" about who would shoulder the $3.5 billion cost.
"None of the other states are interested in paying as this project is unnecessary. Battery technology has already leapfrogged Battery of the Nation."
Her comments follow the release of a report commissioned by the BBF that showed Project Marinus and Battery of the Nation were not necessary for other states to transition to 100 per cent renewables because they could use battery technology instead.
"Stakeholders know that by 2030, more cost effective alternatives will serve the NEM (National Electricity Market) and no one is interested in subsidising an extension cord across Bass Strait for the benefit of multinational corporations owned offshore," Ms Milne said.
The largest battery current in the NEM is the Hornsdale Power Reserve in South Australia, however, it can only hold power for an hour or so.
A spokesperson for the Minister for Energy and Emissions Reduction Angus Taylor said Marinus Link was "critical transmission infrastructure" and would "ensure the reliability, security and affordability of the National Electricity Market".
"Delivering Marinus is the course of action recommended by the Australian Energy Market Operator," they said.
"Marinus will unlock Tasmania's Battery of the Nation pumped hydro capacity, which provides a significant opportunity to deliver long duration storage and dispatchable renewable supply throughout the NEM, putting downward pressure on prices and ensuring continued reliability of our energy system."
Hydo Tasmania's project director for Battery of the Nation, Chris Gwynne, said the NEM will need a variety of storage technologies "to manage grid reliability, stability and affordability as the market transitions over the coming decades".
"Batteries will be critical in the future power system, but they won't be able to do it all," he said.
"We will need technology like pumped hydro to provide longer duration storages from the late 2020s onwards."
Mr Gwynne said Hydro Tasmania's modelling showed there increasing renewable energy sources were driving the growing need "for deep storages in the future energy system".
He said the latest technology cost analysis "confirms the continued cost competitive nature" of developing Marinus and pumped hydro.
"Even with aggressive battery and gas fuel costs (much lower than current assumptions), the Tasmanian opportunities, which also consider the cost of interconnection and transmission, are still the most cost competitive," he said.