A $1 billion fund to invest in clean technology and infrastructure will be the "Kiwibank of the clean economy" and push New Zealand towards carbon neutrality by 2050, Green Party co-leader James Shaw says.

Shaw unveiled the ambitious policy on day one of the Greens' two-day annual conference in Auckland.

Speaking to a room of about 250 party faithful, Shaw said the fund would be a magnet to attract private funding and channel it towards clean projects.

CHRIS MCKEEN/STUFF Green Party co-leader James Shaw unveiled the party's Green Investment Fund policy at the party's annual conference.

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It was an extension on a policy the party unveiled in the 2014 election campaign, where increased royalties from oil and gas would be used to create a profit-oriented Green Investment Bank.

Royalties would be hiked from 46 per cent to 70 per cent.

Chris McKeen Greens Party co-leader James Shaw set a commitment to set up a $1b Green Investment Fund within the first year, if elected to Government.

Shaw said a $100m line of credit would be provided over three years, paid for by the royalty rates on drilling.

Establishing the fund would carry an upfront cost of $10m. Shaw said the Government funds would "act as a magnet" to attract private funds for investment to the tune of $1b.

The fund would have a minimum target rate of return of five per cent, but Shaw expected it to be closer to seven or eight per cent.

Chris McKeen The Green Party annual conference drew about 250 people on day one. The party has unveiled candidate billboards that feature the faces of the candidates for the first time.

It would also have the goal of reducing emissions by a million tonnes of Carbon Dioxide annually, and generate thousands of jobs.

"Not only will the fund help secure the buy-in and capital available in the private sector to achieve our climate goals, it will help create thousands of good, well-paying jobs in the regions and for Maori," Shaw said.

Modelled on similar green investment funds in the Middle East, Europe, Australia and the United States, Shaw said $1 of Government finance could attract up to $10 of private funding.

Fund directors would be independent of Government but would likely have the mandate to invest in infrastructure like renewable energy projects, sustainable agriculture, recycling and waste resource innovations and smart LED lighting in cities and towns.

It was one policy piece in a wider puzzle to make New Zealand carbon neutral by 2050.

Earlier in the year, energy spokesman Gareth Hughes launched an energy plan to make New Zealand powered by 100 per cent renewable electricity by 2030.

Last week, the party's transport spokeswoman Julie Anne Genter launched her plan to commit to an Auckland City to Airport rail system by 2021.

Shaw is expected to release the party's climate change policy closer to the September election.

HOW THE GREEN INVESTMENT FUND WORKS:

* The Government kickstarts the fund with an initial injection of $100m

* Private investors also contribute. Based on overseas funds, the Greens estimate the Government injection could generate up to $1b early on.

* The fund lends money to organisations that have strong plans to build infrastructure or other projects that help to reduce New Zealand's contribution to climate change.

* A project gets funded and built

* The organisation pays back its loan to Fund, over time. Or the Fund's stake in the project gets sold off for a profit.