Solid Energy says its efforts to upgrade Southland lignite into a higher-energy product have taken a step forward with a successful trial in the United States.

General manager for new energy Brett Gamble said joint venture partner GTL Energy had produced high-energy briquettes, reducing the moisture of New Zealand lignite by an average 65 per cent.

That had raised the energy content by about 50 per cent, turning lignite into a product on a par with Ohai coal.