The Spanish company, Fotowatio Renewable Ventures, has a 20-year deal with the ACT government, in which it will be paid up to $7.9 million a year by ActewAGL for the energy it feeds into the grid from the 20MW Royalla farm, off the Monaro Highway at Williamsdale.

It is being paid $186 for each megawatt hour, and is expected to produce an average of 37,000 megawatt hours a year, with payments beginning last week. The maximum generation it will be paid for is 42,293 megawatt hours.

Environment Minister Simon Corbell said the cost of the Royalla solar energy to Canberra households was 25 cents per household a week.

It would produce enough electricity to power 4500 houses and save more than half a million tonnes of greenhouse gas emissions, he said.

Later in the evening, Mr Corbell spoke at a Save Solar forum which more than 300 people attended at the Queanbeyan Kangaroo Rugby League Club, in protest to the Abbott government's new renewable energy target review.

Also on Wednesday, the government approved the 13MW Mugga Lane solar farm being developed by Chinese firm Zhenfa under a similar deal to Royalla.

And bids closed for companies competing to win a deal to generate 200MW of wind power for the territory, powering 65,000 homes. The government did not say on Wednesday how many companies had bid.

The ACT government has a target of 90 per cent of its energy from renewable sources within six years, a goal Mr Corbell said he was confident he could achieve.

Renewable energy would save consumers money in the long-term and "stops them being hostage to the price rises that will inevitably come with gas or coal-fired generation," he said.

"The beauty with a project like this is once the capital cost is meant the fuel source is free, sunshine is free, and that means prices can be much more certain and much more reliable than gas or coal can ever be."

Mr Corbell said the Royalla array was a nation-leading project, the largest solar farm in the country.

"This is a real milestone event for Australia and while the federal government goes backwards, the ACT and the city of Canberra are showing how we can make the shift to a renewable energy future," he said.

Mr Corbell again slammed the federal government's review of its 20 per cent renewable energy target as "regressive and reactionary".

Fotowatio's Australia manager, Andrea Fontana, said given the high capital costs of solar it was crucial to have policy certainty.

"It's impossible to attract capital and investors' confidence without certainty and without long term policies so I would say that without the policies, without certainty, it would be just impossible to see more projects like this developed in Australia," he said.

Spain's Foreign Minister, Jose Manuel Garcia-Margallo, and Spanish ambassador Enrique Viguera attended the Royalla opening.

In the evening, there was standing room only at the Kangaroo Club in Queanbeyan, as hundreds of people turned up to show their support for local Queanbeyan solar businesses and their opposition to the Abbott government's renewable energy target review.

Representatives from multiple Queanbeyan solar companies, including solar technology organisation Dyesol, attended the meetings as well as federal and local politicians including Greens leader Christine Milne.