WHAT IS THE SNOWY HYDRO SCHEME?
* Hydro electricity generator using the Snowy, Eucumbene and Murrumbidgee rivers in the NSW Snowy Mountains
* Largely located in Kosciuszko National Park
* Construction started 1949, finished 1974
* Now has nine power stations with 33 turbines
* 4100MW capacity - provides about 32 per cent of all renewable energy to the east coast grid
* Jointly owned by the NSW (58 per cent), Victorian (29 per cent) and commonwealth (13 per cent) governments
WHAT'S THE SNOWY MOUNTAINS 2.0 EXPANSION?
* Four sites being looked at in a feasibility study to be finished by end of 2017
* Could build up to 27km of new tunnels
* 2000MW boost to capacity - enough to power 500,000 homes
* Could deliver power constantly for almost a week
* $1.5-2 billion price tag
* Likely to take up to seven years to build
* First major expansion of the scheme since it was completed
WHAT IS PUMPED HYDRO?
A pumped hydro scheme has two water reservoirs at different heights connected by a pipe. When power prices rise or there is low supply from other sources like solar and wind, water is released from the upper reservoir and runs through a turbine into the lower one, generating electricity as it goes. When power is cheaper, the water is pumped back up from the bottom to the top. This has the added advantage of using excess power generation.
WHERE IS IT USED NOW?
Snowy Hydro is one of three existing river-based schemes - the others are at Wivenhoe Dam in Queensland and Shoalhaven in NSW. Studies are underway into a new scheme using seawater in South Australia's Spencer Gulf and at an old mine site in Queensland. Academics say there are thousands of potential sites along the mountains of the east coast.
HOW DOES IT COMPARE TO OTHER POWER GENERATION?
Pumped hydro offers all the benefits of other baseload power sources, such as coal and gas, but much quicker, more flexibly and without the emissions. For example, a coal-fired power station can take up to 24 hours to reach full capacity, whereas pumped hydro can do it in one minute. Plus, the technology already exists and it's a fraction of the cost of battery storage.
