Hydro generation accounts for around 65% of New Zealand’s total electricity production and is common in New Zealand due to our geographic advantages of high rainfall and steep rivers.
Hydro generation is the conversion of the energy from water, collected at height and released through a turbine and generator to produce electricity. Many small hydro power stations are 'run-of-river' and can only generate when there is water available but by adding storage reservoirs, water flows can be controlled for use when the electricity is most wanted. The ability of hydro to change its power output quickly and to store water for later generation means that it is very useful in balancing the variability of other renewable generation (such as solar PV and wind) or coping with changes in demand from electricity users.
MainPower is investigating a number of small hydro power stations, particularly where they have additional benefits to the network and dual use of the water (e.g. in combination with farm irrigation). While there are many opportunities for hydro power installations throughout North Canterbury, these have to be balanced against the increasing environmental pressures on our waterways.
MainPower’s first power station is at Cleardale on the north flank of Mount Hutt near the Rakaia River. The power station was constructed in 2010 and operates 24hrs a day, seven days a week, to produce around 4 million kWh's each year, enough energy for around 500 homes. To produce this, the station diverts up to 450 l/s (litres per second) from the upper reaches of Little River and transports it 2.3 kilometres via a buried pipeline to the power station, at which point the water pressure is around 30 bar (300m).
At the power station, the water is injected into a pelton wheel turbine rotating at 1000 rpm (revolutions per minute), which converts the energy into electricity via a 1 MegaWatt generator. Some water is diverted to a nearby irrigation scheme with the remainder discharged back into Little River.