Onekaka Power Station

40°46′56″S 172°41′15″E / 40.78222°S 172.68750°E / -40.78222; 172.68750Dam and spillwaysType of damConcrete archHeight10 m (33 ft)Power StationOperator(s)Onekaka Energy LtdCommission dateNovember 2003Hydraulic head200 m (660 ft)TurbinesTwoInstalled capacity940 kWAnnual generation3.8 GWh

Onekaka Power Station is a small hydro-electric generating station on the Onekaka River, in Golden Bay / Mohua, New Zealand. The first power station on the river was built in 1928–29 to provide power for the Onekaka Ironworks. The original scheme included a concrete arch dam 10 m (33 ft) high, a penstock 1.25 km (0.78 mi) long, and a powerhouse containing a Boving pelton wheel, rated at 250 kW.^[1]

After the Onekaka Ironworks closed, the power station remained in operation from 1937 to 1944, generating electricity for the Golden Bay area.^[2] The scheme was abandoned in the 1950s. A group of local hydro enthusiasts began work on a rebuild in 1995,^[3] and formed a company Onekaka Energy Ltd to manage the re-development and operation of the scheme.^[4] Up to 500 litres (110 imp gal; 130 US gal) a second would be diverted from the Onekaka River,^[5] and opponents expressed concerns that a reduction in minimum flows in the river would affect the native fish, the shortjaw kōkopu.^[6]

The new scheme uses the historic concrete arch dam, but a new penstock was built on the same alignment as the original. The new penstock extends a further 180 m (200 yd), to a new powerhouse downstream from the original site. New generating equipment for the scheme was obtained from salvage of two 500 kW auxiliary hydro-generator sets that had originally been used at the Tuai Power Station, a 60 MW station built as part of the Lake Waikaremoana scheme in the 1920s. The hydraulic head of the station is 200 m (660 ft)^[7] and the rated capacity of the new generating plant is 940 kW.^[3] It was commissioned in November 2003,^[8] and produces 3.5 GWh annually. The output is sold on the New Zealand electricity market.^[3] The scheme produces 10 to 20 percent of the electricity used in Golden Bay.^[9]

One unusual feature of this power station is that it is remotely monitored and controlled using text messages via the cellular phone network.^[3]

• Onekaka Power Station
• 
  Onekaka Dam under construction in the late 1920s
• 
  Onekaka Dam in 2024
• 
  Penstock section
• 
  View of hydro-generators
• 
  Generator
• 
  Power station building

Media related to Onekaka Power Station at Wikimedia Commons
Media related to Onekaka Dam at Wikimedia Commons

• Onekaka Power Station at Nelson Marlborough Rural News