Hydroelectric power in New Zealand
Hydroelectric power in New Zealand has been a part of the country's energy system for over 100 years and continues to provide more than half of the country's electricity needs. Hydroelectricity is the primary source of renewable energy in New Zealand. Power is generated the most in the South Island and is used most in the North Island. Early schemes such as the Waipori scheme commissioned in 1903 and the Lake Coleridge power station commissioned in 1914 established New Zealand's use of renewable hydro energy. By the early 1950s, over of installed  capacity was from hydro energy. By the early 1960s, most North Island hydro sites had been developed while the South Island still had many potential sites. The commissioning of the HVDC Inter-Island link in 1965 made it possible to send large amounts of electricity between the two islands, and from that time hydro capacity in the South Island increased rapidly. Major developments included the 540 MW Benmore Power Station (1966), the 700 MW Manapouri power station (1971), the 848 MW Upper Waitaki River Scheme (1977–85) and the 432 MW Clyde Dam (1992). By the mid-1990s, hydro capacity had reached  over 5,000 MW, and remains around this level today. History. The first industrial hydro-electric power plant was established at Bullendale in Otago in 1885, to provide power for a 20 stamp battery at the Phoenix mine. The plant used water from the nearby Skippers Creek, a tributary of the Shotover River. Reefton was the first town with a reticulated public electricity supply from a significant hydroelectric plant after the commissioning of the Reefton Power Station in 1888. They were followed by Stratford in 1890. The first hydro-electric power station constructed by the government was the Okere Falls Power  Station near Rotorua. The plant began operating in May 1901. Electricity was transmitted at 3300 volts over a route to Rotorua, and was used to drive sewage pumps, and some public buildings including five thermal baths. During the next twenty years private companies and local authorities established a number of stations, including Waipori in Otago and Horahora on the Waikato River. The first large scheme developed by the government was Coleridge in Canterbury, opened in 1914. Other significant early stations include Mangahao (1924), Arapuni (1929) and Tuai (1929), connected to a single North Island grid in 1934, and Waitaki (1935 ) in the South Island. The Waikaremoana cascade was completed in the 1940s with Piripāua and Kaitawa stations. A further seven stations were developed as a cascade on the Waikato River from 1953 and 1970. In the 1950s development of the Clutha River with Roxburgh Dam and the upper Waitaki in the MacKenzie Basin with "Tekapo A" was begun. With commissioning of the HVDC Inter-Island link in 1965, the Waitaki scheme was further expanded with Benmore Power Station (1965), Aviemore Dam (1968), and later Tekapo B, and Ohau A, B and C. In the North Island, the Tongariro Power Scheme  was completed between 1964 and 1983. The plan in 1959 to raise the level of Lake Manapouri for hydro-electric development was met with resistance, and the Save Manapouri Campaign became a milestone in environmental awareness. Later hydro schemes, such as the last large hydro to be commissioned, Clyde Dam in 1992, were also controversial. Generation. Hydroelectric power accounts for 11% of the total primary energy usage in New Zealand with imported oil and oil products making up 70% of the primary energy. Hydroelectric power accounts for 57% of the total electricity generation in New Zealand. Over the decade from  1997 hydroelectric power as a percentage of total net electricity generated went from 66% down to 55%. An increase in coal and gas for electricity generation accounted for the reduction in hydroelectric power as a percentage of the total. Large hydroelectric power schemes have been built in the Central Plateau region of the North Island and in the MacKenzie Basin in the South Island, as well as a series of power stations on the Waikato River. In 2014, hydro generation produced of electricity, representing 57% of the total electricity generated. The percentage of New Zealand's electricity provided by hydro  generation has been between 50% and 60% for the last decade, compared with a high of 84% in 1980. In 2015, the distribution of renewable energy in the total power usage of New Zealand was 80.2%. It ranks second to Norway in countries with official plans to increase renewable power usage to 90% by 2025. This is due to the hydroelectricity expansion from investments in geothermal generation. In general, New Zealand has focused its hydropower production in the South Island and transports energy to the North Island across high voltage wires in a transmission grid. There is a higher demand  for energy in the North Island due to several major cities located there. From 2008 to 2018, hydropower has generated almost 60% of total electricity production in New Zealand, with 82% generation from renewable resources. Currently, New Zealand has over 100 hydroelectric power plants in use. From the early 1900s to 2010, there has been a plateau in energy growth for hydroelectric power systems. There is room to expand on the current hydropower scales in New Zealand, however the industry will not change as drastically as it has in the 20th century. Small unit growth and large run-of-river  plants are the most prominent examples for future hydroelectric developments. Many other renewable energy resources are competitors to hydroelectric because they are less expensive. There are several barriers that prevent the development of hydroelectricity in New Zealand, including cost, geography, and systematic factors. For example, New Zealand hydroelectric systems are low in storage volume. This means that maximum storage of energy is 34 days during the peak of winter. If there is an unusual amount of precipitation one year, then there would be a shortfall in energy from the hydro system. In addition, the cost benefit of using hydroelectric power  over wind or geothermal energy in New Zealand is highly debated. Proposed projects. There are a number of proposed hydroelectric power projects in New Zealand and, despite the demand for more renewable energy, there is opposition to some new hydroelectric projects. Other proposals, at various planning stages, include schemes on the Matakitaki, Matiri, Waimakariri, Clutha, Kaituna and the Gowan Rivers. In 2011, the New Zealand Energy Strategy (NZES) and New Zealand Energy Efficiency and Conservation Strategy (NZEECS) were developed by the government to establish the main priorities of future hydroelectric power development. In 2016, the electric vehicle program was implemented . This program aims to double the number of electric vehicles used each year, with a target of 64,000 electric cars by 2021. Environmental issues. There has been opposition to hydroelectric power on environmental grounds for many decades. The first nationwide environmental campaign in New Zealand was opposition to raising Lake Manapouri for a power station to supply electricity to the Tiwai Point Aluminium Smelter. The Save Manapouri Campaign was a success and the power station was built without raising the level of the lake outside of its natural range. The highly endangered black stilt, which nests on the braided rivers  beds of the South Island, is threatened by changes in river flows as a result of new hydro dams and changes in flow regimes for existing dams. The Upper Waitaki Power Development posed a threat to the black stilt habitat and a programme was set up to lessen the threats. Because of opposition to new HEP stations New Zealand's demand for increased power has been met from coal and gas fired power stations. Engineers have fine tuned some HEP stations such as at Tokaanu to increase output by 20% with the same water use. Hydroelectric power in New Zealand