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Generation

The New Zealand generation sector is made up of many stations of various sizes, types and technologies spread across the country. The Grid New Zealand website provides information on what assets form the National Grid. 

Generating capacity is measured in megawatts (MW). As of early 2009, New Zealand's total generation capacity is about 9000 MW.

There are five major generating companies which, between them, produce more than 90% of New Zealand's electricity:

• Contact Energy is a publicly listed generation and retail company with hydro, gas-fired and geothermal plant.
• Genesis Energy is a state owned generation and retail company. Generation assets include hydro, coal- and gas-fired and wind power.
• Meridian Energy is a state owned generation and retail company, owning primarily hydro and wind generation assets.
• Mighty River Power is a state owned generation and retail company with hydro, geothermal and cogeneration plant.
• TrustPower is a publicly listed generation and retail company with hydro and wind generation plant.

The generating companies plan, construct and operate new generation. At any point in time there are many potential generation projects at various stages of the planning process. These provide a range of options for supplying New Zealand's future electricity needs. 

More than half of New Zealand's electricity is generated from hydro-electricity. The remainder comes from thermal, geothermal and wind power, with smaller amounts from other sources. Each of these technologies has different characteristics.

New Zealand's storage lakes have quite limited operating ranges - for technical and resource consent reasons, each lake's level cannot be lowered below a certain point. It is not possible to completely ‘empty' a hydro lake! The lakes can only hold enough water for a few weeks of winter energy demand. As a result, hydro generation is dependent on inflows from rainfall and snowmelt. When inflows are low for a sustained period, thermal generation must increase output to compensate.

Coal, gas and oil-fired generation are collectively referred to as 'thermal'. While these types of generation are not dependent on weather, they can be constrained by fuel limitations, technical restrictions and resource consent conditions. Like all equipment they have downtime (both planned maintenance and unplanned outages). These constraints need to be managed by the plant owner and the System Operator.