Maraetai — New Zealand

Maraetai is a 360 MW hydro power station in Waikato, New Zealand. It is operated by Mercury Energy. Based on its capacity (estimated), it can supply roughly 360k homes (estimated). It ranks #9 of 50 New Zealand power plants by installed capacity. Commissioned in 1952, it is around 74 years old — an older, legacy facility. As a non-combustion source, it has no direct CO₂ emissions from generation. In context, hydro supplies about 54.8% of New Zealand's electricity; the national grid averages 93 gCO₂/kWh (88.5% low-carbon) (2025).

Plant data: WRI Global Power Plant Database (CC BY 4.0), id WRI1000318.

Capacity provenance

The public capacity above is the current source-record value. A 2026 tracker candidate lists 176 MW for Maraetai I hydroelectric plant, but it is not used as the public primary value until scope is verified (unit vs operating vs installed/project total).

Data provenance

Source of the capacity and fuel values:

capacity: Wikidata P2109; fuel: WRI GPPD

In context: how this plant compares

At 360 MW, Maraetai is well above the median hydro plant in New Zealand (90 MW). Technically it is described as conventional storage. Hydropower converts the energy of falling or flowing water into electricity; output depends on rainfall and reservoir level, and large dams also provide grid balancing and storage.

Capacity comparison computed from the WRI Global Power Plant Database; fuel-type context is general engineering background.

Key facts

Share of New Zealand hydro capacity

8.2% of 4,388 MW across 24 plants in this dataset

Age among peers

8 of 23 dated hydro plants in New Zealand are older

Calculated from the capacity and generation records in this dataset (WRI Global Power Plant Database (CC BY 4.0)).

Capacity vs largest hydro plants in New Zealand

Installed capacity (MW), WRI Global Power Plant Database (CC BY 4.0).

Owner

Operated by Mercury Energy. All plants by this company →

Local climate & thermal context

This hydro plant converts the energy of falling or flowing water through hydro turbines. It sits in a temperate oceanic climate (Köppen Cfb) — Southern Hemisphere, latitude 38.4°S — which shapes how much energy it can produce and how its output varies through the year.

Monthly mean temperature

Heating degree-days here run 13% below the median power plant in this dataset — a proxy for how much extra energy heated equipment must replace through its surfaces in winter.

Climate heat-demand index: 45/100 — this site sits in the mid third of the power plants we cover by heating degree-days.

Climate normals: WorldClim 2.1 (1970–2000 monthly normals, 10 arc-min, CC BY 4.0); zone: Köppen-Geiger world climate classification (Kottek et al. 2006, 0.5° grid). Degree-days & heat-demand index computed by PowerAtlas — a modelled heat-demand proxy, not a measured site figure.

Site climate & environmental severity

This site sits in a moderately corrosive environment (estimated ISO 9223 class C3 — Medium), with humidity / wetness the leading environmental stress.

Indicative estimate via the ISO 9223:2012 informative method (atmospheric corrosivity from temperature, time-of-wetness and airborne salinity), using WorldClim climate normals, the Köppen-Geiger class and coast distance. Indicative, not a measured corrosion rate.

How it compares & nearby plants

The #5 largest hydro power plant of 24 in New Zealand by capacity.

New Zealand has 24 hydro power plants in this dataset, together about 4,388 MW of capacity.

Nearby power plants

• Whakamaru · Hydro · 100 MW · Waikato
• Waipapa · Hydro · 54 MW · Waikato
• Atiamuri · Hydro · 74 MW · Waikato
• mokai · Geothermal · 113 MW · Waikato
• Ohakuri · Hydro · 106 MW · Waikato
• Arapuni · Hydro · 164 MW · Waikato

Location

Coordinates -38.3521, 175.7465 from WRI Global Power Plant Database (CC BY 4.0). View on OpenStreetMap.

Frequently asked questions