Hydro power plant in Waikato, New Zealand. Approximate location -38.3521, 175.7465.
HydroWaikatoNew Zealandconventional storage
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.
Known, modelled and calculated values are kept separate. Missing fields are shown as unavailable.
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).
Capacity claim grade: D_REJECT_KEEP_MASTER - recommended action: keep_master - confidence: rejected_candidate. This follows a claim-based data model: value + scope + source + confidence, rather than silently overwriting records.
The capacity and/or fuel fields on this page include a source-backed provenance label from GEM, an official registry, Wikidata, OSM, or a cross-source match.
capacity: Wikidata P2109 nameplate capacity; fuel: WRI source-record fuel
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.
Installed capacity (MW), WRI Global Power Plant Database (CC BY 4.0).
Operated by Mercury Energy. All plants by this company →
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.
For a plant’s outdoor hardware — heat-recovery steam generators (HRSG), expansion joints, valves, flanges and their insulation — the local climate sets how fast unprotected steel and coatings degrade. This site sits in a moderately corrosive environment (estimated ISO 9223 class C3 — Medium), with humidity / wetness the leading environmental stress.
Higher environmental severity is exactly where protective removable insulation pays back most: a sheltered micro-climate slows corrosion, UV and thermal-cycling damage and extends outdoor hardware service life. This is an indicative site-climate context — not a condition assessment of any specific plant or operator.
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.
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.
Coordinates -38.3521, 175.7465 from WRI Global Power Plant Database (CC BY 4.0). View on OpenStreetMap.
Maraetai is a 360 MW source-record hydro power plant in Waikato, New Zealand, commissioned in 1952.
Its output is enough to supply roughly 360,411 homes (estimated).
Maraetai is operated by Mercury Energy.
