In New Zealand we generate more than half of our electricity from hydro generation.

How hydroelectricity works

Hydroelectric schemes use gravity to drive water through turbines, converting that energy into electricity.

Schemes need continuous, year-round water supplies and vertical drops for water to fall down. Water from streams, rivers or dams flows down steep pipes into turbines, which drive power generators. The water then flows back into a river or stream below the hydro plant.

New Zealand's largest hydro schemes are located in the South Island like Benmore, Manapouri, and Clyde, and the central plateau region of the North Island. The majority of time the power transmitted by high voltage transmission lines to the major demand centres in the North Island. store enough water for schemes to be switched on as required. But run-of-river systems, which don’t have dams, need water to flow year-round down rivers that have steep enough natural drops to power their turbines.

Large scale generation schemes (above 10 MW capacity) are more difficult and expensive to build, but produce large amounts of electricity at low cost. Smaller scale generation (below 10 MW capacity and including micro-hydro schemes that generate less than 10 kW), can be cheaper and easier to build and get consent for, but generate less electricity at a higher cost.

Pros and cons of hydroelectricity

Water stored in dams can be turned into electricity in minutes - a process that gives off no greenhouse gases. However, building dams has implications for the environment, economic, social and cultural. 

Where enough water can be stored, hydroelectricity is reliable and consistent.  However New Zealand has relatively small water storage capacity, and water supplies that can vary greatly from year to year. If there is a shortage of rainfall before or during winter, there is a risk of insufficient generation capacity to provide for demand. The growth in wind-powered generation has eased the hydro sector’s concerns about variable water supply - wind supply is more predictable than water supply, making the supply of renewable electricity more predictable and stable.  

Hydro information - Transpower website

The future of hydroelectricity

Hydroelectricity generation will continue to provide the backbone of New Zealand’s electricity system. There is still technical scope to develop new hydroelectricity generation in New Zealand, but as the major opportunities have already been taken, and there is keen public interest in preserving our waterways, large projects are unlikely.

EECA provides information on small scale hydro generation and resources for local government to help develop renewable energy in New Zealand, including assessments of regional renewable energy potential.

Micro-hydro systems