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.

Hydro dams, like Benmore, Manapouri, and Clyde, 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 great impact on the environment. 

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. This means we need to monitor closely how much water we have for hydro schemes. 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 wind-generated electricity more predictable and stable.  

 Wind generation

The future of hydroelectricity

Hydroelectricity generation will continue to provide the backbone of New Zealand’s electricity system. There is still significant 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 - ENERGYWISE website