Hydroelectric systems

If you have access to the right stream or waterway, hydroelectric systems can be a reliable and economic way to generate your own electricity. Many small hydro schemes already exist on rivers and streams around New Zealand, and there are more opportunities to use water driven generation for remote farms and businesses.

Types of hydroelectric systems

Small-scale hydroelectric systems are generally classified into three sizes:

  • micro-hydro - up to 5 kW
  • mini-hydro - between 5 kW and 20 kW
  • small commercial hydro - between 20 kW and 10 MW.

Micro-hydro systems for buildings are less than 5 kW, and in many cases less than 1 kW. Micro-hydro systems are best suited to rural areas on streams or waterways that flow all year round. The more vertical distance (head) you have between the point where you take the water and where the turbine is located, the more electricity you can generate.

How hydroelectricity works

Hydroelectricity systems use the force of running water to turn turbine blades, which spin a shaft connected to a generator. On rural sites they can be set up wherever water falls from a higher lever to a lower level, for example a waterfall, hillside, stream, or where a reservoir discharges into a river.

The type of turbine you need depends on the vertical distance the water falls and the rate the water flows. Pelton wheels are the type of turbine most commonly used for small scale domestic generation.

Small scale hydro systems don't usually need water storage. A portion of the stream or river is temporarily diverted through a pipe system to the micro-hydro turbine and generator. It's then returned to the same stream or river. This type of system has far less impact on the environment than large scale hydro schemes. If your small scale hydro scheme does need a dam or other form of water storage, you’ll need to get consent.

Hydroelectricity - EECA website
Sustainable Electricity Association of New Zealand (SEANZ)

Checklist for building a micro-hydro system

  • Get expert advice - to help you design and install your micro-hydro system.
  • Make sure the waterway is suitable - ideally it will have a good flow of water year round, and enough vertical drop over a small horizontal distance.
  • Ensure the water supply is reliable - compared with wind or solar generation, micro- hydro systems provide a constant flow of electricity (as long as the volume of water flow remains constant).
  • Check out your rights to the water - you may need a resource consent from your regional council before using water to generate electricity.
  • Make allowances for maintenance - of mechanical, electrical and hydraulic equipment. This may only involve a few hours a month. Intake screens need to be kept clear of silt and debris, and collection lakes may require de-silting every few years.

Cost of setting up a micro-hydro system

The upfront costs vary depending on your location and requirements. Each micro-hydro system is designed to suit the specific features of a property. Running costs are low, so you make ongoing savings. Micro-hydro can be the most cost effective micro-generation technology.

Factors influencing cost

  • Size - larger systems are generally cheaper per kW.
  • Geography and geology - depending on your site, it might take a few days or a week to install your system.
  • Damming - if you need to build a dam to store water it will cost more.
  • Earth works and flood protection.
  • Length of water pipes and electrical cables.
  • Building and resource consents.