Hydro generation systems come in all sizes
Most domestic-sized systems produce an output of less than 5kW of electricity – enough to power a single property depending on usage pattern. These are called ‘micro-hydro’ schemes.
If you’re in a rural area and your property has a stream with a reliable flow, micro-hydro may be a cost-effective and environmentally friendly alternative to a diesel generator or a local lines connection.
Mini-hydro schemes are larger than micro-hydro and typically have a peak output of between 5 and 20kW, but can be larger. Some mini-hydro schemes are large enough to provide electricity for small communities or villages. For example, Haast gets its electricity from a 900kW mini-hydro generator.
How micro-hydro works
In a typical micro-hydro system, water flows downhill through pipes into a small turbine, and the turbine drives an electricity generator.
Some electricity can be used immediately, and the rest can be stored in a bank of batteries or even sent back into the grid.
The exact set-up depends on the circumstances on your property.
How much can it generate?
The amount of electricity you can generate depends on how much water flows in the stream, and the drop in height from the point where the water flows into the pipe to the turbine (this is known as the 'head').
As a rule of thumb: flow rate (litres per second) x head (metres) x 10 = maximum electricity output (watts). So, a stream falling at 10 litres per seconds down a head of 5 metres would give a maximum output of 500 watts.
Bear in mind this is the maximum output. In reality, friction and inefficiencies in the generator can lower the output – sometimes by as much as half.
The average New Zealand household uses about 10,000kWh of electricity a year (just under 27.5kWh each day).
Is it suitable for all properties?
Micro-hydro is really only suitable for a rural property with a stream – with sufficient flow. It works best if:
- the stream doesn't dry up during summer (otherwise you'll need an alternative power supply)
- the stream doesn't flood (this can damage the equipment, unless carefully designed)
- the slope is reasonably steep (to overcome friction in the pipes)
- there is a reasonable head (see above).
One way to create a greater head is through the use of a dam. However, damming even small rivers can be a difficult activity to obtain resource consent for, unless there is an existing dam which can be retrofitted for generation.
Micro-hydro systems don’t need to dam or disrupt streams or rivers. Many micro-hydro schemes operate by diverting smaller volumes of water through pipes and channels before returning the water to the stream bed.
You'll need to check with your local council that upstream water rights haven't been allocated to someone else and, in most cases, you will need council consent to utilise the stream for electricity generation.
Types of system
Every micro-hydro system needs to be designed specifically to fit the particular stream and user requirements. It’s best to leave design to your supplier as there are many things to think about including:
- efficient and practical design
- design of intake
- type of turbine
- environmental impact
- reliability of supply
To install a micro-hydro system, you may need:
- a building consent for any structures you build
- a resource consent for water use (to both remove the water and return it).
You'll also need to talk to the lines company and power retailer if you are planning to connect to the local lines network.
All electrical work must be done by a licensed electrician, except, in unusual situations, where voltages are below 32V alternating current or 50V direct current.
Why choose micro-hydro?
On the right type of property, micro-hydro is a cost-effective and environmentally friendly way to generate electricity. For some rural properties, it can be far more cost-effective than buying and running a diesel generator or connecting to the grid.
Micro-hydro generation has significant environmental benefits. It doesn’t produce greenhouse gases, and saves the transmission losses that occur when electricity is generated at a power station and sent to your property over the national grid.
The cost to install a micro-hydro system is in the region of $10,000-$15,000 for a domestic system with a basic layout. There are some DIY micro-hydro turbine kits available for under $3,000, suitable for small streams but extra set-up costs can be involved with these.
Typical costs include:
- inlet pipes – longer or wider pipes will cost more
- turbine and generator equipment
- earthworks, dam or flood protection work
- a battery bank
- electrical control system
- labour costs, including an electrician and plumber
- electrical cables – the further the generator is from where the power will be used, the more it will cost
- building and resource consent costs.
Maintenance costs are generally very low. You will need to consider the costs of the resource consent process as it can be over $1000 in some regions.
You may be able to recover some costs by selling electricity back to your local lines company, if your property is connected to the grid and your lines company is prepared to enter into a contract with you.
A micro-hydro scheme is particularly worth considering if the alternative is either:
- buying a new diesel generator, or
- paying for an expensive connection to the local lines.
Impact on freshwater fish
New Zealand has several species of native freshwater fish and invertebrates that live in small streams and waterways. They're mostly very small and hide under stones, so you don't notice them.
They used to be much more common, but their habitat is shrinking as wetlands are drained, streams are dammed, and trees and bush are cleared.
Many are endangered – find out more on the Department of Conservation website.
Some of these fish can get a very long way upstream. They can even climb up waterfalls as long as they can keep close to the rock. But they can't jump up even a small vertical drop.
Fish can’t make their way against the flow through a turbine and pipe, and any that come down through the turbine will probably not survive.
If you only divert a fraction of the flow in your stream through an intake screen, and take care to protect the habitat, the fish have a chance to survive.
You will need a resource consent to install a micro-hydro system and the effect on stream ecology will be considered during this process.
Micro-hydro systems are low maintenance and last well if designed correctly. The maintenance requirements aren't complicated, and most of the work you can do yourself.
However, you'll need full, clear written instructions from your supplier – most tradespeople won’t be familiar with these systems. Always follow the manufacturer's instructions.
Electrical work involving mains voltage (230V) must be done by a licensed electrician.
Some equipment may be dangerous. Make sure that unauthorised people do not have access to it.
There should be a valve just above the generator to allow the water to be shut off. Always turn this valve on and off slowly to avoid large pressure build-ups.