above – low head, Pelton and Turgo units. NB that the exploded diagrams are for illustrative purposes and the turbines and generators don’t require self-assembly!
The Pico size band is usually considered to be in the range 500W to 10kW. The electricity generated can be used just like that produced by a wind turbine or solar panel to off-set consumption at the house or farm, with the excess being exported. And just like wind and solar the electricity is eligible for Feed-in Tariffs.
However, hydro is different from wind and solar in that there are more components to consider, including; turbines, intake, penstock (pipe), and consents. These are not really difficult, but it must all be included at the design stage. We find that where the potential is 10kW or above then installers will be prepared to quote for doing the whole job. Where the power is 10kW or less is it almost certainly going to be a DIY project.
Hydropower is created by applying a flow of water to a turbine. The quantity of power is measured in kilowatts and is a function of flow volume and hydraulic pressure at the turbine. Typically water is abstracted from a watercourse and carried by a pipe (penstock) down the side of the hill to the turbine. The turbine runner is turned by the water pressure and thus drives a generator to create electricity.
The power generated is a function of the head (height of column of water – thus pressure) and the rate of flow (cubic metres per second). The equation is:
Power (kW) = Head (metres) x Flow (m3/s) x 5
- 1)Flow is the design flow – that is when the turbine is operating at full capacity
- 2)1m3/s is 1,000 litres/second
- 3)‘5’ is an approximation for the rate of acceleration due to gravity (9.81m/s2) less system losses
For different measures of head and rate of flow the most suitable class of turbine changes: there are three main classes – Pelton, Turgo and Propeller (Low-Head).
PowerSpout Turbines are manufactured in plastic and come in standard sizes – each producing a maximum design output of 1.6kW – when there is sufficient head and flow. If there is an abundance of water and load to be supplied, then multiple turbines can be installed (up to a maximum of 5) to increase the output power.
Turbine examples in situ: