Broad categories of hydropower scheme are listed below with a brief description of each. The scheme will fall into categories or either low or high head and usually either grid connected or off grid. For an explanation of how hydropower is calculated, see the Hydropower Essentials page.

Low Head
The head of water will usually be obtained over a short distance. A correspondingly higher flow rate will be required for a given power output. The physical size of the turbine equipment will be large. Civil building work requirements may be significant unless existing structures such as a weir, sluice gate or former water mill can be adapted for the project. Accurate head measurement will be necessary and possibly head variation over different flow rates. If existing structures will be incorporated, then their dimensions and positioning may have important consequences for the scheme design.

High Head
The head may be gathered over some distance by diverting the water into a pipeline which runs downhill. The turbine is attached to the end of the pipe. The size of the turbine will be smaller compared with a turbine producing similar power under a low head. Building work is required to form the intake and usually a powerhouse which can accommodate the turbine and generating equipment. Less accurate head measurement methods may be suitable for initial site assessment. Some head will be lost in the pipeline and pipe fittings. The pipe diameter, pipe length, pipe material and design flow rate are factors which will affect the extent of head loss. Typically, a head loss value of 5 to 10% is acceptable for many hydropower projects.

Grid connected
A project which allows the generator to connect to a National Grid network. This provides a means for all the power which is produced to be absorbed whether or not it can be used near to the generator. Peak loads (i.e. those which exceed the generator capacity) can be met easily with 'top up' power being draw from the grid. Usually the scheme designer will seek to maximise the energy (kilowatt-hour) production to maximise the scheme revenue and achieve an acceptable return on investment.

Off Grid
A project which is designed to supply loads which are not connected to a national electricity grid. The design criteria for such a project may be quite different from a grid connected scheme. For example, power may be required to meet a fixed number of loads and supply them reliably throughout the year rather than maximise the number of kilowatt-hours generated. Careful assessment of loads will be required (i.e. what loads, how many and the maximum peak load). Early consideration of how the loads will be managed given a finite generator capacity is also important. Usually some form of ballast load is needed to absorb excess power. Peak loads must not exceed the generator capacity unless some form of auxiliary power supply is available (e.g. inverter and battery bank).

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