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| 4.2 Feasibility |
 A feasibility study uses accurate data and looks closely at costs. It can take the project forward from the initial idea to a final design that will support applications for project finance and the necessary licenses. It is therefore wise always to employ a professional to conduct the feasibility study and the detailed design work.
The cost of a full feasibility study carried out by an independent consultant depends on its scope and on the specific characteristics of the site, but would typically be £5,000-£10,000.
For a domestic-scale scheme (i.e. less than 30 kW), a detailed feasibility may not be affordable, and a less detailed Pre-feasibility Study may prove sufficient. This would cover the same basic ground but use approximate data analysed less extensively. It should be possible to commission a pre-feasibility study for less than £4000.
The following essential tasks should form components of a feasibility study:
- Hydrological Survey. Typically, a hydrological survey would produce a flow duration curve. This would be based on long-term records of rainfall and/or flow data, together with a knowledge of the catchment geology and soil types. This long-term information might be backed up by short-term flow measurements. The study should also include an estimate of the required compensation flow.
- System design. This would include a description of the overall project layout, including a drawing showing the general arrangement of the site. The prominent aspects of the works should be described in detail, covering:
- Civil works (intake and weir, intake channel, penstock, turbine house, tailrace channel, site access, construction details)
- The generating equipment (turbine, gearbox, generator, control system)
- Grid connection
- System costing. A clear system costing would include a detailed estimate of the capital costs of the project, subdivided into:
- Civil costs
- The cost of grid-connection
- The cost of electro-mechanical equipment
- Engineering and project management fees
- Estimate of energy output and annual revenue. This would summarise the source data (river flows, hydraulic losses, operating head, turbine efficiencies and methods of calculation) and calculate the output of the scheme in terms of the maximum potential output power (in kW) and the average annual energy yield (kWh/year) converted into annual revenue (£/year).
An additional task, which may form part of the main feasibility report but is often undertaken separately, is the environmental assessment of the scheme, discussed in Section 4.3.
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