Farm Diversification

The key factors in determining the amount of electricity produced are

• Head – the vertical distance (m) the water drops.
• Available Flow rate – the volume of water (m³/second) that is available in the watercourse.

Head: The higher the head the greater the power produced for a given flow of water There are systems that will produce power at heads as low as 0.8 m but for financial viability a minimum head of 2 or 3 metres is desirable.. The rule of thumb is the greater the head the lower the cost of the electricity generating equipment.

Available Flow Rate: The available flow rate in a water course is determined by a number of factors:

• The size of the watercourse catchment draining to the collection point for the generating system.
• The physical characteristics of the catchment terrain such as gradient, vegetation, soil type etc.
• The long term rainfall characteristics of the local area.
• The quantity required to be left in the river for environmental reasons; this will be identified by SEPA.

Power Generated: The power generated from the water can be calculated by formulas which take into account the head, flow rate, gravity, friction and other losses due equipment efficiencies but an indication of the power that can be achieved can be estimated using the equation: Power Produced (kW) = 7 x Available Flow Rate (m3/sec) x Head (m)

Enegry produced is measured in kWh (kilowatt hours) e.g. a site with a 5 kW output will theoretically produce (365 x 24 x 5) = 43,800 kWh of electrical energy per year if it runs at 100% capacity all year round.

Efficiency: The efficiency of hydro electricity equipment is variable with the best units achieving 90% efficiency. Typical overall efficiencies for the micro-hydro systems are lower at around 50 – 70% depending on size, type and location. For example the system discussed in the previous section will only be able to generate between 21,900 and 30,660 kilowatt hours of electrical energy from the available energy of the water flow.

System costs vary depending on the site, type of system used and distance from connection point.

Typical costs are in the region of £2,000 - £9,000 per installed kW.

Costs for low head/high volume installations are generally more expensive per kW installed, on account of the greater size of the equipment required for a given output.

Running costs are in the region of 2% of the installation cost per year, less if a high proportion of the installation cost was infrastructure. The components of the system are simple and require little maintenance and should have a lifespan in excess of 20 years, much longer in many cases.

Under the current feed-in tariff scheme payments for every unit of electricity produced are available for schemes of up to 5 MW. This applies to energy used within the business as well as exported energy. The rate of payment depends on the scale of the installation with the highest rate of 21.9 p/kWh (from 01/04/2012) being available for systems of up to 15 kW installed capacity.

For eligible systems payments will be made for 20 years after the date of commissioning and will change annually with inflation. For current rates refer to DECCs FITs webpage. Further  longer term, benefit will be obtained by offsetting the purchase of existing electricity supplied to the business. Current rates vary between 9 – 17 pence per kilowatt hour (March 2012). In addition an export tariff will be received for surplus energy fed in to the grid. (3.2 p/kWh as of 1/04/12). Producers also have the option to forgo the export tariff and sell excess energy directly to a power company for a premium price.

Schemes in excess of 50 kW can opt for the alternative renewables obligation scheme which may provide a better return for schemes of 1 MW upwards.

Micro-hydro schemes are generally deemed to have a low environmental impact when installed on a suitable site. Allowing fish migration and making sure there is enough water remaining in the watercourse all year round are key aspects when considering a scheme.  Any hydro scheme requires a licence under The Water Environment (Controlled Activities)(Scotland) Regulations 2005.

Before issuing a licence The Scottish Environment Protection Agency (SEPA) need to be satisfied that the proposed scheme will provide greater benefit to the environment, in the form of offset greenhouse gases, then any negative impact it may cause to the affected watercourse and its environs. 

It would be advisable to contact SEPA and the local Planning Authority at an early stage to discuss your application before work commences.

Is your site suitable?
If you are thinking about the possibility of a micro-hydro scheme for a watercourse on the farm, you will need to consider the following points:

• Is there enough head and flow? Head is the vertical fall in the water from upstream to downstream level. Less than 10m would be classed as low, 10 to 50m medium and above 50m would be described as high head. Flow is the volume of water passing per second, measured in m3/second. For smaller schemes, this may be easier to measure in litres per second, where 1000l/sec is equal to 1m3/sec. A basic calculation to assess the power in your watercourses is Power (kW) = 7 (efficiency loss) x flow (m3/sec) x head (m)
• What is the mean flow in your watercourse i.e. what variation in flow can you expect over the year?
• How near are you to a load or grid connection? How easy will it be to transfer the power from point of generation to point of use? 
• Are there any environmental impacts? 
• Do you own all the land or will you need to seek permission from others? 
• What are the planning and environmental licensing requirements?

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Grant-aid is generally incompatible with the feed-in tariff scheme. It is normally a requirement of entry into the scheme that any grants received for a project are paid back prior to entry. In certain cases if excess cost has been incurred in order to bring about an environmental benefit associated with the scheme it may be possible to obtain grant aid for these additional costs.