Cares renewable ENERGY Hydro ENERGY Handbook
Renewable Energy Technologies This Handbook aims to help you to: Learn the fundamentals of renewable hydro energy generation. Explore and discuss the range of technologies and options available to your community. Evaluate which technologies or options may be appropriate for your community. Identify and access valuable online resources for further information and advice. It discusses the variety of technologies that have been employed by community groups across Scotland. The principles of how the technology works is provided along with the key issues regarding installation and operation as well as environmental impacts. The Hydro Energy handbook includes the following sections: Technology description. Technologies available on the market. System requirements. Is the renewables technology suitable for your community group? Introduction to available schemes and grants. Tips for project development. Environmental aspects. Case study. This Handbook is intended as an introductory text, covering the main aspects and issues that need to be considered for each of the technologies listed above. A separate set of Toolkits, (available Autumn 2013) will provide more detailed guidance and tools to assist community groups and rural businesses to develop a renewable energy project. Like the Handbook the Toolkits will be available on the CARES web site: localenergyscotland.org.uk
Hydro Technology description Hydroelectricity involves the conversion of potential energy stored in water held at a height to kinetic energy to drive a mechanical shaft which then drives an electric generator. There is a long history of hydro in Scotland, with one of the first schemes built in the 1890s at Fort Augustus Abbey which was an 18kW system and used to provide electricity for the village and the electric organ at the abbey. More recently, in June 2010, with support through the CARES program, the Abernethy Trust has installed an 89kW run- of- river hydro scheme to provide onsite generation for their facilities. Potential hydro resource Source: Community Energy Scotland Hydro power makes a significant contribution to Scotland s renewable energy generation, with around 1,500kW of installed hydropower capacity, which is enough to power the equivalent of more than 900,000 homes 1. Much of this capacity is large- scale hydropower. However, about 10% (161MW) is smaller- scale hydro, which may be suitable for a community or rural business development. A report published in 2008 by the Forum for Renewable Development in Scotland (FREDS), a Government- chaired body with industry representatives on the opportunity for new hydro in Scotland, identified that there was about 650MW of unexploited hydro resource in Scotland, with an annual potential generation of 2.77TWh. A further study suggested that Scotland s hydro resource could be up to twice this level. Interest in smaller hydro power plants is growing and some communities, estates, and rural businesses now have operating systems, or are looking to re- instate old hydropower schemes. Hydro offers a great opportunity to develop a resource that is local and has a long operating life (typically 50 years+). Other benefits of hydro are that it is a largely predictable resource of renewable energy (the annual generation can be predicted using historical rainfall data/catchment flow data). Depending on the watercourse, hydro schemes can have a high capacity factor of about 50% (this would equivalent to the turbine operating at maximum output for 50% of the year), and typically has a conversion efficiency rate of 60% to 80% for smaller hydro schemes (<100kW). There a wide range of different configurations of hydro scheme, two types are relevant: Run of river in these schemes the water is taken directly from the river, passed through the turbine, and then returned to the watercourse. The hydro scheme generates electricity as and when water is available in the watercourse. When the river dries up and the flow falls below a predetermined level then electricity generation will halt. A range of high- head, medium- head and low- head examples are shown in Figure 2. 1 Statistics from Scottish Renewables, accurate as of the end of 2012.
Storage these schemes use a dam to collect water in a reservoir, this allows electricity generation for extended periods, e.g. when water flow is at a low level. These schemes are often associated with larger infrastructure projects such as flood control or water abstraction. Most community or rural business schemes would typically be expected to be run- of- river systems. System requirements The magnitude of a hydropower installation's potential power output (kw) is directly proportional to two key variables: Head (H) The vertical distance between the water level at the intake point and where the water passes through the turbine (m). Flow rate (Q) the volume of water flowing through the turbine per second, measured in litres/second (l/s), or cubic metres/second (m 3 /s). The head is relatively easy to assess, from the proposed positions of the intake and the powerhouse. Though some allowance is needed for the pressure loss in pipes, screens and other elements of the system. The annual energy output (kwh) depends on how much water is available over the course of the year this will vary with rainfall. It is typical for the water resource in a catchment to be expressed using a flow duration curve (FDC); this shows how much water is available in the watercourse and for what percentage of the time. The FDC is important for both sizing the hydro turbine and also estimating the annual energy yield from the scheme. Determining the flow pattern is a more complex exercise, normally undertaken using a software program. Because the annual output is the product of both variables, the ideal scheme is one with high head and high flow. The nature of river geography is that large rivers with high flow rates tend to run in valleys with modest or low head, while streams that have a high head tend to be in upland areas and have a lower low rate. So a realistic compromise in needed. High head schemes are easier to identify, but many burns in upland Scotland only have significant flow in spate conditions, whereas a hydro scheme needs flow for as much as the year as possible. So burns that drain a catchment area at high level, and then run down a steep slope have potential. Due to the variable nature of the hydro sites, there is a wide range of different scheme configurations that can be used; the key components that comprise a hydro scheme can therefore vary depending on the site.
Figure 1: Key components in high- head hydro run- of- river scheme. Source: British Hydro Association As shown in Figure 3, the major common components of any hydro installation are: The water intake system this can be a system of weirs, dams and screens that extract the water from its normal flow, whilst screening out debris and not allowing aquatic life to enter the water way to the hydro plant. Penstock The main pressure pipe that supplies the water to the turbine is the called penstock. In some schemes, the penstock will take the water directly from the intake to the powerhouse or in other cases there will be a leat. Leat some schemes may use a leat, an open channel, to convey the water horizontally with minimum loss of head closer to the power house, this results in a shorter length of penstock (as depicted). Forebay tank where a leat is used it would be typical to have a forebay tank to allow suspended particles to settle out and smaller debris to be screened out before entering the penstock. Spillways systems with a leat will also typically have spillways to allow excess water to be discharged in a controlled manor from the leat. Power generation system located within the powerhouse, this includes the hydro turbine, electrical generator, turbine control equipment, cabling, grid connection equipment and generation meter (i.e. the infrastructure that converts the potential energy into kinetic energy to generate electricity). Powerhouse unless the hydro plant is located in a dam or other structure in the water course, the hydro machinery will all be located in a powerhouse where protected from the outdoor elements and flooding. Tail race this is the channel that takes water, once it has left the turbine and returns it to the watercourse.
Grid connection most hydro schemes are grid connected as there may be no immediate electricity demand in the vicinity of the powerhouse, all but the very smallest hydro schemes will require a 3- phase grid connection. Hydro power technologies Hydro projects can be broadly classified into three categories according to the available head, these are: Low head up to 10m. Medium head 10m to 50m. High head greater than 50m. Some of the possible arrangements of different small- scale, high/medium/low- head, run- of- hydro schemes are shown in Figure 4. The canal and penstock and penstock only schemes are both high/medium- head configurations, with the mill leat and barrage schemes representing low- head configurations. Figure 2: Examples of high/medium- head and low- head hydro scheme configurations. Source: British Hydro Association. The design requirements for high- and low- head hydro schemes are substantially different. High- head hydro schemes will typically have a lower flow of water, although this water may need to be transported further, while low- head schemes rely on larger volumes of water to achieve the same power output. This is reflected largely on the civil engineering requirements of the scheme and also turbine design/type.
The turbine selection for the scheme is crucial and is dependant both on the available head and the flow characteristics of the site. In addition to these factors the efficiency of the turbine at full and part load conditions and minimum technical flow conditions (below which the turbine will not operate) should be considered. Turbines can be classified by mode of operation either impulse or reaction turbines. Impulse turbines operate in air that is driven by a jet of water, examples of this type of turbine are pelton wheels, turgo and cross- flow. The rotor of a reaction turbine is fully immersed in water enclosed in a pressurised casing. Kaplan, propeller and Francis turbines are all examples of reaction machines. Archimedes screw Source: Community Energy Scotland Turbines that are suitable for low- head applications are typically, Kaplan, propeller, cross- flow turbines and siphonic turbines. While Pelton wheels, Turgo and Francis turbines are all suited to medium/high- head applications. An alternative low- head turbine is the Archimedes screw turbine which is seen by some as a turbine with lower environmental and fish risks, and lower costs. This type of turbine is relatively new to the UK, but the number of installations is increasing. There are also a number of mill sites where waterwheels have been used for electricity generation at low- head sites. Is a hydro scheme suitable for my community group or rural business? Your community group or rural business could consider installing a hydro scheme if: You have a medium/high- head site (with a significant change in watercourse elevation) and a flow all year round. Sites with a short horizontal distance between intake and tail race, and large change in elevation are ideal. You have a low- head site (2m +) where there is a substantial flow of water all year round. You have an old mill site and existing infrastructure that can be used. You have a nearby grid connection point. You have the agreement of all the landowners that scheme would impact on. You have community members or a rural business that are willing to invest in the scheme. Further information is available by contacting Local Energy Scotland on 0808 808 2288 Introduction to available schemes and grants Communities or companies who decide to install a hydro system can take advantage of different supporting schemes. These schemes are subject to significant change, so they are covered in full detail in the accompanying Handbooks. This section is intended to provide a high- level overview of the two main support schemes. FITs up to 5MW FITs were introduced on 1 April 2010 and replaced UK Government grants as the main financial incentive to encourage uptake of small- scale renewable electricity generating technologies. This incentive supports hydropower installations with a total installed capacity up to 5MW.
The FIT rates are highest for small- scale hydropower systems and reduce for larger systems. The EU clearance for the FIT scheme prevents a scheme from claiming the FIT if a public- sector grant has been claimed. FIT rates are now revised downwards annually for hydro and the level of adjustment is calculated based on deployment rates in the previous year. The full list of tariff rates can be found in the Ofgem website. Renewables Obligation (RO) The Renewables Obligation (RO) is the support scheme intended for large- scale renewable energy projects. Most community hydro schemes will use the FIT, as this is a simpler option to register for and it provides higher levels of incentive for smaller schemes. However, it is possible to claim the RO and to claim a public- sector grant. Hydro generating stations that share civil works are regarded as the same generating station. Therefore, their capacity is combined and this can alter the tariff level received. Tips for project development The British Hydropower Association provides information on turbine types and manufacturers, and a useful step by step guide to mini hydro developments. This section provides a selection of tips for installing hydro systems. It should be noted this is not an exhaustive list and all projects present individual circumstances to consider. Contact the CARES program to identify what support is available in developing your hydro project. 1. Establish the head and flow rates available at your site; this should include any changes to head and water levels that might occur at low- head sites when there is increased flow conditions in the watercourse (this can often reduce the available head). 2. Establish the simple payback and financial returns based on the energy yield from the scheme using the flow duration curve or similar long- term data. This should also factor in the hands- off flow that must remain in the water course at all times. It should also consider the minimum flow at which the proposed hydro turbine will operate. 3. Consider construction access for all of the main components of scheme including the intake, penstock and/or leat and powerhouse. 4. Consider the nearest location for a suitable grid connection for the scheme, the cost of grid connection can have significant cost impact if there is not a connection point nearby. 5. Review the Scottish Environment Protection Agency (SEPA) guidance for the hydro site and review the Part A checklists, these can be found in the SEPA Guidance for developers of run- of- river hydropower schemes. 6. Check land ownership along the proposed route of the hydro installation, you will need agreement from, and potentially pay rent to, all parties over which any penstocks or leats cross. 7. Ensure that the installer has correctly sized turbine and adequately meets the sites head and flow characteristics. 8. Check the level of automation proposed for screens and trash racks (that screen out debris), and consider using intakes that do not require cleaning (where debris flows over them ) or have automatic cleaning mechanism. As these reduce manual intervention, this is especially important where the intake is in a remote location.
9. Typically, a hydro scheme will be connected to the local grid; in this case you will need an agreement with the local electricity Distribution Network Operator (DNO) and an agreement with an electricity supplier to purchase your export electricity. 10. Check if the system you choose is eligible for FITs or ROCs. 11. Review the SEPA Guidance for applicants on supporting information requirements for hydropower applications, this may require fish and habitat studies as part of the application for the scheme s abstraction licence. Planning permission is also likely to require some form of environmental statement. 12. Obtain planning permission, abstraction licences and impoundment licences (if required). 13. Although Hydro technology is currently covered under MCS, the installation company and product manufacturers do not need to be approved in order for the customer to be able to claim FITs. It is recommended that references, qualifications and experience are sought from any supplier or installers before engaging with them in the project. Environmental aspects Run of river hydro schemes generally have very few environmental impacts provided they are well designed and the implementation of the schemes are carefully planned. The main impact is on aquatic life and the habitat that is affected by the removal of the water from the watercourse. SEPA has set out specific guidance (see below) for hydro schemes to ensure that suitable provision is made for aquatic life and habitat; this includes some of the following: Adequate provision of fish screens to prevent fish entering the hydro plant and fish passes that allow fish to pass upstream of any structures put in place by the hydro plant, such as inlet screens. There are particular requirements where salmon and trout are present in watercourses where hydro schemes are situated. Fish screens do not apply to Archimedean screws provided there is no screen on the tail race. Protection of low flows in the water course to ensure that the watercourse does not run dry, so a hands- off flow must always remain in the watercourse. The hydro scheme intake must be designed so the hands- off flow is always preserved. Protection of flow variability to ensure that the watercourse does not have only the hands of flow for extended periods of time. Protection of high flows ensures that the maximum flows in the watercourse are not curtailed to significantly by the water abstraction. Protection of downstream transport of sediment ensures that any sediment captured by the scheme is returned downstream. Protection of river banks and river bed from erosion to ensure that the hydro scheme does no accelerate any erosion in the vicinity. The turbine and generator, like all electro- mechanical equipment, hydro schemes produce sound when in operation. This is not typically an issue especially as this equipment is located in the powerhouse, normally be of a stone or brick construction, so this will provide some noise reduction. Consideration to further noise reduction methods should be given where there are likely to be specific sensitivities to noise being introduced into the local environment. Hydro schemes normally have very limited visual impact on the landscape once operational, with only the powerhouse and intake visible in cases where the penstock has
been buried. Both the powerhouse and intake are relatively small structures and can be designed sympathetically with the local environment. SEPA has produced guidance for developers of run- of- river hydropower schemes these should be reviewed at an early stage of developing a hydro project to ensure that the scheme is likely to be acceptable to SEPA, this guidance is separated into: Part A which provides a set of simple checklists that can be used at a very early stage in the planning of a scheme to assess the likelihood that the scheme will be able to obtain a water use licence from SEPA. It is particularly aimed at schemes with an installed capacity of less than about 100kW. Part B is intended to help developers planning any size of run- of- river scheme. It sets out the mitigation measures that SEPA will require to be incorporated into hydro developments for the purpose of protecting the water environment. Case studies The Abernethy Trust has installed an 89kW run- of- river hydro scheme as part of an energy generation scheme. This is principally for on- site electricity use at its School of Adventure Leadership at Ardgour. The energy savings and additional electricity sales from the surplus electricity generation are to be directly reinvested into and for the good of the Ardgour centre.
Commissioned by the Scottish Government and Energy Saving Trust. Produced by Community Energy Scotland Limited and Ricardo- AEA Ltd Queen s Printer for Scotland 2009, 2010, 2011, 2012 This document was last updated July 2013