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As gas and electricity bills soar and concern for our climate increases, the call to shift our reliance on fossil fuels towards a greener alternative grows stronger. Harnessing wind energy through technology such as wind turbines is a fantastic way to do this. This article outlines Glasgow Gust’s proposal for an 11-turbine wind farm at the Mynydd Epynt site in South Wales as part of the Equate Wind Farm Project 2022. Our team, Glasgow Gust, consists of Carys Serries, David Corbett, Felix Biddle, Finbar McFarlane, and Lisa Chestnutt.
Site Selection and Ground Conditions
Figure 1: Site location and elevation map. Site coordinates (460639.2m, 5768439m)
The proposed location, as shown in Figure 1,chosen was Location 5 in Mynydd Epynt which is situated in Wales and lies just north of the Brecon Beacon National Park. The location was chosen as it had many desirable characteristics for a wind farm such as high wind speeds, good terrain, and a considerable distance from any residences. Furthermore, the location has proved fruitful for the onshore wind sector in previous years with an already existing wind farm just south-east of the proposed wind farm location, thus proving that the area is suitable for these developments. Additionally, the topography of the surrounding landscape made for a relatively seamless selection of turbine placement and formation to maximise power and minimise wake losses. As can be seen below the elevation of the site is desirable and with the direction of prevailing wind the landscape moves in a way that can be used to optimise turbine formation.
To assess the quality of the site location in terms of compatibility for construction of the proposed wind farm, the UK Soil Observatory and Geological Viewer Britain databases were consulted, as conveyed in Figure 2:
Figure 2a: UK Soil Observatory results conveyed the proposed location of the wind farm, Figure 2b: The UK Soil Observatory results conveying the soil texture of the proposed location of the wind farm, Figure 2c: The UK Soil Observatory pH results of the proposed location of the wind farm, Figure 2d: Geological Britain Viewer results of bedrock and superficial deposits contained within the proposed location of the wind farm.
As conveyed Figure 2a., most of the location contains intermediate to shallow soil depth (0.5m to 1 m, yellow) as well as specific areas with deep soil (>1m, green). This is ideal as it allows bedrock to be reached without difficulty so the foundations can be linked in, as well as providing enough soil to provide coverage and be compacted around the base for further stability.
The soil texture was then analysed, as conveyed in Figure 2b. The proposed locations of the turbine sites consist of clay (brown), peat (purple), and silty loam (green). This is ideal as all these soil textures are highly resistant to deformation. This means when impacted around the base and over the foundations of the turbines, they are unlikely to move or be pushed aside, therefore offering greater stability. These are also dense soil textures which will offer additional protection from the elements. There is a possibility of unforeseen climate impact from disturbing the peat, which could possibly release CO2, however, scholars are currently undecided on how significant this impact really is.
Figure 2c. conveys that the soil of the location was found to be highly acidic (<5 pH). This poses a risk to construction as it can cause complications with corrosion. This can be mitigated with proper material selection and careful attempts to insulate between the soil and the wind turbine base. The soil can also be treated; however, this is both labour intensive as it would have to be done annually and poses an environmental risk as the local eco-system is adapted to the acidic soil.
Lastly, the geology of the proposed location was analysed. As shown in Figure 2d., no superficial deposits were found in the proposed location. This is ideal as it confirms the consistency of the soil. The bedrock consists of undifferentiated Pridoli rocks of mudstone, siltstone, and sandstone, which are sedimentary. These are soft rocks; therefore, care must be taken to construct in such a way that the force is spread across a large enougharea to avoid any structures sinking. Conversely, this malleability allows for the bedrock to be slightly manipulated to create smooth and uniform areas allowing the foundations to be more easily linked to it.
Choice of Turbine
Three types of turbines were provided in the project; 85m, 95m and 110m high turbines each with their own characteristics. Selecting the correct turbine would prove an essential piece of the project as this would dictate financial risk, power and capacity factor. After deliberation we chose to select the WTG3 for our wind farm as the site had relatively high wind speeds. It was therefore essential to use the largest available turbines. To extract the greatest power from the wind with highest efficiency it is essential the turbine can handle these high winds as if not, the cut-out point may be exceeded regularly and thus valuable time in which the turbine could be extracting energy and supplying power to the grid would be lost.
Table 1 shows the significant characteristics of the turbine:
Table 1: Wind turbine generator type 3 characteristics
Table 2 shows a comparison made of the power outputs of the different turbines across the site. These were compared to finalise our decision for the larger turbine.
Table 2: Rated power of provided turbines for mean, minimum and maximum site wind speeds
The power curve for the 100m turbine can be observed in figure 2, and was used to compare the power rating of each turbine at the given site wind speeds below.
Figure 2: Power curve for WTG3. Shows rated power of turbine with varying wind speeds
Figure 3 shows the proposed site location and neighbouring windfarm.
Figure 3: Proposed site location considering neighbouring wind farm and prevailing wind direction using site wind atlas
Once the turbine choice had been made WAsP was utilized to observe and optimise the wind farms formation. Furthermore, parameters such as power, wake loss and Ruggedness index (RIX) could be analysed closely.
A primary point of focus firstly was the location of a neighbouring wind farm. This had to be analysed closely as its effects could be significant if not considered properly. The locations of the turbines on the existing wind farm were analysed and such it was found that these would not cause significant problems for our farm. To understand the effects of the nearby wind farm, the farm was modelled within WAsP in conjunction with our farm. Wake losses increase by around 1% however there was no significant effect due to the direction of the prevailing winds and where our turbines have been placed.
We could conclude that our farm would not interfere greatly with the other by utilizing WAsP’s wind atlas. We see that the wind direction is most frequent in section 9 of the atlas, corresponding to a W/SW prevailing wind direction. Thus, the blockage effect from the other farm would not incur a great penalty on our farm at any given time. The attitude of the wind turbines hubs will be placed heading into the direction of the most frequent wind direction (section 9) and with the ability to yaw around atlas sections 7-12 when the sites wind direction changes. The winds in these sections were analysed within WAsP further and wind speeds of up to 12 ms-1 were observed in section 9 of the wind atlas using the Weibull distribution curve with lower speeds of around 8.5 ms-1 through the sections with less frequent winds. The Weibull shape factorkkshows extreme consistency in the prevailing wind direction with all turbines taking either a value of 2.37 or 2.36. This strongly confirms the consistency in the wind speed distribution with the given site and turbine placement allowing for consistent power and energy output.
Figure 4 shows an image of the wind speed and elevation analysis that was carried out to observe the best location for the turbines. Here we can see that there are regions of relatively high wind speeds of around 8-9.5ms-1. As can be seen from this image there are plenty of regions of high wind (red regions on contour map) where the turbines can be placed to maximise output. These regions resided on the top of hills generally (blue regions on elevation map).
Figure 4: Mean wind speed andelevation contour mapused to select turbine placement and formation
Table 3 illustrates the consistency of the site winds with each turbine seeing winds above 9.4 ms-1 thus, showing the effectiveness of proper turbine placement. The ruggedness index for the site is also relatively low giving desired site velocity profiles.
Table 3: Individual turbine site ruggedness index and wind speed
Average RIX: 1.54
Average U (ms-1): 9.7 ms-1
Placement was considered in detail as this inevitably have great influence on the turbine efficiency and power output. Generally, it is desired that turbines be placed on tall masts as these sites favour good wind speed conditions. Turbulence can cause substantial fluctuating velocity components in the wind vector; in the vertical direction this is a major problem. Vertical fluctuations can lead to cross-blade air flow that can significantly reduce output and can even damage the rotor blades. As seen below the velocity contours and effects of turbulence on a downstream turbine can be observed. The wake greatly effects the parallel velocity profile so this should be minimised where possible. Figure 5 provides a visualisation of this.
Figure 5: Visualisation of upwind turbine wake effects on downwind turbines
We chose to find areas where the turbines could be placed on the pinnacle of a hill and in a place where they would least effect other neighbouring turbines. The turbines also benefit from delayed flow separation when placed on hills. Having reduced flow separation in turbine locations is desired as separation can induce the onset of turbulence thus creating a velocity profile that is not favourable for the turbine’s performance. Crests of cliffs were avoided to ensure the turbines did not have to negotiate strong turbulent updrafts. Ensuring the turbines see a relatively uniform velocity profile within the boundary layer is essential and the masts of hills allow this. Additionally, the topography studied here has very little fetch effects that need to be considered as the site has similar terrain to that surrounding it. This means the velocity profile over the site will be relatively steady and thus sustaining better wind formation.
The prevailing wind distances from each turbine to the following for the turbines of concern were analysed. This was measured in google earth using a line probe that considered local topography and was to ensure that each turbine had sufficient spacing as, to meet the requirement of the 5-9 RD spacing in the prevailing wind direction and the 3-5 RD spacing in the perpendicular wind direction. This minimises the wake loss. It was measured that each distance is indeed sufficient and thus the non-uniform velocity induced on the wind, through the rotor aerofoils from wake effects (due to tip losses, downwash, and swirl effects) will become more or less uniform by the time the velocity profile meets the next successive turbine in the prevailing wind direction. Figure 6 shows the propsed turbine sites.
Figure 6: Location of all turbines on chosen site indicated by the white diameters and label
Capacity Factor and Annual Energy Production
To calculate the P50 net capacity factor and the P50 energy production of the farm a wide range of factors were considered that would degrade the turbines output for a given period. The sites capacity factor before losses is extremely high reaching upwards of the Betz’ limit hence this is not achievable. Below are the tables of losses and a summary of the annual energy production and other important factors within the wind farm calculations.Figure 7, table 4 and table 5 show the results pertaining to the WAsP simulations.
Figure 7: WAsP output for turbine cluster within site, with key output parameters
Table 4: Turbine site capacity factor losses
Table 5: Key wind farm parameters for site location
Overall, the site gathers a highly desirable P50 net energy generation and even with the harsh losses estimated a great capacity factor was realised as follows:
P50 Energy Generation: 263 GWh
Capacity Factor After Losses: 0.53
Despite wind turbines having no direct greenhouse gas emissions from their everyday operation, there are still some significant environmental impacts to be considered and mitigated as far as possible. One of the biggest areas of concern is the effects of a wind farm on wildlife. This can include the removal of habitats to accommodate the turbines and related infrastructure alongside birds and bats being injured. To reduce the harm to any of the surrounding habitats we will aim to avoid these areas as much as we can, with the placement of the turbines themselves avoiding such habitats. However, in connecting to the national grid over a distance of around 36km we will inevitably run through such habitats. Subsequently, restoration efforts will be made to renew any damaged habitats and to expand other areas to provide wildlife with even more territory than before. With regards to bird and bat life it is unavoidable that some will be struck by the rotating blades as well as injured by the air pressure changes created, however, we strive to make this number as small as possible and we will incorporate multiple techniques to achieve this. One of the most common techniques we plan to use will be that of ultra-sonic ‘boom-boxes’. These sound boxes produce very high frequency noises, which are undetectable by the human ear, to deter both birds and bats away from the turbines during their rotation. When the turbines are not rotating these sound boxes will be switched off to minimise disturbance to them. To further mitigate injuries to birds and bats we plan to monitor any large groups of migrating birds whose flight paths bring them nearby the wind farm, if judged appropriate the turbines will be switched off until the flock passes to reduce the chances of mass bird strikes.
The materials used in the creation of wind turbine farms such as steel, concrete and bitumen are impermeable, meaning it is very hard for water to pass through them. The use of such materials prevents water from penetrating the ground and as such dramatic increases in surface run off can be seen. This increased surface run off can subsequently put the surrounding areas at a risk of flooding during times of high rainfall. This possibility is significantly mitigated by our choice of location having similarly impermeable surroundings and as such the surface run off after our installation should not be noticeably larger than before. The site is also steep with a river nearby, this means that large volumes of water will not accumulate on the surface and saturate the ground. This also makes the site more appropriate for large machinery by preventing the equipment from becoming stuck in sludge. Despite the increases in surface run-off being minimised, Glasgow Gust is still committed to reducing the negative effects of all installations and we will ensure suitable drainage is implemented.
Community Consultation and Social Impact
At Glasgow Gust, we are aware that support from the local community is key to the success of our development. Table 6 summarises how we intend to engage with the community.
Table 6: Community engagement overview
To reduce the resistance we are faced with, we have identified some key concerns and tried to address these from the offset. The development is over 1.5km away from the closest residences, which will reduce the effects of noise and shadow flicker as well as the visual impact of the turbines. Site traffic will adhere to a strict speed limit with deliveries scheduled to avoid peak travel time, and we will work with the council to introduce temporary traffic control measures where and when necessary. The community development fund will provide compensation to residents who can prove their property has been devalued because of the wind farm. The area has a higher proportion of small businesses than the UK average, which are likely to be more reliant on tourism as the site is so close to Brecon Beacons National Park. Whilst business owners may be concerned about a reduction in tourism because of the development, we hope that our visitors centre and learning hub will help to make the wind farm an attractive tourist destination, and so will have a positive impact in this regard.
Glasgow Gust are committed to ensuring our proposal complies with all relevant guidelines. This includes carrying out a full Environmental Impact Assessment (EIA) and adhering to environmental regulations as laid out by Natural Resources Wales (NRW). We will also produce a health and safety policy as outlined in the British Health and Safety Executive (HSE) in order to minimise work-related injuries, deaths, and illnesses. This will involve providing appropriate training for staff and having an accident reporting policy. Welsh planning and construction regulations will also be adhered to, such as those found in technical advice note 8 of the Welsh ‘Planning for Renewable Energy’ strategy document and other existing initiatives.
The proposed wind farm is to be financed by a loan of £89,500,000, to be paid back over a period of 9 years. This amount covers all the upfront costs of constructing the windfarm and the visitor centre to go alongside it. Once this loan is repaid, the profit from the following years can be used to construct two additional turbines to reach the maximum number for this site, which is 13. The full breakdown of how all of this is to be achieved is outlined in tables 7 and 8 below.
Table 7: Cost Overview
Table 8: Revenue Overview
One of the annual costs outlined is our community fund; an amount calculated based on a percentage of our income after overhead costs. This is to go towards forms of community engagement such as contributing to the local community projects and compensating those who have (provably) had their house devalued due to the wind farm.
Taking all of the above considerations into account, as well as additional calculations and simulations, we believe our proposal to be a worthwhile and profitable endeavour. Thank you for taking the time to read our article, and please feel free to get in touch with any questions you may have.