- 1 Introduction
- 2 Isle of Mull
- 3 Proposed System
- 4 Wind Turbine Specifications
- 5 ENVIRONMENTAL, SOCIAL AND ECONOMIC ANALYSIS
- 6 CARBON REDUCTIONS
- 7 Economic Viability
- 8 FUNDING STRATEGY
- 9 SOCIAL RESPONSIBILITIES
- 10 CABLING AND GRID CONSTRAINTS
- 11 CONCLUSION
- 12 Share this:
- 13 Related
As of the 24th of March 2016 the world’s population stood at 7,410,748,138. Births on that day alone reaching over 263,000. As a result children will be born into a world dependent on the burning of fossil fuels as the main method of producing all of the amenities the human race has come to expect in the 21st century. Strain on the environment will be increasing every hour of every day, ultimately wreaking havoc with the natural fabric of our world and creating temperature rises and erratic weather patterns not seen since the last ice age. However, there are ways by which the resulting chaos can be slowed and the damage to the planet become less and less as we progress as an ever more environmentally conscious race.
In response to the growing realization that the way that we create, use and distribute energy is simply not sustainable for the continuation of this planets existence a feasibility study will be undertaken on a smaller scale. This study will model the electrical requirements of the island and will lay out a plan for implementation of a hybrid solar PV/ Wind electricity generating scheme. After going into greater depth as part of my honors project at university this article is a condensed version of what was carried out through the course of the honors project. It is worth noting that this feasibility study is purely theoretical, therefore values may not represent the true outputs whilst in operation.
Isle of Mull
The Isle of Mull is an 875.4 km² island located in the Inner Hebrides in the county of Argyll and Bute. It has a population of 2819 people with roughly 1300 homes currently registered on the island (Scotland, 2011). As a result of low population density there are vast areas of the island that are uninhabited and could be fully utilized for the purposes of energy creation. The island itself is a perfect space to install renewable technologies and the inclusion of solar and wind farms could potentially be powerful enough to produce the entire islands electricity need, greatly reducing the carbon dioxide production of the island. In terms of renewable technologies in place the island community has been working constantly to reduce the carbon dioxide production as a result of their electricity needs. Currently there are a number of renewable technologies in place but only one large scale installation. This comes in the form of a 440 kW hydro scheme that was commissioned in May of 2015, this scheme will provide enough power to provide the electricity needs of 200 homes. Along with reducing the carbon footprint of the island by 450 tones.
ENERGY PRODUCTION CAPABILITIES
As Mull is an island, the climate over the year is different to that of the mainland. As a result it can often be a lot windier as there are no barriers to the wind from the west coming over the Atlantic Ocean, this results in a steadily high wind speed average over the course of the year, perfect for the utilization of wind as an energy source. The resulting wind speed averages over the past twenty years are detailed in figure 1. In addition to this the daily solar irradiances are also detailed in figure 1. This resulting data will be used to size the most suitable application of renewable technologies, in addition it will give a much greater depth in knowledge into the possible outputs that can be expected from the chosen sites.
For the case of simplicity an average electricity usage of 4800 kWh per household has been scoped for this project. This figure is taken from research done by Strathclyde University and has been slightly over sized to account for the inclusion of losses and variations in demand as the islands weather can be more volatile than that of mainland Scotland.
In response to the analysis of the weather patterns on the island it has been deemed suitable to implement a network that consists of 25% production from solar PV and 75% from wind generation. The reason for this being that the wind is deemed to be consistently strong enough to take a larger portion of the load. In addition the number of sunlight hours on the island can severely lessen during the winter months. This works vice versa in the summer months as the wind is relatively low but not low enough that would mean the base load is not attainable, the solar PV would then be producing at near maximum output covering the drop in wind production.
In addition to the initial data captured by NASA’s surface meteorology service detailed in figure one further analysis was required to get a true reflection of the solar availability on the chosen site. The analysis followed the forthcoming methodology.
– Acquire the NASA Surface data
– Disaggregate the data using in house software here at Napier University (Calc 4-09) this would provide an hourly global irradiation spread for each day in each month. Figure 2 shows an example in the form of the month of December.
– Resulting slope Global Irradiation was then used to calculate the diffuse irradiation by using the following equations:
The resulting diffuse irradiation was then utilized in another software developed at Napier University (Calc4-10) which gave an output of the slope global irradiation available at the chosen site for each month of the year. Figure 3 shows the resulting data for the month of December with the cells highlighted in yellow being the available slope global irradiation.
Using this methodology the total slope global irradiance in Wh/day was gained for each month with the spread of the results being detailed in figure 4. The total kWh available annually was found to be 995kWh. This data will be useful for judging the performance of the system annually.
For an easy method of calculating Solar irradiance, follow this link
SOLAR PV ARRAY
Using the methodology detailed in figure 5 the size of the solar PV array will be calculated. The total load in the first section will be taken as the daily requirement for an average house that was detailed in section 2.1.2 25% of this value will be the load required. This will be scaled up to fit the 1300 households that are present on the island. In addition to this the number of sun hours available on the panels for each month must be found using real life data.
As a result of the calculations the total PV array size is calculated to consist of 3420 Panels. This would provide the 25% of the total load even in the darkest months of winter. An inverter is also imperative to the working of the system. This piece of equipment coverts the direct current that is produced from the solar panel and turns it into alternating current which is what is used in our homes and national grid. Two large scale industrial inverters have been chosen as they prove to be the most efficient and effective choice in this application.
For wind turbines to work there needs to be a steady source of wind present at the site that is above the minimum operating wind speed for the wind turbine selected. As the load is already known, wind turbines can be selected that fit the desired output conditions for the operating conditions on the island. The use of a power curve which is provided by the manufacturer will give a good idea of how much will be produced at any given wind speed.
The next step is to get spread of the annual average wind speeds which has been found through the NASA meteorology service. This primitive data is a spread of average wind speeds for each month, however for accuracy this data can be manipulated through the use of a distribution function known as Rayleigh Distribution. This function gives a more realistic spread of how often each wind speed will occur over the course of each month.
In addition to the Rayleigh distribution part of this function allows for the wind speed to be manipulated to account for the difference in height. This makes the wind speeds being used in the distribution function more accurate as it is more likely that the wind speed will change at the hub height of the wind turbine. Table 2 shows the difference in the wind speed at the measured height and the wind speed at the hub height which in this case is 30m. The resulting spread of output for varying wind speeds is shown in figure 8.
Wind Turbine Specifications
In terms of production necessary one turbine would suffice it would be a 1MW turbine and would operate continuously to provide the required load. However in real life situations wind turbines like any other piece of machinery are prone to the occasional breakdown. Therefore it has been decided that two 500kW turbines would be more suitable than one 1MW. This will make sure that there is still production even if one of them is down for maintenance or repair work. The turbines selected are produced by EWT Direct Wind and operate at a maximum of 500kW. They have the following specs:
Two of these turbines will produce the required 75% of the total load of the island continuously over the year whilst providing income to the island in the form of the British governments feed in tariff and export tariff schemes.
ENVIRONMENTAL, SOCIAL AND ECONOMIC ANALYSIS
As with any project of this size, special consideration must be taken to address the local ecology when considering implementation. Renewable energy on a whole has a positive image that is viewed as an environmentally friendly and “green” approach to energy creation, this label must be maintained when taking planning forward as the local environment must be considered. Any local wildlife must be monitored and accounted for, in addition to a report as to whether or not this installation would encroach onto natural habitats and/or breeding grounds. This including birds, as they may have the most direct contact with the most substantial side of this project the wind turbines.
The aim of this project was to first and fore mostly prove that it is feasible to offset a large number of peoples carbon emissions through the implementation of renewable technologies. If this system were to be implemented the reduction of CO2 emissions from the island would total 6725.7 Tones when compared to a coal fired power station.
The Scottish Government has been encouraging the installation of all forms of renewable technologies as part of our ambition to have a 100% renewably sourced electricity grid by the year 2020. As a result both technologies benefit from feed in tariffs based on the amount of electricity they produce over the year. With the solar PV side benefiting from a feed in tariff of 2.7 p/kWh and the wind side receiving 8.46 p/kWh. As a result using the production from each of the technologies a cash flow can be found. This gives an idea of the income the island will receive as a result of installing the two technologies. In addition to the feed in tariff an export tariff for the excess electricity produced is available. This works out at 4.85 p/kWh. Table 4 shows the productions and incomes as a result.
There are several funding strategies available to a project of this size, as previously stated there is particular focus by the current Scottish Government in promoting the use of community renewables as a method of gaining the 2020 emissions targets. As a result it has been deemed appropriate to fund the project through the means of community energy. If there is not enough demand for share offers on the island the resulting shares will be extended to other islands in the area should they wish to offset some of their own carbon emissions. When it comes to the total cost of the system prices are fluctuating but basic prices can be worked out by taking into account similar projects. As a result the below table outlines the rough pricing of the system on a whole.
As stated by the Scottish Planning Policy for Renewable Energy there must be specific importance placed on public participation during the development and planning processes. A fair way of opening up the floor to the concerns of the residents would be to have a public hearing on how to move forward, outlaying the benefits of the project and listening to the concerns and/or criticisms the residents may have with a project of this scale. This will enable the general populous to gain their own opinions on the most accurate and best information that is provided. As a general rule any planning authorities and developers must work closely with the local communities as to provide transparency and trust between the community and the developers.
CABLING AND GRID CONSTRAINTS
Due to the nature of solar power and the requirements for the panels to be linked in strings there will be high cabling demands on this project, the assumption is that the hybrid system can be integrated into the existing grid without major issues. However because of the erratic nature of renewable electricity in terms of production – production values can be very low or very high depending on weather patterns – the existing grid may need upgraded to cope with the demands of this installation.
In conclusion the aim of this study was to provide a short snapshot into the main findings of a larger study that was conducted as part of my honors project at university. In terms of conclusions the data received as part of the research proved that this set up of a Wind and solar PV system working in tandem will comfortably provide all of the electricity requirements of the Isle of Mull.