(Image courtesy of NASA)
Our contemporary society is heavily dependent on the provision of energy, in particular in the form of electricity. Despite many national and international efforts aimed at making energy provision accessible in most parts of the world, more than two billion people in the world do not have access to affordable energy services today. A significant majority of such people reside on the African Continent. One of the key problems facing African energy supply has to do with the inability of local governments to efficiently perform both the collection of biomass material such as crop residues or wood and the conversion of these materials into fuels1. The problem of energy supply has important repercussions for the socio-economic level of African countries. This is evidenced in the fact a convenient, affordable energy stimulates households’ marginal productivity, as a result enabling households, and even whole communities, to escape poverty and begin their socio-economic development 2. It becomes evident that developing a dependable energy sector in African countries is a very important goal.
The challenge of developing Africa’s energy sector is particularly difficult. At present, Africa as a continent produces less than 1% of the world total electricity supply. Apart from the general scarcity of infrastructure in order to maintain an adequate level of electricity supply, there is an additional problem of the inefficiency of its provision where such infrastructure exists. In fact, countries in Africa undergo regular electricity outages which can last in duration from just a few hours to a succession of several days. This intermittent level of electricity supply can be attributed to an inefficient and generally out of date infrastructure. Many of the electrical power stations date back to their installation during the colonial era. The severe problem in technical efficiency has been compounded by endemic poverty and the lack of good management of funds allocated for the maintenance of existing power stations. In view of such problems and an urgent need to develop the energy sector in Africa, the provision energy derived from alternative energy sources is very attractive, especially now amidst the growing environmental concerns and increasingly competitive prices of alternative energy.
There are several reasons why the provision of solar energy is particularly suitable to the African continent. The continent’s latitude and the proximity of its land mass to the equator means that it benefits from constant and strong intensity of sunlight all year round, thereby showing striking solar energy production capabilities3. The general availability of sunlight means African countries have a potentially costless source of energy production. Unlike other forms of energy generation, solar energy can be harnessed for free. This means that it will not make any demands on the already strained financial resources available on the African continent. Hence, the provision of capita for the large-scale infrastructural developments of complex power grids will not be necessary. Secondly, the relatively high level of sunlight in all African countries means that any location on the continent can benefit from solar energy supply.
There are other implications of the need to change to solar energy production in Africa. It has been noted above that Africa generates less that 1% of the world’s total electricity. This energy generation is primarily achieved through nuclear power plants, whose rapid growth on the continent since the mid-1980’s had not brought a proportionate increase in the total output of electricity on the continent4. The problem of nuclear power plants is also connected with the problems of provision of petroleum necessary for their functioning5. It is well documented fact that the extraction, refining and the utilization of petroleum in the transport industry causes significant environmental problems through pollution. Solar energy production can significantly lower the environmental impact of the present forms of energy generation in Africa. At the same time, Africa’s documented petroleum reserves of 60 billion barrels will not able to meet all the energy demands of the African pollution in the long run6. Therefore, there exists a strong demand to promote and develop an alternative source of energy production. The generation of energy from solar power can have the double advantage of keeping the commendably low levels of industrial pollution while initiating a certain resource boom in the form of higher labour demand7.
(Image courtesy of Center for energy and processes, Ecole des Mines de Paris/Armines/CNRS)With reference to the map above, it has been estimated that the solar power systems if installed in the red areas, that is those corresponding to the North-West USA, Chile, Argentina, North Africa, Saudi Arabia and China, could meet the world's current total primary energy demand, with a certain surplus of energy, with a conversion efficiency of 8 per cent8. This can be shown in quantitative terms. For example, photovoltaic systems, with conversion efficiency of 8 percent, if installed in the red areas discussed above would produce an average electric output of 18TWe. This figure corresponds to an energy output of 13,567 Mtoe per year. Such projected output is larger that the world electric output of 11, 741 produced in 20069. This effectively means, as the analysis by Yansane indicates, that electricity provided by solar cells can be gainfully substituted for other forms of energy production, while successfully providing for all the daily needs associated with energy consumption. These facts indicate quite clearly the potential that solar powered electricity generation systems have even at the current stage of its technological development.
How Solar Panels Work
Solar panels collect solar radiation from the sun and actively convert that energy into electricity. Solar panels are comprised of several individual solar cells10. The functioning of these solar cells can be compared to the similar functioning of large semiconductors. The solar cells utilize a large-area p-n junction diode11. When the solar cells are exposed to sunlight, the p-n junction diodes convert the energy from sunlight into usable electrical energy12. The energy generated from photons striking the surface of the solar panel allows electrons to be knocked out of their orbits and released; the electric fields in the solar cells pull these free electrons in a directional current, from which metal contacts in the solar cell can generate electricity13. A larger number of solar cells in a solar panel and the higher the quality of the solar cells, the greater will be the total electrical output that the solar panel can produce14. This conversion of sunlight to usable electrical energy has been dubbed the Photovoltaic Effect15. It has been reported that as of May 2009 the solar energy industry's highest conversion efficiency of solar panel stands at 22.8 percent16.
There are various crucial factors which have to be considered when designing and operating solar panels for energy generation. One of the central features for the design of solar panels has to do with its ability to provide electricity during the absence of sunlight. The fact that the amount of electric current generated by a solar cell is directly proportional to the intensity of sunlight shows the importance of such a design feature. For it is self-evident that there will be times when the absence of sunlight is quite pronounced, such as when there is a heavy cloud cover or during night time. At such periods, no electricity can be generated unless stored energy from sunlight is available for electricity generation. Consequently, a photovoltaic energy storage system is required. The most common of which are batteries equipped with a voltage regulator to prevent an overcharge of batteries.
When operating solar panels, their efficiency can be optimized by using movable mounts that follow the position of the sun in the sky. This is important since one of the central features of the solar panels is their direct dependence of their performance on the amount of sunlight received. Rotation of the dynamic mounts has the advantage of increasing the solar panel efficiency, and hence its electricity output, by enabling the solar panel to get the maximum amount of direct exposure to sunlight17.Choosing the right system18
Determining the size of the photovoltaic system is crucial. If system design is undersized, this will result in the undergeneration of electricity. Conversely if the system is over sized, this will result in excess capacity and will represent an unnecessary expenditure of financial resources. The PV system design starts with a definition of the electrical loads. The initial system cost will be directly proportional to the amount of energy that the system is designed to provide. The electrical load is directly proportional to the electrical consumption of appliances which use the generated power. Consequently, a reduction of the load requirement (kWh) by 50 per cent will lead to a price reduction of the PV system by 50 per cent, thereby saving a substantial amount of capital for the potential investor.
The potential costs of running a solar panel system can be illustrated below:
The daily load can be calculated as follows:
Daily Load = Watts used by appliances x Time in use
In order to determine an approximate cost of a photovoltaic system to power the total daily load, various types of the photovoltaic (PV) system have to be taken into account. Provided that the PV system is ‘simple’, the total daily load has to be multiplied by three. Similarly, if the system is ‘typical’, then it should be multiplied by four and when it is ‘complex’, it should be multiplied by five. Let us say that a simple photovoltaic cell generates 500 watt-hours per day. Then we can determine the approximate cist of such system will be represented by 500x3 that amounts to $1500.
About 1.9 x 108 TWh per year is absorbed by the land surfaces of the Earth, from a continual energy input to the upper atmosphere of 1.8 x 1017 W. When we compare this with the total energy requirement of humanity (excluding food and wood) of 1.3 x 105 TWh/yr, we find that there is a sufficient amount of sunlight reaches the land in 6 hours capable of supplying the humanity’s energy needs for one whole year.
The Advantages of Solar Energy Production20
There are significant advantages to solar energy production. Clean Energy Ideas have provided an exhaustive list of some of these advantages which I would like to highlight here. The first advantage has to do with the fact that solar energy production is environmentally friendly. During their operation solar panels do not produce any pollution. The only pollution connected with solar panels may be associated with the process of their manufacture, transportation and manufacture. This is a very significant advantage for the use of solar panels since it not only limits the utilisation of the diminishing supply of fossil fuels in energy generation but as a consequence instantly eliminates all the devastating environmental effects that the latter have had and continue to have.
The second advantage of solar panels, as illustrated by Clean Energy Ideas, is their convenience. To begin with, solar panels operate very quietly and, as such, do not contribute to noise pollution. Secondly, electricity can be generated using solar panels in remote locations that are not linked to a national grid. An important example of such location is space, where satellites are powered by high efficiency solar cells. An added benefit of the installation of solar panels in remote locations is that such panels are usually much more cost effective since the laying of required high voltage wires is not required. Similarly, solar panels can be installed on rooftops, which eliminate the problem of finding the required space for solar panel placement. Solar energy can be very efficiently produced over a large area of the globe, and new technologies will allow for a more efficient energy production on overcast days. Finally, solar panels are financially convenient as well. Despite the fact that the initial investment of solar cells may be high, once installed, they will provide a free source of electricity, which will pay off over the coming years.Cons of Solar Energy21
The major obstacle to the adoption of solar energy is the initial cost of solar cells. Currently, prices of highly efficient solar cells can be above $1000, and some households may need more than one. This makes the initial installation of solar panels very costly. Solar energy is only able to generate electricity during daylight hours. This means for around half of each day, solar panels are not producing energy for a home requiring power storage batteries, which can take up private space. Equally important is the effect of the inconstancy of weather. The weather patterns directly affect the efficiency of solar cells and areas with low sunlight or high cloud cover won’t utilize solar panels efficiently. Due to the fact that significant levels of atmospheric pollution can interfere with the level of sunlight received by the solar panels, there is an inevitable risk of inefficiency in heavily polluted areas such as large cities and urban centres.
Research Analyst, Sun Strides Foundation
1-2. Africa's natural resources key to powering prosperity. May 2008. pg 3
3-8. Abdoulaye M. Yansane. National Solar Power Research Institute, Inc.
9. Matthias Loster. Total Primary Energy Supply.
10-15, 17. Solar Panel Information (SPI). How Do Solar Panels Work.
16. SANYO Develops Ultra-thin HIT Solar Cell with the World's Highest-level Conversion Efficiency of 22.8%
18. The Solar Electric Option. A joint Publication of the Arizona Corporation Commission and the Arizona Department of Commerce Energy Office.
19. Help Save the Climate (HSC). How Much Energy Does the Sun Provide?
20. Clean Energy Ideas. The Pros and Cons of Solar Energy.
An Introduction to Wind Power Generation
The conversion of wind power into forms of energy which can be used to power everyday, home appliances is one of the most attractive solutions from environmental and ecological perspectives. Of similar importance is the fact that wind power generation is a sustainable and economically advantageous form of energy generation. There is a general consensus among scientists that widespread reliance on fossil fuels, and the resulting high-levels of pollution, has contributed to global climate change. This global climate change has the potential for causing an adverse environmental impact, as well as possibly contributing to a significant loss of human lives in the future. As a result, the capability to generate power from a ‘clean’ source of energy such as wind is an important technological development. Moreover, apart from the self-evident environmental benefits of wind power, it should be emphasized that in economic terms it is also a cost-competitive energy resource. For example, research within the United States Department of Energy has shown that the cost of wind power generation across the nation has fallen from 25 cents/kWh in 1981 to an average of 4 cents/kWh in 2008, with half of the projects being conducted in the range of 3.3 to 5.2 cents/kWh, including the federal production tax credit.
A Case Study: Wind Power Generation in Africa
Given the advantageous nature of wind power generation, particularly in economic terms, it presents an important answer to some of the current energy problems facing the African climate. Despite the fact that levels of technological development are not uniform across the continent, several African countries have inadequate and intermittent provisions of power. This suggests a pressing need for a viable alternative to the conventional forms of power generation to be implemented on the continent. Despite the prima facie attractiveness of wind power development on the African continent it should be noted that natural obstacles to such realisation will remain. The African continent has a much lower wind resource due to the continent’s average low altitude as well the atmospheric heating caused by its proximity to the equator1. However, two factors make the rapid expansion of wind power production a viable and important substitute to fossil fuels. The first factor is the relatively low economic cost of generating energy from wind. The second factor is that the rapid growth and global momentum of the wind power industry makes it an alternative energy source of energy which may be disadvantageous to ignore. It has been estimated that the global, infrastructural capacity for wind power generation has increased by 36% in the 2007-2008 period, which accounts for a potential generation of an additional 27,000 megawatts (MW) of power across the globe, as well as shows an infusion of $51.5 billion into the wind power industry2. Such a significantly large increase in global investments will ultimately increase the efficiency and cost competitiveness of the global wind industry, thereby making it a very attractive power generating source for African countries.
How Wind Power Works
At this point of our introduction to wind power generation, it may be useful to go over some of the details involved in the process. In the case of wind power generation, there is a direct and proportional relationship between the wind conditions, such as strength and frequency, and the amount of power that is generated. This means that in any instance an increase in the strength and frequency of the wind there will be a corresponding increase in power produced by the wind turbines. The relationship between the wind speed and the power generated is also proportional in a ratio of 1:3. For every increase in the speed of the wind, there will be a three-fold increase in the power output, which means that a doubling of the wind speed will increase power output by eight times 3 . This fact demonstrates that the utilization of wind power generating turbines at specific times when there is a notable and recurring presence of higher-wind speeds has a clear economic advantage. As a result, the practical consideration of seasonal and daily variations prior to installation will ensure optimum power yields for the wind turbines.
Due to the determining influence of wind speed on the corresponding wind power, a classification of wind speeds has been constructed. Wind speeds are classified into seven classes in a continuous gradation from class one, which is the lowest class, to the highest, which is class seven. The calculation of wind speeds is usually undertaken by a wind resource assessment team. This team makes their estimates based on the recorded, average wind speeds above a section of land. These estimates are used to determine the wind class that is to be assigned to the area under consideration4.
This estimation of wind speed, and the corresponding ranking according
to wind class, has its first practical significance in its relation to
the operational capability of the wind turbines. The technical
particularity of the wind turbines resides in the fact that they only
operate over a limited range of speeds. The implication of this feature
of the wind turbines is that their performance or lack of performance
is to a significant extent determined by the wind speed in a particular
area. For example, a wind with a low speed may not be
able to turn the wind turbines, while in the presence of a strong wind
the turbines may have to be shut down in order to avoid structural damage5.
The second practical significance of the classification according to
wind class is that it clearly demarcates the range of wind speeds that
are most suitable for generating sufficient quantities of power for
public consumption. In this respect, it has been noted that wind speeds
in classes three and above, that is, those wind speeds which are in the
range of 6.7 – 7.4 meters per second m/s and above, are typically most
suited to power production on a scale that can satisfy the basic needs
of potential consumers6. It follows from the preceding consideration
that in order to maximize the production of power, there is a strong
preference for the construction of wind turbines on sites which have an
abundant supply of the higher wind classes. I have included a table
below which shows the wind class ranking, a category which is known as
the wind power density, and the ranges of wind speeds corresponding to
each wind class.
Classes of Wind Power Density at Heights of 10m and 50m
Several important features of the wind power generation process can be summarised from the table shown above. The table provides a summary of the estimates of the different ranges of wind speeds and links them to the particular wind classes and elevation. The table also introduces the concept of the Wind Power Density (WPD) mentioned above which provides an estimate of the wind energy per unit area which can be generated from the wind resource in a specific site. This means that it is possible to determine, in watts per square meter, the specific power productivity of turbines located at different sites. This WPD range is specified with respect to the elevation above the ground of a specific site: at a relatively low elevation of 10 meters above the ground and its lower wind speed to the higher elevation of 50 meters with its correspondingly larger wind speeds. It can be observed that the wind speeds tend to increase with a greater level of elevation.
The 'specific yield' is a term that is used to describe the annual energy output per square meter of area swept by the turbine blades as they rotate 8. The current conversion rate of wind power to electricity stands at 40 per cent. At sites with average wind speeds of seven m/s, a typical turbine will produce about 1,100 kilowatt-hours (kWh) per square meter of area per year. The production of power is directly related to the length of the turbine blades. For example, provided that a turbine has blades that are 40 meters long, with a total swept area of 5,029 square meters, the power output will be about 5.5 million kWh for the year. This means that an increase in blade length, and a corresponding increase in the total swept area, will have a significant effect on the energy per square meter swept by the turbine blades 9. As a result, the technical features of the wind turbines are very important in the consideration of the amount of power that a specific site needs to generate for its consumers.
Other Technical Features of the Wind Turbines
Under external observation, it can be shown that horizontal axis wind turbines consist of three big parts: the tower, the blades, and a box behind the blades which is called the nacelle. The nacelle is a central feature of the wind turbine. It is responsible for the wind turbine’s general function of converting the motion caused by the wind resource at a specific site into electricity. Large turbines don't have tail fans-they have hydraulic controls that orient the blades into the wind in the place of the tail fans 10 . In the most typical design, the blades are attached to an axle that runs into a gearbox. The gearbox, or transmission, steps up the speed of the rotation, usually from about 50 rpm up to 1,800 rpm. The faster spinning shaft spins inside the generator which produces AC electricity 11. Electricity must be produced at just the right frequency and voltage to be compatible with a utility grid 12. Since the wind speed varies, the corresponding variable speed of the generator can produce fluctuations in the electricity. One solution to this problem is to have constant speed turbines, where the blades adjust, by turning slightly to the side, in order to slow down when wind speeds are particularly high. Another potential solution is to use variable-speed turbines, where the blades and a generator change speeds in accordance with the wind conditions. Such variable-speed wind turbines use sophisticated power controls to fix the fluctuations of the electrical output. A third approach is to use low-speed generators.
Specifications of Wind Turbines
Modern electric wind turbines come in a few different styles and many different sizes, depending on their use. The most common style, irrespective of the size of the turbine is the "horizontal axis design", that is, with the axis of the blades being horizontal to the ground. In terms of size, small wind turbines are generally used for providing power off the grid: these range from highly compact 250-watt turbines designed for charging up batteries on a sailboat, to 50-kilowatt turbines that power dairy farms and remote villages. Large wind turbines are mostly used by utility companies to provide power to a grid system. Usually, turbines in this size range have a markedly large range of power provision: they can provide anything from 250 KW to the 3.5 to 5 MW, the latter representing the performance of significantly bulkier wind turbines which are located for use offshore. It has been estimated that in 2008, the average land-based wind turbines had a capacity of 1.67 MW 13. These different types of wind turbines are usually placed in groups in known windy locations
A collection of such wind "farms" can consist of a few or hundreds of turbines, providing enough power for tens of thousands of homes 14.
Advantages of Wind Energy15
Zero emissions - There is no emission of CO2, sulphur, nitrogen oxide, particulates, trace metals, or solid waste as opposed to the traditional reliance on fossil fuels. This means that the implementation of wind energy production can have a marked impact on human caused global warming and the acid rain, pollution, asthma, and other negative environmental/health consequences that this is known to produce.
Renewable - Wind is in constant supply. This has an advantage over alternative sources of energy such as coal, oil, and gas, whose supply may significantly diminish in the future.
Free - Because wind is an abundant natural resource without the need for processing, it can power production with operational costs which are effectively zero.
Declining costs - As installed capacity has increased, costs have dropped 85% in 15 years to <$0.05 per kWh. The DOE has set a goal of $0.025 per kWh by 2002 (1)
The promotion of the construction of sites for wind power generation has the benefit of creating new jobs and new businesses, thereby strengthening the U.S. economy.
Quick installation - Once a site has been selected and permits approved, wind turbine installation can be completed in months (compared to years required for all the activities connected with the installation of gas, coal, or nuclear plants).
Phased growth – It is possible to increase production capacity as consumer needs grow.
Mass appeal - Opinion polls consistently demonstrate strong popular support for clean-burning, renewable technologies like wind power.
Self-sufficiency - Because it can be developed domestically, wind power reduces U.S. reliance on imported energy.
Price stability - Unlike fossil fuel prices, which fluctuate due to factors beyond our control, wind power comes with a relatively fixed price, one likely to drop considerably over time.
Small footprint - Wind turbine towers are known to have minimal interference with other economic activities such as farming or livestock rearing associated with a particular site.
Low impact - Wind turbine operation offers little physical threat to wildlife and natural habitat.
Disadvantages of Wind Energy 16
High initial investment – Initially about 80% of the investment costs involve capital expenditure on machinery, and 20% of such costs go to site preparation and installation. However, following this initial phase of investment, there are minimal operating and only routine maintenance expenses.
Noise - Today's large wind turbines make less noise than the background noise you hear in your own home, 45 dB as opposed to 50 dB.
Aesthetic/visual impact - Today's turbines are sleek and appealing to the general public.
Intermittent – The wind must blow between the speeds of 16 mph and 60 mph for power generation. At present, wind energy cannot be easily stored. Electricity providers are usually trained to divert other energy sources to meet their energy demands. However, at the current rate of technological innovation, storage technology (batteries) should improve markedly over time.
Distribution - Wind turbines must be situated in proximity to the existing power distribution infrastructure (transmission lines), otherwise the costs of distribution may rise significantly.
Research Analyst, Sun Strides Foundation
1. Graham Richard, Michael. Enercon E-126: The World’s Largest Wind Turbine (For Now). http://www.treehugger.com/files/2008/02/enercon_e126_largest_wind_turbine.php
2. Global Wind Energy Council (GWEC). 2008. Global Wind 2008 Report Online http://www.gwec.net/index.php?id=153
3. US Department of Energy, Office of Energy Efficiency and Renewable Energy. 2009 “20 Percent Wind Energy by 2030: Increasing Wind Energy’s Contribution to US Electricity Supply”
4. Afriwea. There is Wind in Africa! Published in African Development Bank (ADP FINESSE Africa newsletter, August 2004)
5. UCSUSA. How Wind Energy Works.
6. Health link. Wind Pros and Cons, Myths and Misconceptions http://www.citizensinaction.org/windproscons37.html
- Alternative Energy: Alternative energy news and information resources about renewable energy technologies
Alternative Energy Country Analysis