Wind Energy

Wind energy is one of the cleanest, most environmentally friendly energy sources in the world. It is cheaper than solar energy and widely available. Once installed the maintenance expenses are relatively low and the availability of the system (the percentage of time that the wind turbine is ready to generate) amounts to more than 98%. Further advantages include:
- Easy and quick installation
- Generation of local employment (can be locally manufactured)
- Economical (no fuels etc. needed)

Problems of using wind energy include the variation in wind speed, which depends on the time of the day, season, and weather conditions. Precise knowledge of the annual wind speed pattern at the site is required, which should be gained through a careful monitoring of the wind before installing the system. In addition, wind power is non-dispatchable, meaning that for economic operation, all of the available output must be taken when it is available. Therefore some sort of storage, usually batteries, is needed to use off-grid wind energy. Last but not least aesthetic reservations can sometimes hamper the construction of a wind turbine.

System Components
An off-grid wind energy-system usually consists of the following components:
- Wind turbine: Wind turbines are available in a rich variety to meet the needs for almost all kinds of applications, e.g. different power ratings or different types and levels of voltages. For off-grid-situations, turbines with rotor diameters of up to 20m and up to 100 kW of rated power are used. They are usually mounted on towers (80-120 feet high).
- Storage medium: The storage medium, usually a battery, makes the energy available at low wind speeds or "no-wind-days“. The battery can be expected to last up to 15 years.
- Voltage regulator: A voltage regulator or charge controller is an essential part of nearly all power systems that charge batteries. Charge controllers block reverse current and prevent battery from getting overcharged. Some controllers also prevent the battery from getting under- or discharged, protect from electrical overload, and/or display battery status and the flow of power.
- Inverter: Most household appliances use AC. Therefore, inverters are usually added to the system to convert DC into AC

Wind Energy in Africa
Currently 865 MW of wind energy capacity are installed in Africa and the Middle East (which is a rather small amount compared to e.g. Europe with 76.125 MW) . But like on the global scale wind energy becomes more important in Africa, too: for example, Kenya's Lake Turkana Wind Power consortium (LTWP), which should be fully operational in 2012, is supposed to provide 300 MW of power, satisfying almost 30% of the country's energy needs.
Off-Grid Wind Energy
According to the World Wind Energy Association, "the majority of the African population still has no access to electricity grids. [Therefore] small, decentralised and stand-alone wind energy systems, in combination with other renewable energies, will have to play a key role. This process of deploying technologies for rural electrification is still in its early stage. The main limiting factors are still the lack of access to know-how as well as to financial resources.“ Windmills can be used as stand-alone systems or as energy-providers for a local mini-grid. A Hybrid-Power-System (combination of wind-energy and a conventional diesel-generator) is among the most-commonly used minigrid-systems in projects of the World Bank, which is the biggest financier of off-grid rural electrification in developing countries.

Uses
Potential uses include water pumping, grinding and milling, refrigeration or micro-irrigation, battery charging, icemaking, schools, remote health posts or small scale commercial applications . Similar to solar-home-systems (SHS), wind-home-systems (WHS) are being piloted in some developing countries. A WHS is a commercially available, compact wind-turbine system (US-$ 600) that can deliver a monthly amount of energy comparable to a large SHS, depending on the average wind speed .

References
Abu-Jasser, Assad (2010): An Off-Grid Wind Energy System powering a Residence in Gaza, in: Journal of Applied Sciences in Environmental Sanitation, Volume V, No N, pp. 100-109. (http://www.trisanita.org/asespaper2010/asesvne100e1092010.pdf)
Alliance for Rural Electrification: Hybrid Power Systems based on Renewable Energies: a suitable and and cost-competitive solution for rural electrification. (http://www.ruralelec.org/fileadmin/DATA/Documents/06_Publications/Position_papers/ARE-WG_Technological_Solutions_-_Brochure_Hybrid_Systems.pdf
Global Wind Energy Council (2009): Global Wind Report 2009, Brussels. (http://www.gwec.net/fileadmin/documents/Publications/Global_Wind_2007_report/GWEC_Global_Wind_2009_Report_LOWRES_15th.%20Apr..pdf)
World Bank (2008): Designing Sustainable Off-Grid Rural Electrification Projects: Principles and Practices, Operational Guidance for World Bank Group Staff, Washington D.C. (http://siteresources.worldbank.org/EXTENERGY2/Resources/OffgridGuidelines.pdf?resourceurlname=OffgridGuidelines.pdf)
World Wind Energy Association (2010): World Wind Energy Report 2009, Bonn. (http://www.wwindea.org/home/images/stories/worldwindenergyreport2009_s.pdf)
Links
Alliance for Rural Electrification, http://www.ruralelec.org/30.0.html
Lake Turkana Wind Power consortium, http://laketurkanawindpower.com