Impact Partner Content: Absa | by Justin Schmidt, Head of New Sectors, Absa
In article three of a four-part series by Justin Schmidt, Head of New Sectors at Absa, he will unpack Wind with next weeks final articles unpacking the technologies which are changing the future state of the industry. South Africa will see a large investment into generation from wind farms in the coming decade, with this source of energy equating to 23% of the total generation capacity by 2030. In other words, this will be the fastest growing energy source in South Africa in the coming decade. While this is promising you won’t be able to install a huge tower and wind turbine at your business premises. In this article, wind turbine solutions for households and businesses will be explored and although many of us would love to have a wind turbine producing energy at home, the practical implications are explored below.
An introduction to Wind Energy
In this article we will not discuss the large utility-scale wind farms that you see but rather address the small-scale market. For many years, small-scale wind turbines have been used for electricity production in remote communities and for charging batteries. In South Africa, windmills have been used on farms for pumping water and electricity production. There are two types of small-scale wind turbine technologies namely: Vertical-axis wind turbines (VAWT) and Horizontal-axis wind turbines (HAWT).
Since the wind is basically moving air, energy contained in it is in the form of kinetic energy. The energy from the wind is extracted by rotor blades of the turbine causing the rotor and drive shaft to rotate within the turbine. This rotating shaft has mechanical energy which in converted into electrical energy within the generator of a turbine.
Small-scale wind turbines used for producing electricity for businesses or households generate DC power and must be converted to AC power using an inverter in order to supply appliances or machinery. Wind speeds can vary rapidly and may cause rapid fluctuation in the power produced by wind turbines. For this reason, small scale wind turbines are typically installed with some sort of buffering system such as capacitors or batteries to store energy and feed electricity at a steady rate. The schematic shows the typical layout of an installed wind turbine system to supply electricity to a business or household.
Wind energy potential of an area is characterized by its average wind speed. It is essential to measure the available resource, at the site of installation, for at least one year prior to installation. This is to better understand the available resource, potential energy yield from a wind turbine when installed and the financial feasibility thereof. Unlike solar energy, the availability and frequency of wind in a specific area can vary significantly year-to-year.
Source: WASA
The map depicts the Wind Atlas for South Africa (WASA) and was developed through the South African Wind Energy Project (SAWEP) by the South African National energy Development Institute (SANEDI), South African Weather Services (SAWS), Council for Scientific and Industrial Research (CSIR), University of Cape Town (UCT) and the Danish Research Institute . WASA provides the annual mean wind speeds at elevations of 50m, 100m and 200m for the entire country but the map indicates the potential at 100m elevations only. From the colour scale it is clear where the higher potential is (red) and who has lower potential (blue).
Unfortunately, the WASA is more representative of the potential for large-scale wind turbines, rather than small-scale wind turbines, which are positioned at much lower elevations where wind speeds and wind turbine performance will be largely affected by the surrounding terrain and infrastructure such as tall buildings.
Small-scale turbines operate effectively for annual mean wind speeds of 4 m/s and higher. These speeds are experienced throughout most of the country at a 100m elevation, however this could be significantly less at 10m where small scale wind turbines will be mounted.
Financial considerations for your business when investing in Wind
In most cases, small scale wind turbines is not the most cost effective renewable energy solution on a per kilowatt basis, however its energy production in areas that experience high and consistent wind or where energy access is limited it may prove its application superior when compared to other renewable energy technologies.
Small scale wind turbines are more expensive based on per kilowatt of capacity when compared to large-scale wind turbines. Furthermore, the need for energy storage devices i.e. batteries, tends to increase the capital and overall cost of the system over its lifespan. It should however be noted that the need for battery storage in wind turbine systems allows for more control of the release of the energy generated, allowing excess generated energy to be stored or consuming generated energy from batteries during peak-demand periods of the day when electricity rates are higher. This allows owners to maximise savings when offsetting energy consumed from the grid.
Lifespan and costs of Wind Turbines
Due to the moving parts in a Wind Turbine, there is a greater maintenance requirement than what we had noted for solar PV installations. Wind turbines have an expected life span of 20 to 25 years and should be serviced annually to ensure optimal performance. Servicing of wind turbines usually involves visual and noise checks for any blade or component failure which could diminish its performance. Servicing may also include the lubrication of components, if required. Most wind turbine systems make use of battery systems and inverters, which are also subject to maintenance and replacement after several years. Batteries require regular checks and maintenance and are also subject to replacement after several years depending on the specific type of battery technology used. Typically, inverters should be replaced after every 10 years of its service life. Servicing costs and warranty periods of all system components should always be checked in advance with the installer.
Suitable implementation
The target market for small scale wind turbines includes households, businesses, remote farms and lodges. Farms are well suited for HAWT since they are mostly in open areas with minimum obstructions allowing wind to blow with ease, whereas VAWT is suited for residential and commercial (businesses) applications in urban areas, where surrounding buildings could negatively affect the performance of HAWTs. VAWT also carries the benefit of being low and roof mounted (less of a visual impact) and creating less noise when compared to HAWT.
Due to its intermittent nature, wind energy requires another source of energy for stand-alone units in remote areas in order to smooth out the variability. Small-scale wind turbines are a favoured technology in stand-alone off-grid systems installed in remote rural areas, where it operates in conjunction with solar PV systems to generate electricity. These result in a hybrid system providing reliable power for off-grid electricity generation. When solar and wind technologies are together, both can be used simultaneously or sequential depending on the weather conditions.
Conclusion
While there is a place for small-scale wind technology it is clearly not as easy to adopt as solar PV or solar thermal and we have seen less uptake of this technology by households and businesses. We have seen, for example, that a lack of adoption in the agricultural industry has led to a hesitance to invest in this technology as no-one wants to be the test case. As energy prices continue to rise and more focus is placed on the small-scale wind sector we hope to see greater adoption, albeit not as quick as the rate we will be seeing large wind farms being built.
