Assessing the potential for urban wind energy in Cape Town

As the demand for alternative and renewable sources of energy grows worldwide, it has been argued that small-scale Urban Wind Energy (UWE) could have the potential to provide a significant portion of the electricity demand for urban areas. However there is currently a lack of knowledge surrounding the realisable potential for UWE, especially in the South African context. In order to gain a better understanding of the potential for UWE and the barriers acting against its widespread uptake, it is essential to first quantify the resource potential. This study appraise and evaluate the UWE resource potential at six locations in Cape Town, South Africa in order to gain a solid understanding of the UWE resource potential and thus begin to build the knowledge base around UWE. In order to meet the research objectives, wind data was obtained from the South African Weather Service for six locations in Cape Town at five minute recording intervals for a period of two years. These locations were: The Royal Cape Yacht Club located in the Table Bay harbour, the Astronomical Observatory located in Observatory, and the Kirstenbosch Botanical Gardens located in Kirstenbosch, the Molteno reservoir located in Oranjezicht, the Automatic Weather station located near the Cape Town International Airport as well as the Cape Town Weather Office (WO) station which is also located at the Cape Town International Airport. The data sets are then analysed using a script written in the programming language R in order to quantify the wind energy resource potential of the chosen locations. The wind energy resource potential of each site was combined with four commercially available wind turbines power curves in order to calculate the expected annual energy production values of the various turbines at the each of the locations. Results from this study highlight the significant variability resource potential of the wind regime that occurs between the six locations. The lowest yearly average wind speed was 2.044m/s which was recorded at the Kirstenbosch recording station, while the highest average wind speed was 5.06m/s which was recorded at the WO station. The average of all six stations for the two year period was 3.24m/s. Therefore the WO station had the highest energy potential with a value of 1474 kWh/m²/year and the station with the lowest energy potential was the Kirstenbosch station with a value of 80 kWh/m²/year. Combining these resource potential values with power cures from four commercially available wind turbines yields the Annual Energy Production (AEP) values for the chosen site and wind turbine. These AEP values also varied drastically with the high of 4304 kWh/year being calculated for the SkyStream turbine at the WO station and a low of just 0.66 kWh/year being calculated at the Kirstenbosch station with the Turby turbine. This variability hampers the wide spread uptake of small scale wind power as the results from one area cannot be reliably used to infer the wind resource potential at another nearby site. Out of the six chosen locations in the Cape Town area, three of the locations (Royal Cape Yacht Club, the Automatic Weather Station (AWS), and the Cape Town Weather Office (WO)) showed potential for the installation of a small scale wind turbine, with the Horizontal Axis Wind Turbines (HAWTs) performing better than the Vertical Axis Wind Turbines (VAWTs). This is possibly due to the lower cut in wind speeds of the HAWTs compared to the cut in wind speeds for the VAWTs. The conclusions of this study show that the UWE resource potential in Cape Town is characterised by high resource variability between the various locations. Three of the six locations that were evaluated showed potential for UWE installations. This study has identified the major challenges associated with UWE to be the turbulence, lower hub heights of the wind turbines (this study used 20m as the standard hub height), and variability of the wind regime between locations