The application of boundary layer climatology and urban wind power potential in smarter electricity networks

Smart electricity networks that address energy demand, efficiency and sustainability concerns are predicated on the ability to capture renewable energy in a controllable manner. Such networks will have a particular role in cities, where increasing demand is inevitable but this requires that primary (renewable) energy resources, including that of wind, is better understood. In this paper, the role of wind energy systems, as integral components of a smarter urban electricity network, is considered using a model of the urban wind resourcein Dublin, Ireland that is based on boundary layer theory and meteorological observations. This model is used in conjunction with an electricity network model to investigate the implications of wind energy contributions for the delivery of electricity.

The available wind resource in a city is estimated from wind observations at a conventional meteorological station located at Dublin Airport, outside the city. These observations are used to estimate the parameters of the logarithmic wind profile and establish a wind value at a height well above the roughness effects of the urban surface. This value is then employed to estimate wind speed within the inertial sub-layer of the urban boundary layer (UBL). The model is tested at two sites in Dublin: a suburban site with relatively low buildings and mature vegetation and a city centre site with taller buildings and little vegetation. At each site wind-speed and direction is recorded at a level that is approximately 1.5 times the average height of surrounding buildings using a three-dimensional sonic anemometer. The results indicate that in urban environments, there is a viable wind resource at heights 1.5-2 times the average building height and that estimates based on an understanding of the urban surface roughness can produce good estimates. This suggests that mapping the aerodynamic roughness of the city can provide insight into the potential wind resource across the urban area and the positioning of wind turbines to create a distributed generation (DG) system.

Integrating a DG system into an electricity distribution network is not straightforward as it must account for bidirection power flow and variability in voltage. Bidirectional power flow and in particular reverse power flow from the DG has the effect of causing the network voltage to rise. To investigate the implications of such a system for consumers connected to a DG system, a typical mean year of the urban wind resource is used to model power flow for a section Dublin suburban electricity network. The results suggest significant amounts of electricity derived from wind energy can be accommodated. From a smart network perspective, this type of holistic analysis is required if wind energy is to contribute significantly to meeting energy demand.