Micro (Wind) Generation: \u27Urban Resource Potential & Impact on Distribution Network Power Quality\u27

Of the forms of renewable energy available, wind energy is at the forefront of the European (and Irish) green initiative with wind farms supplying a significant proportion of electrical energy demand. This type of distributed generation (DG) represents a ‘paradigm shift’ towards increased decentralisation of energy supply. However, because of the distance of most DG from urban areas where demand is greatest, there is a loss of efficiency. The solution, placing wind energy systems in urban areas, faces significant challenges. The complexities associated with the urban terrain include planning, surface heterogeneity that reduces the available wind resource and technology obstacles to extracting and distributing wind energy. Yet, if a renewable solution to increasing energy demand is to be achieved, energy conversion systems where populations are concentrated, that is cities, must be considered. This study is based on two independent strands of research into: low voltage (LV) power flow and modelling the urban wind resource. The urban wind resource is considered by employing a physically-based empirical model to link wind observations at a conventional meteorological site to those acquired at urban sites. The approach is based on urban climate research that has examined the effects of varying surface roughness on the wind-field above buildings. The development of the model is based on observational data acquired at two locations across Dublin representing an urban and sub-urban site. At each, detailed wind information is recorded at a height about 1.5 times the average height of surrounding buildings. These observations are linked to data gathered at a conventional meteorological station located at Dublin Airport, which is outside the city. These observations are linked through boundary-layer meteorological theory that accounts for surface roughness. The resulting model has sufficient accuracy to assess the wind resource at these sites and allow us to assess the potential for micro–turbine energy generation. One of the obstacles to assessing this potential wind resource is our lack of understanding of how turbulence within urban environments affects turbine productivity. This research uses two statistical approaches to examine the effect of turbulence intensity on wind turbine performance. The first approach is an adaptation of a model originally derived to quantify the degradation of power performance of a wind turbine using the Gaussian probability distribution to simulate turbulence. The second approach involves a novel application of the Weibull Distribution, a widely accepted means to probabilistically describe wind speed and its variation. On the technological side, incorporating wind power into an urban distribution network requires power flow analysis to investigate the power quality issues, which are principally associated with imbalance of voltage on distribution lines and voltage rise. Distribution networks that incorporate LV consumers must accommodate a highly unbalanced load structure and the need for grounding network between the consumer and grid operator (TN-C-S earthing). In this regard, an asymmetrical 3-phase (plus neutral) power flow must be solved to represent the range of issues for the consumer and the network as the number of wind-energy systems are integrated onto the distribution network. The focus in this research is integrating micro/small generation, which can be installed in parallel with LV consumer connections. After initial investigations of a representative Irish distribution network, a section of an actual distribution network is modelled and a number of power flow algorithms are considered. Subsequently, an algorithm based on the admittance matrix of a network is identified as the optimal approach. The modelling thereby refers to a 4-wire representation of a suburban distribution network within Dublin city, Ireland, which incorporates consumer connections at single-phase (230V-N). Investigations relating to a range of network issues are considered. More specifically, network issues considered include voltage unbalance/rise and the network neutral earth voltage (NEV) for increasing levels of micro/small wind generation technologies with respect to a modelled urban wind resource. The associated power flow analysis is further considered in terms of the turbulence modelling to ascertain how turbulence impinges on the network voltage/voltage-unbalance constraints

The Small Wind Energy Estimation Tool (SWEET) –a practical application for a complicated resource

Of the forms of renewable energy available, wind energy is at the forefront of the European (and Irish) green initiative with wind farms supplying a significant proportion of electrical energy demand. Increasingly, this type of distributed generation (DG) represents a “paradigm shift” towards increased decentralisation of energy supply. However, because of the distances of most DG from urban areas where demand is greatest, there is a loss of efficiency. One possible solution, placing smaller wind energy systems in urban areas, faces significant challenges. However, if a renewable solution to increasing energy demand is to be achieved, energy conversion systems in cities, where populations are concentrated, must be considered. That said, assessing the feasibility of small/micro wind energy systems within the built environment is still a major challenge. These systems are aerodynamically rough and heterogeneous surfaces create complex flows that disrupt the steady-state conditions ideal for the operation of small wind turbines. In particular, a considerable amount of uncertainty is attributable to the lack of understanding concerning how turbulence within urban environments affects turbine productivity. This paper addresses some of these issues by providing an improved understanding of the complexities associated with wind energy prediction. This research used detailed wind observations to model its turbulence characteristics. The data was obtained using a sonic anemometer that measures wind speed along three orthogonal axes to resolve the wind vector at a temporal resolution of 10Hz. That modelling emphasises the need for practical solutions by optimising standard meteorological observations of mean speeds, and associated standard deviations, to facilitate an improved appreciation of turbulence. The results of the modelling research are incorporated into a practical tool developed in EXCEL, namely the Small Wind Energy Estimation Tool (SWEET). This tool is designed to assist engineers gain an intuitive appreciation of the limitations associated with this form of energy. It is only through an understanding of such limitations that informed decisions can be made which ultimately facilitate more intelligent installations

Estimating the Yield of Micro Wind Turbines in an Urban Environment: A Methodology

Micro wind turbines currently have the majority share of micro (electricity) generation installations in Ireland. These technologies are being installed predominantly in rural environments, and current applications to the Distribution Services Operator (DSO) for connection of all types of micro generator stand at less than 500. Poor market dissemination of information and research findings compounded with poor options for spill payment - as well as onerous planning restrictions do not –it appears - create a platform conducive to encouraging development in this market. This paper outlines the complexities associated with evaluating the wind resource within an urban environment and investigates the means to ‘estimate’ wind regimes in an urban environment based on an extrapolation of a reference wind speed from a rural environment into the urban area. Methodologies for estimating the wind speed in such circumstances are considered with modeled wind data – benchmarked against wind data acquired from a site in the city centre - being applied to a set of commercially available wind turbines

Irish Large Scale Solar PV Opportunities: a Viability Analysis Prioritising the Influence of System Harmonics

This paper considers the techno-logistical considerations involved in designing for a large scale (\u3e100 kW) distributed generation (DG) opportunity. The logistical considerations involve site feasibility assessment in terms of resource, land requirements and PV plant design, whereas the technical considerations prioritise the impact that PV inverters can have on the performance of a power system; particularly in the context of the detrimental effects manifested by harmonic distortions. The analysis demonstrates that without proper consideration of the PV system configuration and how PV inverters are employed, capacity rating breaches will affect both the DSO and the consumer. Ultimately, the results point towards a need for policy measures that encourage power system studies at the logistical stage of development to encourage what is ‘the ultimate’ in a sustainable energy resource

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

Impact Assessment of High-Power Domestic EV Charging Proliferation of a Distribution Network

Transport electrification is becoming the mainstream as a means to improve efficiency, performance, andsustainability of transportation systems. Electrical vehicles (EVs) can help to de-carbonise the environment, but a downside isthe technical issues presented to the low-voltage distribution network. To quantify the stochastic nature of transport-affectedelectrification, probabilistic load flow is employed. Monte Carlo-based simulation is applied to accommodate the probabilisticuncertainties associated with variable EV charging patterns. This study considers high-power charging (up to 11 kW) at thedomestic level while monitoring power quality variations (voltage drop, voltage unbalance factor, voltage sag) standards. Thiswork focuses on the Irish and UK, distribution system operator\u27s–transmission system operator\u27s perspectives, as it will help toidentify the likely impacts due to high-EV charger proliferation at household locations. The results indicate that if a 3.68 kWcharger is used at the domestic level, it is possible for 40% of total household consumers to connect EVs directly to thedistribution network without any power quality breaches. Furthermore, the proliferation of EV can be increased up to 100% ifconstrained to the start, and middle portions of the network (relative to the feeder substation transformer). For higher chargercapacities (up to 11 kW), a bottleneck is presented regarding a resultant voltage unbalance factor

The Potential for Power Quality Problem Mitigation Through STATCOM

Consideration of spatial and temporal diversity of EV charging demand has been demonstrated to reduce the estimating impacts on the distribution networks. The data formulation is based on impact studies of Electrical vehicles (EV s) on distribution networks. It is suggested that Distribution System Operator (DSO) could benefit for new innovation/advancement in the market (BESS-STATCOM) in a way that makes networks more reliable/robust, In this regard such innovation creates more opportunities for demand side management, reduces planning uncertainties associated with stochastic nature of EV charging and makes space for demand side management. This work considers probabilistic load flow in a representative unbalanced distribution network and through Monte Carlo simulation increased the hosting capacity for DG/EV is considered in an Irish/UK context. Furthermore, this paper considers the potential for a distribution network deployed STATCOM in supporting EV penetration, while maintaining appropriate power quality (voltage) standards. To reduce the computation burden of Monte Carlo simulation an alternative (novel but simple) method is applied. In terms of the Irish/UK DSO perspective, this work will help to increase the hosting capacity of DG/EV without breaching power quality limits

Estimating the Wind Resource in an Urban Area: a Case Study of Micro Wind Generation Potential in Dublin, Ireland

The micro-turbine wind market in cities faces significant challenges due to the complexities associated with the urban terrain but, if a renewable solution to increasing energy demand is to be achieved, energy conversion systems where populations are concentrated, that is cities, must be considered. This research evaluates the urban wind resource by employing a physically-based empirical model to link wind observations at a conventional meteorological site to those acquired at urban sites. The approach is based on urban climate research that has examined the effects of varying surface roughness on the wind-field between and above buildings. Here, this is applied to link observations at Dublin Airport, outside the urban area, to those made at an urban and sub-urban site in Dublin where instruments were placed near roof-level and well above roof height. The log model to describe the vertical wind profile is tested against observations made over the course of a year. It is shown to have sufficient accuracy to assess the potential for micro–turbine energy generation in cities and illustrates that the urban wind resource can be evaluated from measurements made at a nearby site, adjusted for the urban site location

Swarm electrification: A comprehensive literature review

In the global North, the need to decarbonize power generation is well documented and the challenges faced are endemic to the design of the electrical grids. With networks relying on centralized generation, it can be difficult to replace fossil-fuel power plants with renewable energy sources as generation may be intermittent causing grid instability when there is no ‘spinning reserve’ [1]. In parts of the global south, however, many under-electrified nations have high levels of solar irradiance. This, combined with falling prices for solar panels, is allowing for alternative paths to electrification from costly grid extensions and has resulted in grids built from the bottom up [2]. These grids can vary considerably in scale and capacity, dubbed micro-grids, nano-grids, and pico-grids. They can utilize AC, DC, or both and generally have either a centralized or distributed topology where each design has specific advantages and disadvantages [3]. Bangladesh has seen an unprecedented proliferation of small solar home systems. After performing a case study Groh et al. [4] discovered much of the generated electricity was not being utilized

Role of reactive power (STATCOM) in the planning of distribution network with higher EV charging level

In recent years, new trends in electrification of the transport sector have been a major concern for distribution grid operators. New types of flexible, uncontrollable loads, such as EV, influence the reliability of distribution networks. This work is related to the distribution system planning framework, with a particular focus on uncoordinated flexible EV loads. The main focus is the enhancement of the hosting capacity of EVs on distribution networks, while maintaining power quality (especially voltage magnitude and voltage unbalance), which is ultimately a pre-requisite for increasing prosumer engagement. Several EV charging scenarios, in the context of UK/Irish distribution networks with increased penetration of EV prosumers are considered. The results show that reactive power compensation through STATCOM, in the context of EV integration, can provide continuous voltage support and thereby facilitate 90% penetration of network customer EV connections at a normal EV charging rate (3.68 kW). If fast charging (up to 11 kW) is employed, \u3c30% of network EV customers can be accommodated due to bottlenecks presented by the substation transformer loading