Maximising Penetration of Distributed Generation in Existing Urban Distribution Network (UDN)

Electrical power generation is currently moving towards greater penetration of distribution generation (DG), using multiple small generators instead of fewer and larger units. This can potentially create improvements in efficiency, by allowing use of waste heat (cogeneration). However, it also generates new problems related to control and co-ordination of large numbers of DGs, usually connected across the urban distributed network (UDN). In particular, concerns about security of supply and reliability together with the integration of new energy resources, are presenting a number of new challenges to system operators. One of the major changes that are being observed is the connection of significant levels of generation to the UDN. To accommodate this new type of generation the existing UDN should be utilised and developed in an optimal manner. It is well known that present arrangements for planning, dispatching and protection of central power generators are not directly applicable to the new technology. This thesis presents a mathematical method that facilitates the large scale integration of CHP generation, as the most common type of DG, connected onto the UDN. A new methodology is developed to determine the optimal allocation and, size of CHP generation capacity with respect to the technical, environmental and economic constraints of the UDN. The method estimates the adverse impact of any particular constraints with respect to the size and location of DG/CHP plants connected into the UDN. Also, the method provides the basis for quantifying the contribution that DG/CHP units makes to the security of energy supply i.e to what extent the particular DG/CHP can reduce the operational performance demand for the UDN facilities and substitute for the network assets. The method is implemented and tested on a 34 busbars network that represents a section of an UDN. The impact of CHP generation on losses in the UDN is also analysed and incorporated into the optimal capacity allocation methodology. The installation of CHP generation is leading to a major change in the way UDNs are designed and operated. UDNs are now used as a media to connect geographically distributed energy generation to the electrical power system, thereby converting what were originally energy supply networks to be used both for distribution and harvesting of energy. A mathematical model in the form of a Multiple Regression Analysis is presented in order to determine the maximum capacity of CHP generation that may be connected in a given area, while taking account of connection costs as well as technical, environmental, economic and operational setting constraints. Results obtained from various analyses related to the network performance and management are used as data for multiple regression analysis. These analyses include: load flow, fault analysis, environmental and economic analysis. The increased applications of CHP generation presents a substantial challenge to the existing connection policies used to connect CHP plant into UDNs. The section of a typical Irish UDN is used as a case study, and with reference to the available network parameters, the cost and benefits of CHP generations are determined under a number of planning and operational strategies. It is shown that a substantial increase in the net benefits of CHP generation is gained if the appropriate connection method is applied from the start and equally that significant CHP generation connection costs are sustained if ad hoc methods are employed. Connection of CHP generation can profoundly alter the operation of a UDN. Where CHP generation capacity is comparable to or larger than local demand there are likely to be observable impacts on network power flows and voltage regulation. In fact, two major problems to be considered are the voltage levels and operation of protection during faults and disturbances. New connection of CHP generation must be evaluated to identify and quantify any adverse impact on the security and quality of local electricity supplies. There are a number of well-established methods to deal with adverse impacts caused by CHP generation connection into a UDN. While a range of options exist to mitigate adverse impacts, under current commercial arrangements the developer will largely bear the financial responsibility for their implementation. The economic implication can make potential schemes less attractive and in some instances have been an impediment to the development of CHP generation in urban areas. Development of a CHP generation system connection algorithm corresponding to the Least Cost Technically Acceptable (LCTA) method is absolutely vital in order to maximise the penetration of CHP generation into existing UDN with respect to different UDN/CHP system operational settings/constraints and minimal economic implication. In this thesis, results from a number of mitigation methods analysis are compared and used to create the connection process algorithm. This algorithm equally can be applied in the connection process of other distribution generation technologies into existing UDNs

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

Long-Term Durability of Rooftop Grid-Connected Solar Photovoltaic Systems

Compared to their initial performance, solar photovoltaic (PV) arrays show long-term performance degradation, resulting in lower like-for-like efficiencies and performance ratios. The long-term durability of polycrystalline silicon (p-Si) solar PV modules in three roof-top grid-connected arrays has been examined. Electrical output, ambient temperature, cell temperature, solar irradiance, solar irradiation, and wind speed data were collected at hourly intervals from 2017 to 2021 from three 50 kWp PV installations in Northern Ireland. The results show the extent to which higher PV temperatures associated with more intense solar radiation decrease efficiency, fill factor and maximum power output for PV arrays in a temperate climate. Long-term durability trends for grid-connected roof-top solar photovoltaic systems can be obscured by diurnal and seasonal changes in environmental conditions. To reduce the influence of variable conditions, performance ratios (PRcorr) were “corrected” using the measured annual average cell temperature (Tcell_avg). Introduction of this temperature-correction reduced the seasonal variation of the performance ratio. Using temperature-corrected performance ratios, long-term (in this case those seen after fiveyears operation) performance degradation trends become evident with high confidence after six months for one PV array and within three years for the two other arrays. If lower statistical confidence in trends is acceptable, long-term degradation rates can be identified within one year of operation for all PV arrays examined. These results have the important implication that relatively short-duration outdoor PV performance monitoring may be reliably used to estimate long-term degradation and/or to calibrate normally-conducted accelerated testing

Impact of Combined Heat and Power Generation on an Industrial Site Distribution Network

Presence of Distributed Generation (DG) in Industrial Site Distribution Network (ISDN) can represent a significant impact on the operational characteristics of the network. Present planning and operation criteria use for ISDN are in general not suitable to cope with the presence of a significant DG capacity. The presence of DG provides considerable benefits from both engineering and economic viewpoints. However, it changes radial configurations of the distribution feeders. Consequently it may cause coordination failure to existing protection system which is originally set based on radial configuration. In addition, high penetration of DG into ISDN may increase feeder loss, and cause system voltage profile out of a required range. Distributed Generation may have a significant impact on the system and equipment operation in terms of steady state operation, dynamic operation, reliability, power quality, stability and safety for both ISDN user and electricity suppliers. The idea behind the connection of DG is to increase the reliability of power supplied to the customers, make use of a locally available resource and, if possible, reduce losses in transmission and distribution systems. The specific benefits depends on the local conditions and installation owner’s interest. The reasons for installing DG at ISDN include: i) Combined Heat and Power Plant (CHP) – High Efficiency ii) Standby/emergency generation-enhanced reliability The effect of the DG units on these quantities strongly depends on the type of DG units and the type of ISDN. DG units can be either directly connected to the ISDN, such as synchronous or asynchronous generators, or via a power electronics converter. In all these cases, the power flow in the ISDN as well as the network losses and the voltage control are affected. The introduction of DG alters the characteristics of the network. The number of technical constraints and factors are impacted by the amount of DG that is connected