Article

Fair consumer outcomes in the balance: Data driven analysis of distributed PV curtailment

Authors:
To read the full-text of this research, you can request a copy directly from the authors.

Abstract

This study analyses distributed photovoltaic (D-PV) system curtailment and impacts on consumers in response to high network voltages. Novel analytical techniques are applied to a unique real-world operational dataset of over 1,300 D-PV systems in South Australia to identify ‘tripping’. Data-driven methods are valuable due to the diverse range of D-PV conditions. South Australia is an insightful case study due to its D-PV rich network, where around one third of standalone housing now has a PV system. Findings suggest that overall curtailment is low, however some sites experience significant impacts of up to 46-95% curtailment per day, particularly during spring. The uneven distribution of impacts raises concerns regarding fairness, however network solutions to increase hosting capacity must be carefully balanced given the potential costs imposed on consumers without D-PV. Upscaling the estimated D-PV generation loss to all of South Australia indicates a total value of $1.2m-$4.5m per year in lost value to consumers with D-PV, considering clear sky days. Implications for policy makers and network operators are discussed in the context of strong projected D-PV uptake in Australia, and around the world. It is proposed that data-driven methods could inform future regulatory assessment processes to improve outcomes for all consumers.

No full-text available

Request Full-text Paper PDF

To read the full-text of this research,
you can request a copy directly from the authors.

... Apart from this, two previous Australian studies looked specifically into D-PV curtailment. Stringer et al. [4] studied D-PV system tripping curtailment due to high voltage conditions and assessed its impacts on energy users. The results indicated that the overall curtailment was low however, some energy users experienced significant curtailment up to 46-95% curtailment per day during spring. ...
... The authors emphasized the importance of using real operational data when informing regulatory processes to improve fairness of curtailment. The method developed for estimating D-PV tripping curtailment in [4] is also adopted in this study (Section 4.2.2.1). Miller et al. also conducted a data driven analysis to assess curtailment in [5]; however, the study was limited by small sample size. ...
... The D-PV tripping analysis adopted the methods developed in [4] to identify the start and end points for periods in which D-PV generation reduced to near zero. The linear method is applied to non-clear-sky days, whilst the polyfititeration method is applied to clear-sky days in most cases, as described in [4]. ...
Conference Paper
Australia has world leading uptake of distributed PV (D-PV) and increasing installations of battery energy storage systems (BESS). D-PV and BESS can provide various economic and environmental benefits to energy users, network companies and other industry stakeholders. However, integrating increasing levels of D-PV into electricity networks present a range of social, technical, and regulatory challenges such as voltage management in low voltage networks. To help distribution network service providers in managing network voltage effectively, it is increasingly required that inverter-based D-PV and BESS implement one or more of the following power quality response modes (PQRM): tripping (anti-islanding and limits for sustained operation), Volt-VAr (V-VAr) and Volt-Watt (V-Watt). The PQRMs can curtail power output which may limit opportunities and revenue that D-PV and BESS owners obtain from their investments. On the other hand, these modes can help with the management of voltage. Curtailment and Network Voltage Analysis Scoping Study (CANVAS) is a RACE for 2030 scoping study by the Collaboration on Energy and Environmental Markets at UNSW, including industry partners AGL, SA Power Networks and Solar Analytics. The study analysed two datasets including 1000 BESS sites from AGL’s Virtual Power Plant trial and 500 D-PV sites from Solar Analytics’ customer database both within the metropolitan Adelaide, focusing on the first two PQRM modes: tripping (anti-islanding and limits for sustained operations) and V-VAr curtailment. The study found a range of V-VAr response behavior from BESS and D-PV likely to be due to different installation dates and legacy standard settings. The tripping and V-VAr curtailment were not significant for most energy users (less than 1% of total generation); however, some energy users lost up to 20% of their total generation. This clearly raises the issue of fairness in relation to curtailment which will become a more prevalent issue as D-PV penetration increases.
... Through this participation, consumers can also schedule their loads based on dynamic electricity prices [2]. The motives for consumers to engage in such activities include: (1) reducing carbon footprint, (2) economic profitability; and/or (3) raising living standards through seeking comfort [3]. However, the increased engagement of consumers in such activities may impose new challenges to the operation of the system. ...
Article
Full-text available
Distribution system planning and operation has seen many structural changes due to the increased participation of consumers in the energy market and the adaptation of new technologies such as distributed energy resources (DERs), electric vehicles (EV) and local energy storage systems (ESSs). Despite the convenience of such technologies and the gradual drop in their prices, new technical challenges (e.g., excessive power losses) have emerged at the system level. Over the past few decades, power loss minimization in distribution systems has gained popularity and the need for loss sensitivity analysis (LSA) frameworks has become a necessity for its successful implementation. Existing work on LSA mostly focuses on system planning aspects through DER optimal placement and sizing. However, enabling LSA-based system operational applications is a vital step toward the successful transition to modern distribution systems (MDSs). Therefore, this paper presents a comprehensive overview on the state of the art in LSA for MDSs. First, the theoretical formulations of existing LSA methods are summarized. Then, the applications of LSA in distribution systems are highlighted. Finally, based on the analysis of literature, open research gaps and future research pathways are discussed.
... The penetration of solar generated electricity in the national grid often requires generators to closely follow load demand changes with additional storage or curtailment of generation [7], which raises the cost of production [8,9]. For optimal operation of the energy market, network planning and scheduling requires efficient solar power forecasts at both short-time (>10 min to 5 h) and longer term (>5 to 48 h) scales [10]. ...
Article
Full-text available
Solar energy production is affected by the attenuation of incoming irradiance from underlying clouds. Often, improvements in the short-term predictability of irradiance using satellite irradiance models can assist grid operators in managing intermittent solar-generated electricity. In this paper, we develop and test a satellite irradiance model with short-term prediction capabilities using cloud motion vectors. Near-real time visible images from Himawari-8 satellite are used to derive cloud motion vectors using optical flow estimation techniques. The cloud motion vectors are used for the advection of pixels at future time horizons for predictions of irradiance at the surface. Firstly, the pixels are converted to cloud index using the historical satellite data accounting for clear, cloudy and cloud shadow pixels. Secondly, the cloud index is mapped to the clear sky index using a historical fitting function from the respective sites. Thirdly, the predicated all-sky irradiance is derived by scaling the clear sky irradiance with a clear sky index. Finally, a power conversion model trained at each site converts irradiance to power. The prediction of solar power tested at four sites in Australia using a one-month benchmark period with 5 min ahead prediction showed that errors were less than 10% at almost 34–60% of predicted times, decreasing to 18–26% of times under live predictions, but it outperformed persistence by >50% of the days with errors <10% for all sites. Results show that increased latency in satellite images and errors resulting from the conversion of cloud index to irradiance and power can significantly affect the forecasts.
Technical Report
Australia has world leading uptake of distributed PV (D-PV) and increasing installations of battery energy storage systems (BESS). Recent reports estimate one in four households own D-PV and installation rates are anticipated to grow in the years ahead. D-PV and BESS can provide various economic and environmental benefits to energy users, network companies and other industry stakeholders. However, integrating increasing levels of D-PV into electricity networks present a range of social, technical, and regulatory challenges. Voltage management in low voltage networks is one of the most imminent challenges posed by the integration of increasing levels of D-PV. Traditionally, in a network with uni-directional energy flow, distribution network service providers (DNSPs) set the LV voltages at the higher end of their allowed range to maintain reasonable voltages during periods of peak demand and hence voltage drop. However, as energy flows bi-directionally through the LV network with increasing levels of D-PV installations, D-PV exports can increase the local voltage range. To help DNSPs in managing network voltage effectively, it is increasingly required that D-PV and BESS inverters implement one or more of the following power quality response modes (PQRM): 1. Tripping (anti-islanding and limits for sustained operation) on excessive voltages 2. Volt-VAr (V-VAr) 3. Volt-Watt (V-Watt) The PQRMs can curtail power output which may limit opportunities and revenue that D-PV and BESS owners obtain from their investments. On the other hand, these modes can help with the management of voltage and therefore, support the integration of higher levels of D-PV. The Curtailment and Network Voltage Analysis Scoping Study (CANVAS) is a RACE for 2030 scoping study conducted by the Collaboration on Energy and Environmental Markets at UNSW, with industry partners AGL, SA Power Networks (SAPN) and Solar Analytics. As a five-month scoping study, CANVAS’s main motivation is to develop preliminary socio-technical insights to inform industry stakeholders and policy makers about the current state of D-PV and BESS curtailment due to PQRM requirements. CANVAS consists of two research streams, social science and technical, with both delivering evidence-based results that have important implications for Australia’s fast growing and ever-changing energy landscape, where previous evidence-based results and studies have been limited. The full and succinct public reports can be accessed via RACE for 2030 webpage, under Fast Track reports: https://www.racefor2030.com.au/publications/
Article
Full-text available
With high electric vehicle (EV) adoption, optimization of the charging process of EVs is becoming increasingly important. Although the CO2 emission impact of EVs is heavily dependent on the generation mix at the moment of charging, emission minimization of EV charging receives limited attention. Generally, studies neglect the fact that cost and emission savings potential for EV charging can be constrained by the capacity limits of the low-voltage (LV) grid. Grid reinforcements provide EVs more freedom in minimizing charging costs and/or emissions, but also result in additional costs and emissions due to reinforcement of the grid. The first aim of this study is to present the trade-off between cost and emission minimization of EV charging. Second, to compare the costs and emissions of grid reinforcements with the potential cost and emission benefits of EV charging with grid reinforcements. This study proposes a method for multi-objective optimization of EV charging costs and/or emissions at low computational costs by aggregating individual EV batteries characteristics in a single EV charging model, considering vehicle-to-grid (V2G), EV battery degradation and the transformer capacity. The proposed method is applied to a case study grid in Utrecht, the Netherlands, using highly-detailed EV charging transaction data as input. The results of the analysis indicate that even when considering the current transformer capacity, cost savings up to 32.4% compared to uncontrolled EV charging are possible when using V2G. Emission minimization can reduce emissions by 23.6% while simultaneously reducing EV charging costs by 13.2%. This study also shows that in most cases, the extra cost or emission benefits of EV charging under a higher transformer capacity limit do not outweigh the cost and emissions for upgrading that transformer.
Article
Full-text available
The rapid increase in the number of PV installations in current low voltage (LV) distribution networks brings many technical operational challenges. This claims for the deployment of control strategies to deal with these concerns, especially those related to overvoltage issues. Based on this, this paper presents a comprehensive assessment of the performance of PV inverters operating with droop control for overvoltage mitigation using a stochastic methodology based on a Monte Carlo approach. The uncertainty related to the PV generation and the users' consumption behavior is fully considered through advanced statistical modeling techniques. Voltage magnitude and loading indexes are used as key metrics to assess the technical performance of the distribution network, simulated using OpenDSS, under two droop-based control strategies: Active Power Control (APC) and coordinated Reactive and Active Power Control (RPC-APC). The effects of curtailed energy on the PV users’ revenue is also analyzed. A case of study based on real smart meter data from The Netherlands is used. According to the obtained results, both control strategies are effective to mitigate voltage violations. Nevertheless, for the case of 100% PV penetration, the droop-based coordinated RPC-APC allowed an 18% more of exported energy than the droop-based APC control strategy.
Article
Full-text available
Active power curtailment of residential PV systems is an effective way to mitigate technical issues in distribution networks. However, existing curtailment schemes can treat households unfairly; e.g., Volt-Watt schemes increasingly being adopted worldwide inherently penalize PV systems at remote locations in radial feeders. Nonetheless, whether fairness is improved or not by alternative curtailment schemes depends on how the impacts on households are considered. In this context, household-centric metrics that quantify PV harvesting, energy export and financial benefit are used along with the Jain’s fairness index to assess fairness from different perspectives. To explore the trade-offs brought by schemes that consider fairness differently, four linearized, three-phase Optimal Power Flow (OPF)-based schemes are proposed to determine, periodically, short-term curtailment settings. Using a real Australian 22kV feeder and realistically modelled LV networks with 4,500+ households, a detailed comparison is carried out considering also a Volt-Watt scheme. Results demonstrate that all the schemes that consider fairness are effective in removing locational penalizations. However, in terms of fairness, their performance across the adopted metrics reveals noticeable trade-offs. This highlights the need for decision-makers to determine the metric from which fairness can be based upon in a way that aligns with their respective policies.
Article
Full-text available
Cloud transients cause rapid fluctuations in the output of photovoltaic (PV) systems, which can significantly affect the voltage levels in a low-voltage (LV) grid with high penetration of PV systems. These voltage fluctuations may lead to violation of the existing power quality standards. This study estimates the impact of rapid PV output fluctuations on the power quality in an existing LV grid by performing load flow analyses for scenarios in the years 2017, 2030 and 2050 using PV data with 20-second resolution. In this study, we propose a system for the mitigation of PV output fluctuations by altering the charging processes of electric vehicles (EVs) and we assess the effectiveness of the proposed system. Results indicate that PV output fluctuations have minor impact on the voltage levels in the year 2030, but PV output fluctuations induce considerable voltage fluctuations in the year 2050. The magnitude of the voltage fluctuations is dependent on the location in the grid, the installed PV capacity and the grid configuration. These voltage fluctuations can induce visible and annoying light flicker for a significant part of the day in the year 2050. Implementing the proposed system shows that EV technology can contribute in reducing the amount of visible and annoying light flicker considerably, however at the expense of increased charging costs for EV owners.
Article
Full-text available
The widespread deployment of autonomous inverter‐based solutions for mitigating voltage and frequency excursions caused by high‐penetration photovoltaic (PV) systems has drawn increased attention due to their potential impact on PV production. It is now important to quantify the amount of solar energy curtailed as a result of the activation of inverter‐based grid support functions (GSFs). This study proposes a methodology for estimating the impact of volt–watt on customer PV energy curtailment using smart meter voltage data. This method estimates maximum possible curtailment for a given volt–watt curve based on the customer smart meter voltage during the time period of interest. This study compares the proposed methodology with field measurements using irradiance and customer inverter data from Hawaii as well as with results from a previous simulation‐driven study on the impact of advanced inverter GSF activation on PV energy curtailment. Results show that the proposed method for estimating lost PV production caused by volt–watt control aligns reasonably well with field measurements and computer simulations for hundreds of customers. The proposed method could be used to estimate customer energy curtailment, which could inform future compensation mechanisms for utilities leveraging customer‐sited resources to mitigate high voltage and defer infrastructure upgrades.
Article
Full-text available
Behind-the-meter solar photovoltaics (PV) have the ability to impact the distribution system due to the significant fluctuations in energy production and potential reverse power flow. While these phenomena are well understood, this research will investigate the level of solar penetration at which voltage rise and flicker are observed on a real-world distribution network. Using solar power data measured at four second intervals from the Renewable Energy and Smart Grid Laboratory at Louisiana State University alongside detailed feeder data provided by a local utility, we investigate the impact of increasing levels of solar PV penetration on voltage rise and long-term flicker. Results suggest that feeders can handle up to 10% of customers installing 7-kW behind-the-meter solar systems before voltage rise and flicker are observed. For levels above 30% penetration, feeders experience significant power quality issues. We find that the safe penetration level of a specific feeder depends on the system’s topology.
Article
Full-text available
Residential demand profiles typically demonstrate a mismatch between energy demand and PV supply. Different solutions are proposed, such as demand side management and energy storage systems. Nevertheless, costs and environmental impacts of some technologies (e.g. batteries) are high. This paper proposes two system designs: Home Energy Storage (HES) and Community Energy Storage (CES). Besides electricity storage, heat storage is used in the two system designs to supply domestic hot water and space heating. Furthermore, the trade-offs between the different storage mediums in relation to costs are analyzed. To achieve that, different methodologies are used to size the electricity and heat storage mediums for HES and CES. Next, a multi-objective mixed integer linear programming model is developed to optimize the operation costs and CO2-emissions for each system design. After that, the model is tested on a residential community situated in Cernier (Switzerland). The results demonstrate that CES performs better than HES on economic and environmental performance due to economies of scale and the optimally sized storage capacity of the battery in CES. Currently, none of the proposed system designs is economically feasible. However, the sensitivity analysis shows that a profitable system design can be obtained for both HES and CES, when the electricity storage (i.e. battery storage) size is reduced and the heat storage (i.e. water storage tank) size is increased.
Conference Paper
Full-text available
Residential-scale photovoltaic (PV) inverters available in the market are embedded with two key functions designed to help mitigating voltage rise issues: Volt-Watt and Volt-var. Volt-var has attracted significant attention as it does not involve generation curtailment. However, residential-scale PV inverters are sized (kVA) to meet the peak active power generation of the panels (kW). Since active power generation is typically prioritized, their capabilities to absorb reactive power (kvar) during high generation periods will be limited. Using a real UK LV network, this work provides a comprehensive analysis to understand the extent to which the adoption of Volt-var control helps managing voltage rise issues. Considering different Volt-var curves and PV penetrations, results demonstrate that Volt-var control is ineffective when reactive power is needed the most. Furthermore, reactive power increases currents and, therefore, asset utilization. This highlights the importance of considering the kVA rating of inverters when adopting solutions involving reactive power.
Article
Full-text available
This study investigates the technical and financial potential of an aggregation of residential heat pumps to deliver demand response (DR) services to the Dutch Frequency Containment Reserve (FCR) market. To determine this potential, a quantitative model was developed to simulate a heat pump switching process. The model utilizes historical frequency and heat pump data as input to determine the optimal weekly bid size considering the regulations and fine regime of the FCR market. These regulations are set by the Dutch Transmission System Operator (TSO). Two strategies were defined that can be employed by an aggregator to select the optimal bid size; the ‘always available’ scenario and the ‘always reliable’ scenario. By using the availability and reliability as constraints in the model, the effects of TSO regulations on the potential for FCR are accurately assessed. Results show a significant difference in bid size and revenue of the strategies. In the ‘always available’ scenario, the average resultant bid size is 1.7 MW, resulting in €0.22 revenue per heat pump (0.5kWp) per week. In the ‘always reliable’ scenario, the average resultant bid size is 7.9 MW, resulting in €1.00 revenue per heat pump per week on average in the period 03-10-2016–24-04-2017. This is based on a simulation of 20,000 heat pumps with a total capacity of 1 MWp. Results show a large difference in potential between the two strategies. Since the strategies are based on TSO-regulations and strategic choices by the aggregator, both seem to have a strong influence on the financial potential of FCR provision. In practice, this study informs organizations that provide FCR with knowledge about different bidding strategies and their market impact.
Article
Full-text available
This paper investigates the interplay between the German incentive regulation and renewable capacity integration. A comprehensive review of the current incentive regulation scheme and its 2016 amendment is first presented. Then, results of ten representative interviews with large-scale distribution system operators are analyzed. Firstly, all necessary grid integration measures could so far be implemented. Secondly, creating proper incentives for intelligent operating equipment to partly substitute conventional grid expansion remains a challenge. Thirdly, the new curtailment regulation of 2016 is welcome, but will not become a substitute for grid expansion as long as renewable integration rates are high. Moreover, the discussions on further improvements to the incentive regulation scheme reveal a distribution conflict between grid operators and grid users.
Article
Full-text available
Currently, renewable energy is rapidly developing across the world in response to technical, economic and environmental developments, as well as political and social initiatives. On the other hand, excessive penetration of distributed generation (DG) systems into electrical networks may lead to various problems and operational limit violations, such as over and under voltages, excessive line losses, overloading of transformers and feeders, protection failure and high harmonic distortion levels exceeding the limits of international standards. These problems occur when the system exceeds its hosting capacity (HC) limit. The HC is a transactive approach that provides a way for the distribution network to be integrated with different types of energy systems. Accordingly, HC assessment and enhancements become an essential target for both distribution system operators and DG investors. This paper provides, for the first time, a systematic and extensive overview of the HC research, developments, assessment techniques and enhancement technologies. The paper consists of four HC principal sections: historical developments, performance limits, perceptions and enhancement techniques. Besides, practical experiences of system operators, energy markets and outcomes gained from real case studies are presented and discussed. It was concluded that success in integrating more distributed generation hinges on accurate hosting capacity assessment.
Article
Full-text available
Photovoltaics (PVs) have been widely reported as causing power quality problems for electricity distribution networks. Much of this literature gives the impression that networks, particularly low voltage networks, were effectively and proficiently managed and operated before the rise of PVs and that this new technology is causing problems that did not previously exist and would not currently exist if there were no rooftop PV systems. The purpose of this paper is to examine measured data of power quality at the customer service point of four random households in four different distribution networks in Australia. This is the first report of power quality examination from the perspective of the end-user (solar households). The results show that the low voltage distribution networks reported in this study do not have networks that meet required power quality standards-and this cannot be attributed to the rooftop PV systems reported here. The paper proposes that power quality failures in these low voltage networks could be attributed to poor historical management, missed opportunities to embrace PVs as a means of better network management, lack of acknowledgement of the emergence of the prosumer and lack of total quality management and systems thinking.
Conference Paper
Full-text available
Increasing penetrations of utility-scale PV introduce more operational uncertainty to power systems, as it firstly creates more short-term imbalance between demand and supply due to the variable and only partially predictable behaviour of PV over short time frames, and secondly displaces conventional generation which traditionally assists in managing system imbalance and provides inertia to resist short-term frequency deviations. In the Australian electricity market, frequency control ancillary services (FCAS) are used to purchase regulation services to correct short-term uncertainty within the 5-minute dispatch period, and contingency services to correct manage sudden unexpected changes in demand or supply. However, it is unclear if and how these arrangements might need to change with more PV. One risk is that penetrations of PV might be unnecessarily unlimited given the present uncertainties of its impacts. This paper seeks to address some of these questions by analysing the short-term operational characteristics of utility-scale PV in the Australian National Electricity Market, at the timescale of seconds. Several studies have been carried out to understand the short-term characteristics of PV output, including the magnitude and frequency of output fluctuations and ramp rates over different timescales in different regions. However, the limited availability of high resolution data for utility-scale PV has hampered such work. Our study analyses four second-resolution output from four utility-scale PV plants (20 MW-100 MW) that are registered generators in the Australian National Electricity Market (NEM). The statistical analysis examines the significance of PV output fluctuations at this 4-second timescale. The results show that the variability over a four second time interval is insignificant, but that extreme events, with ramp rates of the size of the entire utility PV plant, potentially sufficient to trigger frequency regulation and contingency services, do occur albeit infrequently. These events are much more likely to be caused by operation issues rather than cloud transients, a challenge shared by conventional generation which is also subject to sudden unexpected forced outages. Although the current level of PV penetration in the NEM is low such that the impacts are barely visible, the variability of combined PV plants suggests that there is more frequency occurrence of large magnitude change in aggregated PV power output. This study represents the first stage of work assessing the scale of the variability challenge imposed by utility PV, and hence appropriate management options.
Article
Full-text available
This paper discusses the technical, regulatory and policy challenges inherent in planning and operating power systems with high penetrations of Distributed Energy Resources (DER): generators, flexible demand and energy storage connected within electricity distribution networks. Many liberalised electricity systems worldwide are seeing growth in DER including significant capacities of distributed renewable generation. The paper starts from the premise that optimal distribution networks are those that satisfy the objective of a lowest cost power system whilst meeting customers’ expectations of reliability and societal desire for sustainability. It highlights major challenges that policy makers face in respect of market and regulatory arrangements that support energy and flexibility provision from a large number of small, variable and often uncertain resources. These challenges include the need to respect the technical limits of the system and ensure its operability, development of well-designed mechanisms to support innovation, and an appropriate share of risk between market actors. A key contribution of the paper is to discuss the opportunities offered by more active distribution system operation as a substitute for capital investment and its regulatory and policy implications. Finally, the paper presents priorities for policy to facilitate a highly distributed electricity system.
Conference Paper
Full-text available
Consumers in Australia have made substantial investment into Distributed Energy Resources (DERs) and in particular, rooftop solar PV. However, there remains limited visibility of the technical conditions experienced by these technologies in the LV network. An improved understanding of these technical conditions has the potential to support more transparent, technically and economically appropriate investment and operational decision making by both consumers and network utilities. In this study, a suitably anonymised data set of voltage measurements at 2,010 sites across Australia with distributed PV provided by Solar Analytics is analysed. Our assessment highlights that, generally, voltage conditions on the low voltage networks at sites with distributed PV are high; the great majority of measurements are greater than the nominal voltage for each network region with some potential for non-compliance. Voltage conditions were also found to vary significantly over the course of the day for different regions and seasons, in accordance with varying net demand and, presumably, network voltage control actions. Importantly, a wide range of voltages are observed during solar generation periods as well as times of lowest load, with low voltage conditions seen at peak load periods in some jurisdictions. These variations have implications for the performance of distributed PV including questions of voltage 'headroom' for PV generation, the challenges of managing low voltage excursions at times of peak demand, as well as for network voltage management more generally. The study highlights the benefits of improved visibility regarding power quality conditions on the low voltage network.
Article
Full-text available
The integration of rooftop photovoltaic systems in the low-voltage distribution grids has become a major international trend, helped by the sinking prices for photovoltaics. One of the key questions revolves around the technical challenges brought about by the grid integration of these decentralized systems. This paper therefore analyzes the substantial practical experiences of ten representative German distribution system operators, who play a leading role in this field. Our findings show that grid expansion measures are primarily undertaken to ensure compliance with the permissible limits for voltage and current. Grid optimization measures represent the most economical initial step and include, for instance, changes in grid structure and wide-area control. Once their potential is maximized, classic grid expansion measures such as laying parallel cables are implemented. In individual cases, the low-voltage grid is reinforced by so-called intelligent operating equipment such as voltage regulators or voltage-regulated local distribution transformers. Moreover, improved grid planning measures lead to a better use of the available low-voltage grid capacity. The practical solutions successfully implemented by German distribution system operators should also prove relevant for other countries that are currently planning the deployment of decentralized renewable energies.
Article
Full-text available
Australia has likely the world's highest residential PV system penetration. In this paper, the impact of distributed PV on peak demand at different distribution network zone substations (ZSs) is assessed by upscaling 15 minute PV generation data from 270 distributed PV systems across Sydney, Australia and comparing it with load data from around 138 ZS serving the Sydney region. Gross load (load had there been no PV) was estimated, allowing the impact of current and higher PV penetrations on the value and time of peak at the different ZSs to be assessed. A probabilistic assessment of the impact of PV on ZSs is conducted, based on the availability of PV during the peak demand periods. To better understand the impact of PV on peak demand, K-means clustering is used to group ZSs based on PV generation during peak periods as the clustering features. Mapping of PV availability across percentage of peak times for all ZSs highlights the inter-annual variability of peak reductions, and the potential impact of short term load shifting. The impact of different penetration levels of distributed PV on the peak demand of the entire distribution network is also assessed by aggregating the ZS loads. Full text: http://ieeexplore.ieee.org/document/8036203/
Conference Paper
Full-text available
The incorporation of distributed PV generation data into power system planning and operation is becoming increasingly important as penetrations of PV systems on Australian distribution networks continue to grow. However, the availability of such data is currently very limited. The APVI Live PV Map (Live Map) provides near real-time distributed PV generation estimates in 57 different regions across Australia based on some 6000 PV systems reporting their generation on-line. This data has a wide range of potential applications including, for example, network planning or PV performance assessment. In this paper we investigate the characteristics of the PV systems contributing to the Live Map database, in order to assess its accuracy and suitability for providing total distributed PV generation estimates for power system planning and operational purposes. The study compares the sample of PV systems contributing data to the Live Map database with the total set of PV systems in Australia, according to the Clean Energy Regulator's (CER's) database. Representativeness is assessed in terms of PV system location, size, age, and inverter manufacturer. The accuracy of the APVI Live Map PV generation estimates for individual regions is assessed by comparison with a separate database of historical interval metered household PV generation from the Ausgrid network. Finally, an example of the application of distributed PV data to electricity network planning is provided to highlight the potential value of these PV generation estimates.
Article
Full-text available
High penetrations of photovoltaic (PV) systems in distribution grids have brought about new challenges such as reverse power flow and voltage rise. One of the proposed remedies for voltage rise is reactive power contribution by PV systems. Recent German Grid Codes (GGC) introduce an active power dependent (APD) standard characteristic curve, ${rm Q}({rm P})$, for inverter-coupled distributed generators. This study utilizes the voltage sensitivity matrix and quasi-static analysis in order to locally and systematically develop a coordinated ${rm Q}({rm P})$ characteristic for each PV system along a feeder. The main aim of this paper is to evaluate the technical performance of different aspects of proposed ${rm Q}({rm P})$ characteristics. In fact, the proposed method is a systematic approach to set parameters in the GGC ${rm Q}({rm P})$ characteristic. In the proposed APD method the reactive power is determined based on the local feed-in active power of each PV system. However, the local voltage is also indirectly taken into account. Therefore, this method regulates the voltage in order to keep it under the upper steady-state voltage limit. Moreover, several variants of the proposed method are considered and implemented in a simple grid and a complex utility grid. The results demonstrate the voltage-regulation advantages of the proposed method in contrast to the GGC standard characteristic.
Article
Full-text available
Local PV storage systems are emerging in Germany as PV feed-in tariffs have dropped below electricity prices for households. These PV storage systems provide the opportunity to increase the local consumption of locally generated PV energy. The so called self-consumption does not imply an explicit benefit for highly PV penetrated distribution grids suffering PV related voltage rises. Hence, this paper introduces several local voltage control strategies using PV storage systems. These strategies focus on adding a voltage control capability to self-consumption strategies through a combination of voltage dependent battery charging, automatic reactive power provision as well as PV power curtailment. Their potential to smooth the grid integration of PV while increasing self-consumption is assessed through grid simulations and an economic evaluation. In conclusion, PV storage systems which are capable of voltage control can improve PV grid integration and provide a benefit to storage system owners.
Article
Full-text available
This work discusses the technical and economical benefits of different active and reactive power control strategies for grid-connected photovoltaic systems in Germany. The aim of these control strategies is to limit the voltage rise, caused by a high local photovoltaic power feed-in and hence allow additional photovoltaic capacity to be connected to the mains. Autonomous inverter control strategies, which do not require any kind of data communication between the inverter and its environment, as well as an on-load tap changer for distribution transformers, is investigated. The technical and economical assessment of these strategies is derived from 12-month root mean square (rms) simulations, which are based on a real low voltage grid and measured dc power generation values. The results show that the provision of reactive power is an especially effective way to increase the hosting capacity of a low voltage grid for photovoltaic systems.
Article
Full-text available
The objective of this paper is to provide an assessment on voltage profiles in residential neighborhoods in the presence of photovoltaic (PV) systems. The network was modeled in PSCAD using common feeder characteristics that Canadian system planners use in suburban residential regions. A simulation study was performed to investigate potential voltage rise issues in the network up to 11.25% total PV penetration in the feeder and LV transformer capacity penetration up to 75%. Results indicate that the PV penetration level should not adversely impact the voltage on the grid when the distributed PV resources do not exceed 2.5 kW per household on average on a typical distribution grid. Moreover, the role of feeder impedance, feeder length, and the transformer short circuit resistance in the determination of the voltage rise is quantified.
Article
Solar photovoltaic (PV) systems generate electricity with no marginal costs or emissions. As a result, PV output is almost always prioritized over other fuel sources and delivered to the electric grid. However, PV curtailment is increasing as PV composes greater shares of grid capacity. In this paper, we present a novel synthesis of curtailment in four key countries: Chile, China, Germany, and the United States. We find that about 6.5 million MWh of PV output was curtailed in these countries in 2018. We find that: Policy and grid planning practices influence where, when, and how much PV is curtailed; Some PV curtailment is attributable to limited transmission capacity connecting remote solar resources to load centers; PV curtailment peaks in the spring and fall, when PV output is relatively high but electricity demand is relatively low. We discuss available measures to reduce PV curtailment as well as increasing PV curtailment in the contexts of evolving grids and energy technologies.
Article
This article presents an overview of the photovoltaic solar energy integration in the South American energy matrix. This work addresses aspects such as requirements established in the grid codes to connect solar plants to the power grid, the necessary protections for the connection of small-scale photovoltaic systems, the provision and prospects of ancillary services and the energy and solar potential of the region. This research aims to highlight a summary on different aspects of connecting photovoltaic systems to the grid in 8 countries in South America with similar socioeconomic development. In this way, it is possible to compare connection requirements and regulations for each country, resulting in a view of the best practices to introduce photovoltaic facilities in the region. As a result of the study, Chile is pointed out as the South American country with the highest penetration of photovoltaic energy due to the expressive levels of solar irradiation. It is also the country that presents the strictest criteria concerning the integration of photovoltaic generators to the electrical grid.
Article
Highly spatially resolved data from across Great Britain (GB) are combined with a distribution network modelling tool to assess impacts of distributed photovoltaic (PV) deployment up to 2050 on local networks, the costs of avoiding these impacts, and how these depend upon context. Present-day deployment of distributed PV, meter density, and network infrastructure across GB are found to be highly dependent on rurality, and data on these are used to build up three representative contexts: cities, towns, and villages. For each context, distribution networks are simulated, and impacts on these networks associated with PV deployment and growth in peak load up to 2050 calculated. Present-day higher levels of PV deployment in rural areas are maintained in future scenarios, necessitating upgrades in ambitious PV scenarios in towns and villages from around 2040, but not before 2050 in cities. Impacts of load growth are more severe than those of PV deployment, potentially necessitating upgrades in cities, towns, and villages from 2030. These are most extensive in cities and towns, where long feeders connect more customers, making networks particularly susceptible to impacts. Storage and demand side response are effective in reducing upgrade costs, particularly in cities and towns.
Article
In some cases, increased deployment of distributed photovoltaic (PV) systems can impact the distribution grid, including causing steady-state voltages and thermal loading of lines and equipment to deviate from operational limits. We present techno-economic analysis of three possible solutions for mitigating these effects on two real feeders: traditional infrastructure upgrades, autonomous volt-var controls, and a distributed energy management system (DERMS). We focus on issues arising in aggregate from residential and small commercial PV systems at different penetration levels and use a bottom-up approach that couples cost modeling with sequential hosting capacity analysis and quasi-static time-series simulation. We compare trade-offs for each solution in terms of effectiveness, upfront capital costs, operating costs, PV output curtailment, and distribution system losses. We find that volt-var controls offer the lowest cost option for hosting capacity expansion but cannot mitigate all violations at high penetration levels. For the feeders studied, the range of upfront cost for the DERMS and traditional upgrades is similar, but the DERMS results in a greater expansion of the hosting capacity. However, unlike traditional solutions, DERMS also involves higher level of PV curtailment than is observed with autonomous volt-var controls.
Chapter
The continuing increase of photovoltaic (PV) generation in distribution systems comes with difficulties in keeping voltages within acceptable limits, especially during peak generation. Two conventional alternatives exist to solve these overvoltage issues: to install voltage regulation equipment (AVR) or curtail PV generation, but there is no existing procedure to aid distribution system operators (DSO) in choosing either solution from an economical perspective. This project presents a methodology to evaluate the two aforementioned alternatives. The equivalent annual cost of installing automatic voltage regulator systems in the network was compared to the annual compensation awarded to curtailed PV generator owners. Several case studies were explored and show that in some situations, curtailment can be more cost-effective depending on the curtailment compensation scheme used, amount of PV penetration, location of PV in the network, and demand profiles. Additionally, the researchers explored the economic viability of using curtailment in conjunction with existing AVR installations instead of installing additional AVRs.
Article
The development and deployment of advanced distribution management systems (ADMSs) is imperative to address the increasingly complex operational challenges faced by aging electric power distribution systems, while ensuring reliable and resilient operations. Along with integrating the processes across multiple systems that are typically isolated, an ADMS allows for the development of applications that can readily access information from various subsystems, apply advanced analytics, and effectively control and coordinate traditionally segmented systems. This article presents an overview of ADMS applications for emerging electric power distribution systems and identifies future research directions. PDF Available: https://www.nxtbook.com/nxtbooks/pes/powerenergy_010220/index.php#/p/62
Article
Many countries have experienced a surge in the level of the penetration of solar PV systems in the last decade. A huge portion of the newly deployed PV systems are connected to low voltage Grid. High Penetration of PVs at this level could potentially disrupt the normal operation of distribution network. A major concern is the impact of these units on power quality indices. Namely, photovoltaic panels could increase the level of voltage and current unbalance, deteriorate harmonic distortion and cause the voltage rise. These concerns may prohibit higher pentation levels of PVs. Thus, proper assessment techniques are vital for network operators for the planning and decision-making process. On the other hand, many characteristics of PV system are inherently uncertain. These uncertainties should be properly modeled in assessment framework. The main effort of research communities is to propose new methodologies that could model the uncertainty of solar power generation and stochastic assessment methods that could accurately estimate the state of the operation of the network with different levels of penetration of solar photovoltaics. This paper provides a comprehensive review of recent publications and trend of research activities regarding methods of representing uncertain variables and stochastic assessment techniques for power system quality analysis.
Article
This paper proposes an impact-assessment framework to appropriately assess the impacts of two different types of distributed solar photovoltaic (DPV) installation on a realistic distribution network. To examine the spontaneous customer-based installations, a detailed Monte Carlo-based technique is introduced. For the controlled utility-based installation, a multi-objective optimization problem for the sizing and location of DPV installation is formulated aiming to improve energy loss, voltage deviation, and voltage fluctuation, avoiding reverse power flow and voltage violation. Solar insolation study is performed using light detection and ranging (LiDAR) data to estimate the potential of the network for DPV installation. In addition, a synthetic load profile modeling is developed to create yearly electricity load profiles for all the buildings in the given distribution network. The proposed framework is applied to a local distribution network with synthetic load profiles, Geographic Information System (GIS), and realistic solar insolation. It is found that for customer-based installation, voltage violation occurs beyond 30% of DPV penetration level, demonstrating the necessity of utility-based installation scheme for higher penetration ratios. Beyond a specific threshold, the probability of reverse power flow significantly increases in customer-based installation. Therefore, to achieve higher penetration ratios without reverse power flow and other negative impacts, utility-aided installation is necessary.
Article
This paper presents the benefits of the solar photovoltaic technology and the operation challenges corresponding to the large-scale integration of this technology in the distribution networks. A voltage control algorithm is proposed to mitigate the adverse effects of PV generation on the voltage profile of the distribution network. An operation planning framework is proposed that captures the heterogeneous objectives of the generation and demand entities and features limited information sharing among these entities.
Article
In concert with the transformation of conventional passive power distribution system, distributed energy resources (DERs) have progressively become participants in the provision of electricity services in active distribution networks (ADNs). In this paper, we propose a systematic valuation process to quantify the value of DERs in the ADN context. The paper first provides comprehensive insights into the impacts of DERs on ADN and the society as a whole. Given the technological, locational, and temporal diversity of DERs, a two-part scheme is developed to value and compensate DER portfolios proposed by customers and independent third parties. In particular, DERs are valued for their benefits and costs in both short and long terms. An integrated resource planning model is formulated to quantify the value of a given DER portfolio to be installed, where bi-level optimization techniques are applied to coordinate decisions on ADN planning and operations. In order to determine the short-term operation benefits of the DER portfolio on a continuous basis, a retail market operation model is developed based on peer-to-peer energy transactions among prosumers, when the impacts of DERs on ADN operations are monetized by distribution locational marginal prices. It is finally concluded in the paper that the proposed valuation scheme will not only contribute to the proactive investment of DERs in ADN but also help enhance the role of DERs in offering affordable, reliable, resilient and sustainable electricity services to customers.
Article
Residential air-conditioner loads are known to be a key driver of summer demand peaks for some electricity industries. Such demand peaks occur infrequently but have potentially severe implications for network and peaking generation plant investment, and hence electricity prices for end users. Detailed assessments of air-conditioner peak demand have, however, been hampered by limited residential consumption data, and even when interval meter data is available, the complexities of other household loads and behavior. This study utilizes data from a significant appliance level consumption monitoring project in Sydney, Australia, to analyze the actual contribution of air-conditioners to regional summer demand peaks. K-means clustering is used to characterize air-conditioner load profiles across a large number of households at times of these overall demand peaks. These clustered air-conditioning load profiles, combined with a number of possible load control strategies, are then used to estimate possible peak load reductions from air-conditioner demand response across the Australian State of New South Wales. Our findings suggest that residential air-conditioning presents a significant demand response opportunity, approaching perhaps 9% of total peak demand in some circumstances.
Article
Driving through many neighborhoods of Hawai'i, it is hard to miss the nearly ubiquitous rooftop solar photovoltaic (PV) systems that have popped up during the past eight years or so. Relatively high electricity costs associated with island grids, coupled with various incentives, have made it cost-effective to install solar over the last eight years, as evidenced by the PV-deployment chart in Figure 1. On the most populous island, O'ahu, the PV nameplate acgenerating capacity of 502 MW totals nearly half of the annual peak load for the entire island, which is 1.1 GW . Of that 502 MW of PVs, 54% is from private rooftop solar-nearly 50,000 residences or roughly one of every three single family homes. But Hawaiian Electric, the local utility, has no way to monitor or control the PV generation, even for most nonresidential systems. This means that on sunny days, up to approximately half of the PV generation is outside of the utility's control. This poses many challenges for utility planners and operators-challenges that Hawaiian Electric has been working diligently to address, along with various partners, notably the U.S. Department of Energy (DOE), the National Renewable Energy Laboratory (NREL), and its Energy System's Integration Facility (ESIF). This article describes how Hawaiian Electric has worked with engineers in NREL's Power Systems Engineering Center to improve the way its grid operates with very high levels of distributed PVs, largely by changing the way the PV inverters are operated.
Article
Distributed photovoltaic (PV) generator systems (especially rooftop PV) have been increasing significantly in electrical power systems. However, due to the variability of their output power, it is challenging to integrate large number of these PV generator systems into the existing electrical grid. These distributed PV generator systems can cause large voltage fluctuations due to the oscillation in their power output and reverse power flow in highly penetrated areas. While real power curtailment is an option to manage voltage issues, it reduces the production of this clean energy and is governed by policies and contracts. Traditionally, the use of reactive power to control voltage on a power grid is done through maintaining the voltage within a tolerable range by using transformer tap-changers (TPC), capacitor banks (CB), voltage regulators (VR), static synchronous compensator (STATCOM), and static Var compensators (SVC). Installation and maintenance costs of these devices can be quite high and some have relatively slow response times on the order of many seconds. A smart PV inverter can help regulate voltage by absorbing and injecting reactive power (Var) to/from the grid by using the Volt-Var control function. This paper presents an experimental analysis of the inverter Volt-Var control method for voltage regulation. The capacitive (i.e., Var injection) and inductive (i.e., Var absorption) effects of using a smart inverter and its ability to influence the voltage at the distribution level is investigated in this paper. When the smart PV inverter injects reactive power, it increases the distribution voltage. Conversely, voltage is reduced when the smart inverter absorbs reactive power. As a result, electric power utilities can control the distribution voltage without installing additional devices on the power network. The analyses from a field deployment under the Maui Advanced Solar Initiative Project in Hawaii is discussed here.
Article
Photovoltaic (PV) power generation is an important component for the future energy system. High penetration of PV power in a power distribution system might however lead to problems with overvoltage and overload. In this study, a method for PV power curtailment and placement of decentralized energy storage is developed to control voltage, feeder currents and distribution substation overloading. The method determines an individual feed-in power limit for each PV system owner based on a voltage-power relationship. Measured data from a 10 kV/400 V three-phase distribution grid in the Swedish municipality of Herrljunga with more than 5000 end-users and simulated PV electricity production data are used for a case study to verify the model. The method is evaluated for yearly PV electricity production of up to 100% of the yearly electricity consumption. The results show that the method is able to prevent overvoltage for all penetration levels in the studied distribution grid, reduce the number of feeders affected by overcurrent and lower the maximum load on the two substations.
Article
Technological advances, environmental awareness and, in several countries (including the UK), financial incentives lead to the adoption of PV (photovoltaic) systems. Economic viability, an important consideration for investment in residential PV, is dependent on the annual energy yield which is affected by distribution network based factors such as point of connection to network, network hosting capacity, load profiles etc. in addition to the climate of the location. A computational algorithm easy on resources is developed in this work to evaluate the effects of distribution network on the annual energy yield of residential PV systems under scenarios of increasing PV penetration. A case study was conducted for residential PV systems in Newcastle upon Tyne with a generic UK distribution network model. Results identified penetration levels at which PV generation curtailment would occur as a consequence of network voltage rise beyond grid limits and the variation in the percentage of annual energy yield curtailed among the systems connected to the network. The volatility of economic performance of the systems depending on its location within the network is also analysed. The study also looked at the impact of the resolution of PV generation profiles on energy yield estimates and consequently economic performance.
Article
In this paper, we propose a comprehensive scheme to determine a suitable method and timing for upgrading the voltage control method. Voltage control methods are expected to be upgraded in accordance with the photovoltaic (PV) penetration in distribution systems. The suitable method and timing detailed in this paper are based on the limit of the PV penetration rate, which is constrained by the regulated voltage deviation. The upgrade process involves moving the on-load tap changer (OLTC) control method from the conventional scalar line drop compensator (LDC) method to the vector LDC method or centralized control method. Then, a static var compensator (SVC) or step voltage regulator (SVR) is installed. The locations of the SVR and SVC are determined to maximize the PV penetration rate. The suitable method and timing are demonstrated using a general distribution system. In addition to the numerical simulations, experiments are performed using an active network system with energy resources. The experimental results are consistent with the numerical simulation results, thus validating the proposed scheme. The maximum PV penetration rate obtained using the OLTC control method is 55%. Whereas, the installation of the SVR and SVC increased the rate to 95% and 100%, respectively.
Article
The rapid development of photovoltaic (PV) systems in electrical grids brings new challenges in the control and operation of power systems. A considerable share of already installed PV units is small-scale units, usually connected to low-voltage (LV) distribution systems that were not designed to handle a high share of PV power. This study provides an in-depth review of methods and strategies proposed to prevent overvoltage in LV grids with PV and discusses the effectiveness, advantages, and disadvantages of them in detail. On the basis of the mathematical framework presented in this study, the overvoltage caused by high PV penetration is described, solutions to facilitate higher PV penetration are classified, and their effectiveness, advantages, and disadvantages are illustrated. The investigated solutions include the grid reinforcement, electrical energy storage application, reactive power absorption by PV inverters, application of active medium-voltage to LV transformers, active power curtailment, and demand response. Coordination between voltage control units by localised, distributed, and centralised voltage control methods is compared using the voltage sensitivity analysis. On the basis of the analysis, a combination of overvoltage prevention methods and coordination between voltage control units can provide an efficient solution to increase the PV hosting capacity of LV grids.
Article
Distribution voltage profiles are subjected to overvoltage limit violations from high penetration of grid-connected photovoltaic (PV) systems. Such voltage rises seen at the point of PV interconnection can be mitigated by adaptively changing the active and/or reactive power injection from the PV inverter. This work proposes a local voltage regulation technique that utilizes very short-term (15 seconds) PV power forecasts to circumvent imminent upper voltage limit violation or an overvoltage scenario. To provide these PV generation forecasts, a hybrid forecasting method is formulated based on Kalman Filter theory, which applies physical PV generation modeling using high resolution (15 seconds) data from on-site measurements. The proposed algorithm employs an active power curtailment based on these PV power forecasts, when the reactive power estimate given by a droop-based method cannot provide the desired voltage regulation within predefined power factor limits. The curtailment threshold values are calculated in such a way that this voltage regulation technique can reduce possible voltage limit violations. The effectiveness of the proposed method is demonstrated with case studies developed on a standard test feeder with realistic load and PV generation profiles. Index Terms— High photovoltaic (PV) penetration, distribution voltage regulation, overvoltage prevention, active power curtailment, solar forecasting, Kalman Filter (KF).
Article
Deployment of high-penetration photovoltaic (PV) power is expected to have a range of effects – both positive and negative – on the distribution grid. The magnitude of these effects may vary greatly depending upon feeder topology, climate, PV penetration level, and other factors. In this paper we present a simulation study of eight representative distribution feeders in three California climates at PV penetration levels up to 100%, supported by a unique database of distributed PV generation data that enables us to capture the impact of PV variability on feeder voltage and voltage regulating equipment. We find that feeder location (i.e. climate) has a stronger impact than feeder type on the incidence of reverse power flow, reductions in peak loading and the presence of voltage excursions. On the other hand, we find that feeder characteristics have a stronger impact than location on the magnitude of loss reduction and changes in voltage regulator operations. We find that secondary distribution transformer aging is negligibly affected in almost all scenarios.
Article
Australia has seen a strong uptake of residential PV systems over the last five years, with small scale distributed generation systems now accounting for around 10% of peak capacity within the Australian National Electricity Market. As uptake further increases, there is concern about the ability of distribution networks to maintain reliability and power quality without requiring substantial additional infrastructure investment, and in some locations PV installations are no longer being allowed. This paper evaluates the effectiveness of real and reactive power control of distributed PV inverter systems, to maintain and improve network power quality. High resolution PV output data has been collected at a number of trial sites in Newcastle, Australia and network impact simulations undertaken for an example long rural feeder gathered from the Australian National Feeder Taxonomy Study. These show how localised PV inverter controls can regulate distribution network voltages, reduce network losses, increase the network hosting capacity and hence the uptake of distributed renewable energy.
Article
In this paper, the overvoltage problems that might arise from the integration of photovoltaic panels into low-voltage distribution networks is addressed. A distributed scheme is proposed that adjusts the reactive and active power output of inverters to prevent or alleviate such problems. The proposed scheme is model-free and makes use of limited communication between the controllers, in the form of a distress signal, only during emergency conditions. It prioritizes the use of reactive power, while active power curtailment is performed only as a last resort. The behavior of the scheme is studied using dynamic simulations on a single low-voltage feeder and on a larger network composed of 14 low-voltage feeders. Its performance is compared to a centralized scheme based on the solution of an Optimal Power Flow problem, whose objective function is to minimize the active power curtailment. The proposed scheme successfully mitigates overvoltage situations due to high photovoltaic penetration and performs almost as well as the Optimal Power Flow based solution with significantly less information and communication requirements. (c)2015 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE.
Article
This paper proposes a centralized control methodology for optimizing nodal voltages of distribution networks by acting on the reactive power produced by PV-inverters. Control actions are centrally evaluated in real-time by solving a constrained dynamic optimization problem aimed at minimizing the voltage deviation from a reference value. The solution of this problem is obtained by adopting an algorithm operating in the continuous time domain based on a fast artificial dynamic system involving the sensitivity theory. By this approach the controller is able to promptly respond to any change in the system operating point, allowing its adoption in the continuous time domain. However, it must be considered that the injection of the reactive power provided by PV-inverters entails greater conduction and switching losses, causing a reduction in the active power output, thus implying less incomings. As a consequence, these additional operating costs have been analyzed and evaluated in order to establish an economic compensation mechanism able to guarantee fair reimbursement to PV generators engaged in this regulation service. Computer simulations performed on an MV distribution system, demonstrate the effectiveness of the proposed control scheme under different operating conditions, confirming its ability to control the network in real-time.
Article
This paper examines plug-in electric vehicle (PEV) grid integration, which is a specific, yet significant, component of the overall innovation being adopted by the electric power system. We propose a PEV charging policy that considers transmission and distribution integration issues and reacts to market signals across time scales and systems. More specifically, we propose that the PEV should make economic charging decisions every 5 min based on a real-time market energy price signal. On the time scale of seconds, the PEV provides voltage support for the distribution network, which may allow increased penetrations of distributed photovoltaic (PV) solar arrays. Simulation results using Electric Reliability Council of Texas wholesale power market data suggest that this voltage support service may be provided at a low cost to the individual PEV owner ($5-$50 per year). Therefore, this may prove a more attractive option for supporting distributed PV arrays than distribution network upgrades such as tap-changer-equipped transformers. Finally, we demonstrate the feasibility of our control algorithm through a test system located at the National Renewable Energy Laboratory.
Article
Joseph Wiedman, a partner with Keyes, Fox & Wiedman LLP, represents the Interstate Renewable Energy Council (IREC) in state-level rulemakings and other forums on many topic areas essential to increasing consumer access to renewable energy including development of best practices concerning shared solar, net metering program design, interconnection standards, consumer access to data, wholesale and retail market design and on many other issues central to IREC's mission. Mr. Wiedman has been deeply involved in the development of shared solar programs across the country including the development of pioneering shared solar programs in Colorado and Delaware. Mr. Wiedman holds a J.D. from the University of California — Berkeley and a Masters in Regulatory Economics from Illinois State University.
Article
As non-controllable power sources, photovoltaics (PV) can create overvoltage in low voltage (LV) distribution feeders during periods of high generation and low load. This is usually prevented passively by limiting the penetration level of PV to very conservative values, even if the critical periods rarely occur. Alternatively, one can use active power curtailment (APC) techniques, reducing the amount of active power injected by the PV inverters, as the voltage at their buses increase above a certain value. In this way, it is possible to increase the installed PV capacity and energy yield while preventing overvoltage. This paper investigates a number of approaches for sizing and controlling the PV power generated by 12 net-zero energy houses equipped with large rooftop PV systems in a typical 240 V/75 kVA Canadian suburban radial distribution feeder. Simulations of a one year period with typical solar irradiance and load profiles are conducted with PSCAD to assess the performance of the different approaches in terms of overvoltage occurrence, sharing of the burden for overvoltage prevention per house and total energy yield of the residential PV feeder.