Search

The proliferation of rooftop solar PV has caused reverse power flow in low voltage distribution networks leading to elevated voltage levels. As the voltage is raised, PV inverters reduce output power to combat voltage rise and may result in inverter shutdowns causing PV curtailment (loss of PV output power). Residential battery storage can store excess PV energy and hence reduce reverse power flow, over voltage and PV curtailment. This study aims to determine the reduction in PV curtailment achieved by the installation of optimally sized residential battery storage. A method to calculate the reduction in PV curtailment and the reduction in corresponding financial losses incurred by PV owners and the energy market is presented. The method is applied to an 11-kV feeder in South Australia along with prevailing feeder and inverter voltage limits. Results show that with the installation of optimally sized battery storage, PV curtailment and the corresponding financial losses can be reduced by more than 50%. Refereed/Peer-reviewed

This paper presents an analysis of the system effects of reverse power flow in distribution feeders. Continued increases in the number of small-scale photovoltaic (PV) panel installations within the network has led to low or reverse power flows in distribution feeders at times of high solar energy availability, and substantial weather-induced load variation, among other impacts. In the event of a large loss of generation, under-frequency load shedding of these distribution feeders is one tool that network operators use to arrest the frequency decline. The penetration of distributed PV generation leads to low availability of load to shed, or the chance of inadvertently removing generation, which can lead to power system failure. This paper explores these effects on the largest power system in Western Australia and suggests methods to mitigate the impact of increasing DER penetration on under-frequency load shedding schemes.

Battery energy storage (BES) has the ability to solve many power system problems especially in systems with renewable energy resources integrated. Due to the intermittent nature of solar photovoltaic (PV) generation, different problems have arise such as voltage fluctuation and reverse power flow. Besides, duck curve issue has become more significant with the increasing amount of PV integrated in the power system as first raised by the Californian Independent System Operator. Studies on these issues has become important in order to solve the steep ramp and over generation problems caused by duck curve issue. The duck curve issues based on general Malaysia load profile and PV pattern are studied in this paper. Besides, the feasibility of BES in solving these issues with suitable BES capacity is investigated. The results show that the BES has the ability to solve the duck curve issues through proper control of BES charging and discharging operation.

Integration of the renewable energy sources (RES) in distribution systems is accompanied with a lot of challenges to power system protection, control and operation. This integration can cause reverse power flow that affects the voltage stability of the power system. To avoid the power system instability, the monitoring of the integration of RES is necessary. In this paper a hybrid algorithm is proposed to monitor reverse power flow, and then it was tested on the IEEE-39 and IEEE-118 node test feeders.

The impact of PV generation distributed in a low voltage transmission line depends on many factors: The distribution lines and PV generators characteristics, its location, operational control, local meteorological conditions, electricity consumption profile, and the electricity cost variation. An atypical and challenging behavior of photovoltaic distributed generation (DG) insertion in consumer units (CUs), implies in some circumstances, as the reverse directionality of the power flow between the load equipped with a photovoltaic system generator and the electrical grid, when a CU contains a distributed generation and low power consumption, the power flow will be directed to the power electric grid. In this work, the modeling of a low-voltage real feeder was performed, setting the variables of the system under real operating conditions. As result, voltage levels variability throughout the feeder, the electrical losses, and the asymmetry between the phases were observed. Through simulation scenarios, the occurrence of voltage increase under different penetration scenarios of distributed generation was verified and there was a 10% increase in reference voltage as well as the occurrence of higher electrical losses by reverse current, reaching 1200% more with a DG penetration, in the massive presence of the photovoltaic generator. The mitigatory action used in this work was able to attenuate the negative impacts to the feeder circuit, ensuring the integrity grid and the consumer unit.

The growth of photovoltaic systems (PV) and battery energy storage systems (BESS) will become a challenge for distribution players. In this way it is important to understand how these systems can impact on the distribution grid operation. For this, a study was developed considering the insertion of PV on IEEE 13 buses test feeder, based on different penetration levels. These levels were calculated contemplating two different parameters: the one most used in Brazil, and the parameter that consists in an extended criterion used worldwide. Considering these possibilities, different penetration levels of photovoltaic were defined. In conjunction with photovoltaic generation, a BESS was inserted in the same feeder, in order to evaluate the impacts of this system. From the simulations was possible to evaluate the tap changes, the voltage profile, power losses and the total energy, including if there was reverse power flow at any moment during one day.

In the last decade, there has been a tremendous growth in the field of grid-tied Photovoltaic (PV) generating plants in INDIA. With the recent government subsidies and reduction in the panel prices, the generation capacity has increased from a few kilowatts to hundreds of Mega-Watts. This rapid escalation in the penetration level on the grid has increased the utility companies’ concerns about its impact on the power quality of the system.In the current scenario, the penetration levels of the Photovoltaic generating in INDIA is very low to create any kind of significant power quality issues on the grid, however, power quality issues such as current harmonics and power factor have been identified in some cases. But with the increase in the penetration levels of PV generator on the grid, it may start affecting the overall power quality of the system. Power system stability and security issues, voltage variation (i.e. sag & swell), reverse power flow, power factor, and harmonics are the major power quality issues that may arise due to increased PV penetration. This paper gives an overall review of different power quality issues that may arise due to the increased penetration level of a PV generator on the grid.

Negative impacts of large-scale rooftop photovoltaic (PV) penetration may cause performance deterioration of distribution grids. Consequently, a rooftop PV hosting capacity analysis is becoming a concern of utility. In this work, a proposed method based on Monte Carlo process is developed to assess the PV hosting capacities on the basis of substation power factor. To consider the actual conditions, three selected feeders including feeder F1, feeder F2, and feeder F3, with distinct grid characteristics from Yogyakarta Province of Indonesia are employed. To obtain a detailed result of the rooftop PV hosting capacity, the customer with rooftop PV is randomly selected one by one. The proposed method is performed with over/undervoltage, substation power factor and reverse power flow limit. The comparative study is provided to investigate the impacts of the operational limits on the rooftop PV hosting capacity. Since the load demand and PV output vary with the time, the analyses are conducted in a time-series framework. In this work, constant PQ of loads is assigned, and all rooftop PV systems are assumed to have unity power factor. The results show that the substation power factor limit is more restrictive compared to overvoltage limit and reverse power flow limit. The substation power factor limits the rooftop PV penetration on feeder F1, feeder F2, and feeder F3, respectively, 86.52%, 79.37%, and 85.85% faster than reverse power flow limit. The results also indicate that the substation power factor decreases with the increasing of rooftop PV penetration.

This paper proposes a decentralized charging control method of a battery energy storage system (BESS) that can prevent the over-capacity of a pole transformer in low-voltage (LV) distribution systems due to reverse power flow from the photovoltaic generation system. The distribution system operator provides the charging parameters defined as the relationship between the state-of-charge (SoC) and the charging threshold determined by using only the LV-distribution system configuration and the demand-side information to customers. Each BESS charges the power according to the provided parameters. A high charging amount can be maintained by automatically changing the charging mode based on the change in SoC. Results of the numerical simulation demonstrate that the proposed method can prevent the over-capacity of PTr and maintain the high charging amount of a BESS in LV-distribution systems. Further, the maximum power flow at the distribution substation and the distribution losses in MV-distribution system can be reduced.

DC-feeding Microgrid (DCMG) which can integrate plural DC-driven facilities by using information is considered as a future energy system for rural shore area. To balance supply and demand in the DCMG, a set of fuel cells and electrolyzer (FCE) systems is proposed as an energy storage system instead of conventional battery systems. DCMG including FCE, PV and DC loads are assumed, the mode controlling method for FCE to balance supply and demand is proposed in this paper. As a result, FCE is controlled by proposed method and can balance supply and demand without reverse power flow to utility grid.

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.

Utility-scale renewable energy systems are rapidly increasing in the market and converting conventional power supply networks to sustainable power supply networks (SPSNs). This requires the redesign of the configuration of these networks for optimal and reliable operation. In this paper, we tackle this problem by considering switches in an SPSN and a new model of utility-scale photovoltaic stations (PVSs). In addition, export power, i.e., reverse power flow to a connected external network is considered. An optimization approach called one-at-a-time-search is adapted and used to solve the formulated mixed-integer nonlinear programming (MINLP) problem. The objective is to minimize the power loss and meanwhile to minimize the curtailed power generated from the PVSs. A 5-bus test SPSN is used to show that circa 40 % of energy losses can be saved.

This paper performs a power flow modelling of a distribution grid considering the presence of electric vehicles (EVs) and distributed generation, in this case, photovoltaic panels (PV). Thus, this work aims to analyse the impacts on the distribution transformer in different levels of electric vehicle and distributed generation penetrations. The simulations are performed in three stages: 1st Stage: Modelling of different levels of EVs penetration in relation to the total amount of houses: 25%, 50%, 75% and 100%; 2nd Stage: Network analysis with penetration of EVs and PVs of equal magnitudes of 25%, 50%, 75% and 100%; 3rd Stage: Viability of the maximum penetration of EVs recharge with the aid of FV distributed generation. The results show the importance of distributed generation to relieve the distribution transformer load. However, a reverse power flow is observed due to PV penetration, which can be mitigated with a planned and coordinated insertion in the right proportions of EVs and PVs.

Photovoltaic (PV) penetration in Low-Voltage (LV) networks is expected to increase in the following years, posing a series of problems in the operation pf low-voltage networks. Among the most important challenges imposed, is the reverse power flow caused by high injected energy from distributed PVs during peak irradiation hours. This is the reason of voltage rises above the permissible limits. Amongst other solutions, such as active power curtailment and reactive power absorption, the installation of distributed Energy Storage Systems (ESS) seems to be an attractive solution since it can absorb surplus power locally, avoiding curtailment methods, power flow losses on the feeder and grid reinforcements. As the cost of storage is decreasing, ESS are expected to be increasingly adopted by prosumers. This work evaluates the influence of such systems on the voltage profile of LV feeders and on the self-consumed energy of prosumers. Intensive simulations on a benchmark feeder assess the conflicted benefits of power system operators and ESS owners.

The low voltage (LV) distribution cable networks were installed some decades ago but the new paradigm in electric power engineering generates new requirements from these old assets. The distributed generation, storage and new appliances can cause high variation of load and reverse power flow, nevertheless the LV cable grid was not designed to these new stresses. The aggregate load and generation can surpass the rated capacity of the cable lines causing short term temperature increasing. This temperature stress can decrease the expected lifetime of the cable lines. In this study the short term thermal overload of LV distribution cables was investigated. The experiments were executed on PVC insulated LV cable samples and electrical and mechanical properties of the cable jacket were investigated. The effect of these short-term overloads on the expected lifetime of cables is introduced and non-destructive measurement for tracking the effect of the short term thermal overloads on the cable is suggested.

This paper deals with the analysis of the customer voltage characteristic in distribution system interconnected with large scale PV system. There would be many power quality issues which are caused by reverse power flow of PV system interconnected with distribution system. In order to analyze the effect of PV system on the customer voltage, detailed modeling method of distribution system and modified modelling method of PV system are proposed using PSCAD/EMTDC in this paper. So far, less than dozens KW of PV system can be simulated with the existing modelling method. Therefore, a new modeling method which can simulate the large scale PV system is proposed by considering the relationship equation on the phase and voltage in the current control algorithm. From the simulation result of proposed modelling method, it is confirmed that an optimal operation method in distribution system is suggested by analyzing the effect of PV system on customer voltage.

Existing technologies can mitigate voltage fluctuation and reverse power flow effectively. At the same time, complementing solar PV with energy storage resources and flexible loads creates opportunities to earn new revenues from wholesale electricity markets, enhancing both the reliability value and the monetary value of these clean energy resources.

This paper discusses reverse power flow from a home cogeneration system (H-CGS) in terms of energy conservation and influence on electric power systems. Data for actual electricity and hot-water demand observed in a family including two adults and two children for a year were used as a case study for a typical installation. When the reverse power flow is allowed except for during late night, in consideration of the influence on the electric power system, the reduction in annual primary energy consumption can be increased by about 40% relative to that in the operation without reverse power. The reverse power flow is large during the daytime in winter season, because the power output of H-CGS is large in order to meet the large hot-water demand. Even if reverse power is allowed throughout a day, the primary energy conservation is almost the same as that in part-time reverse power operation, while the reverse power during late night is as large as that during daytime. Finally, the economic value of reverse power flow as a measure for reducing CO2 emission was evaluated. The result shows that the economic value of reverse power flow in PR operation corresponds to 23,000 yen/t-C. © 2009 Wiley Periodicals, Inc. Electron Comm Jpn, 91(10): 11– 19, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecj.10162

The integration of solar PVs which is projected to increase over the years creates concerns over stability. Reverse power flow occurs due to high PV penetration into the power system network. PV placement at proper locations in a transmission system is essential to maintain voltage stability. Improper placement will caused voltage stability of the system to be affected. However, if the PVs are connected at a strategic location it will lead to a more stable system. This paper presents a methodology for PV source placement in the transmission system while maintaining the stability of the. Voltage Stability Index (VSI) will be used as an indicator to measure the stability status of the system. Two test systems will be used for simulation for this research, the IEEE 30 Bus and 57 Bus Test System. The simulation results showed that proper placement of the PV source in the transmission system will lead to better stability to the system.

We have developed an optimal management planning method for the efficient use of a photovoltaic generation system with heat pump water heater and battery storage. This plan can prevent shortage of hot water while minimizing the cost and maximizing customer convenience and can deal with multiple scenarios corresponding to uncertainties in forecasting PV output, hot water and electricity demand. A simulation was performed to analyze daily operation with the proposed planning method in terms of year-round hot water demand, electricity demand, and PV output. An experiment was also conducted using the heat pump water heater to demonstrate the proposed method.

Japanese government plans to introduce photovoltaic (PV) systems 20-fold by 2020 compared to the 2005 level, and then grid-connected PV systems are expected to increase rapidly. At the same time, however, there is concern that a large scale PV systems introduction might bring an excess of supply when the electricity demand is low such as in spring or autumn in Japan. Meanwhile, heat pump water heaters (HPWHs) are highly efficient water heaters and have been introduced rapidly. If hot water is stored in the daytime using HPWHs, it will contribute to absorb economically a part of the excess of PV output. In this paper, we propose a use of residential HPWHs in the daytime as a means of PV reverse power flow restriction. And we evaluate how the difference of the actual demand patterns influences on PV reverse power flow restriction and HPWH power consumption.

The research carried out to investigate the ability of power transformers to facilitate the required power flows associated with the anticipated high penetrations of small scale embedded generation (SSEG), within small-scale energy zones (SSEZs) is described. A small-scale energy zone is defined as a section of low-voltage, network with a high penetration of SSEGs, controllable loads and energy storage units. SSEZs, coupled with active control techniques, have the potential to assist the growth of SSEGs by removing network constraints and enabling blocks of aggregated and controlled SSEGs to participate more effectively in energy markets and network operational tasks. The research focused on identifying the reverse power flow and thermal-rating constraints imposed by power transformers. The analysis was performed using an approved UK generic PSCAD/ EMTDC electrical network model, with varying levels of SSEGs. Simulations were carried out examining cases with a uniform distribution of SSEGs contained within a number of SSEZs. It was observed that in some cases the reverse power flow capability of the primary transformers would exceed if each customer installed an SSEG with a rating of approximately 1 kW.