Search

—We aim to estimate solar resource of Mongolia using satellite data in combination with limited ground measurements. Visible channel images provided by Japanese Geostationary Meteorological Satellite (GMS) Himawari 8 are correlated with ground-based measurements of solar irradiation to derive parameters of the semi-physical model.

This paper presents the evaluation results of a long-term performance of 2 type PV module from actual data measured over a period of more than 6 years in the Gobi Desert of Mongolia. For the purpose of estimating solar energy potentials and durability of PV systems in the Gobi desert area, a data acquisition system, which includes crystalline silicon (c-Si), polycrystalline silicon (p-Si) modules and precision pyranometer, thermometer and anemometer, have been installed at the Sainshand city in October, 2002. This system has been measuring 23 parameters including solar irradiation and meteorological parameters in every 10 minutes. It has been observed that the high output gain due to the operating condition in an extreme low ambient temperature and the PV module degradation rate indicated over -1.5[%/yr] after 6 years exposure test.

Renewable energy-based generators are constantly being deployed to future grids. It is expected that their share in overall generation will increase in the future. These novel devices have unknown characteristics and cause novel issues in power system operation. Traditional distribution networks have been operated as passive networks. These devices, such as smart inverters, change this paradigm completely. Due to these considerations, grid operators insist on enforcing strict grid-integration requirements. These rules are developed to ensure the impact of the connected devices is minimized and their behavior can be accounted for, at least to some extent. Testing different devices for different grid codes is a daunting task. Since such tests are undertaken in lab environment with manual control and data collection, they are prone to errors, time-consuming and inefficient. A solution is required to standardize and automate such tests. This will provide consistent testing ability and minimize testing times and errors due to human-intervention. This article presents the design and implementation of an integrated testing platform. Steps of lab equipment integration and associated challenges are presented along with their solutions. Several smart inverter behavior tests are executed, and results are presented. The test durations are compared with traditional test durations and the benefits are reported. It is discovered that use of such platform can increase the system testing efficiency by 85 % while minimizing human-errors, inconsistencies and man-hours required to run the tests.

The power hardware-in-the-loop (PHIL) simulation has become a popular testing approach due to the flexibility it provides and the high-fidelity of its results. It is expected to be utilized as an advanced laboratory testing scheme to validate the grid support functions of distributed energy resources (DERs) because it can evaluate the interaction between the power system and DERs. Despite the strong demand to utilize the PHIL simulation for such testing, the literature that elaborates on the practical design of PHIL simulation based testing (hereafter called “PHIL testing”) environment including laboratory device setup, power system models, and test procedures is very limited. The simulation models, interfacing with the tested equipment, and data collection approaches are all different parameters that need to be fine-tuned for the successful execution of PHIL testing. It is vital for such successful test experiences to be shared to build universal knowledge around PHIL testing. In order to fill this knowledge gap, this paper presents such practical and essential techniques for the PHIL testing to share the knowledge for promotion of the PHIL simulation utilization. The development of PHIL testing environment to validate the smart inverter functions, i.e., volt-var function and frequency-watt function, is focused on in terms of laboratory setup, power system modeling, interfacing, and test procedure. The volt-var and frequency-watt functions of a 500 kW smart inverter of photovoltaic are validated on the basis of the presented techniques. Detailed test configurations, test procedures, and simulation models are presented along with obtained test results.

The ratio between the photovoltaic (PV) array capacity and that of the inverter (INV), PV-INV ratio, is an important parameter that effects the sizing and profitability of a PV project. It is important to find the balance between cutting down costs by under-sizing the inverter and maximizing profits by generating more energy. This becomes much more important where smart inverters with voltage control abilities are utilized. Smart Inverters have the ability to actively take part in voltage control and, thus, increase the injected power. This would require a larger capacity than usual, as some reactive power flow needs to be accommodated to limit the voltage rise. Excess capacity can be utilized to implement smart inverter functionalities and inject more energy under conditions where conventional inverters would cap their generation. Furthermore, PV-INV ratio studies in the literature focus on large-scale, grid-connected PV systems. This paper focuses on investigating PV-INV ratio for residential PV systems with smart inverters. These are connected to low-voltage distribution systems where voltage rise issue is more apparent. A new simulation tool that can model smart inverter functionalities is utilized to investigate the impact of PV-INV ratio on overall power generation. Different smart inverter functions are implemented for comparison. Based on simulation results, the overall costs and power generation are documented for different PV-INV ratios. Finally, a cost-benefit analysis is performed to find out which PV-INV ratio yields the maximum profits with minimum costs.

The high penetration of the distributed energy resources (DERs) encourages themselves to implement grid-supporting functions, such as volt-var control. The quasi-static time-series (QSTS) simulation is an essential technique to evaluate the impact of active DERs on the grid. Meanwhile, the increase of complexity on the circuit model causes a heavy computational burden of QSTS simulation. Although circuit reduction methods have been proposed, there have been few methods that can appropriately handle the distribution system (DS) with multiple voltage control devices, such as DERs implementing volt-var control. To address the remaining issues, this paper proposes an offline bus aggregation method for DS with volt-var control. The method determines the volt-var curve for the aggregated bus on the basis of historical data to reduce error in the aggregated model, and its offline process solves the computational convergence issue concerned in the online one. The effectiveness of the proposed method is validated in the simulation using a Japanese low-voltage DS model. The simulation results show that the proposed method can reduce the voltage error and computational time. Furthermore, the versatility of the proposed method is verified to show the performance does not heavily depend on how to select historical data for model-building.

Inertia reduction due to inverter-based resource (IBR) penetration deteriorates power system stability, which can be addressed using virtual inertia (VI) control. There are two types of implementation methods for VI control: grid-following (GFL) and grid-forming (GFM). There is an apparent difference among them for the voltage regulation capability, because the GFM controls IBR to act as a voltage source and GFL controls it to act as a current source. The difference affects the performance of the VI control function, because stable voltage conditions help the inertial response to contribute to system stability. However, GFL can provide the voltage control function with reactive power controllability, and it can be activated simultaneously with the VI control function. This study analyzes the performance of GFL-type VI control with a voltage control function for frequency stability improvement. The results show that the voltage control function decreases the voltage variation caused by the fault, improving the responsivity of the VI function. In addition, it is found that the voltage control is effective in suppressing the power swing among synchronous generators. The clarification of the contribution of the voltage control function to the performance of the VI control is novelty of this paper.

Nominal values reported for PV Systems are measured at carefully-controlled test conditions. While being strictly standardized to achieve a good benchmarking capability for different, newly manufactured panels; these conditions hardly exist in real-life implementation sites. To add to the problem, highly varying climate, precipitation, scorching sun and freezing snow wear out these systems in the long run. Therefore, actual performance of any PV system is, inevitably, different than those reported under standard test conditions. In order to have a more accurate expectation of power generation over the lifetime of a system, it is important to know the impact of local conditions and the resilience of PV panels to them. To this end, several outdoor performance studies have been reported around the world and the literature is growing. This work reports the impact of Fukushima's weather, which is known to be windy in autumn and have heavy snowfall in the winter, on the installed PV systems. Also, numerous panels belonging to different PV technologies and manufacturers are installed side-by-side to compare the variation in their performances and, thus, benchmark their quality and resilience. To investigate possible impact of micro-climate, or local geographical conditions, two test sites in Fukushima Prefecture are utilized. Finally, a sample PV system calculation is presented to showcase the impacts of these findings on a PV system in planning and operation stages.

Grid codes around the world are requiring grid-support functions (GSFs) and standardized interoperability interfaces for distributed energy resources (DERs) to address the rapid increase of renewable energy. However, these new GSFs need to be assessed to ensure the desired power and communication capabilities exist in the field. The IEEE 1547.1 standard outlines the conformance test procedures for DER devices and is currently undergoing a major revision to align it with IEEE 1547–2018. Once it is published (anticipated in mid-2020), GSFs in commercial PV inverters in USA and Canada will be certified to the IEEE 1547.1 conformance test procedures. Several international research laboratories are collaborating to develop a versatile open-source DER testing platform that performs automated testing of DER devices. This community of laboratories is developing open-source IEEE Std. 1547.1 test scripts to lower barriers to DER vendor internal equipment evaluations, ease product compliance testing at certification laboratories, and provide research institutions a tool to study DER behaviors. In this work, test scripts were used for test verification of GSFs, including limit active power, constant reactive power, active power-reactive power (watt-var), and prioritization of GSF response for several DER devices. Sample test results for these DER GSFs and test protocol recommendations are presented in this paper.

High penetration of renewable energy based distributed generators is a common goal for many electricity companies. While providing clean and cheap energy on the one hand, these active components create unprecedented problems in the grid. Arguably the most prominent one is causing unacceptable voltage rises due to power injection. Traditional solution is to cap the renewable energy generation. This turns into a double loss as the available energy is not captured and the installed equipment is not fully utilized. Introduction of smart inverters is aimed at solving these intertwined concepts. Impact of smart inverters on the distribution network operation has been recently reported in the literature. However, multiple smart inverter operation where several devices try to influence the power flow has not been thoroughly investigated. This paper focuses on analyzing the operation of several smart inverters that are running in Volt-Var mode and are connected to the same distribution feeder. Furthermore, considering the number of roof-top PVs in neighborhoods and the difficulty in simulating the individually, a simplification method is developed. In this fashion, multiple smart inverters operating in the same feeder are modeled in an aggregated way for easier calculation. Finally, simulation results are presented for analysis and validation.

As the number of distributed energy resources (DERs) increase, power systems become harder to control. To harmonize the traditional system and such novel technologies, the holistic comprehension of the integrated system is necessary. Microgrid, which can be used to electrify isolated communities in sub-Saharan Africa or small islands in the Pacific Ocean, is one of the application destinations of the novel technologies. The renewable-energy based DERs are suitable for the microgrid operation because they can be set up with a small capital and utilized at a small scale. However, renewable energy is intermittent and time-dependent. To achieve reliable and continuous supply of energy, a generation portfolio including different generators needs to be created so that they can balance each other. This requires the use of a sophisticated control system in the microgrid. Operation of these control need to be validated before actual deployment. In this paper, a commercial microgrid controller is tested in an integrated test environment. Test environment in the lab is utilized to set up a microgrid and hardware-in-the-loop (HIL) test is added to simulate additional conditions. Testing with real hardware equipment increases the fidelity of the test results while real-time simulation adds to the diversity. Such validation is crucial to the project’s success before on-site deployment.

Deep penetration of distributed generators have created several stability and operation issues for power systems. In order to address these, inverters with advanced capabilities such as frequency and reactive power support the grid. Known also as Smart Inverters (SIs), these devices are highly dynamic and contribute to the power flow in the system. Notwithstanding their benefits, such dynamic devices are new to distribution networks. Power system operators are very reluctant toward such changes as they may cause unknown issues. In order to alleviate these concerns and facilitate SIs integration to the grid, behavior studies are required. To that end, this paper presents a power hardware-in-the-loop test set up and tests that are performed to study fault behavior of SIs connected to distribution networks. The details of the software model, SI integration with the real-time simulator, test results, and their analyses are presented. This experience shows that it is not trivial to connect such novel devices with simulation environments. Adjustments are required on both software and hardware fronts on a case-by-case basis. The encountered integration issues and their solutions are presented herein. The fault behavior of the SI with respect to the fault location is documented. It is observed that for faults that are close to SIs, momentary cessation of generation is observed. This needs to be tackled by device manufacturers as this phenomenon is very detrimental to health of a power system under fault conditions. Extensive PHIL test results show that several factors affect the fault behavior of an SI: fault location and its duration, SI mode of operation as well as extra devices housed in the casing. These results and their in-depth analyses are presented for a thorough understanding of SI behavior under fault conditions.

In order to make effective use of PV-PCSs and battery storage PCSs, it is important to develop and evaluate behaviors in power system, grid interconnection, their control and protection equipment, etc. A HILS (Hardware in the Loop Simulation) test facility was developed for these purposes which was consisted in combination with real-time simulator and actual hardware of their PCSs. RTDS of RTDS Technologies Inc. for real-time simulator, MX 30 of AMETEK Inc. as a signal amplifier of RTDS analysis results and the SMA 20 kW PCS for actual hardware were used for the HILS test facility. In the simulation, power system included PV-PCS is simulated by the RSCAD which is an exclusive software of RTDS. A dynamic PQ source model provided in the RSCAD library was used instead of the actual PCS model. AC voltages Vac and AC currents Iac are detected from the actual PCS and feedback to the RTDS. In the simulation program, we calculate instantanious real power P and reactive power Q in real time using Vac and Iac in order to set as a command of the dynamic PQ source model. For the HILS test, we analyzed behaviors of the PV-PCS during grid faults. And the results were compared with off-line simulation using a PV model provided in the RSCAD library.

It has been pointed out for a long time that test table materials greatly influence EMC testing. Although there are several studies on radiated emissions testing, there have been no reports on radiated immunity testing. Therefore, it was verified whether test table materials had influence on electric field strength in testing.

Although it is very popular among environmentalists, the replacement of fossil-fuel based generation with new age renewable energy (RE) creates problems in grid operation and stability. The intermittent nature of these resources as well as their inverter-based connection structure hinder the traditional operation of electrical networks. Consequently, the RE penetration level has been kept low to limit their impact on the infrastructure. In order to maximize RE potential, novel solutions are required and smart inverters with advanced inverter capabilities can be just that. Coupled with battery energy storage systems (BESS), they can manage RE intermittent behavior and provide auxiliary services such as frequency and voltage support. However, large scale deployment of these power conditioning systems (PCS) at distribution level can create enormous problems. To cope with this challenge, their behavior should be closely scrutinized and interoperable operation must be guaranteed with a series of tests before actual deployment. Smart Grid International Research Facility Network (SIRFN) has the services of 15 distinct labs to develop standard testing protocols and knowledge on best practices. A consortium of labs around the globe ran tests in their facilities and developed standard testing procedures for BESS. Building on that experience, IEEE P2004 project aims at developing standard hardware-in-the-loop (HIL) testing procedures for PCS. This will improve the testing capabilities since different systems can be easily modeled and verified in HIL. This paper documents these standardized testing efforts and the role of Fukushima Renewable Energy Institute, a part of SIRFN and IEEE P2004, in achieving these goals.

The purpose of this study is to investigate concentrator photovoltaic (CPV) system performance. The performance of the CPV system depends on the climate and the environment condition more than the conventional flat-plate photovoltaic (PV) system. Moreover, the characteristic due to the angle of incidence (AOI) solar irradiance is extremely important. Therefore, the grid-connected PV and CPV systems installed in Japan are investigated to clarify these performance issues in this paper. The performance analysis results including performance ratio and alignment and tracking error data from one year of operation are presented and discussed.

Nowadays, investors, customers, and even suppliers focus on the bankability of photovoltaic (PV) technologies. However, few studies have investigated the annual net effect of solar spectrum. In this study, we estimate the net effect of the solar spectrum on the annual energy yield of c-Si and a-Si modules by two parameters. One parameter is a direct calculation from spectral factor (SF). The other parameter uses average photon energy (APE) and a regression line or curve. The estimations by the two parameters are quite consistent, whereas there is 1.2% difference between the estimations at most. Therefore, APE would be a useful index to quantify the effect of the solar spectrum.

The performance of photovoltaic (PV) modules is generally rated under standard test conditions (STC). However, the performance of thin-film photovoltaic modules is not unique even under STC, because of the “metastability”. The effects of the light soaking and thermal annealing shall be incorporated into an appropriate energy rating standard. In this study, the change in I–V characteristics of thin-film PV modules caused by the metastability was examined by repeated indoor measurements in addition to round-robin outdoor measurements. The investigated thin-film modules were copper indium gallium (di)selenide (CIGS), a-Si : H, and a-Si : H/µc-Si : H (tandem) modules. The increase in the performance of the CIGS module between the initial and final indoor measurements was approximately 8%. Because of light-induced degradation, the indoor performance of the a-Si : H and a-Si : H/µc-Si : H modules decreased by approximately 35% and 20%, respectively. The performance was improved by about 4–6% under high temperature conditions after the initial degradation. The results suggest that the performance of thin-film silicon modules can seasonally vary by approximately 4–6% only due to thermal annealing and light soaking effects. The effect of solar spectrum enhanced the outdoor performance of the a-Si : H module by about 10% under low air mass conditions, although that of the a-Si : H/µc-Si : H modules showed a little increase. The currents of these a-Si : H/µc-Si : H modules may be limited by the bottom cells. Therefore, it is required to optimize the effect of solar spectrum in addition to the effects of light soaking and thermal annealing, in order to achieve the best performance for thin-film silicon tandem modules. Copyright © 2013 John Wiley & Sons, Ltd.

In recent years, several large-scale solar power plants, called mega solar power plants, have been built at various locations. Inspection of a faulty solar panel is important for the maintenance of solar panels. However, previous methods of determining a fault in a solar panel required removal of panels from the solar power plant. In this paper, a cooperative robot system using wire-parallel mechanism is proposed for the realization of on-site inspection. Based on Vector-Closure and manipulability, the design of the system is described.

The maximum power temperature coefficients of a-Si modules are negative in indoor measurements, whereas the performance increases with module temperature in outdoor measurements. In order to resolve the discrepancy, we investigate the temperature coefficients of a-Si modules by two different methods corresponding to two different time scales. The results are that the temperature coefficient for a shorter time scale of several hours is negative, although the temperature coefficient for a longer time scale of seasons is positive. These results suggest that the discrepancy in temperature coefficient is partially caused by the effects of thermal annealing and light soaking. Therefore, the history of module temperature and received solar irradiance would be required for the correction of the performance of a-Si modules. In addition, we reveal that the effect of solar spectrum is also a contributory factor in the discrepancy.

Photovoltaic (PV) systems have become popular globally as an important candidate in the establishment of low-carbon electrical and civil systems. Since the early 1990s, globally, many PV systems have been installed, and their performance parameters such as annual yield, performance ratio, and system losses have been monitored in order to understand their basic characteristics; these data also help in the development of these systems and in analyzing their reliability. In Japan, the performance of residential PV systems was evaluated and reported. However, these evaluations were carried out using older systems, and the current status and the performance trend for each installation year have not been sufficiently evaluated and discussed. Therefore, this report aims to provide a macroscopic evaluation of the performance trends of PV systems by using the monitoring data of systems that were installed between the year 2000 and the year 2007. As a result of the evaluation, we have concluded that the performance ratio of these systems improved to an average of 0.72 until fiscal year 2000 and to 0.78 after fiscal year 2001. For investigating the factors behind this increase in performance ratio, we have focused on characteristics of the actual system capacity (capacity of each PV module measured at the point of shipment) and inverter efficiency. Copyright © 2010 John Wiley & Sons, Ltd.

The performance of six photovoltaic (PV) modules composed of polycrystalline silicon (pc-Si), amorphous silicon (a-Si), and hydrogenated amorphous silicon/crystalline silicon (a-Si:H/c-Si) modules was investigated at eight locations in Japan from August 2007 to December 2008. In addition, solar irradiance, solar spectrum, and module temperature were simultaneously measured in these round-robin measurements. In this study, we evaluate quantitatively the effects of module temperature and solar spectrum on the performance of the PV modules as thermal factor (TF) and spectral factor (SF), respectively. Furthermore, we investigate the variation in module performance, which is converted into module performance under standard test conditions (STC) using the TF and SF. In the case of the pc-Si modules, the variations in performance ratio under STC (PRSTC) for these modules range from 0.056 to 0.074 through the round-robin measurements. The TF indicates that the contribution of module temperature to the variation in performance is large, between about 15 and 20%. However, the SF suggests that the contribution of solar spectrum is quite small, less than 3%. In the case of the a-Si modules, the contribution of module temperature is about 8%. The performance is largely influenced by solar spectrum, more than 12% at its maximum. Consequently, the variations in the corrected PRSTC of the a-Si modules are between 0.117 and 0.141. These large variations may result from the effects of thermal annealing and light soaking. The variation in PRSTC of the a-Si:H/c-Si module is similar to that of the pc-Si modules. Copyright © 2010 John Wiley & Sons, Ltd.

In order to disseminate Photovoltaic (PV) technologies into the energy network, the cost down is not only important, but also improving the performance of the PV system is significant issues. Long-term reliability is one of the most important issues in terms of PV system performance. Previous researches were mainly focused on the reliability of PV modules, but the PV system is composed of a power conditioner, wiring, junction box, and so on. To improve the reliability of PV systems, it is important to accumulate trouble cases focused on all components of PV system. In this paper, we aim at evaluation of the reliability for the PV system on the early stages of PV system's lifetime by using large number of Japanese PV systems' data from the field Test in Japan. New Energy and Industrial Technology Development Organization has been running the “Field test project in Japan” from 1992. In this project, PV system users have cooperated with the collection of monitoring data and reported on the information of maintenance and certain failures of PV systems for 4 years after installation of PV system. Using those reports each year of installation, we evaluated reliability of PV systems by means of parameters such as Mean Time Between Failure, Mean Time To Repair, and the suspension time of PV system. As a result, the main trouble of PV systems was related power conditioner, and a few trouble of PV module was caused by typhoon. Moreover, the trend of the failure rate before FY 2000 of installation was demonstrated as the trend of initial failure in “bathtub curve;” however, the trend of its after FY 2001 of installation was indicated as the accidental failure in “bathtub curve.” Further, the operator simply forgot to restart the power conditioner after maintenance or suspensions of PV system in many trouble cases, and the user did not notice that it had been suspended for a while. These trouble cases can be avoidable easily through the effective alarm such as error message of power conditioner systems with monitoring systems. Thereby, monitoring with the evaluation method of PV systems is one of the important technologies due to the long-term reliability and stable operation. Copyright © 2010 John Wiley & Sons, Ltd.