Utility-scale Photovoltaic Power Plants Research Articles

Efficiency and benchmarks for photovoltaic power generation amid uncertain conditions

Photovoltaic (PV) power generation systems are highly subject to weather and site conditions, thus, the construction of PV power plant projects must consider these uncertainties. This study analyzes the monthly electricity generation of 249 utility-scale PV power plants in Japan to evaluate their electricity generation efficiency. Applying the generic data envelopment analysis, benchmark values were identified for power generation from PV power plants. Furthermore, we implemented a Monte Carlo experiment to evaluate the impact of variability in solar irradiance and temperature on power generation efficiency. For our analysis, we considered three inputs—solar irradiance, temperature, and installed capacity—and electricity generation as the output. The results showed that inter-regional gap in the efficiency score between the west and north regions is 0.03, and this can be covered by a 0.1 increase in the DC/AC ratio. Additionally, variability in weather conditions affect both the efficiency of a power plant and production possibility frontier, in turn causing the benchmark values for a generic decision-making unit to vary. Increasing the generation capacity of power plants and operating them more efficiently is essential to expanding the use of renewable energy resources.

How do seasonal and technical factors affect generation efficiency of photovoltaic power plants?

Regions with limited space for constructing renewable power generation systems need to maximize electricity generation by optimizing the operational efficiency of existing plants and selecting an optimal location for the new construction of PV power plants with favorable weather conditions and surrounding environment. Utilizing monthly input and output data, including four inputs (solar irradiation, temperature, number of modules, and photovoltaic (PV) array rated capacity) and one output (electricity generation) from utility-scale PV power plants, meta-frontier data envelopment analysis was employed in this study to identify factors contributing to power generation inefficiency. Additionally, a Monte Carlo experiment analyzed the impact of solar irradiation uncertainty on power generation efficiency. The findings revealed that the average power generation inefficiency during the study period was 0.445, primarily attributable to seasonal and technical factors. Since these factors are difficult to control once a power plant is in operation, it is important to select an optimal site for power plants by considering meteorological and geographical data. Moreover, the results indicated a significant gap between observed and simulated values of power generation efficiency, arising from variations in weather conditions, power plant site area, and the data used in the research. Employing PV modules with higher electricity output levels can boost the DC/AC ratio, thereby increasing power generation, enhancing efficiency, and contributing to a stable power supply, thus reducing daily and seasonal fluctuations in power generation.

Investigation of Geometric and Hardness Parameters of Tank Track Grooves Equipped on Photovoltaic Cleaning Robot

The utilization of photovoltaic (PV) cleaning robots has proven to be an effective method for maintaining the conversion efficiency of utility-scale PV power plants by mitigating the impact of dust accumulation. However, ensuring the safe operation of these robots, resembling tanks in appearance, particularly in wet working conditions, relies heavily on their adherence to PV panels. This study focuses on assessing the slip resistance of candidate materials coated on endless polyurethane timing belts, which are equipped on PV cleaning robots to enable the efficient cleaning of uneven and misaligned PV arrays. A novel apparatus is proposed to evaluate the coefficient of static friction (COSF) of slip specimens, considering factors such as outsole patterns, area density, and shore hardness. The results highlight the significant influence of shore hardness and area density on the slip resistance of the specimens. Based on the findings, it is recommended to design track grooves with hexagon or zigzag patterns and maintain a low area density (e.g., 0.44 g·mm−2) to ensure the safe operation of PV cleaning robots, irrespective of the working conditions they encounter. By addressing the slip resistance challenge, this research contributes to the overall efficiency and reliability of PV cleaning robots, enhancing their performance in maintaining clean and optimal PV panel surfaces.

Accelerating the energy transition towards photovoltaic and wind in China

China’s goal to achieve carbon (C) neutrality by 2060 requires scaling up photovoltaic (PV) and wind power from 1 to 10–15 PWh year−1 (refs. 1–5). Following the historical rates of renewable installation1, a recent high-resolution energy-system model6 and forecasts based on China’s 14th Five-year Energy Development (CFED)7, however, only indicate that the capacity will reach 5–9.5 PWh year−1 by 2060. Here we show that, by individually optimizing the deployment of 3,844 new utility-scale PV and wind power plants coordinated with ultra-high-voltage (UHV) transmission and energy storage and accounting for power-load flexibility and learning dynamics, the capacity of PV and wind power can be increased from 9 PWh year−1 (corresponding to the CFED path) to 15 PWh year−1, accompanied by a reduction in the average abatement cost from US$97 to US$6 per tonne of carbon dioxide (tCO2). To achieve this, annualized investment in PV and wind power should ramp up from US$77 billion in 2020 (current level) to US$127 billion in the 2020s and further to US$426 billion year−1 in the 2050s. The large-scale deployment of PV and wind power increases income for residents in the poorest regions as co-benefits. Our results highlight the importance of upgrading power systems by building energy storage, expanding transmission capacity and adjusting power load at the demand side to reduce the economic cost of deploying PV and wind power to achieve carbon neutrality in China.

Life cycle multi-objective (geospatial, techno-economic, and environmental) feasibility and potential assessment of utility scale photovoltaic power plants

Bridging the gap between sustainability theory and good practice of utility-scale photovoltaic deployment requires strategic planning considering multiple criteria. This study, for the first time, integrates meteorological and air quality parameters and lifecycle costs and environmental emissions with geospatial, techno-economic parameters in determining potential and suitability of photovoltaic power plants. For two system orientations, technical potential based on timeseries of meteorological parameters is estimated after development of irradiance and aerosol optical depth maps. Besides others, project lifecycle and water-use costs are introduced in levelized cost of electricity calculation. Site suitability is estimated based on site-specific techno-economic parameters and annual dust load. Lastly, comparison between lifecycle environmental impacts, considering twelve different indicators of proposed plant and natural-gas fired power plant (as reference) is performed for different capacity powerplants. Cumulative resource potential ranging from 7497 to 14141 GW is identified for Pakistan. Levelized Cost of Electricity is in range of 0.026–0.041 USD/kWh, highly competitive with global estimates and less than the residential tariff in the country. Major contribution (∼81%) to the cost estimates is made by capital generation whereas the second highest is by infrastructure-parity components (∼12%). With inclusion of aerosol optical depth in site suitability analysis, the extremely suitable class area decreases by 3.81%. Overall, net environmental impact avoided over the lifecycle increases with increase in rated capacity following a logistic curve, and is approximately 5 and 10 times higher for 50 and 100 MW power plants, respectively.

LVRT and Reactive Power/Voltage Support of Utility-Scale PV Power Plants during Disturbance Conditions

This paper proposes a control technique for a large-scale grid-connected photovoltaic (PV) plant that maintains the connection of an inverter to the grid voltage under different types of faults, while injecting a reactive power to accommodate the required grid connection. This control strategy is suggested to improve the low-voltage ride-through (LVRT) capability of grid-connected PV power generation plants. A 20 MW solar PV power plant is modeled and simulated using Matlab/Simulink. The power plant is composed of 10 parallel groups of arrays with a power rating of 2 MWp. The solar PV arrays are connected to a medium-voltage side-rated 22 KV to the utility grid. A dynamic analysis of the grid-connected large-scale solar PV power plant is introduced. This analysis is accomplished in order to determine the impact of three-phase short-circuits at the point of common-coupling (PCC), where the solar PV power station is connected to ensure a practical voltage level by injecting active and reactive power. The reactive power support allows for faster restoration of voltage values at the PCC. When subjected to transient disturbances, the stability of the studied system relies on both the type of the disturbance and the initial operating situation. The disturbance may be either small, resulting from electrical load changes, or large, such as from a transmission line short-circuit (fault) and significant generator loss.

OPTIMIZATION OF THE NUMBER OF BUSBARS IN CRYSTALLINE SILICON SOLAR CELLS

With the growth of the photovoltaic (PV) market, the optimization of the efficiency of PV cells comes into focus; as crystalline silicon (c-Si) cell efficiencies get closer to the material’s maximum theoretical efficiency, every decimal increase counts, with front metallization improvement being one of the many possible approaches. Optimizing the front metallization is a low-cost variation of the already known and merchandised PV technologies, bringing to the table the possibility of optimizing shading and resistive losses, and improving the final efficiency of the cell. In this study, c-Si PV cells were simulated with different numbers of busbars and at various irradiance levels, to obtain STC efficiency and to calculate the global efficiency for a given irradiance distribution, based on one year of one-second resolution data. The chosen location for which cells were optimized for was Brotas de Macaúbas, in Northeastern Brazil, that being a representative location for where utility-scale PV power plants are being deployed in the country. The chosen location also presents frequent over-irradiance events and overall high irradiance levels, with 31,72% of the annual energy being incident at irradiance levels above STC irradiance, for which cell efficiency is measured at. The cell efficiency simulations were carried out in the Griddler 2.5 software for a c-Si PERC M12 cell with up to 15 busbars and for irradiance levels from 0 to 1800 W/m2. Despite the expected rise at the optimum number of busbars due to higher irradiance levels, the research concluded the optimum busbar number for STC efficiency (5BB) is still the optimum number of busbars considering the irradiance distribution of the location, despite the slight reduction in efficiency when real conditions were considered (0,48%). In conclusion, simulations showed that changing the number of busbars alone did not manage to improve the global cell efficiency for the evaluated site.

Nanometer-Scale Measurement of Grid Finger Electrical Conduction Pathways to Detect Series Resistance Degradation of Utility-Scale Silicon Solar Cells

We report on an electrical conduction mechanism for series resistance (Rs) degradation observed in a utility-scale photovoltaic power plant by imaging the local resistance at the Ag/Si interface of the c-Si front metallization. Scanning spreading resistance microscopy imaging with nanometer (nm) scale spatial resolution revealed that the number of point or small-area electrical contacts decreased substantially in a degraded cell compared to an unaffected cell, demonstrating the root cause of Rs degradation. The decrease in electrical contacts is likely caused by a structural change—the Ag particles in contact with the Si cell (or via a nm-thickness tunneling glass layer) aggregate into bulk Ag, and a highly resistive glass frit forms a belt shape at the Ag/Si interface. This resistive belt, with a thickness of ∼1 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">μ</i> m, blocks the current conduction from the cell emitter to the Ag grid. Our microscopy results help to unravel unambiguously the degradation mechanism and demonstrate an example of the multiscale characterization approach for understanding degradation in field-weathered PV module.

Energy analysis of utility-scale PV plant in the rain-dominated tropical monsoon climates

To limit the adverse impact of fossil fuel-generated power, energy generation from solar photovoltaic (PV) power is gaining importance. A lot of utility-scale PV power plants are being installed in tropical regions owing to the increased sunshine hours especially during the summer season. The influence of rain on the performance of PV power plants during monsoon seasons in a tropical climate is not studied in detail. This paper analyses the operational performance of a 2 MWp photovoltaic plant commissioned at the Kuzhalmannam site, Palakkad district, Kerala State, South India. The methodology includes the analysis of standard performance metrics of the plant utilizing two-year measured data and comparison with other climates. The PV plant's average performance ratio (PR) is 73.39, with an average of 15.41% capacity utilization factor (CUF) over the study period. The most deficit generation for the PV plant is observed in the months from June to August, which are part of the Southwest monsoon season. It is observed that the monsoon seasons prevailing in the region have a more substantial influence leading to a 35% reduction in energy generation from the annual average generation. Further, a comparison with other climates revealed that the specific yield obtained in rain-dominated monsoon tropical climates is lesser than dry and temperate climates.

Ground-mounted vs floating photovoltaic (PV) power plant: a trade-off using game theory in utility-scale PV power plant investment decision making

The development of a renewable energy power plant in Indonesia will increase rapidly in the future in line with the long-term electricity policy to achieve the renewable energy target of 23% by 2025. One type of renewable energy power plant that will be highly developed is the Photovoltaic (PV) power plant, both built on the ground or floating type. Floating PV power plants do not require large amounts of land. However, the construction of a floating PV requires a floater system along with mooring and anchoring, which costs up to 20-30% of the project cost. This paper aims to optimize and simulate the critical factors so that investors and utility companies can make a decision whether to build a PV power plant on land or floating in a used mine area. Critical factors that affected the PV power plant development are analyzed using Critical Success Factor Analysis. Furthermore, the analysis is carried out using Game Theory to obtain optimal decisions. Based on the analysis, if the other critical factors are assumed to be the same, the construction of a floating PV Power Plant in a typically used mining area will provide optimal commercial value at a depth of reservoir of fewer than 60 meters. If the depth of the reservoir is more than 60 meters, the ground mounted PV will provide a more optimal commercial value.

Fault Diagnostic Methodologies for Utility-Scale Photovoltaic Power Plants: A State of the Art Review

The worldwide electricity supply network has recently experienced a huge rate of solar photovoltaic penetration. Grid-connected photovoltaic (PV) systems range from smaller custom built-in arrays to larger utility power plants. When the size and share of PV systems in the energy mix increases, the operational complexity and reliability of grid stability also increase. The growing concern about PV plants compared to traditional power plants is the dispersed existence of PV plants with millions of generators (PV panels) spread over kilometers, which increases the possibility of faults occurring and associated risk. As a result, a robust fault diagnosis and mitigation framework remain a key component of PV plants. Various fault monitoring and diagnostic systems are currently being used, defined by calculation of electrical parameters, extracted electrical parameters, artificial intelligence, and thermography. This article explores existing PV fault diagnostic systems in a detailed way and addresses their possible merits and demerits.

Robust and Fast Detection of Small Power Losses in Large-Scale PV Systems

Due to the fast growth in global installed photovoltaic (PV) capacity, performance monitoring for large-scale PV systems is an increasingly relevant and important topic. A large volume of research exists in this field, but there is a need for comparison of different methods and their performance toward relevant metrics, a broad discussion of the different choices involved, and subsequent consolidation. In this article, we focus on the detection of small power losses on string-level. We discuss the different choices involved in building a robust string performance monitoring scheme. We suggest the following approach: 1) identify bad data quality and do data-filtering; 2) calculate the daily specific yield on string level; 3) calculate the relative difference in specific yield between the strings (relative yield); 4) identify historical faults; 5) correct for seasonal variations; and 6) apply control charts to detect performance losses in new data and issue alarms/report to the system operators. Based on data from a utility scale PV power plant we compare different control charts in terms of detection time and sensitivity. We show that the cumulative sum (CUSUM) median and the Tukey-CUSUM charts are the most promising fault detection methods of the ones we have tested. We can robustly detect faults causing a performance loss of about 1% within 35 days of the drop in performance.

An Online Novel Two-Layered Photovoltaic Fault Monitoring Technique Based Upon the Thermal Signatures

The share of photovoltaic (PV) power generation in the energy mix is increasing at a rapid pace with dramatically increasing capacity addition through utility-scale PV power plants globally. As PV plants are forecasted to be a major energy generator in the future, their reliable operation remains of primary concern due to a possibility of faults in a tremendously huge number of PV panels involved in power generation in larger plants. The precise detection of nature and the location of the faults along with a prompt remedial mechanism is deemed crucial for smoother power plant operation. The existing fault diagnostic methodologies based on thermal imaging of the panels as well as electrical parameters through inverter possess certain limitations. The current article deals with a novel fault diagnostic technique based on PV panel electrical parameters and junction temperatures that can precisely locate and categorize the faults. The proposed scheme has been tested on a 1.6 kW photovoltaic system for short circuit, open circuit, grounding, and partial shading faults. The proposed method showed improved accuracy compared to thermal imaging on panel scale fault detection, offering a possibility to adapt to the PV plant scale.

How much power is lost in a hot-spot? A case study quantifying the effect of thermal anomalies in two utility scale PV power plants

Methods for quick and accurate detection and diagnosis of defects in PV systems are increasingly important as the global photovoltaic (PV) capacity continues to grow at a rapid pace. Two of the most used methods for defect detection involve aerial infrared thermography and data analysis of production data. In this work, we combine the two methods to analyze two utility scale PV plants, providing new understanding about the two methods. We report on the percentage and distribution of thermal anomalies of different categories and quantify their relationship with performance on string level. We find that the most important parameter for determining production losses on string level is the number of module substrings containing thermal anomalies. Due to the large variability of the effect of different thermal signatures, as well as uncertainties in the estimate of the string performance, we find no clear correlation between performance and thermal signature category or temperature. However, a whole hot cell is the thermal signature that on average has the smallest impact on the power output on string level. Finally, in our data, the performance of a string of 20 modules with 3 bypass diodes is on average reduced by 1.16 ± 0.12% per module substring containing thermal anomalies.

Aerial infrared thermography for low-cost and fast fault detection in utility-scale PV power plants

The uptime of utility-scale solar photovoltaic (PV) power plants is of utmost importance for meeting contractual energy yields and expected capacity factors. Aerial Infrared Thermography (aIRT) is a non-destructive, no-downtime, fast and cost-effective method for monitoring large-scale PV power plants and assisting in fault detection. The use of aIRT techniques aims at increasing the quality and service life of PV plants especially in sunny and developing countries such as Brazil, where there is a shortfall of specialised workforce and the costs for a detailed supervisory system of utility-scale PV power plants are high. This paper presents an analysis of an aIRT flight campaign over four utility-scale PV plants in the northeast of Brazil. Two types of measurement equipment have been tested and compared, resulting in more stability and efficiency using a commercially available solution. This solution was also equipped with a RGB camera that accelerated the inspections, since it helped to differentiate defects from hot spots caused by soiling and vegetation over the modules, which were common. Different methods for fault detection were also tested and it was concluded that post-flight image analysis provides faster results. The most common faults that can happen in the early operation of PV power plants and how operators should address and prevent them were also discussed. The most common defect detected during the campaign were disconnected cell substrings. However, disconnected strings had the most impact on the power plants energy performance.

Analysis of the cloud enhancement phenomenon and its effects on photovoltaic generators based on cloud speed sensor measurements

The irradiance incident on photovoltaic (PV) generators can considerably exceed the expected clear sky irradiance. Due to this phenomenon, called cloud enhancement (CE), the maximum power of the PV generator can exceed the rated power of the inverter connecting the generator to the grid. CE event characteristics and the effects of CE on the electrical operation of PV generators were studied based on measured irradiances and cloud edge velocities. Over eleven months in San Diego, California, the highest measured peak irradiance was 1466 W/m2. In addition, the highest simulated average irradiances for up to 1 MW generators were over 1400 W/m2. The largest lengths for CE events exceeding 1000 W/m2 were multiple kilometers. These results indicate that even large utility-scale PV power plants can be affected significantly by CE events. Moreover, the operation of three PV plants was simulated during around 2400 measured CE events with a detailed spatiotemporal model. The effects of inverter sizing on the operation of the plants were also studied, and the negative impacts of CE on the operation of PV systems were shown to increase with the increasing DC/AC ratio. During the CE events, the energy losses due to power curtailment were from 5% to 50% of the available energy production. While CE affects the operation of the PV plants, these effects were small in terms of aggregate energy since CE events that most strongly impact PV system operation are very rare, meaning that CE does not cause major problems for the operation of PV systems.

Extreme solar overirradiance events: Occurrence and impacts on utility-scale photovoltaic power plants in Brazil

In contrast to the decades-long accumulated experience of photovoltaic (PV) installations in more temperate climates, the effects of some extreme operating temperatures and extreme solar irradiance levels start to become more noticeable with the uptake of large-scale PV in the sunbelt regions of the world. One such effect is caused by extreme solar overirradiance events, which up to now have been reported in the literature much more for their scientific interest than as a potential problem affecting the operational performance of PV power plants. Solar overirradiance events with a time span of tens of seconds or minutes are associated with the high operating temperatures prevailing in the field at many sites where utility-scale PV power plants start to become widespread, deleterious effects can be observed, which will negatively impact the performance of these generators. Using irradiance data from seven solar measuring stations deployed over distinct regions in Brazil, many of which are hosting megawatt-scale PV power plants, this paper reports on several extreme solar overirradiance events, with measured values above 1367 W/m2 up to 1845 W/m2, lasting from many seconds to a few minutes. Analysis of impacts and consequences from these events on the operational performance of PV generators are addressed, mainly focused on combiner box fuses, inverter overload losses, and inverter maximum power point tracker.

Novel grid connection interface for utility‐scale PV power plants based on MMC

The ever-increasing integration of photovoltaic (PV) energy has led to the fast development of utility-scale PV power plants worldwide. A novel grid connection interface for utility-scale PV power plants based on the modular multi-level converter (MMC) is explored. The grid connection interface is a DC boost interface by nature. It adopts the multistring topology, employs DC/DC boost converters, utilises a centralised MMC, and integrates an energy storage system. Meanwhile, the two-level control system for the DC boost interface is also designed. Compared with the conventional AC boost interfaces, the proposed DC boost interface avoids problems regarding reactive power transmission, harmonic resonance, and synchronous stabilisation. It also improves the power quality, efficiency, and the integration capacity of the PV generation. A case study of a utility-scale PV power plant with the DC boost interface is carried out in PSCAD/EMTDC. The simulation results validate the effectiveness and the merits of the DC boost interface under different operation conditions. The proposed DC boost interface proves more suitable for utility-scale PV power plants in areas with high solar irradiance. It also lays a solid foundation for the future research regarding the control and protection of utility-scale PV power plants.

Impact of Battery Cost on the Economics of Hybrid Photovoltaic Power Plants

In recent years, photovoltaic (PV) technology has experienced a rapid cost reduction. This trend is expected to continue, which in many countries drives interest in utility-scale PV power plants. The main disadvantage of such plants is that they operate only when the sun is shining. The installation of PV modules together with energy storage and/or fossil fuel backup is a way to solve that issue, but consequently increases the costs. In the last few years, however, lithium-ion batteries as well have shown a promising price reduction. This paper studies the competitiveness of a hybrid power plant that combines a PV system, lithium-ion battery and gas turbine (GT) compared to conventional fossil-fuel power plants (coal and natural gas-fired) with focus on the battery cost. To fulfil the demand an auxiliary GT is used in the hybrid PV plant, but its annual generation is limited to 20% of the total output. The metric for the comparison of the different technologies is the levelized cost of energy (LCOE). The installation of the plants is showcased in Morocco, a country with excellent solar resources. Future market scenarios for 2020 and 2030 are considered. A sensitivity analysis is performed to identify the key parameters that influence LCOE.

Real-Time Monitoring System for a Utility-Scale Photovoltaic Power Plant.

There is, at present, considerable interest in the storage and dispatchability of photovoltaic (PV) energy, together with the need to manage power flows in real-time. This paper presents a new system, PV-on time, which has been developed to supervise the operating mode of a Grid-Connected Utility-Scale PV Power Plant in order to ensure the reliability and continuity of its supply. This system presents an architecture of acquisition devices, including wireless sensors distributed around the plant, which measure the required information. It is also equipped with a high-precision protocol for synchronizing all data acquisition equipment, something that is necessary for correctly establishing relationships among events in the plant. Moreover, a system for monitoring and supervising all of the distributed devices, as well as for the real-time treatment of all the registered information, is presented. Performances were analyzed in a 400 kW transformation center belonging to a 6.1 MW Utility-Scale PV Power Plant. In addition to monitoring the performance of all of the PV plant’s components and detecting any failures or deviations in production, this system enables users to control the power quality of the signal injected and the influence of the installation on the distribution grid.