Utility-scale PV Plants Research Articles

NYSolarCast: A solar power forecasting system for New York State

Solar energy generation capacity will need to be greatly increased to meet aggressive clean energy targets by New York State (NYS), which are 70% renewable energy (RE) generation by 2030, and 100% by 2040. Because solar energy is a variable, weather-driven resource, accurate forecasts of solar energy generation both in nowcast (intra-day) and day-ahead time horizons are necessary for electric utilities and independent system operators, as they maintain grid stability and maximize RE use.Meeting this need for NYS, a gridded, open-source solar power forecasting system called NYSolarCast was developed (https://github.com/ncar/NYSolarCast_delivery). NYSolarCast makes 15-min resolution predictions of global horizontal irradiance (GHI) on a 3-km grid covering all of NYS, which are then used to estimate solar power generation both for select utility-scale PV plants (15-min resolution) and for zone-aggregated distributed PV (1-h resolution). The statewide GHI forecasts are made by applying the StatCast statistical forecasting model, which is trained on over two years of GHI observations from pyranometers at all 126 NYS Mesonet stations and gridded numerical weather prediction forecasts from both the Weather Research and Forecasting model tuned for solar applications (WRF-Solar®) and NOAA’s operational High-Resolution Rapid Refresh (HRRR) model. Forecasts are made at each NYS Mesonet site and then blended outward into the rest of the grid. This paper gives an overview of NYSolarCast performance for intra-day (0–6-h) GHI and power forecasts during a one-year period.

Architecture of symmetrical bifacial perovskite/Si/perovskite PV modules and LCOE comparison in bifacial applications

Perovskite on silicon tandem technologies offer a promising way to overcome the efficiency limit of single-junction crystalline silicon modules and are therefore widely studied. Besides the cost reduction potential of using tandem modules in utility-scale PV plants, the application of bifacial PV modules offers additional opportunities to reduce costs by increasing the energy yield. However, the bifaciality factor of tandem PV modules using bifacial crystalline silicon solar cells is typically lower than that of single-junction bifacial modules, considering the asymmetric architecture of the module with higher front-side than rear-side efficiency. In this study, we assess a symmetrical bifacial triple-junction perovskite/silicon/perovskite PV module architecture which allows for a significant improvement of the PV module rear side efficiency. Cost of ownership, energy yield and levelized cost of energy modeling show the superior performance of such modules compared to crystalline silicon and perovskite/silicon tandem modules specifically in vertical mounting applications that are used e.g.in AgriPV or noise protection PV walls on highways.

Prolonged degradation and reliability assessment of installed modules operational for 10 years in 5 MW PV plant in hot semi-arid climate

The current work presents detailed degradation and reliability assessment of installed PV modules in grid tied 5 MW solar PV plant in hot semi-arid climate. Defects and failures of 336 modules out of 2078 visually inspected c-Si modules with 10 years of operational period in hot semi-arid climate is evaluated using FMECA statistical tool and I-V curve measurement. The novelty of the research conducted is presenting long term degradation of PV modules in utility scale PV plant installed for 10 years in outdoor environment in remote location, carrying FMECA analysis of visually degraded modules along with on-field electrical characterization. Correlation of identified defect and failures with electrical parameters of PV module is also presented. The results obtained indicate light and dark EVA discoloration, EVA discoloration with cell and metallization discoloration, snail trails, backsheet burnt, glass breakage with or without cell cracks to be the most dominant and frequently occurring defects and failures with high severity. The inspected plant has considerable degradation as compared to other plants in the same area in hot semi-arid climate and therefore degradation investigation of the plant is important in identifying various possible causes of observed degradation and studying impact of degradation on module performance. Based on the results obtained and analysis conducted, several important preventive and corrective measures along with important recommendations have been enlisted for mitigating failures and improving the system performance.

Performance evaluation of a 20 MW grid-coupled solar park located in the southern oceanic environment of Ghana

In line with government efforts to increase renewable energy in the energy generation mix to 10 percent by the year 2030 and to promote cleaner production in the power sector, ambitious efforts are being made to promote the implementation of utility-scale solar PV plants with ample policy backing. However, performance information is not readily available since implemented large-scale projects are few. This study examines the performance characteristics of a 20 MW grid-tied solar PV plant located about 2 km away from the Gulf of Guinea at the Southern part of Ghana. The study uses a combination of PVsyst simulation and analysis of monitored data spanning the year 2018. The site meteorological data was obtained through NASA satellite and Meteonorm 7.1 station. Monitored data analysis showed that the power plant delivered a total annual energy of 26,480 MWh to the utility grid, whilst simulations gave total annual energy of 29,154 MWh. The final PV array yield values of 3.68 kWh/kWp/d and 4.06 kWh/kWp/d were obtained from the monitored and predicted analysis. Monitored data analysis gave plant performance ratio and capacity factor values of 72.8% and 15.1% whilst simulations produced 80.2% performance ratio and 16.6% capacity factor. The actual and simulated annual average system losses recorded were 0.056 h/d and 0.065 h/d, and the monitored and predicted overall system efficiencies obtained were 11.39% and 12.32%. Carbon emissions savings analysis revealed that the power plant saved 12,181 metric tons in the year 2018. The study gives an insight into valuable performance statistics, seasonal and year-round response relative to the coastal southern part of Ghana. The monitored data and operating experience of the PV system can be applied for the deployment of future large-scale projects in the southern part of Ghana, including other oceanic tropical climate regions in the world.

A feasibility study of the 1.5-axis tracking model in utility-scale solar PV plants

Many solar tracking technologies have been developed with the aim of improving the energy performance of solar PV installations. Among these, single-axis tracking (SAT) systems give good economic prospect for ground-mounted PV plants but experience inevitable power loss when the trackers diverge from the incident solar irradiance during winter. The 1.5-axis tracking (1.5AT) model is developed in recent years to achieve a balance between the benefits and shortcomings of the SAT and dual-axis tracking (DAT) systems. Despite the anticipated superiority of the 1.5AT, there is a lack of literature on the methodology to analytically study the potential and feasibility of the 1.5AT model, especially from a global perspective. In this paper, a comprehensive feasibility study has been conducted to evaluate the energy performance and shading analysis of the 1.5AT model. The developed methodology serves as a general benchmark to explore the prospects of the 1.5AT model at different geographical locations and seasons. This encourages further research and deployment of the 1.5AT model as a potential alternative to improve the return of investment for various PV system stakeholders.

An empirical approach to frequency droop characterization from utility‐scale photovoltaic plants operation in a power system

PV plant power excursions can have adverse implications on grid frequency. This phenomenon is observable due to inherently uncertain cloud transients across a local PV plant. Hence, provision of decision-based controllers for centralized power inverters becomes imperative for supporting local grid operations. Such controllers can be improved to better counteract minutes-based PV power deviations from its stable equilibrium. Thus, grid frequency deviations require further investigation at PV plant point of interconnection to the grid. In this research, single and spatially distributed utility-scale PV plants operation is studied on a real-time power system simulator, under fast-changing meteorological conditions at different PV site loading levels ( P P V − r e f ). Software-in-the-loop Monte Carlo simulation is conducted and an empirical approach is proposed for characterizing minutes-based variations in grid frequency originating from PV plant operation, that is, power fluctuations at different P P V − r e f . The power−frequency curve obtained at the PV site can be incorporated in form of an empirical frequency droop function in characteristics curve of adjacent auxiliary power source(s). A prominent feature of this adaptive frequency droop is that it considers PV site loading levels during different hours, giving it leverage over common practice constant droop(s). A hardware-in-the-loop platform is presented allowing field derivation of adaptive frequency droop curves using hardware PMU time-series data analytics.

Degradation Analysis of Utility-Scale PV Plants in Different Climate Zones

Accurate performance modeling of utility-scale PV plants is crucial for reducing the risk of investment, as well as improving operations and maintenance. In spite of much research, the precise rate at which PV plants degrade is still not well known. This article uses a well-known methodology for calculating degradation rates to assess the impact of climate on long-term performance. The RdTools analytic approach is used to perform a comparative case study of two utility-scale PV plants with the same setup and almost identical technology yet located in distinct climates. A significant difference is observed between the degradation rates of each park. The median of the nominal system degradation rate measured at the dc-side of the inverters in the hotter and more humid climate is -1.4%/yr, with 95% of the inverters between -1.5%/yr and -1.3%/yr, whereas in the temperate climate the median rate is -0.94%/yr, with 95% of the inverters between -1.0%/yr and -0.9%/yr. These results suggest that climate zones must be included when evaluating the long-term performance of PV plants.

Performance and Optimization of Commercial Solar PV and PTC Plants

Installation of solar PV arrays at utility scale is gaining popularity nowadays because of the significant reduction in the cost of components as well as the global push towards clean energy. Solar PV plants along with Parabolic Trough Collector Solar thermal plants has the highest potential among the available Renewable Energy (RE) technologies existing in the world. The objective of this paper is to optimize the performance of commercial Solar PV and PTC power plant for a potential location and hence to arrive on a most feasible configuration for the site. A representative site located in the Abudhabi region of UAE considered for the study. This paper also details on the annual performance of the proposed plant along with its technical aspects. PVSYST 6.7.7 and SAM software is used to design the optimal size and its specifications of a 100MW PV grid connected system at Abu Dhabi (UAE) region. The design and arrangements of the system verified using simulation results. The annual energy generated from the designed utility-scale solar PV plant from PVSYST 6.7.7 calculated as 161198MWh/year with a performance ratio (PR) of 74.8% per year where as for PTC it has calculated as 157152MWh/year by using SAM. The STC (Standard Testing Condition) for the specification of PV modules are normalized operating conditions when testing the module. Design parameters such as module orientation, array yield, reference yield, final yield, global horizontal irradiation (GHI), and ambient temperature and loss factors evaluated. To evaluate the economic feasibility of proposed plant, the levelized cost of electricity (LCOE) is determined as $0.04404/kwh for Solar PV and as $0.01533/kwh for PTC, which is used to calculate lifecycle cost and energy production.

Endogenous Soiling Rate Determination and Detection of Cleaning Events in Utility-Scale PV Plants

As the deployment rate of PV power plants continues to soar, the need for robust, scalable methods for performance analytics increases. In this paper, we demonstrate the usefulness of one approach for quantifying soiling rates in utility-scale PV power plants endogenously, i.e., directly from the production data. The temperature corrected performance ratio, normalized to a clean state, is used to derive the soiling ratio (SR). Cleaning events, caused by either rain or manual cleaning, are automatically detected by positive shifts in the running median of the SR time series. Soiling rates are then estimated by the rate of change of the SR between the cleaning events, which is determined by linear regression. The method is validated on data from three utility-scale PV power plants in the Middle East, yielding soiling rates that are in the range 0%-0.18%/day at least 50% of the time, with a median of 0.1%/day.

Conflict cause analysis between stakeholders in a utility-scale PV plant and its policy improvement methods in Korea

Despite the technological advances and the Korean government's ongoing efforts to expand the PV market, disputes related to the quality and performance of the utility-scale PV systems are not uncommon. Therefore, actual dispute cases in Korea are analysed to elicit their root causes and suggest effective remedies in this paper. This analysis focuses on the following three types of disputes caused by: (i) PV system installation quality, (ii) PV system performance degradation and (iii) natural disaster damage. Based on interviews and examination of the PV plants in dispute, it was drawn that conflicts between the stakeholders stem from limitations to utility-scale PV plants’ evaluation and technical dispute management, lack of PV module reliability and lax contract terms for procurement. To mitigate the conflicts between domestic PV stakeholders, the following four policy improvements are suggested: improvements of PV plants’ deployment procedure and quality assurance system that can detect failures of equipment in early stages, introduction of a government-led dispute settlement system, enforcement of strict quality standards for PV modules and provision of information on PV procurement specifications. The lessons and suggested remedies will help policy makers understand the domestic PV market and redesign the policies for mitigation of potential disputes.

A mixed-integer formulation of OLTC dynamics to minimize distribution and subtransmission tap changes induced by wind and solar power variations

Transformers equipped with an on-load tap-changer (OLTC) are the primary voltage regulators in sub-transmission and distribution networks. As the size of variable generation grows in respect to local feeder demand, the varying bidirectional flow of active power in the feeders interferes with the operation of the OLTC transformers. Currently most grid codes require utility-scale wind and PV plants to strictly regulate the voltage at the point of interconnection. This is typically achieved by installing dynamic reactive support in the form of STATCOM or SVC with instantaneously controllable setpoints and no switching cost. An effective and robust voltage coordination scheme would rely on voltage setpoints of these devices as the primary control input. Thus it is crucial to coordinate these new Volt/VAr controllers with the OLTC transformers to eliminate unnecessary tap changes and consequently reduce substation failure risk and maintenance cost. This paper introduces a centrally coordinated voltage control scheme that determines the optimal voltage setpoint based on variation of wind and solar generation in a given time window with the objective of reducing tap-change operations and resistive losses. Later the paper introduces an equivalent mixed-integer programming formulation that finds the same optimal control output but at a higher computational efficiency. Finally the paper discusses the results of the implementation of the MIP-formulation of the voltage control scheme on the DTE/ITC system serving Eastern Michigan.

Analysis of Solar Farm Site Selection Based on TOPSIS Approach

Energy is necessary for industrial activities and social development. Due to environmental effect of fossil fuels and resource limitation, the importance of using renewable energy is growing. One of the most appropriate renewable energies is solar energy. Photovoltaic cells directly convert solar energy to electricity. In addition to PV technology, selecting an appropriate site is a main concern for PV power plant installation. The aim this article is to select suitable site for photovoltaic installation in a case study, Iran. Four different locations are the primary options for utility scale PV plants installation and the best choice is selected based on a MADM method, TOPSIS.

The effect of wind direction on the performance of solar PV plants

The impact of wind direction on the overall performance of a utility-scale PV plant was studied by analyzing field data from Hadley solar farm in the UK. The solar PV plant utilizes a fixed-tilt system with the PV panels facing south at a 20 degree angle. The hypothesis is that when wind blows from the south the total power production of the solar PV plant increases in comparison with non-southerly wind events, provided that all other determining factors, such as solar irradiance, ambient temperature, and wind speed are the same. During the case study of January 1 to July 1, 2017, 42 pairs were identified, each of which includes two cases with equal solar irradiance, equal ambient temperature, and equal wind speeds but different wind directions; in one case wind is from the north and in the other one wind blows from the south. The hypothesis was found to be true across all 42 pairs, i.e., the power production of the solar PV plant was always greater in the event of southerly winds. One takeaway from this finding is that wind direction and wind speed frequencies need to be taken into account along with other climatic factors to have an optimal site selection for establishing a solar PV plant. The more frequent the southerly wind occurs, the more power can be extracted from the PV panels. The other practical conclusion of this study is that it is more efficient to build fixed-tilt solar PV plants on areas oriented along the west-east direction.

Power Management for Improved Dispatch of Utility-Scale PV Plants

This paper proposes a rule-based power management algorithm to enable the dispatch of a utility-scale PV power plant consisting of a hybrid energy storage system, in accordance with the Australian national electricity rules. This algorithm is purposely designed to regulate the instantaneous power of a PV plant with the same level of dispatchability as conventional power plants. Additionally, the proposed algorithm is robust under large forecasting errors (up to 60%) of solar irradiance and it can be easily implemented in practice. Specifically, this algorithm can be executed within seconds even when considering detailed market operation and model nonlinearities. A 30 MW PV plant, including a 7.5 MW/1.25 MWh vanadium redox battery and a 1.5 MW/0.25 MWh suppercapacitors bank, has been modeled using MATLAB/Simulink and PLECS software environment. The simulation results were based on various scenarios and confirmed the effectiveness of the proposed power management algorithm. It has been shown that even in the worst-case scenario of solar forecasting error of 60%, the proposed algorithm still managed to deliver over 94% of the available energy for a given solar irradiance profile of one month.

Potential of rooftop solar photovoltaics in the energy system evolution of the United Arab Emirates

Solar power, and in particular solar photovoltaics (solar PV), is a rapidly growing source of energy in many regions of the world. However, the contribution of solar power in Middle East and North Africa (MENA) countries has been minor even though these countries possess some of the best levels of solar insolation globally. Recently, though, this has been changing. Changing hydrocarbon markets in the region, technology advances in solar PV and rapidly falling costs make solar power increasingly attractive to MENA countries that are actively diversifying their energy systems away from dependence on hydrocarbon fuel sources. Although utility-scale CSP and PV plants have been the focus through 2014, rooftop solar PV is being positioned to play potentially an important role in the United Arab Emirates (UAE)'s future energy mix. In this paper, rooftop solar PV in the UAE is taken as a case study for the evolution of a MENA energy system toward an increasingly sustainable power generation mix. The results show that rooftop solar PV can be an economically viable technology choice and hence will increasingly become part of regional energy strategies as technology costs continue to fall and tariff reforms continue to gain traction.

Solar energy from Negev desert, Israel: Assessment of power fluctuations for future PV fleet

Power output fluctuations have a potentially negative effect on utility grid stability, especially in isolated power systems such as that of Israel. Thus for the successful large scale application of photovoltaic power (PV) in an isolated system it is of particular importance to have a proper selection of photovoltaic sites together with an appropriate distribution of installed power.The Negev desert in Israel is an ideal location for utility scale PV plants, where the average annual global horizontal radiation is above 2000 [kWh∗m−2∗year−1]. In spite of the 10% goal of renewably energy production by year 2020, in 2013 less than 1% of Israel's electric energy needs are supplied by PV and now is the best time to propose a proper spatial distribution of PV fleet in Negev that will limit the extreme fluctuations originated from the fleet without significantly reducing the utilized solar energy.This paper presents a method of comparing different PV development scenarios by ranking them according to expected power fluctuations.The irradiation fluctuation rank formulated in this paper was calculated using data of global irradiation measured during one and a half year with a 1minute sampling time on seven sites in Israel's Negev desert. This rank values were compared for a large number of different possible geographical distributions of PV power plants.Results show that the rank decreases with distribution of the same PV power over an increasing number of sites. The rank shows similar trends for the period of a year as well as for different seasons. Allocating PV power with different weights between a fixed number of sites influences the number of extreme power fluctuations. The PV fleet configuration with the minimum rank value shows the minimum number of extreme power fluctuations that will affect system frequency.