Utility-scale Photovoltaic Array Research Articles

Simulated Impact of Shortened Strings in Commercial and Utility-Scale Photovoltaic Arrays

The deliberate removal of photovoltaic modules from a string can occur for various reasons encompassing maintenance, measurements, theft, or failure, reducing that string length relative to others when replacement modules are not available and there are not any viable alternative makes and models that could be inserted. This phenomenon, delineated in our prior experimentally validated research, manifests two significant effects: (1) a shift in the ideal maximum power point and (2) the induction of potentially substantial reverse currents in the shortened strings at open-circuit voltage, VOC. However, the scalability and asymptotic limits of these observed behaviors concerning array size remained undetermined. In this study, we elucidate the operational dynamics of such arrays by manipulating two mismatch-contributing variables in simulated arrays of up to 900 strings: the number of removed modules per string (indicative of the level of mismatch, ranging up to 5) and the quantity of shortened strings (1 to 60). Simulation outcomes underscore that mismatch severity impacts array operation more than the proportion of shortened strings. This research delves into the practical ramifications of operating with shortened strings, including implications for low-irradiance operation and the manifestation of deleterious reverse currents (>35 A in specific cases), emphasizing the need for careful array configuration for optimal performance and safety in these implementations.

Fault Location in Solar Farms

Power delivery interruption and catastrophic failures are some of the potential consequences of undetected faults in photovoltaic (PV) arrays. A voltage protection scheme with the minimum number of sensors which is capable of detecting, classifying, and locating line-to-line (intrastring and cross string), line-to-ground, and open-circuit faults in a utility-scale PV array is proposed in this article. The proposed protection scheme consists of three steps. In the first stage, by a simple and efficient algorithm occurrence of any disturbance in the system is detected using some voltage sensors. At this stage, faulty strings in the PV array are also identified. In the second step, using a new least squares-based method, fault and shading conditions are discriminated from each other. Finally, in the third step, the faults inside the faulty string are located using a new method based on multiclass artificial neural networks. Fault location methods that have been developed so far require a large number of sensors or additional equipment for the exact location of faulty modules inside the fault string, but in the proposed method, only one sensor is used per string for fault localization. The proposed scheme for detection and location of faults is evaluated by simulating a typical system in different conditions.

The Observed Effects of Utility-Scale Photovoltaics on Near-Surface Air Temperature and Energy Balance

AbstractUtility-scale solar power plants are a rapidly growing component of the renewable energy sector. While most agree that solar power can decrease greenhouse gas emissions, the effects of photovoltaic (PV) systems on surface energy exchanges and near-surface meteorology are not well understood. This study presents data from two eddy covariance observational towers, placed within and adjacent to a utility-scale PV array in southern Arizona. The observational period (October 2017–July 2018) includes the full range of annual temperature variation. Average daily maximum 1.5-m air temperature at the PV array was 1.3°C warmer than the reference (i.e., non-PV) site, whereas no significant difference in 1.5-m nocturnal air temperature was observed. PV modules captured the majority of solar radiation and were the primary energetically active surface during the day. Despite the removal of energy by electricity production, the modules increased daytime net radiation Q* available for partitioning by reducing surface albedo. The PV modules shift surface energy balance partitioning away from upward longwave radiation and heat storage and toward sensible heat flux QH because of their low emissivity, low heat capacity, and increased surface area and roughness, which facilitates more efficient QH from the surface. The PV modules significantly reduce ground heat flux QG storage and nocturnal release, as the soil beneath the modules is well shaded. Our work demonstrates the importance of targeted observational campaigns to inform process-based understanding associated with PV systems. It further establishes a basis for observationally based PV energy balance models that may be used to examine climatic effects due to large-scale deployment.

Investigations into best cost battery-supercapacitor hybrid energy storage system for a utility scale PV array

Abstract In this paper, a hybrid energy storage system (HESS), combining a battery and a supercapacitor (SC), is studied for dispatching solar power at one hour increments for an entire day for 1 MW grid connected photovoltaic (PV) arrays. HESS relies on PV for charging and not the grid, and hence is immune to fluctuating electricity prices. The battery and SC are intended to supply predetermined constant power, but not to provide ancillary services for the grid operation. To develop a cost-effective energy storage system, a low pass filter (LPF) is used to allocate the power between a battery and a SC. The best cost of the energy storage is calculated based on the time constant of the LPF through extensive simulations. Several rule-based algorithms based on the battery state of charge (SOC) are developed to estimate the grid reference power for each one-hour dispatching period. An economic comparison of using different kinds of the algorithms for estimating the grid reference power are also presented in this study. The objective is to better understand the annual energy storage cost for hourly dispatching solar power. The actual solar data of four different days as a representative of each season recorded at Oak Ridge National Laboratory are used in the simulations. The relationship between the actual PV cell temperature and the ambient temperature in power output calculations are also considered and their effects on energy storage price calculations are presented in this paper.

Voltage-Based Protection Scheme for Faults Within Utility-Scale Photovoltaic Arrays

Permanent power loss and major catastrophic failures are among the potential consequences of undetected faults within photovoltaic (PV) arrays. This paper proposes a voltage-based protection scheme that detects, classifies, and locates string-to-ground, string-to-string, and open-circuit faults in utility-scale PV arrays. The protection scheme operates based on the magnitude and wave-shape properties of voltage signals. Some salient features of this method include its capability to distinguish between fault and partial shading conditions, and its independence from meteorological data. The performance of the proposed approach is assessed on two utility-scale grounded PV arrays under various conditions. Moreover, the proposed method is tested on an experimental setup of a small grid-connected PV array. Simulation and experimental results verify the scheme’s accuracy, high speed, and scalability.