Open Access
The potential of forecasting in reducing the LCOE in PV plants under ramp-rate restrictions
(Elsevier, 2019) Cirés Buey, Eulalia; Marcos Álvarez, Javier; Parra Laita, Íñigo de la; García Solano, Miguel; Marroyo Palomo, Luis; Ingeniería Eléctrica, Electrónica y de Comunicación; Institute of Smart Cities - ISC; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren
An increasing number of grid codes are requiring the limitation of the PV output power fluctuation over a given time scale. Batteries represent the most obvious solution to smooth power fluctuations, with the corresponding negative impact on the PV energy cost. However, short-term forecasting is currently being proposed as a tool to reduce battery capacity requirements or even completely remove it. Although these solutions decrease or avoid the battery cost, it also entails some energy curtailment losses which obviously raise the final cost of PV energy. This energy losses, currently unknown, are independent of the forecasting accuracy and represent the minimal additional cost in the hypothetical case of a perfect prediction. Thus, this paper compares Levelized Cost of Energy (LCOE) of three ramp-rate control strategies in order to determine which would give the lowest cost: battery-based, ideal short-term forecasting, or a combination of both. Results show that curtailment losses would be small enough to make battery-less strategy an appropriate choice, so it is worthwhile improving short-term forecasting in view of the potential LCOE savings. Database is taken from high resolution measurements recorded for over a year at 8 PV plants ranging from 1 to 46 MWp.
Open Access
A PV ramp-rate control strategy to extend battery lifespan using forecasting
(Elsevier, 2022) González Moreno, Alejandro; Marcos Álvarez, Javier; Parra Laita, Íñigo de la; Marroyo Palomo, Luis; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
This study analyses and presents a new ramp-rate control algorithm for smoothing PV power fluctuations, designed to address three fundamental objectives: to reduce battery cycling, to meet minimum storage requirements and to be able to operate, without ramp-rate violations, with real publicly-available forecasting. The algorithm was compared to three benchmark methods and, as a performance limit, also to a hypothetical perfect prediction. Different performance variables were analyzed for all the strategies within a restricted ramp-rate constraint (2%/min): minimum storage requirement, battery power distributions, throughput energy, state of charge (SOC) distributions, degradation (calendar and cycling), expected battery lifespan and levelized cost of energy (LCOE). The proposal proves to be the most cost-effective smoothing technique and the simulation results show that its performance is comparable to the obtained with the use of an assumed perfect prediction.
Open Access
Inverter-based PV ramp-rate limitation strategies: minimizing energy losses
(IEEE, 2022) González Moreno, Alejandro; Marcos Álvarez, Javier; Parra Laita, Íñigo de la; Marroyo Palomo, Luis; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
This work analyzes the reduction of power generation in strategies that regulate the PV ramp-rate by using inverter limitation. Although the operating principle implies some energy production losses, not all these losses are necessary. Three different strategies were simulated using experimental 5-second data collected throughout a year at a 38.6 MW PV plant, and their energy losses were obtained for different ramprate levels. An improvement in one of these strategies is proposed and evaluated. The main findings suggest that the proposed modification has the potential to drastically reduce annual production losses to insignificant levels. Regardless of the ramp-rate constrain, simulation results evidenced energy losses bellow 1%.
Open Access
Outdoor performance of a CdTe based PV generator during 5 years of operation
(IEEE, 2022) Guerra Menjívar, Moisés Roberto; Parra Laita, Íñigo de la; Marcos Álvarez, Javier; García Solano, Miguel; Marroyo Palomo, Luis; Ingeniería Eléctrica, Electrónica y de Comunicación; Institute of Smart Cities - ISC; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren
Together with the huge growth of the traditional crystalline silicon (Si-x) PV manufacturers, other thin-film solar cells have also emerged such as cadmium telluride (CdTe) manufacturers. They are characterized by the fact that they were created to reduce costs and by the scarcity of silicon, from which the rest of the modules are made. Despite they need more space to generate the same amount of energy as crystalline modules, their price is supposed to be much lower, and argue that they have a better performance at high temperatures. However, real comparisons between the outdoor performance of CdTe and Si-x modules have been scarcely addressed in the literature. This paper provides a comparison under real operating conditions of a CdTe photovoltaic generator versus a conventional silicon generator during 5 years of operation in a mid-latitude area, identifying the causes of the differences observed.
Open Access
Control strategies to smooth short-term power fluctuations in large photovoltaic plants using battery storage systems
(MDPI, 2014) Marcos Álvarez, Javier; Parra Laita, Íñigo de la; García Solano, Miguel; Marroyo Palomo, Luis; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa
The variations in irradiance produced by changes in cloud cover can cause rapid fluctuations in the power generated by large photovoltaic (PV) plants. As the PV power share in the grid increases, such fluctuations may adversely affect power quality and reliability. Thus, energy storage systems (ESS) are necessary in order to smooth power fluctuations below the maximum allowable. This article first proposes a new control strategy (step-control), to improve the results in relation to two state-of-the-art strategies, ramp-rate control and moving average. It also presents a method to quantify the storage capacity requirements according to the three different smoothing strategies and for different PV plant sizes. Finally, simulations shows that, although the moving-average (MA) strategy requires the smallest capacity, it presents more losses (2–3 times more) and produces a much higher number of cycles over the ESS (around 10 times more), making it unsuitable with storage technologies as lithium-ion. The step-control shown as a better option in scenery with exigent ramp restrictions (around 2%/min) and distributed generation against the ramp-rate control in all ESS key aspects: 20% less of capacity, up to 30% less of losses and a 40% less of ageing. All the simulations were based on real PV production data, taken every 5 s in the course of one year (2012) from a number of systems with power outputs ranging from 550 kW to 40 MW.
Open Access
Ramp-rate control in large PV plants: battery vs. short-term forecast
(IEEE, 2018) Marcos Álvarez, Javier; Parra Laita, Íñigo de la; Cirés Buey, Eulalia; Wang, Guang Chao; García Solano, Miguel; Marroyo Palomo, Luis; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoa eta Telekomunikazio Ingeniaritza; Institute of Smart Cities - ISC
The changeability in the power produced by utility-scale PV plants caused by shadows due to passing clouds can compromise grid stability. Traditionally, some kind of energy storage systems (ESS) is proposed as the solution to reduce power variations below the limits imposed by new grid codes regulations. However, recent short-term forecast sources open the door to control the variability without batteries, using only inverter limitation. This option entails some energy curtailment losses that has not been yet addressed. This paper quantifies these losses for the first time using a meaningful database of 5 s one year data for a 38.5 MW PV plant in a perfect forecast scenery. Finally, we compare the economic cost of installing a lithium-ion battery vs. the inverter limitation solution. The results obtained indicate that battery-less strategies must not be neglected for ramp-rate control, since they can be more cost-effective using perfect forecast for any ramp value.
Open Access
Influence of control in cycling degradation when batteries perform PV ramp-rate control
(IEEE, 2023) González Moreno, Alejandro; Marcos Álvarez, Javier; Parra Laita, Íñigo de la; Marroyo Palomo, Luis; Ingeniería Eléctrica, Electrónica y de Comunicación; Institute of Smart Cities - ISC; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
This work studies the importance of the correct selection of control parameters in order to avoid unnecessary cycling in batteries when they perform PV smoothing. The classic ramp-rate control method (CRRC) is studied as smoothing technique and the key role of the state of charge (SOC) control is analyzed for a real 38.5 MW PV plant, particularly the influence of proportional gain (K). Depending on K, battery cycling degradation (CyD), power requirements, SOC limits and throughout energy performance were discussed. According to the results, the correct tuning could prolong battery lifespan by reducing cycling degradation up to 80% (depending on the fluctuation restrictions and K) and avoiding unnecessary energy losses, power requirements and undesirable SOC operation levels. Finally, a simple general rule is proposed to set K value when CRRC is used and its applicability is tested by simulating two additional PV plants with rated power of 1.1 and 75.6 MW.
Open Access
Analysis of a CIS based PV generator versus a multicrystalline generator under outdoor long-term exposure
(IEEE, 2021) Parra Laita, Íñigo de la; Guerra Menjívar, Moisés Roberto; Marcos Álvarez, Javier; García Solano, Miguel; Marroyo Palomo, Luis; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren; Institute of Smart Cities - ISC; Ingeniería Eléctrica, Electrónica y de Comunicación
The worldwide growth of the PV market has been almost exponential during the last years. Together with conventional crystalline (c-Si) PV modules, “new” commercially available PV technologies such as copper indium selenide (CIS) based solar cells have appeared achieving a similar efficiency comparable to c-Si at similar production cost. In addition to the use of cheaper materials, CIS solar cells manufacturers claim some enhancements such as lower temperature coefficient or higher absorption of diffuse light that achieve to reduce the cost of electrical energy. Although several papers deal with this topic, little is known about real comparisons between CIS technology and conventional crystalline at a PV generator level with real test conditions. This paper analyses the in-field performance and degradation of a commercially available CIS solar based PV generator compared to a conventional c-Si one during four years of operation attributing the differences observed to the possible factors that can influence in both technologies.
Open Access
Gain of bifacial PV modules on horizontal single-axis trackers in desert climates
(IEEE, 2024-11-15) Parra Laita, Íñigo de la; García Solano, Miguel; Marcos Álvarez, Javier; Marroyo Palomo, Luis; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoa eta Telekomunikazio Ingeniaritza; Institute of Smart Cities - ISC; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa, PJUPNA2023-11389
Over the last few years, the demand for bifacial PV modules has continuously increased. However, there are still some aspects regarding their outdoor performance under real conditions that need further investigation. This paper analyzes the bifacial PV modules gain obtained over one year in a horizontally tracked PV power plant located in the Atacama Desert, Chile. The study was carried out over the course of a year for two different types of trackers: a standard tracker as used in the rest of the plant and a tracker that, according to the manufacturer, is specially designed to maximize the production of the bifacial modules. The results show that bifacial PV modules with a conventional tracker are able to gain approximately a 5% in terms of both radiation and production whereas the bifacial PV modules mounted on the special bifacial tracker can gain up to 5.8% and 6.1 % respectively.
Open Access
A tool for the performance evaluation and failure detection of Amareleja PV plant (Acciona) from SCADA
(2015) Muñoz Escribano, Mikel; Parra Laita, Íñigo de la; García Solano, Miguel; Marcos Álvarez, Javier; Pérez, Miguel; Ingeniaritza Elektrikoa eta Elektronikoa; Institute of Smart Cities - ISC; Ingeniería Eléctrica y Electrónica
This paper describes a tool developed for the performance evaluation and failure detection in a 45.6 MWp PV plant installed by the company Acciona in Amareleja (Portugal). The paper describes the PV plant configuration and its SCADA (Supervisory Control And Data Acquisition), the measured variables and the main functionalities of the software. Some of these functionalities are the automatic and accurate PSTC (Power under standard test conditions1) calculation for each generator and for the whole PV Plant, the reference production that would be delivered by the PV plant assuming a 100% availability, the hierarchy of SCADA alarms, the detection of long-term trends and degradation in PV generators, possible hidden problems in the different equipment and systems composing the PV plant, etc. This tool entered into operation in 2011 and is working properly since then.