BUSCADOR RECOLECTA

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., This work was supported in part by the Spanish State Research Agency (AEI) under grants PID2019-111262RBI00/AEI/10.13039/501100011033 and PID2019-110816RB-C21-I00/AEI/10.13039/501100011033

Due to high competitiveness in the PV sector, despite the low degradation rate of crystalline silicon PV modules (below 0.5%/year), it is still important for utilities to know its actual value due to its impact on energy yield and hence, profitability, over the lifetime of a PV plant. However, uncertainties related to both the influence of downtime periods due to problems that may appear under normal operation of a commercial PV plant and to the measurement of degradation rates at PV plant level make this a challenging task. In order to obtain a significant value, in this paper, three measuring methods with different uncertainty sources are used for 82 MWp of PV modules on different locations in Spain and Portugal over 10 years. According to the different methods used and PV plants analyzed, excluding PV plants with problems, a range of degradation rates between 0.01 and 0.47%/year has been found. The overall average value observed is 0.27%/year. The findings of this work have also revealed the great importance of good operation and maintenance practices in order to keep overall low degradation rates., This work has been supported by the Spanish State Research Agency (Agencia Estatal de Investigación, AEI) under grant PID2019‐110816RB‐C21/AEI/10.13039/501100011033.

This paper proposes an energy management strategy for a residential microgrid comprising photovoltaic (PV)
panels, a small wind turbine and solar thermal collectors. The microgrid can control the power exchanged with
the grid thanks to a battery and a controllable electric water heater, which provide two degrees of freedom to the
control strategy. As input data, the proposed control strategy uses the battery state of charge (SOC), the temperature
of the hot water tank, the power of each microgrid element as well as the demand and renewable
generation forecasts. By using forecasted data and by controlling the electric water heater, the strategy is able to
achieve a better grid power profile while using a smaller battery than previous works, hence reducing the overall
cost of the system. The strategy is tested by means of simulation with real data for one year and it is also
experimentally validated in the microgrid built at the Renewable Energy Laboratory at the UPNA., The authors would like to acknowledge that this work has been
partially funded under grants PID2019-110816RB-C21 and
PID2019–111262RB–I00 by the Spanish State Research Agency (AEI/
10.13039/501100011033). And also by VLIR-UOS and the Belgian
Development Cooperation (DGD) under the project EC2020SIN322A101
(2020-EXT-007).

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., Support of the Spanish State Research Agency (AEI) under grants PID2019111262RB-I00 and
PID2019-110816RB-C21. Open access funding provided by Universidad Pública de Navarra.

This work deals with the design of a Fuzzy Logic Control (FLC) based Energy Management
System (EMS) for smoothing the grid power prole of a grid-connected electro-thermal microgrid. The
case study aims to design an Energy Management System (EMS) to reduce the impact on the grid power
when renewable energy sources are incorporated to pre-existing grid-connected household appliances. The
scenario considers a residential microgrid comprising photovoltaic and wind generators, at-plate collectors,
electric and thermal loads and electrical and thermal energy storage systems and assumes that neither
renewable generation nor the electrical and thermal load demands are controllable. The EMS is built through
two low-complexity FLC blocks of only 25 rules each. The first one is in charge of smoothing the power
prfile exchanged with the grid, whereas the second FLC block drives the power of the Electrical Water
Heater (EWH). The EMS uses the forecast of the electrical and thermal power balance between generation
and consumption to predict the microgrid behavior, for each 15-minute interval, over the next 12 hours.
Simulations results, using real one-year measured data show that the proposed EMS design achieves 11.4%
reduction of the maximum power absorbed from the grid and an outstanding reduction of the grid power
profile ramp-rates when compared with other state-of-the-art studies., This work was supported in part by the projects 2019-PIC-003-CTE and 2020-EXT-007 from the Research Group of Propagation,
Electronic Control, and Networking (PROCONET) of Universidad de las Fuerzas Armadas ESPE, in part by the Belgian Development
Cooperation (DGD) and the VLIR-UOS under the project EC2020SIN322A101, in part by the Spanish Ministry of Industry and
Competitiveness under Grant DPI2017-85404 and Grant PID2019-111443RB-100, and in part by the Spanish State Research Agency
(AEI/10.13039/501100011033) under Grant PID2019-110816RB-C21 and Grant PID2019-111262RB-I00.

Upgraded metallurgical grade silicon (UMG-Si) PV modules have failed to make their space in the PV market, which was partly to the uncertainty on their in-field performance that brings the wide disparity of results published over the years. The most-recently developed UMG-Si PV modules have demonstrated similar initial degradation and efficiencies under standard test conditions (STC) to those obtained with conventional solar grade silicon (SoG-Si). Nevertheless, their performance under operating conditions other than STC and its impact on the energy production are key aspects that have not yet been properly characterized in the literature. This article analyzes the in-field performance of a PV generator comprised of recently developed UMG-Si modules. This performance was compared to that of another PV generator comprising standard polysilicon modules. The cells and modules of both types of generators were made by the same manufacturer in the same period and on the same production lines, which guarantees that performance differences encountered are exclusively due to the silicon employed. Contrary to the previous experience, this article reveals that UMG-Si modules do not necessarily present a better temperature performance than today's conventional modules. The analyzed UMG-Si modules presented 1.6% less efficiency under low irradiance conditions, but this different irradiance performance led to an insignificant difference (less than 0.5%) in their energy production. No significant degradation was measured in both UMG-Si and SoG-Si modules during the two-year analyzed period, being the final energy performance of both types of modules essentially the same. These results can be considered as highly representative of the current state-of-the-art of UMG-Si technology., This work was supported by the Spanish State Research Agency and the ERDFEU under Grant PID2019-110816RB-C21 and Grant PID2019-111262RB-I00.

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., This work was supported in part by the Spanish State Research Agency (AEI) under grants PID2019-111262RB-I00/AEI/10.13039/501100011033 and PID2019-110816RB-C21-I00/AEI/10.13039/501100011033

This work presents a novel control method for multi-megawatt photovoltaic (PV) plants that is able to regulate each plant inverter and the battery system to mitigate PV power fluctuations. The proposed control method makes it possible to implement different PV ramp-rate control strategies based on the use of batteries and the limitation of inverters during positive fluctuations, which have been conceptually proposed in the specialized bibliography, but have omitted how to perform the coordination between PV generators. The dynamic model and the tuning of the control parameters are presented and the method is used to correctly implement different inverter-limitation strategies using 5-second data from a real 45 MWp PV plant. Furthermore, a new control strategy is proposed. This strategy reduces curtailment losses to negligible values and takes into account and addresses the intrinsic asymmetry in the battery charging and discharging capability, an issue that has been overlooked in the specialized bibliography. The results show that the proposed control method can effectively control each of the multiple inverters in order to obtain the desired PV plant operation to regulate the battery charging power, even during highly fluctuating scenarios., The authors to acknowledge the support of the Spanish State Research Agency (AEI) under grants PID2019111262RB-I00 and PID2019-110816RB-C21. Alejandro González-Moreno would like to thank the Universidad Pública de Navarra (UPNA) for its financial support. Open access funding provided by Universidad Pública de Navarra.

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., This work was supported in part by the Spanish State Research Agency (AEI) under grants PID2019-111262RBI00 and PID2019-110816RB-C21-I00 as well as the Doctoral
Scholarships funded by Public University of Navarra (UPNA).

Durability of photovoltaic (PV) modules is of great concern not only from the point of view of cost-effectiveness but also from the point of view of safety and sustainability. The backsheet of a PV module is one of the most critical parts of the PV module from the point of view of protection and also one of the most important sources of PV modules' failure; hence, it is of great importance to understand its different forms of failure. In this paper we analyze the case of an 8-MW PV plant, which had suffered a rapid degradation of their PV modules' backsheets. The case is especially relevant as all the PV modules are from the same model and manufacturer but with different backsheet materials (polyamide and fluoropolymer) and different times of exposure: on one hand, all PV modules originally installed in the plant (i.e., 6 years under operation when tested), and also, extra modules that had been stored indoors for replacement and had been mounted in the plant for less than 1 year when tested, serving as reference modules. In this paper we present the signs of degradation of these PV modules after different times of exposure under real operation using different on-field and laboratory tests. We propose different techniques for rapid diagnosis of backsheet degradation so that the problem can be detected at a very early stage, before it results in major energy losses or in safety issues., This work has been supported by the Spanish State Research Agency(AEI) and ERDF-UE under grant PID2019-110816RB-C21. We would like to thank the Universidad Pública de Navarra for funding the Open Access fee.

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%., This work was supported in part by the Spanish State Research Agency (AEI) under grants PID2019-111262RBI00/AEI/10.13039/501100011033 and PID2019-110816RBC21-I00/AEI/10.13039/501100011033 as well as the Doctoral Scholarships funded by Public University of Navarre (UPNA).