María Martínez

Soiling effects comparison between CPV plants in continental and desert climates

This paper presents the results obtained in the analysis of soiling effects in the energy production of CPV systems placed in desert areas (Abu Dhabi). These results are compared with the ones obtained from similar systems placed in continental climate areas, as it is the center of Spain at ISFOC headquarters. While the reduction in the energy generation because of soiling accumulation was less than a 10% at ISFOC, at Abu Dhabi it seems that it can reach values of 80% relatively fast, therefore a good cleaning policy becomes mandatory in climatic areas like Abu Dhabi.

Operation and maintenance results from ISFOC CPV plants

The analysis of field operation and maintenance data collected during a period of over eight years, from CPV installations consisting of three different CPV technologies (including second generation of one of these technologies), has allowed us to get valuable information about the long-term degradation of the CPV systems. Through the study of the maintenance control ratio previously defined and by applying the root cause analysis methodology, the components responsible for the most unplanned interventions for each technology were identified. Focusing maintenance efforts on these components, a reduction of the unplanned interventions and the total cost of maintenance has been achieved over the years. Therefore, the deployment of an effective maintenance plan, identifying critical components, is essential to minimize the risk for investors and maximize the CPV power plants lifetime and energy output, increasing the availability of CPV installations, boosting market confidence in CPV systems.

Indoor characterization at production scale: 200 kWp of CPV solar simulator measurements

In order to complement ISFOC’s characterization capabilities, a Helios 3198 CPV Solar Simulator was installed in summer 2010. This Solar Simulator, based on a parabolic mirror and a high-intensity, small area Xenon flash lamp was developed by the Instituto de Energia Solar in Madrid [1] and is manufactured and distributed by Soldaduras Avanzadas [2]. This simulator is used not only for R&D purposes, but as a quality control tool for incoming modules that are to be installed in ISFOC’s CPV plants. In this paper we will discuss the results of recent measurements of close to 5000 modules, the entire production of modules corresponding to a small CPV power plant (200 kWp). We scrutinize the resultant data for signs of drift in the measurements, and analyze the light quality before and after, to check for changes in spectrum or spatial uniformity.

8 years of CPV: ISFOC CPV plants, long-term performance analysis and results

ISFOC is an R&D center focused on CPV in Puertollano (Spain). It was founded in 2006 and has 2.3MW of CPV plants in operation and connected to the grid since 2008. Therefore, for the time of the conference ISFOC has more than 8 years of real operation data. The performance analysis has been focused on ISFOC – La Nava CPV plant: 800kW of Concentrix (Soitec), SolFocus and Isofoton and one flat PV plant mounted on two-axis tracker. The main result obtained is that the rate of performance decrease obtained for a mature CPV technology and IEC 62108 certified is in the range of flat PV values, this means that the CPV technology does not present higher degradation rates than flat PV.

Influence of ambient conditions in the power rating of CPV modules

The determination of the ideal conditions for making the measurements to power rate a CPV module is a challenge. In general, all the methods proposed are establishing a range of filters for ambient conditions, when power rating a CPV module. In this paper, the influence of different filters in the deviation of the nomimal power rated is presented for 3 different CPV technologies using two different methods to obtain the nominal power (CSTC IEC62670 draft and PVUSA). The objective is to obtain an approach of how accurate the calculations are depending on the ambient conditions filtering. The result is that, using commercially available meteorological instrumentation and simple filters, the deviation of the power rated can be smaller than 2%.

Assessing the suitability of metal-wrap-through solar cells for low-concentration PV systems

The suitability of metal-wrap-through solar cells has been explored through a set of solar cells developed and optimized by Fraunhofer ISE for LCPV operation. Flexural strength testing and finite element modeling give evidence of the feasibility of MWT cells as a receiver for low concentration PV systems. MWT cells encapsulated as receivers withstand mechanical stresses equivalent to very large thermal loads (higher than those defined in the qualification standard) and show no fatigue effects after a number of bending loading cycles equivalent to their expected lifespan. Dark I-V curve screening and the comparison of electroluminescence images monitor cell damage. Large losses are found under non-uniform concentrated light, which implies that a strong tradeoff still lies between acceptance angle and efficiency. A redesign of the MWT cell metal grid or via spacing might be required to reduce series resistance losses under realistic concentrated spot illumination profiles.The suitability of metal-wrap-through solar cells has been explored through a set of solar cells developed and optimized by Fraunhofer ISE for LCPV operation. Flexural strength testing and finite element modeling give evidence of the feasibility of MWT cells as a receiver for low concentration PV systems. MWT cells encapsulated as receivers withstand mechanical stresses equivalent to very large thermal loads (higher than those defined in the qualification standard) and show no fatigue effects after a number of bending loading cycles equivalent to their expected lifespan. Dark I-V curve screening and the comparison of electroluminescence images monitor cell damage. Large losses are found under non-uniform concentrated light, which implies that a strong tradeoff still lies between acceptance angle and efficiency. A redesign of the MWT cell metal grid or via spacing might be required to reduce series resistance losses under realistic concentrated spot illumination profiles.

NoDustPV project: Development and testing of anti-soiling coatings

The soiling accumulation over the surfaces of photovoltaic (PV) and concentrated photovoltaics (CPV) modules decreases the annual energy production. In this work, an anti-soiling coating for PV glasses and lenses to avoid or decrease the soiling deposition onto PV and CPV modules is presented. Three different anti-soiling coatings are deposited over the surface of real lenses and glasses. The anti-soiling performance is tested by measuring the surface free energy of the uncoated and coated samples. The results show that the plasma treatment of the samples before anti-soiling application increases the performance of the coating. Regarding the effect of curing process, the results indicate that the curing process is not significant to increase the anti-soiling performance. Among the three formulations tested, F1 is the best one for glass material and F3 is the best one for poly methyl methacrylate (PMMA) lenses. In the near future, in order to detect any adverse effect in the light transmission in the long-term, the samples will be tested in the lab with accelerated aging tests to verify its durability and reliability in time.The soiling accumulation over the surfaces of photovoltaic (PV) and concentrated photovoltaics (CPV) modules decreases the annual energy production. In this work, an anti-soiling coating for PV glasses and lenses to avoid or decrease the soiling deposition onto PV and CPV modules is presented. Three different anti-soiling coatings are deposited over the surface of real lenses and glasses. The anti-soiling performance is tested by measuring the surface free energy of the uncoated and coated samples. The results show that the plasma treatment of the samples before anti-soiling application increases the performance of the coating. Regarding the effect of curing process, the results indicate that the curing process is not significant to increase the anti-soiling performance. Among the three formulations tested, F1 is the best one for glass material and F3 is the best one for poly methyl methacrylate (PMMA) lenses. In the near future, in order to detect any adverse effect in the light transmission in the long-...

MPPT implementation for the outdoor characterization of CPV modules

One of the challenges during the characterization of CPV modules is to deal with the thermal behavior. During normal operation in the field the concentrator is connected to the inverter and a fraction of the energy coming from the sun is dissipated with the corresponding conversion into electricity. On the other hand, when making the characterization of CPV modules, they are usually kept in VOC between I-V sweeps, what means that none energy is converted into electricity resulting in a higher operation temperature. Current standards, like IEC-62108:2007 and IEC-62670-3 C01 draft, define that, during the outdoor characterization, the CPV module should be connected to an electrical load to maintain it near MPP between I-V sweeps, what simulates normal operating conditions. The easiest solution could be to use mini-inverters, but it is an expensive solution and not easily adaptable to the different technologies. ISFOC has designed and developed a low-cost MPPT equipment that can be easily implemented in an o...

Environmental testing results over a tracker drive train

Environmental testing following the draft of the IEC62817 standard has been carried out at ISFOC using a Soitec Solar tracker drive. The objective of this work is twofold; first to assure that the tracker design can perform under varying conditions and survive under extreme conditions and secondly to test the viability and usefulness of the tests described in the standard. After some changes in the device under test (specifically, gear-box oil) the drive system produced satisfactory results, assuring its performance under operational temperatures. Therefore, this work has demonstrated that the tests described in the standard are useful for detecting early failures.

CPV hybrid system in ISFOC building, first results

PV Off-Grid systems have demonstrated to be a good solution for the electrification of remote areas [1]. A hybrid system is one kind of these systems. The principal characteristic is that it uses PV as the main generator and has a backup power supply, like a diesel generator, for instance, that is used when the CPV generation is not enough to meet demand. To study the use of CPV in these systems, ISFOC has installed a demonstration hybrid system at its headquarters. This hybrid system uses CPV technology as main generator and the utility grid as the backup generator. A group of batteries have been mounted as well to store the remaining energy from the CPV generator when nedeed. The energy flows are managed by a SMA system based on Sunny Island inverters and a Multicluster-Box (figure 1). The Load is the air-conditioning system of the building, as it has a consumption profile higher than the CPV generator and can be controlled by software [2]. The first results of this system, as well as the first chances of improvement, as the need of a bigger CPV generator and a better management of the energy stored in the batteries, are presented in this paper.