Accurate and simple mathematical models are usually required to assess the performances of photovoltaic devices. In particular, it is common practice to use explicit models to evaluate the current-voltage (I-V) performance curves, mainly based on simple analytical expressions that enable the parameters determination with a little computational effort. Six different explicit photovoltaic models (i.e., explicit I-V equations) by different authors (Akbaba & Alattawi; El-Tayyan; Karmalkar & Haneefa; Das/Saetre et al.; Das; and Pindado & Cubas) are analyzed and compared. This comparison is carried out by fitting these models to eight I-V curves for different technologies, including Si, Si polycrystalline, Ga-As, and plastic solar cells. The accuracy of each model depends on the photovoltaic technology to which it is applied. The best fit to each I-V curve studied is normally obtained with a different model, with an average deviation under 2% in terms of short-circuit current (normalized RMSE). In general, the model proposed by Karmalkar & Haneefa shows the highest level of accuracy, and is a good fit for all I-V curves studied.

The IDR/UPM Institute is the research center responsible for the Master in Space Systems (MUSE) of Universidad Politécnica de Madrid (UPM). This is a 2-year (120 ECTS) master's degree focused on space technology. The UPMSat-2 satellite program has become an excellent educational framework in which the academic contents of the master are trained through project-based learning and following a multidisciplinary approach. In the present work, the educational projects developed and carried out in relation to spacecraft power systems at the IDR/UPM Institute are described. These projects are currently being developed in the framework represented by the aforementioned MUSE master's program and UPMSat-2.

Abstract:In the present work, the research derived from a wide experience on cup anemometer calibration works at IDR/UPM Institute (Instituto Universitario de Microgravedad "Ignacio Da Riva") is summarized. This research started in 2008, analyzing large series of calibrations, and is focused on two main aspects: (1) developing a procedure to predict the degradation level of these wind sensors when working on the field and (2) modeling cup anemometer performances. The wear and tear level of this sensor is evaluated studying the output signal and its main frequencies through Fourier analysis. The modeling of the cup anemometer performances is carried out analyzing first the cup aerodynamics. As a result of this process, carried out through several testing and analytical studies since 2010, a new analytical method has been developed. This methodology might represent an alternative to the classic approach used in the present standards of practice such as IEC 64000-12.

At present, the development of small-size satellites by universities, companies and research institutions has become usual practice, and is spreading rapidly. In this kind of project cost plays a significant role. One of the main áreas are the assembly, integration and test (AIT) plans, which carry an associated cost for simulating environmental conditions. For instance, in the power subsystems test and, in particular, in the testing of solar panels, the irradiance and temperature conditions might be optimum so the performance of the system can be shown next to real operational conditions. To reproduce the environmental conditions in terms of irradiance, solar simulators are usually used, which carries an associated increase in cost for testing the equipment. The aim of this paper is to present an alternative and inexpensive way to perform AIT plans on spacecraft power subsystems, from a testing campaign performed using outdoor clean-sky conditions and an isolation system to protect the panels. A post-process of the measured data is therefore needed, taking into account the conditions in which the test has been accomplished. The I-V characteristics obtained are compared with a theoretical l-diode/2-resistor equivalent electric circuit, achieving enough precisión based solely on the manufacturer's data.

In this article, simplified and easy-to-work-with equa-Q1 5 tions for the Lambert W-function are derived. This function is 6 widely used to solve equations related to photovoltaic systems. More 7 specifically, this mathematical function represents a useful tool 8 when modeling solar cells/panels performance (that is, the current-9 voltage curve) by analytical approaches. However, the Lambert 10 W-function has a complex solving process which might represent 11 an unaffordable mathematical challenge for a great number of pro-12 fessionals/technicians in the photovoltaic industrial sector. Simple 13 approximations for the Lambert W-function on both of its branches 14 (positive and negative) are proposed in this article. The results of 15 the present article show a simple but accurate way for photovoltaic 16 systems modeling, even when these systems comprise a maximum 17 power point tracking subsystem. 18 Index Terms-1-diode/2-resistor model, I-V curve, Lambert W-19 function, maximum power point tracking (MPPT), photovoltaic 20 systems performance, solar cell, solar panel. 21 I. INTRODUCTION 22 R ENEWABLE energy plays a very important role in reduc-23 ing fossil resources consumption [1], which is a present 24 and urgent need for mankind due to problems, such as global 25 warming, climate change and air pollution [2]. Among the 26 different renewable energy sources, solar energy is probably the 27 most relevant, as it is clean, safe, and unlimited [3], [4].