The Course on Photovoltaics at the CTU in Prague

At the Faculty of Electrical Engineering of the CTU in Prague a course on Solar Energy Exploitation Systems, mostly oriented in the field of photovoltaics, was introduced in 1995 as an optional course. The course was developed to give undergraduate students information about the full set of important problems connected with photovoltaics from photovoltaic effect, cell construction and technology to applications, including operating conditions and economical and ecological problems. Details about the course were published in [3]. Since the school year 2006/7, a course in Photovoltaic Systems, dealing with PV system technology (28 hours of lectures, 28 hours of exercises) forms part of the master study programme in Electrical Engineering and Information Technology. Synopsis of lectures on Photovoltaic Systems is shown in Table 1. Education in Photovoltaics at the CTU in Prague has been in more details described in [4].

Week

Content

1.

Solar energy (spectra, geographic position and influence of climate).

2.

Photovoltaic effect

3.

Solar ceiis, basic structure and characteristics

4.

Singie-crystaiiine, polycrystaiSine and thin film solar ceiis

5.

Construction and technology of highly-efficient solar ceiis

6.

Construction and technology of PV modules

1.

Modules with concentrators, hybrid systems

3.

Photovoltaic systems — basic types

9.

Stand-alone systems. Grid-connected systems

10.

Energy storage for photovoltaic systems

11.

Applications of photovoltaic systems

12.

Operating conditions of photovoltaic systems

13.

Economic and environmentai aspects of photo voltaic s

14.

Present trends in the field of photovoltaics.

Table 1. Synopsis of lectures on Photovoltaic Systems

2. Exercises

Exercises are a very important part of the course orienting the course in a particular direction. The developed laboratory exercises deal with photovoltaic system applications, and are adapted to the requirements of electrical engineers. The exercises have been divided into three blocks. The first block deals with detailed measurements of PV cell characteristics and the influence of important external parameters (light intensity and temperature) and internal parameters (series and parallel resistance) on the shape of these characteristics and on cell efficiency. PV cell measurements are performed on square (102 mm x 102 mm) silicon cells (both single-crystalline and poly-crystalline) using

image071

Подпись:illumination with a halogen bulb. The basic circuit used for measuring I-V characteristics in all four tasks is schematically shown in Fig.1. From measured characteristics parameters VOC and ISC and the maximum power point characterised by Vmp and Imp are extracted. Results of measurements are dependences of VOC, ISC, fill factor FF and maximum power Pmp on given parameters [6].

The second block consists of three laboratory tasks concerned with measuring the

Подпись: characteristics of PV modules: • measurements on a solar module - dc load system • measurements on a solar module - charge controller - battery - dc load system

• measurements on a solar module — dc/dc — dc/ac system

Подпись: Fig. 2. Laboratory exercises with set of halogen lamps Подпись: Fig.3. Homogeneity of irradiance on the module are in the laboratory equipment

For measurements on modules are used 26 Wp standard (12 V) modules and they were performed in last courses in front of the building using natural sunshine. The measurements outside of building were relatively strongly influenced by the temporary weather. Even from one viewpoint it gives students a sample of real applications, from another viewpoint it complicates the exercise programme that should be performed in accordance with a given timetable. For this reasons there have been prepared laboratory measurements on PV modules using set of halogen lamps and reflecting walls as a solar source, as shown in Fig 2. The homogeneity of irradiance on the module area is very good, differences from the mean value are less than 5%, as demonstrated in Fig.3. A disadvantage of using halogen bulb is, that the PV modules must be cooled (a van below the PV module can be seen in Fig.2.).

image076 Подпись: Rz

One of the circuits used (for measurements on an off-grid PV system with battery and inverter) is shown in Fig.4.

At measurements, problems with connection of PV modules in parallel and in series, influence of partial shading on I-V characteristics are also demonstrated.

Подпись:
The third block of tasks analyses data obtained from an on-grid demonstration PV system, and includes a small, simple photovoltaic system project (both off-grid and on-grid). To demonstrate the function of photovoltaic systems in real operating conditions, a 3kWp demonstration, on-grid connected photovoltaic system has been built at the Czech Technical University in Prague on the roof of the Faculty of Electrical Engineering. (This installation has been supported by the State Fond of Environmental Policy of the Czech Republic and has been realised by the company Solartec s. r.o,

Roznov p Radostem.) The block diagram of the system is shown in Fig.5. The photovoltaic modules are situated at the flat roof of the Czech Technical University, Faculty of Electrical Engineering with the aim of demonstration a photovoltaic system (on-grid connected) and of evaluating the potential of using roof top photovoltaic systems under conditions of real urban utilization. This system allows monitoring of data about performance of three photovoltaic fields with different tilt angle. Collected data give important information about system performance in both fa? ade and on-roof applications. Input and output data (dc voltage, dc current, ac voltage, ac current, instant power and energy produced) supplemented by PV field temperature and intensity of solar radiation are available online at http://andrea. feld. cvut. cz/fvs.

Synopsis of laboratory exercise on Phtovoltaic Systems is shown in Table 2.

Week

Content

1.

Organization, introduction

2.

Laboratory measurements on solar cells — explanation

3.

Comparison of V-A characteristics of different solar cells

4.

Influence of series resistance on solar cells parameters

5.

Influence ofparallel resistance of solar cells parameters

6.

Temperature dependence of solar cell parameters

7.

Laboratory measurements on PV modules — explanation

8.

Measurements of solar module characteristics

9.

Measurements on a solar module — dc load system

10.

Measurements on a solar module — dc/ac system

11.

Grid-off PV system design (simulation)

12.

Grid connected PV system (simulation, demonstration)

13.

Technical visit at 40 kWp grid-connected PV system

14.

Final test

Table 2. Synopsis of practical exercise

4. Conclusions

The course on Photovoltaic Systems oriented in the field of photovoltaics performed at the Faculty of Electrical Engineering of the Czech Technical University in Prague at the undergraduate level has been discussed. The course gives information on both device and application approach with application oriented laboratory measurement tasks. Laboratory measurements are prepared to give student practical knowledge about cell characteristics, module characteristics and system behaviour. The course has become suitable for all branches of study in the field of electrical engineering.

References

[1] Hirshman W., Herring G. and Schmels M.: Gigawarts — the measure of things to come, Photon International, No.3, 136 — 166, (2007)

[2] Jager-Waldau A., PV Status Report 2006 (Research, Solar Cell Production and Market Implementation of Photovoltaics), Office for Official Publications of the European Communities, Luxembourg (2006)

[3] Benda, V, Development of a Course on Photovoltaic Systems. Solid State Phenomena. no. 97-98, pp. 133- 138.(2004)

[4] Benda, V., Education in the Field of Photovoltaics at the Czech TechnicalUniversity in Prague, this Proceedings, paper #269 (2008)

[5] Goetberger, A., Knobloch, J. and Voss, B.: Crystalline Silicon Solar Cells, J. Wiley & Sons., Chichester, 1998

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