As advanced, the device developed to have a practical approach to the above described topics consists on three main components: a variable light source, a load simulator and a set of monocrystalline solar cells. In addition to these main components, the kit is completed by a solarimeter and two general purpose electrical multimeters. Any elementary spreadsheet software is can be used for data analysis and graphic representations.

The light source is constituted by fifteen identical wells containing an incandescent lamp. The lamps are connected to the mains by a box, including corresponding fifteen switches and a feeding power selector. Each well is designed to allocate a 2V monocrystalline cell at the top (Figure 5). Every cell is illuminated by the lamp at the bottom, being the value of irradiance at the top of the well determined by the solarimeter prior the experiment.

Fig. 5 Main box structure and views of cells arrangement in the proposed device

Using the load simulator, the characteristic curve of each cell is drawn once irradiance is known. The load simulator is a potentiometer connected to the positive and negative poles of the cell [5]. The corresponding cell voltage and current are measured for different values of potentiometer resistance ranging from the short circuit to the open circuit situations. The table of experimental I-V pairs allows the graphical representation of characteristic curve for each value of irradiance. All the cells have free terminals that can be further interconnected by the use of available cables according to a selected series-parallel configuration. Once cells are interconnected, the corresponding lamps are switch-on and the curve of the complete generator can be obtained.

The curves for shaded cells in modules can be studied after simultaneous load simulation on cells (series or parallel connected) placed on wells with their corresponding lamps switched-off or regulated to a lower electrical feeding.

The past, the present and the future are inseparable fields for research and study in any area of human activity. Italy’s Archive on the History of Solar Energy is already providing new insights regarding the contributions made by Italian pioneers of the 19th and 20th centuries, which continue to play a role in modern or future solar energy.

For example, the archives of Giacomo Ciamician (chemist), Gaetano Vinaccia (architect and city- planner), and Giovanni Francia (mathematician) contain information that show how their pioneering work can also today be an inspiring source for researchers and scholars. Their pioneering ideas, including details that have never been published or were otherwise overlooked, can be found in a letter or in a private note, in a project or in drawings. These ideas can contribute to view Italian solar energy history in a new light.

2. Conclusion

The solar archives collection put together so far shows that in Italy there have been scientists who made original and unique contributions to the understanding and application of modern or future solar energy long before the first oil shock of 1973, such as Ciamician, Vinaccia, and Francia.

They were internationally acknowledged for their work, although they were soon forgotten after their death. Italy’s Archive on Solar Energy History should contribute to rediscover the work of these and other pioneers to the benefit of, first and foremost, researchers and scholars, but also many other professionals interested in the advancement of solar energy science, technology, and application.

6. Acknowledgements

In writing this paper I had the benefit of accounts from and contacts with many people. I would like to thank in particular M. Martelli, R. Merola, G. Nebbia, P. P. Poggio, E. Terenzoni, and the heirs of G. Francia, D. Gasperini, F. Grassi, V. Storelli and G. Vinaccia.

References

[1] C. Silvi, Can the History of Energy Technology and Use educate us for a Solar Energy future? The Italian Case, ISREE-9 Proceedings, ISES SWC 2003, Goteborg (Sweden); Italian version ‘Frammenti di storia dell’energia solare in Italia’ at www. gses. it 2008.

[2] Stanford Research Institute for AFASE, Applied Solar Energy Research: A Directory of World Activities and Bibliography of Significant Literature, Burda E. J. (Ed), Stanford, California, 1955.

[3] G. Righini and G. Nebbia, L’energia solare e le sue applicazioni (Solar energy and its application). Giangiacomo Feltrinelli Editore, Milano, 1966.

[4] H. Rau, L’energia solare (Solar energy). Arnoldo Mondadori Editore, Verona, 1964.

[5] C. Silvi, Nasce a Brescia l’Archivio nazionale sulla storia dell’energia solare (Italy’s Archive on Solar Energy History launched in Brescia), Italia Energia, 2006; www. gses. it 2008.

[6] R. Merola, M. Martelli, Fonti per la storia dello sfruttamento dell’energia solare conservate presso l’Archivio Centrale dello Stato (Archival sources for the history of solar energy preserved at Central State Archive), Seminar “I pionieri dell’energia solare incontrano le nuove generazioni (Solar energy pioneers meet new generations)”, Rome (Italy), April 4, 2008; www. gses. it 2008.

[7] E. Terenzoni, Fonti per la ricerca storica sull’energia solare negli archivi italiani: strumenti di lavoro e ricerca (Archival sources and tools for historical research in Italy on solar energy), Seminar “I pionieri dell’energia solare incontrano le nuove generazioni (Solar energy pioneers meet new generations)”, Rome (Italy), April 4, 2008; www. gses. it 2008.

[8] P. P. Poggio, Il ruolo della memoria sull’energia solare (History’s role in solar energy), Seminar “I pionieri dell’energia solare incontrano le nuove generazioni (Solar energy pioneers meet new generations)”, Rome (Italy), April 4, 2008; www. gses. it 2008.

[9] G. Azzoni, Il museo dell’energia idroelettrica. Dalla goccia alla scintilla (The Museum of Hydroelectricity. From the drop to the spark), Rivista AB Atlante bresciano n.95 estate 2008; www. gses. it 2008.

[10] C. Silvi, The work of Italian solar energy pioneer Giovanni Francia (1911 — 1980), Proceedings ISES SWC 2005; www. gses. it 2008.

[11] C. Silvi, Storia e attualita del fondo Giovanni Francia (1911 — 1980) (History and current events associated with Giovanni Francia Archive, Seminar ‘L’archivio di Giovanni Francia e il solare termico a concentrazione (Giovanni Francia Archive and concentrating solar thermal)’, at Fondazione Luigi Micheletti and Museo dell’Industria e del Lavoro "Eugenio Battisti, Brescia, May 15, 2008; www. gses. it 2008.

[12] G. Nebbia, Giovanni Francia: un breve ricordo (A brief remembrance of Giovanni Francia), Seminar ‘L’archivio di Giovanni Francia e il solare termico a concentrazione (Giovanni Francia Archive and concentrating solar thermal)’, at Fondazione Luigi Micheletti and Museo dell’Industria e del Lavoro "Eugenio Battisti, Brescia, May 15, 2008; www. gses. it 2008.

[13] C. Silvi, Solar Building Practices and Urban Planning in the Work of Gaetano Vinaccia (1889 — 1971), Poster presentation, Proceedings International Solar Cities Congress, Oxford, 2006; www. gses. it 2008.

[14] C. Silvi, Remembering the founder of ISES ITALIA, ISES Newsletter December 2005.

[15] C. Silvi, La storia della pompa Somor e dei suoi inventori (The story of Somor pump and its inventors), Poster exhibition at “La Fiera del Sole”, Osnago, May 15 — 18, 2008; www. gses. it 2008.

[16] M. Venturi, V. Balzani, M. T. Gandolfi, Fuels From Solar Energy. A Dream of Giacomo Ciamician,

The Father of Photochemistry, Proceedings ISES SWC 2005; www. gses. it 2008.

[17] G. Nebbia, G. B. Kauffman, Prophet of Solar Energy: A Retrospective View of Giacomo Luigi Ciamician (1857-1922), the Founder of Green Chemistry, on the 150th Anniversary of His Birth, Chem. Educator 2007, 12, 362-369; www. gses. it 2008.

[18] G. Nebbia, La ricerca storica sullo sviluppo dell’energia solare (History research on the development of solar energy), Seminar “I pionieri dell’energia solare incontrano le nuove generazioni (Solar energy pioneers meet new generations)”, Rome (Italy), April 4, 2008; www. gses. it 2008.

Walid El Baba

Lebanon Solar Energy Society

1- Purpose of the works

It is important in our area and mainly in Lebanon where there is more than 300 sunny days yearly to develop a large solar energy foot print through a wide cultural change according to age group together with a large awareness campaign at a national level. Information dissemination and awareness equipment/projects constitute an essential part of this work to sustain the Renewable Energy Technologies in Lebanon and in the world.

2- Methodology

We can divide the age groups in 4 categories:

1st group: 12 — 15 years old (students in secondary schools)

2nd group: 15 — 20 years old (Technical schools)

3rd group: 20 — 25 years old (Students-Engineers)

4th group: above 25 years old (Engineers, installers, industrials etc…)

For a better representation, only 4 cells have been selected to be interconnected. The undertaken experiments were the following:

After settling the same illumination level in each cell lamp, individual cells characteristic curve was generated by potentiometer method to evaluate the observed differences in shape and basic cell parameters. As result (Figure 6), intrinsic mismatch phenomenon became evident, showing this set of 4 cells a maximum difference in short circuit current of 30 mA and 0,14 Volts in open circuit voltage (average mismatch 2,5 %)

Fig 6. Schematic arrangement for individual cell curves generation and results for 4 selected cells

The interconnection modes here considered were a 4 cell series combination (4s) and a 2 combinations of 2 series cell junction parallel combination (2s-2p). By the potentiometer method, curves for the reference illumination level in all the cells were again obtained, in this case, for each complete generator. Table 1 and Figure 7 summarizes the obtained results.

Fig. 7 Characteristic curve for 4s (left) and 2s-2p (right) interconnections

Among other results, as the current/voltage addition laws verification, it must be highlighted how the worst mismatched cell in the series interconnection (#3) determines the short circuit current of the whole generator, as expected according theoretical basis.

To study the mismatching due to partial shadowing of interconnected elements in the PV generator, the above 4s cells configuration has been selected. Shadowing of one of the series cells has been provoked by lowering the electrical feed to the lamp of one of the cells (Figure 8).

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Fig. 8 Experimental arrangement for the study of mismatch effect provoked by partial generator shadowing

In this situation, potentiometer was used to draw corresponding load curves either for the complete mismatched generator and the shadowed cell. Figure 9 includes the obtained results as well as the corresponding curve for the no partially shadowed 4 cells series combination.

As result, in short circuit conditions, mismatched 4 cells generator is clearly affected by the lower current yield of shadowed cell, which determines the maximum current of the whole set, whereas open circuit voltage maintains its value. In this case, the reduction in generators parameters reach up to 35 % because mismatch degree has a higher value as usual in externally caused cells unbalance.

Regarding the electrical characteristics of mismatched cell under this situation, Figure 9 also clearly show how this cell is affected by a reverse biased current coming from the rest of the cells generator. The used illumination levels and cell number in this experiment have been set to preserve mismatched cell integrity.

3. Conclusions

This work describes an experimental arrangement developed at UAL aimed to serve as educational tool in courses and lessons on PV generators performance and the study of specific effects as the mismatch loses in modules or arrays. All the components of the device are low cost and easily available in most of the university laboratories and the results of the experiences curves can be immediately related to the theory. As future improvements, cells temperature follow-up, specific light source use and safety diodes study will be considered.

References

[1] Kaushika N. D. and A. K. Rai, Energy 32-5 (2007) 755-759.

[2] Alonso-Garcia M. C., J. M. Ruiz and F. Chenlo, Solar Energy Materials and Solar Cells 90-3 (2006) 329-340.

[3] Kaushika Narendra D, Guatam Nalin K. Energy yield simulations of interconnected solar PV arrays. IEEE Trans Energy Convers 2003;18(1):127—34.

[4] Woyte A., J. Nijs and R. Belmans; Solar Energy 74-3 (2003) 213-217.

[5] Osterwald C. R. (2003) Standards, Calibration and Testing of PV Modules and Solar Cells, in Markvart T. and L. Castaner (Eds.) Practical Handbook of Photovoltaics: Fundamentals and Applications. pp. 793-856. Elsevier, Oxford.

Ziva Kristl*, Mitja Kosir, Ales Krainer

University of Ljubljana, Faculty of Civil and Geodetic Engineering,
Chair for Buildings and Constructional Complexes
Jamova cesta 2, 1000 Ljubljana, Slovenia
Tel ++386 1 4768 609, Fax ++386 1 4250 688
*E-Mail ZKristl@fgg. uni-lj. si

Abstract

At the Faculty of Civil Engineering, University of Ljubljana the senior year students attend course on bioclimatic design of buildings. In the academic year 2006/2007 they carried out a joint study [1] dealing with interaction among daylight levels and heating energy demand of their buildings in relation to properties of the applied glazing. Students also discussed the concept of passive house in relation to inside environment quality and compared the passive and the bioclimatic concepts. In the case of 27 student-selected buildings calculations showed that change from double to triple window glazing resulted in average reduction of specific heating energy demand (Qn/Au) by 14.4%. The same intervention at the same building configuration resulted in reduction of average illuminance level (Eav-eq) by immense 25.3%. Very similar results were obtained in an independent parallel study [2] carried out by the staff of Chair for Buildings and Constructional Complexes (KSKE).

Keywords: living environment, teaching, holistic approach

1. Introduction

In recent years sustainability in buildings has gained its importance in professional as well as in laic circles and it is often presented as the next big thing in construction industry. Just a brief look into the history of architecture reveals that sustainability has always been an integral part of construction. What has changed in the last century is that the technology, materials and speed of construction have altered dramatically. Despite of these changes in modern construction, sustainability should still be viewed as an integral part of design and building.

At the Faculty of Civil Engineering (FGG), University of Ljubljana (UL) the senior year students attend course on bioclimatic design of buildings. The lectures comprise building physics course, bio­climatic design principles, energy sources and innovative materials. The objective of the seminar is to nudge future civil engineers to use their knowledge in a holistic way. In this line of thought advanced technologies as well as old traditional principles are presented and the students are expected to apply them in their projects. In the academic year 2006/2007 the students were involved in a discussion about whether to use technological maximum for a specific area (e. g. reduction of heating demand) and if/how this decision influences other areas of internal environment design (e. g. daylighting). They carried out a joint study dealing with interaction among daylight levels and heating energy demand of

1

their buildings in relation to U, g and tv values of the applied glazing. Because the reduction of thermal transmittance influences optical properties of glazing as well, we were primarily interested to what degree the decrease of U value deteriorates daylighting in a building. Lower U values also reduce the transmission losses of a building (but also solar gains), so we also compared the degree to which the energy balance of a building improves due to better glazing and considered if lower heat losses compensate poorer daylighting of internal spaces.