The Pioneering Work On Linear Fresnel Reflector ... - GSES

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on an area of approximately 8.2 x 7.9 m 2 . It had 7 aluminum mirrors, 8 meters long and 1 meter wide, parallel to each other on an east-west line. Each mirror rotated around its lengthwise axis, concentrating solar radiation on a linear boiler positioned parallel to the mirrors at a height of about 6 meters. The rotary motion was the same for all the mirrors, and was obtained by means of an electronic command guided by the sun itself. The boiler was slightly less than 8 meters long and 25 centimeters wide. It was protected on the front (the side facing the mirrors) by the honeycomb structure and on the back by appropriate insulation and a lostheat-recovery device [15]. Two flat vertical mirrors limited energy loss on the west side in the morning and on the east side in the afternoon; otherwise, reflected energy would reach the boiler only during the midday hours, due to the short length of the mirrors. In the design for the large solar plant described in Francia’s patent no. 18634, of which the Marseilles plant was the first unit, the aluminum-mirror strips were much longer than the boiler is high, which eliminated the need of protective mirrors on the sides. Likewise, the Marseilles unit was designed to be scalable; the length of the strips of mirrors could be tripled or quadrupled and their number increased. The plant was built with off-the-shelf materials in order to simplify the construction and reduce costs, with the idea to perfect them based on the experimental results obtained with the prototype. The plant generated 38 kg/h of steam at 100 atm and 450°C. The plant was expected to supply around 1200 thermal kWh annually per square meter of mirrors in Marseille, making a total of 67,200 kWh per year. If the plant had been built in Sicily, Francia calculated that production would have reached 1600 kWh per year per square meter, for a total of 89,600 kWh annually. According to Francia’s evaluation at the time, with a large-scale plant, the power output could be much cheaper per kWh than that generated from oil. For Francia, the use of flat mirrors was fundamental in order to build large-scale plants, as he stated in his correspondence with M. Touchais, a collaborator of Marcel Perrot [16] [17]. In the late sixties, Francia, in cooperation with his collaborators, elaborated the "Solar City Project – Hypothesis for an Urban Structure", by inventing a wholly new kind of urban complex for a population of around 100,000. This complex relied on the use of solar energy for natural and artificial lighting, for heating household water, for space heating and cooling, and for the production of electricity. The design centered around repeatable, independent and energetically autonomous units (18). The drawing in figure 7, dated circa 1965, shows Francia’s vision of a large LFC integrated in an urban context. Fig. 7. Francia’s drawings of the envisioned large solar LFC power plant integrated in an urban context of circa 1965 (Francia Archive, Musil Brescia). After building his first LFC, Francia built the first PFC in 1965 at the Sant’Ilario solar station and began focusing mainly on solar towers, on which he devoted his efforts in the following years. He believed solar energy would become competitive for power generation only when solar boilers were improved to the point when they could produce steam at pressures above 150 atmospheres and temperatures above 500°C, a goal that seemed more likely achievable with solar towers than with linear concentration systems at the time. His work on LFC technology was thus put on the back burner.
In the late 1970s, Francia worked as a consultant for the construction of the industrial-scale solar tower facility at the Georgia Institute of Technology, in Atlanta, and for the 1 MW Eurelios power plant at Adrano, in Sicily, the first of its kind anywhere in the world to be connected to the electricity grid. Despite the fact that from 1965 onward his focus was mainly on solar towers, Francia still continued to envision large-scale LFC plants as illustrated by the following artist’s rendering, from a brochure written by Francia and his collaborators just before his death in 1980. Fig. 8 – Artist’s rendering of an LFC solar power plant designed by Giovanni Francia and collaborators in late 1970s [19]. 4. Conclusion The documentation from various archives, as briefly illustrated in this paper, gives us better insight into the pioneering work on LFCs in Italy. It shows that there were various attempts to develop large solar concentration systems by using a Fresnel type multiple collector area and increasing boiler efficiencies starting in the early 19 th century. In facing this challenge Giovanni Francia succeeded during the 20 th century, in just a few years, from the late 1950’s to the mid 1960’s. After his first experiments on anti-radiating structures or honeycombs, he devoted his work to the development of LFCs and PFCs, not only proving to the world that solar energy could be collected at high temperatures to generate solar electricity, but also proposing the integration of large solar power plants in urban contexts, as it can be seen from his drawings and his solar city project. Acknowledgements In writing this paper I had the benefit of accounts from and contacts with many people. I would like to thank in particular P. Castellazzi, G. Nebbia, P. P. Poggio, and the heirs of G. Francia. References * [1] K. Butti, J. Perlin, A Golden Thread – 2500 years of Solar Architecture and Technology, Cheshire Books, Palo Alto, CA USA, 1980. [2] C. Silvi, Can the History of Energy Technology and Use Educate us for a Solar Energy future? The Italian Case, ISREE-9 Proceedings ISES Solar World Congress 2003, Göteborg (Sweden).
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