**2. Genesis and context of solar energy use**

314 Sustainable Growth and Applications in Renewable Energy Sources

materials. Logically, the assessment of the life cycle of PV systems will raise concerns about their compatibility with the global approach of sustainable development in terms of ecological footprint, economic profitability and social acceptability. Social acceptability is even more fundamental in terms of the sustainability since the user should adopt a less traditional energy approach. Will solar energy, which is perceived as the future of renewable energies, be able to challenge of meeting the essential concepts of clean and green

Fig. 1. Diagram of Photovoltaic Conversion and Practical applications

energy?

Although the history of solar energy dates back to the earliest days of humanity, its evolution has been extremely slow and laborious, swinging between euphoria, aborted attempts, total disinterest and re-birth. The first time this resource was used in prehistoric times, namely when the rays of the sun were captured and used to kindle flames, apparently took place in Mesopotamia, in the Arabic desert.

The ancient Greeks were the first to describe the famous "burning mirrors" or solar reflectors, the ancestors of parabolic mirrors, created with silver, copper or brass, which were used to light the Olympic flame (Butti & Perlin, 1980). In addition, solar energy was used by the ancient Greeks in a passive form which had a major impact on the architecture of homes since, even in that distant time, deforestation was an issue, resulting in a shortage of charcoal as a result of the unchecked use of this fuel for heating and cooking.

The Roman Empire quickly adopted similar architectural habits since the Romans were also suffering from an over-consumption of charcoal. Outrageous taxes were even imposed for the domestic use of wood (Butti & Perlin, 1980). In 1515, Leonardo da Vinci attempted to build a giant mirror, a primitive solar concentrator, intended to transform the rays of the sun into heat for commercial purposes (Butti & Perlin, 1980; Lhomme, 2004). It would only be during the Industrial Revolution of the 19th century that the solar energy pioneers would emerge in a universe suddenly filled with scientific and technological effervescence in order to improve energy performance and eliminate dependency on wood and charcoal. However, these efforts, while praiseworthy and ingenious, were only partially successful.

One of the most brilliant and prolific of these pioneers was Augustin Mouchot, the French inventor of the first solar engine in 1880. Despite his scientific fervour and his obvious desire to demonstrate the potential of solar energy, he failed to draw France into the Solar Age (Butti & Perlin, 1980). William Adams improved on Mouchot's prototype by installing a group of mirrors to boil the water to a faster way and doing his utmost to demonstrate the great potential of solar energy for the British Empire (Bradford, 2006). John Ericsson, invented the "caloric" engine in 1833, which used hot air as the operating fluid; this air was provided by a solar engine, thereby limiting energy losses (Butti & Perlin, 1980; Bradford, 2006). These pioneers provided the basis of thermodynamic solar energy, by transforming the rays of the sun into energy.

In 1839, Edmond Becquerel first observed the PV reaction, which involves the creation of a spontaneous electrical current when a chain of conductive elements was lit. The first solar batteries, ancestors of modern solar cells, used selenium and were developed in 1883 by Charles Fritts. At that time, they had an efficiency of 0.2% (Lhomne, 2004). In 1921, Albert Einstein explained the PV effect that earned him the Nobel Prize in physics. According to history, Einstein considered the description of the PV effect of greater value than the theory of relativity (Bradford, 2006).

Between 1900 and 1915, the first efforts were made to market thermodynamic solar energy. Aubrey Eneas built and sold two immense machines to be used as boilers; they were equipped with more than 1700 individual mirrors generating 2.5 steam horsepower. Unfortunately, a major storm and hailstorm overpowered his inventions and forced him to abandon any idea of pursuing this line of research as he concluded that his projects were not economically viable (Butti & Perlin, 1980; Bradford, 2006). In 1912, Frank Shuman, one of the greatest visionaries in matters of solar energy, built a plant in Egypt that was strangely similar to modern solar power plants. Unfortunately, it was destroyed during the battles

Photovoltaic Conversion: Outlook at the Crossroads

Lhomme, 2004).

inclinations (Labouret & Villoz, 2009).

(Krauter, 2006; Xakalashe & Tangstad, 2011).

(EPIA/Greenpeace, 2011).

Between Technological Challenges and Eco-Strategic Issues 317

Located nearly 150 million km from Earth, the Sun is a huge nuclear power plant—the oldest in the history of mankind—and has a capacity of 25 million kW/h per gram of hydrogen, its main component. The nuclear fusion of one kg of hydrogen releases an energy value of 8.3 million tons oil equivalent (Lhomme, 2004). Since the sun accounts for some two billion tons of material, over 90% being hydrogen of which it uses 600 million tons per second, the energy produced is unimaginable. In fact, it produces 4 x 1017 GW, or the equivalent of 400 million billion nuclear power plants! The Earth receives only a tiny fraction of this energy (Centre National de Recherche Scientifique, n.d.;

The major characteristics of sun energy, despite a certain ubiquity, are a large regional disparity and more or less marked by seasonal imbalance. For instance, the average energy received by Europe is 1,200 kWh/m2/y vs 1,800 to 2,300 kWh/m2/y in the Middle East (EPIA/Greenpeace, 2011). Latitude, exposure and altitude are parameters that influence the overall daily and seasonal radiation. Tropical regions corresponding to 25–30 degrees

Climatologists have long endeavoured to assess the solar energy of a given area as thoroughly as possible and even be able to predict the evolution. Statistics on solar radiation were therefore compiled from data collected to input into valuable databases (EPIA/Greenpeace, 2011). Assembling data of a given region based on different criteria is strategic for the design and dimensioning of PV systems, especially their orientations and

Characterization of increasingly sophisticated global solar energy resources is a sign of PVs' promising potential. Thus the calculations by the International Energy Agency (US IEA) lead to surprising conclusions. Installing PV systems on only 4% of the area of the world's driest deserts would likely be able to provide all of humanity's primary energy needs

The PV effect consists in the direct conversion of solar energy into electricity (Fig.1). Three interdependent and successive physical phenomena are involved: a) the optical absorption of light rays, b) the transfer of the energy from the photons to the electrons in the form of potential energy; c) the collection of the electrons excited in this manner so that they recover their initial energy. The ideal converter is still the semi-conductor, since both the conductivity and the collection method are both sufficient and efficient. However, there are two major obstacles with respect to PV conversion. The first one is related to the photons and electrons. In fact, not all the photons are absorbed and not all of the excited electrons are collected. This impacts the energy performance of a semi-conductor, one of the key parameters for the PV industry. In practical terms, the performance of a solar cell is the maximum power produced, expressed in Watts-peak (Wp) and the higher the Wp is, the better the performance of the cell is (Goetzberger & Hoffman, 2005 ; Labouret & Villoz, 2009). The other major obstacle is the price of the solar module. Development of the technologies and the PV materials is continuing while the two goals are to increase energy performance and reduce the cost of the Wp beneath the symbolic threshold of \$1 US/Wp

latitude are sunnier compared to European countries above the 45-degree parallel.

**4. Technological aspects from solar energy to photovoltaic electricity** 

**3. Solar radiation: Geophysical considerations and energy potential** 

that took place in Northern Africa during World War I. Moreover, the advent of fossil fuels, with more affordable costs and better performances, ruined all efforts for the economic existence of solar energy for close to 50 years.

In 1954, the idea of solar energy was revitalized as a result of the efforts of Gerald Pearson, Calvin Fuller and Daryl Chapin, three researchers who developed the first silicon solar cells with an initial efficiency of 6% which soon increased to 14% (Singh, 1998). The first commercial applications started in 1958 but these cells were essentially used for space applications. Even though the terrestrial use of solar energy was slow, the scientists and the public were enthusiastic (Goetzberger & Hoffman, 2005; Bradford, 2006; Krauter, 2006).

The development of solar PV systems was strongly influenced at the outset by the price of fossil fuels. Thus, the oil crisis of the 1970s and the sudden increase in the price of oil revealed the precariousness of fossil energy resources and encouraged the solar industry. As a result, the Solar Energies Research Institute was created in the USA and the first subsidies were granted, injecting three billion dollars. In 1979, solar panels were installed on the roofs of the White House, a gesture considered highly symbolic (Bradford, 2006). Thermodynamic solar energy, however, declined in the 1970s and 1980s, for the benefit of by PV energy (Vaille, 2009). At that time, the USA accounted for 80% of the solar market. However, when the price of oil once again declined in the 1980s and the early 1990s, the enthusiasm for solar energy dropped and the solar panels were removed from the White House. Nevertheless, research into PV technologies continued, but was less sustained (Bradford, 2006).

During the 1990s, the world became aware of the need to revise energy policies based on sustainable development and concerns about climate change. Obviously, these issues involved the consideration of the level of energy consumption as well as the environmental consequences (such as greenhouse gas emissions, GHG) and the precariousness of fossil resources (Bradford, 2006). Thus, more attention was paid to PV solar resources.

This time, Europe took the lead in this industry which was predestined to flourish. Thus, of the 40 GW of solar electricity generated in 2010, 30 GW were generated by the European Union, of which 17 GW were produced by Germany. For the same year, Japan and the United States trailed behind with 3.6 GW and 2.5 GW respectively (EPIA, 2011).

The applications of PV are incredibly diverse at present, ranging from small to large, including solar calculators, irrigation pumps, the heating of single-family homes, and solar facilities (roofs, facades, etc.) connected to the power grid (Labouret & Villoz, 2009; Bradford, 2006). PV systems are interesting because they can also be installed in zones that are completely devoid of electrical networks or energy infrastructures, particularly in certain developing countries where the isolated segments intended for rural electrification are experiencing a veritable boom (Singh, 1998). Current applications and future projections differ by region since socio-economic concerns are dissimilar. Thus, in the developed countries, future visions focus on the large-scale integration of PV energy in the urban environment. The idea of a city as a gigantic PV power plant is germinating in peoples' minds as they wait for a large-scale study on the potential environmental and social impacts (Gaidon et al., 2009). In the developing countries, PV energy provides added value and is becoming a symbol of progress and openness to the world, outside the outlying rural zones that could enjoy the benefits (Singh, 1998).

that took place in Northern Africa during World War I. Moreover, the advent of fossil fuels, with more affordable costs and better performances, ruined all efforts for the economic

In 1954, the idea of solar energy was revitalized as a result of the efforts of Gerald Pearson, Calvin Fuller and Daryl Chapin, three researchers who developed the first silicon solar cells with an initial efficiency of 6% which soon increased to 14% (Singh, 1998). The first commercial applications started in 1958 but these cells were essentially used for space applications. Even though the terrestrial use of solar energy was slow, the scientists and the public were enthusiastic (Goetzberger & Hoffman, 2005; Bradford, 2006;

The development of solar PV systems was strongly influenced at the outset by the price of fossil fuels. Thus, the oil crisis of the 1970s and the sudden increase in the price of oil revealed the precariousness of fossil energy resources and encouraged the solar industry. As a result, the Solar Energies Research Institute was created in the USA and the first subsidies were granted, injecting three billion dollars. In 1979, solar panels were installed on the roofs of the White House, a gesture considered highly symbolic (Bradford, 2006). Thermodynamic solar energy, however, declined in the 1970s and 1980s, for the benefit of by PV energy (Vaille, 2009). At that time, the USA accounted for 80% of the solar market. However, when the price of oil once again declined in the 1980s and the early 1990s, the enthusiasm for solar energy dropped and the solar panels were removed from the White House. Nevertheless, research into PV technologies continued, but was less sustained

During the 1990s, the world became aware of the need to revise energy policies based on sustainable development and concerns about climate change. Obviously, these issues involved the consideration of the level of energy consumption as well as the environmental consequences (such as greenhouse gas emissions, GHG) and the precariousness of fossil resources (Bradford, 2006). Thus, more attention was paid to PV

This time, Europe took the lead in this industry which was predestined to flourish. Thus, of the 40 GW of solar electricity generated in 2010, 30 GW were generated by the European Union, of which 17 GW were produced by Germany. For the same year, Japan and the

The applications of PV are incredibly diverse at present, ranging from small to large, including solar calculators, irrigation pumps, the heating of single-family homes, and solar facilities (roofs, facades, etc.) connected to the power grid (Labouret & Villoz, 2009; Bradford, 2006). PV systems are interesting because they can also be installed in zones that are completely devoid of electrical networks or energy infrastructures, particularly in certain developing countries where the isolated segments intended for rural electrification are experiencing a veritable boom (Singh, 1998). Current applications and future projections differ by region since socio-economic concerns are dissimilar. Thus, in the developed countries, future visions focus on the large-scale integration of PV energy in the urban environment. The idea of a city as a gigantic PV power plant is germinating in peoples' minds as they wait for a large-scale study on the potential environmental and social impacts (Gaidon et al., 2009). In the developing countries, PV energy provides added value and is becoming a symbol of progress and openness to the world, outside the outlying rural zones

United States trailed behind with 3.6 GW and 2.5 GW respectively (EPIA, 2011).

existence of solar energy for close to 50 years.

Krauter, 2006).

(Bradford, 2006).

solar resources.

that could enjoy the benefits (Singh, 1998).
