**5. Practical applications**

318 Sustainable Growth and Applications in Renewable Energy Sources

The material currently used preponderantly in the design of PV cells is silicon, which is abundant in nature, accounting for 90% of the global market for the production of the modules. More than 80% of the silicon used is in crystalline form with an energy performance between 14% and 22% for a solar cell, compared to 12%-19% once assembled in modules (Labouret & Villoz, 2009; EPIA/Greenpeace, 2011; Xakalashe & Tangstad, 2011). There are currently three generations of photovoltaic cells. Those referred to as the first generation are made of crystalline silicon. The cells are provided in plates or wafers and have to be made from very pure silicon, using a manufacturing process that is still very onerous (Goetzberger & Hoffman, 2005; Labouret & Villoz, 2009; Jaeger-Waldau, 2010). The price of the solar module based on first generation cells is estimated at close to \$2 US/Wp

The second-generation solar cells, so-called thin layer cells, require less material and should cost less to design. Their development is more and more promising since their market share grew from 5% in 2005 to 16%-20% in 2009. Their production capacity, estimated at about 10 GW in 2010, could grow to 20 GW in 2012 and 70GW in 2015 (Jaeger-Waldau, 2010). The thin-layer solar cells include, first and foremost, amorphous silicon, with a very uncompetitive performance of between 4% and 8% although the price per Wp is advantageous, approximately \$1.3 US in 2011 (EPIA/Greenpeace, 2011; SolarServer, June 2011). The second generation also includes other polycrystalline thin-layer films, particularly those based on cadmium telluride (CdTe), copper indium selenide (CIS) and its alloy copper indium gallium selenide (CIGS). The average performance of the CdTe cells is between 8% and 10%. The price per Wp was \$0.81 US in the first quarter of 2010 and at the end of the same year, CdTe modules contributed to the production of almost 14% of the PV

In theory, the CIS and CIGs cells have the highest performance for thin-layer cells, which is estimated at 20% in laboratory tests. However, the modules installed yield only 7% to 12%. Nevertheless, this technology is in the early stages of development and the manufacturing process is still complex, particularly since indium is a material that is in high demand in the flat screen (LCD) industry, which makes its use in PV systems problematic (Labouret &

The objective set for the third generation cells is in the vicinity of 30% and these cells rely on innovative technologies. This group includes primarily: a) multi-junction cells with a thin layer of silicon or gallium arsenide combined with a solar concentrator, b) organic polymer cells or poly-electrochemical cells, also called Grätzel cells; c) thermophotovoltaic cells, primarily with an indium arsenide base (EPIA/Greenpeace, 2011). The multi-junctions, equipped with solar concentrators with a factor of up to 1000, are by far the most performing, with a record performance of 35.8% announced in 2009. However, the applications remain limited since they are confined to the space and military fields (Chataing, 2009; Guillemoles, 2010). While the performances of the organic cells are lower, from 8% to 12%, interest in such cells and particularly the Grätzel cells is growing since the production costs are constantly declining with an interesting price outlook estimated at \$0.73 dollars US (0.5 Euros) per Wc in 2020 (Chabreuil, 2010;

One of the emerging technologies in the field of PVs is nanotechnology, which uses nanocrystalline particles or quantum dots, which would significantly increase the efficiency of the conversion compared to conventional semi-conductors (Nozik et al., 2010). Current

(Xakalashe & Tangstad, 2011; SolarServer, 2011).

Villoz, 2009; EPIA/Greenpeace, 2011).

EPIA/Greenpeace, 2011).

solar electricity generated by thin-layer cells (Jaeger-Waldau, 2010).

The solar modules consist of cells assembled in series, encapsulated between supports made of tempered glass, a special Tedlar® type plastic or "solar" resin, and then framed. In order to amplify their power, the modules may be grouped in voltaic panels or even voltaic fields with power output ranging from 1 kWp (kilowatt peak) to more than 100 kWp (Antony et al., 2010).

The two types of PV systems in use are autonomous (off-grid system) systems and those connected to the public electrical network (on-grid system); they differ in terms of their finality and the nature of their components. The electricity produced by the autonomous systems is consumed on site whereas that generated by facilities connected to the network is intended to fully or partially supply that network (Labouret & Villoz, 2009; Antony et al., 2010).

Moreover, there is a hybrid system, an intermediary and emerging form of the PV market that allows connection to another source of energy. Efforts to combine sources of energy are continuing particularly as a complementary source of energy although this type of system remains complex, laborious and onerous (Goetzberger & Hoffman, 2005; Labouret & Villoz, 2009).

There are many applications for autonomous systems such as internal market for solar gadgets (calculators, clocks, etc.), solar home systems and water pumps. These systems are still a preferred solution for developing countries where more than two billion people are not connected to an electrical network and have no hope of being connected to one someday (Goetzberger & Hoffman, 2005; Labouret & Villoz, 2009). Nevertheless, despite their appeal as sources of energy and their potential for development, these systems are still the source of major concerns requiring intense consideration so as to ensure both their sustainability and their wide-scale generalization in developing countries.

In this case, it would be possible to enhance their tangible added value in the global energy landscape. First, apart from the internal market and "sun-related" applications such as pumping or ventilation, the autonomous systems would have to include judicious storage batteries in order to accumulate excess electricity, but these batteries are problematic. The financing for the autonomous generators is the first negative element since, even if only 20%-30% of the initial investments are for storage, the reduced lifespan of the batteries (batteries have to be replaced every 2, 5 or 10 years) results in a final cost that could amount to 70% of the total costs (Labouret & Villoz, 2009).

It is a fact that the positive development of individual solar systems in the developing countries is having pernicious effects since that easier access to electricity could lead to an increase in the acquisition of electrical appliances and, consequently, to the overuse of batteries, thereby reducing their lifespan (Goetzberger & Hoffman, 2005). Moreover, the scarcity of training on autonomous systems, aggravated by the high rate of illiteracy in the developing countries, could result in difficulties in maintaining the batteries which, obviously, influences their durability. Thus, the integration of batteries, although essential for autonomous systems, will have an impact on their costs, already high (\$500 to \$1500 US), thereby handicapping, to a certain extent, their generalization in terms of rural electrification in developing countries (Goetzberger & Hoffman, 2005; Labouret & Villoz, 2009).

Photovoltaic Conversion: Outlook at the Crossroads

(Aladjidi & Rolland, 2010).

Hoffman, 2005).

2011).

standards (Aladjidi & Rolland, 2010; EPIA/Greenpeace, 2011).

Between Technological Challenges and Eco-Strategic Issues 321

In addition to readjusting the silicon market as a condition for stability requiring the consolidation of firms, the real issue with respect to reducing the price of the units involves improving the manufacturing process through automation. Thus, major efforts should be made to improve refining capacity, reduce the thickness of silicon wafers and increase conversion performances through an equitable manufacturing process that respects specific

Although there are still good days ahead for silicon, the development of various emerging technologies in the field of photovoltaics would necessarily have a most beneficial effect since they would either use less silicon, as in the case of amorphous or micro-crystalline cells, or they would use innovative materials other than silicon

The lifespan of the PV systems is a key parameter not only for the assessment of the overall cost of the systems but also for estimating the EPBT and ERF. Most of the manufacturers of PV units provide performance guarantees, namely a life span between 20 and 25 years at 80% of the minimum nominal power for both crystalline and cadmium telluride units, while stating that this average would be a minimum estimate and not a definitive value since it would be estimated at 40 years in 2020 (Labouret & Villoz, 2009; EPIA/Greenpeace, 2011). The improvement in lifespan is both technological and technical in nature since it is closely related to the stability of the PV systems in use elsewhere, which are negatively impacted by a deterioration process that affects both the solar units, despite the encapsulation of the cells, and the support frame. This degradation can result from the aging of the semiconductors, the delamination or loss of adhesiveness between the solar cells and from the intrusion of humidity. The fragility of the systems has a major impact on the energy performance during operation. However, only few studies were done on the estimation of losses, while a decrease in performance of 1%-2% per year was observed for some systems (Goetzberger &

The cost of maintenance, including the ongoing control of the performance and the appearance of the systems as well as their cleaning, remains low and is estimated to be between 0.01 and 0.1 Euro/kWh (PVResources, 2011). However, integrating storage batteries in the autonomous systems, which are characterized by a decrease in lifespan of a factor of 2 for every 10 degrees Celsius as a result of corrosion, leads to a long-term increase

The average price of the solar electricity generated depends, among other things, on the initial installation costs and the rate of sunshine and is estimated at 0.22 Euro/kWh in Europe and remains, despite a significant decrease of 40% between 2007 and 2009, less competitive than the electricity generated using fossil fuels, which is evaluated between 0.09 and 0.27 Euro/kWh (EPIA/Greenpeace, 2011). However, there is no shortage of programs intended to make PV systems profitable, such as investment contributions (subsidy, green loan), tax benefits (reduction, exoneration) and direct pricing support, including the compensatory redemption rate systems in place in several European Union countries,

Germany was the first country to implement a law giving priority to renewable energy and has been a powerful driving force behind the development of PV programs. This law, and others which have been based on it, establishes the right to inject solar energy into the public network and to be reimbursed per PV kWh (EPIA/GREENPEACE, 2011; PVResources,

in the cost of the investment as seen earlier (Labouret & Villoz, 2009).

particularly Germany and Italy (Goetzberger & Hoffman, 2005).

The other issue with respect to autonomous systems concerns the nature of the batteries, which are essentially lead-based. The lead battery has two disadvantages: the most particular concern is the potential effect on public health and safety and its impact on the environment, mainly resulting from the presence of lead, a toxic heavy metal. Concerns are not only to the manufacture and handling of this type of battery but also to end-of-life recycling (Vest, 2002).
