Chapter 1: Global Progress, Prospects, and Sustainability Challenges of Solar Photovoltaic Technologies: Quo Vadis?

%

Percentage

$

Dollar

a-Si

Amorphous silicon

Al

Aluminum

BIPV

Building-integrated photovoltaics

BOS

Balance of system

c-Si

Crystalline silicon

CdS

Cadmium sulfide

CdTe

Cadmium telluride

CIGS

Copper indium gallium selenide

CIS

Copper indium selenide

CMERI

Central Mechanical Engineering Research Institute

CNY

Chinese yuan

CO₂

Carbon dioxide

CSIR

Council of Scientific and Industrial Research

FPV

Floating photovoltaics

GaAs

Gallium arsenide

GW

Gigawatt

In

Indium

kW

Kilowatt

kWh

Kilowatt hour

m³/day

Cubic meter per day

MNRE

Ministry of New and Renewable Energy

MW

Megawatt

NDRC

National Development and Reform Commission

OECD

Organisation for Economic Co-operation and Development

P

Phosphorus

p-Si

Polycrystalline silicon

PERC

Passivated emitter and rear cell

PV

Photovoltaic

RIKEN

Rikagaku Kenkyūjo

Sb

Antimony

SMSL

Silicon Module Super League

Tri c-Si

Tri-crystalline Silicon

TWh

Terawatt hour

UK

United Kingdom

USA

United States of America

W

Watt

YEKA

Yenilenebilir Enerji Kaynak Alanları

µm

Micrometer

The photovoltaic (PV) effect is the fundamental principle involved in solar cells for converting natural or artificial light into electricity. The vital building block of the solar PV is the solar cell, which is a two-terminal device, and it conducts like a diode in the dark and produces a potential difference when excited by photons. When light falls on the surface of the cell, photons help to excite the electrons to higher energy states, and there exists a difference between the initial and the final energy states. The doping effect pulls the excited electrons away to the external circuit. The extra energy of these excited electrons produces a difference in potential and drives the electrons through the load in the external circuit. Different PV cells joined together form a module, and various modules connected in series and parallel form a PV array. The electrical efficiency depends on the length and intensity of light falling on the PV system, as well as the type and quality of the cells, material, and auxiliary components within the module.

It is a difficult task to evaluate the different PV technologies available in the market and those under development. At the basic level, all these technologies employ an active material that absorbs the incident light and generates charge when connected to the load. In general, these technologies fall into three main categories: crystalline silicon (c-Si), thin-film cells, and emerging thin-film technologies, as shown in Fig. 1.1 (Akinyele et al., 2015). Researchers around the world have made tremendous efforts to find new technologies with lower costs, resulting in the invention of thin-film technologies. Compared to older PV technologies, thin-film technology has significantly lower material consumption and production costs, although it also has comparatively low efficiency. Furthermore, some thin-film technologies cause harmful environmental effects due to the presence of elements such as cadmium and tellurium. Eventually, research to get rid of these toxic elements resulted in the development of organic or polymer PV technologies. Organic PV technology lags with a low efficiency of 4%–5%, but it is attractive due to its lower cost and eco-friendly nature. Hybrid technologies, a combination of crystalline and non-crystalline silicon materials, are also available with efficiencies of 10%–20%. Figure 1.2 illustrates the energy yield analysis of the three types of technologies over the years for estimating the performance of PV modules in outdoor conditions in Southern Norway (Midtgard et al., 2010).

The last few decades have seen greater developments in terms of efficiency for c-Si than for thin-film and emerging technologies. At present, single-crystal cells have attained an efficiency of 24.70% in standard test conditions. The cost of mono c-Si and polycrystalline silicon (p-Si) has decreased in the last decades, making them superior to other technologies. The mono c-Si consists of a silicon p-n junction, which is manufactured by the Czochralski process, and involves the growth, melting, and pulling of the crystal ingot. The process consists of subjecting the wafers to chemical etching, diffusion, edge isolation, anti-reflective coating, and making of metal contacts. Manufacturers guarantee a conversion efficiency of 15%–20% for mono c-Si technologies (Fakouriyan et al., 2019). Tri-crystalline silicon (Tri c-Si) provides more mechanical stability than c-Si and consists of three tilted mono c-Si grains. Researchers (Lackner et al., 2020) have reported an efficiency of 33.30% for a wafer with an active thickness of 280 µm. Unlike the previously mentioned technologies, p-Si technology competes for cost and performance and provides higher production output. The technology addresses the metal contamination and defects in the crystal structure, and possesses the same conversion efficiency of its mono c-Si counterparts. The front contacts of the PV panels were discarded for the total irradiation to fall on its surface for the advanced cell known as an emitter wrap-through. This technology concentrates more on enhancement in efficiency than material optimization. Manufacturers report conversion efficiency between 15% and 20% with emitter wrap-through technology (Soley and Dwivedi, 2019). Gallium arsenide (GaAs), which falls under crystalline technology, offers higher conversion efficiency with a multi-junction structure by alloying GaAs with aluminum (Al), indium (In), phosphorus (P), and antimony (Sb). The technology possesses lighter weight and allows higher thermal resistance, which makes it suitable for space and concentrator PV applications. So far, the technology has achieved a higher efficiency of around 39% when compared to other technologies, but it is very expensive.

Thin-film technologies include cadmium telluride (CdTe), copper indium gallium selenide (CIGS), copper indium selenide (CIS), and cadmium sulfide (CdS). The manufacturing involves sputtering a thin layer of these materials on the substrate. These technologies offer significant material optimization and provide a reduced material thickness of 10 µm. However, conventional c-Si technology offers a 230 µm thickness. Due to the incorporation of thinner materials in its fabrication, these technologies provide lower conversion efficiency than c-Si PVs. Researchers have tried to enhance the efficiency by depositing various materials and alloys on the substrate, and presented amorphous silicon (a-Si), copper indium diselenide, CdTe/CdS, and thin poly c-Si on cheaper material. Among the thin-film technologies, a-Si offers higher efficiency with larger light absorptivity. The disordered silicon structure of the technology causes the formation of defect states and the reaction of a-Si with hydrogen results in a stable a-Si:hydrogen. This technology provides a laboratory-level efficiency of 12%, which reduces to 4%–8% when exposed to sunlight. However, the manufacturing cost of a-Si modules was higher when compared to mono c-Si and poly c-Si modules. CdTe/CdS cells are a promising technology due to the larger direct absorption coefficient of the material and cost-effective manufacturing, which could deliver efficiencies higher than 15%. Large-scale PV plants use these materials, but the major hurdle faced by this technology is the environmental hazard. After decommissioning the modules, the recycling of cadmium is essential. The presence of the rare element enhances the production cost, which adds to the challenges faced by the technology. A laboratory-level cell efficiency of 20% and module efficiency of 13% was guaranteed for CIGS/CIS technology by manufacturers. Another disadvantage of CIS technology is that it undergoes degradation when exposed to radiation. The scarcity of indium, higher production cost, and lower output are some of the disadvantages CIGS faces in the market. Just like CIGS, CdTe also undergoes photodegradation and requires barrier coatings to rectify the degradation.

A global climatic crisis, greenhouse gas emissions, inconsistent energy supply, unaffordable energy services, and fluctuating oil prices result in the necessity to consider non-conventional energy sources. The share of non-conventional energy sources for power production has increased globally. Despite the considerable development in the power sector, the contribution of renewables in energy consumption shows moderate growth. The lagging of non-conventional energy share in the cooling, transport, and heating sectors is probably due to the inadequate regulatory frameworks and sluggish developments in technology transfer. However, the advantages regarding renewable energy sources, including reduction of greenhouse gas emissions and conservation of existing fossil fuels, have created much appreciation among the public for their usage. The removal of subsidies from conventional energy sources further increases the investments in non-conventional sources rather than fossil fuels.

The implementation of renewable sources to meet global power needs decreases the release of toxic pollutants and greenhouse gases. Hence, the requirement of alternate sources of energy is inevitable for the survival of humans to reduce dependence on conventional energy sources. The intermittent energy source, the sun, contributes significantly to future energy needs. Within the last few decades, solar PVs have emerged as a pioneering renewable energy technology. Environmentally friendly solar energy reduces the negative impact on the atmosphere and converts solar energy to heat or electricity using thermal or PV systems. Stand-alone PV systems generate megawatt power and act as a power-generating source for various applications.

In 1883, Charles Fritts developed a solar cell using selenium on a thin layer of gold that provided efficiency as low as 1% (Bentaher et al., 2014). Later, many researchers worked on the photovoltaic effect and received patents for solar cells. In the 1950s, Bell Labs developed solar cells for space applications (Bosi and Pelosi, 2007). In the early 1990s, some countries started deploying large-scale PV plants. Feed-in tariffs were initially introduced by the German government to support investment in non-conventional energy. The growth in PV installation in countries such as Japan, the United States of America (USA), China, Germany, and Spain rose exponentially in the early 2000s.

Europe had been leading in global module manufacturing and PV research and development since the beginning of the 21st century. However, in 2007, China started deploying PV production units after realizing the strategic and political impact the sector could make in the global market (Zhang and He, 2013). Soon afterward, Europe lost its pioneering status as China took over the vast market in PV production. However, data collection of solar cell production is a bit complicated, since private companies have started investing. Some companies reveal only their exporting figures and there is no standard reporting format to estimate the production figures, resulting in uncertain solar cell production data. However, in 2015, a group of six c-Si module suppliers, called the Silicon Module Super League (SMSL), was formed, and it now supplies almost half of the world's PV requirement (Awate et al., 2018). In 2019, SMSL revised its entry conditions, and now a total of nine module suppliers are part of the organization (Fig. 1.3) (Colville, 2019).

Absolute PV module prices as well as the structure vary based on the technology. The PV module cost and balance of system cost are incorporated to estimate the capital cost of the PV system. The PV module cost consists of PV cell, manufacturing, and assembling costs. The balance of system (BOS) consists of structural, electrical system, and storage expenses. The Global Solar Investment Report (Bloomberg NEF, 2019) presents a study of technology trends and PV costs of various technologies. The price of a crystalline PV module has decreased from US$80/watt (W) in 1976 to $0.27/W in 2018. The price is expected to decline further to $0.14/W by 2030. The study shows that mono c-Si will dominate the market from 42% at the end of 2018 to 64% at the end of 2021. Innovations in technology, economies of scale, and manufacturing experience could be the probable reasons for these cost reductions. The prices mentioned for PV are factory gate prices, but the retail prices vary between 35% and 45% higher. Based on the installation type (rooftop or ground-mounted), the BOS cost varies between US$1.60/W and US$1.85/W. For small-scale and residential PV systems, the BOS and installation cost are 55%–60% of the total PV system costs (O'Callaghan, 2016). The BOS costs of rooftop systems are more costly than ground-mounted systems, as the former requires more expenditure for the construction of the roof to attach the PV modules. However, the electrical system costs are the same for both systems.

The total cost of the PV system depends on the module costs, type of installation, and the BOS costs. Based on the technology, PV module costs vary; however, the overall PV costs are determined by the PV plant size, mounting type, project location, the incentive provided by the country, and the size of the market. Figure 1.4 illustrates the cost of PV systems in various countries for residential applications (IRENA, 2012). The different price systems could be due to the difference in incentive schemes given by each country to the residents, which are not enough to reduce the PV costs. Had the incentives not aligned with the reduced PV manufacturing costs, PV plant installers could maintain the higher prices. This PV cost will result in larger system prices for countries with higher PV subsidies.

The beginning of 2019 has seen a cumulative global PV capacity growth of more than 500 gigawatt (GW) (IRENA, 2020), which could meet the demand of around 2.60% of global electricity consumption. Figure 1.5 illustrates the growth of the worldwide PV market since 2000 (IRENA, 2016; 2020). In the last decade, the PV sector reported a cumulative global PV growth rate of 40% per year. Since the start of 2013, countries in Latin America, Asia, Africa, and America have initiated rapid deployments. China grabbed the largest market share and has been a pioneer in PV cumulative installations since 2012. Figure 1.6 illustrates the cumulative PV deployments in different parts of the world since 2006 (IRENA, 2016; 2020). On a technology level, the global renewable energy capacity expanded from 1226.85 GW in 2010 to 2536.85 GW in 2019, with Asian countries constituting an increase from 387.28 GW in 2010 to 1118.96 GW in 2019. The worldwide capacity of solar PV technologies has grown to 580.15 GW (2019) from 40.27 GW (2010), with the most considerable contribution from Asian countries (56.90%) (IRENA, 2020). On a global scale, China ranks first in the installed PV capacities in 2019, followed by Japan, the USA, Germany, India, and Italy. These figures indicate a transition of energy from the fossil system to non-conventional energy sources. These statistics, in turn, means that the PV system should lead energy supply in the coming decades. As per the forecast (IRENA, 2020), the global solar PV capacity will reach 8500 GW by 2050, which is equivalent to 18 times the present global cumulative capacity. This prediction suggests a global opportunity for PV manufacturing industry.

In Asia and the Oceanic region, China, India, and Japan had the largest solar PV markets in 2019 [Fig 1.7(a)] (IRENA, 2020). All the countries in these regions and Europe [Fig. 1.7(b)] benefited from regulatory frameworks. Germany and Italy together constitute almost more than 50% of the PV installations in Europe. However, in India, state-level auctions supported by government subsidy programs helped the country to attain a top five global rank in cumulative PV installations. In South America, Chile and Brazil host almost 79.41% of PV deployments in the region [Fig. 1.7(c)]. Africa, with only 6.37 GW of solar PV in total, was more fragmented with South Africa, Egypt, Morocco, and Réunion as its largest PV markets [Fig. 1.7(d)] (IRENA, 2020).

A study of the 37 member countries of the Organisation for Economic Co-operation and Development (OECD) found that the final energy intensity of these countries grew by 14% between 2007 and 2017. The share of the non-conventional energy sources in total final energy consumption increased by 44%, and the usage of non-fossil energy sources improved by 42%. The regulatory frameworks initiated by the governments in countries including Japan, France, Australia, the United Kingdom (UK), and the Netherlands are supportive. They are proceeding toward the auction-based process, which encourages developers to outbid one another, resulting in lower power prices for consumers.

The situation is a bit different for non-OECD countries, for which the following discussion concerns countries with the largest installed capacities. The Chinese Ministry of Finance (Shaw, 2020) reduced the subsidy in budget allocation by 50% in 2020 [Chinese yuan (CNY)1.5 billion] as compared to 2019 (CNY3 billion). Out of this, the government allocated CNY500 million for residential rooftop PV systems and CNY1 billion for distributed PV and utility PV projects. China's National Development and Reform Commission (NDRC) reduced the guided electricity prices for utility PV systems by CNY0.05/kWh for the three categories. For residential PV and distributed PV systems, the prices have decreased, respectively, by CNY0.1/kilowatt hour (kWh) and CNY0.05/kWh.

India has seen a proportional growth in the economic sector and electricity supply due to the larger share of renewable energy and a reduction in coal utilization plants. The country has a dedicated Ministry of New and Renewable Energy (MNRE) for policy development in the renewable sectors. The government has a target of 100 GW solar PV by 2022 (Mohammed et al., 2019) and launched competitive auctions with long-term power purchase agreements with fixed-price contracts. The depreciation tax benefit for plant developers was lowered from 80% to 40% in 2017, which is advantageous for PV power-generating systems, different PV solar collectors, and electrically operated vehicles. Despite the COVID-19 pandemic, the power generation capacity and storage auctions that took place in the country have attracted US$10 billion to US$20 billion. The rooftop PV generation capacity reached 5.95 GW in June 2020, of which commercial and industrial arrays comprise 4.37 GW; residential includes 0.80 GW and the public sector is 0.77 GW, with the capital expenditure payment totaling to 4.10 GW of purchases (Bridge To India, 2020).

Turkey attained a cumulative PV installation capacity of 5.99 GW in 2019, of which unlicensed PV systems constituted 5.82 GW (IRENA, 2020). The government installed the first integrated solar ingot–wafer–module–cell manufacturing factory on 15 June 2020 to make panels with 500 megawatt (MW) capacities. Despite a promising market in Europe, a stuttering economy, fluctuating PV policy landscape, and Yenilenebilir Enerji Kaynak Alanları (YEKA) tenders have undermined the nation's solar progress. The introduction of a new net metering system reduced the payback period of the rooftop from 16 years to 11 years for new installations.

As of 2019, the total cumulative installed PV capacity of Ukraine reached 5.93 GW (IRENA, 2020), with US$10 billion investment in the renewable energy by the government. A reduction of 15% feed-in tariff rates was implemented on 1 August 2020 for plants with capacities of 1 MW or more and commissioned between 1 July 2015 and 31 December 2019. From 31 October 2020, the investors in big PV power plants could expect around 30%–60% feed-in tariff reductions.

Vietnam's annual growth rate of energy demand has reached about 8.50%, and it will increase to 6.60 terawatt hour (TWh) in 2021 and 15 TWh in 2023. In 2019, the cumulative installed PV capacity reached 5.69 GW. However, concerns about future blackouts has led the government to attract investors with incentives. With a weak grid system in the country, almost 60% of utility-scale projects suffer power curtailment, and the government is trying to transition to a rooftop solar market. In April 2020, the government renewed the feed-in tariffs, which are now 10%–24% lower than the ones that expired on June 2019.

Renewables play a significant role in the electric grid as a substantial power source, and hence PV has a bright future in the coming decades. However, with the advancement in technology, PV is in transition, with innovations occurring across the globe. The revolution includes inventions of new technologies for efficient solar cells, incorporation of artificial intelligence to enhance power production and operation efficiency, recycling, and end-of-lifecycle management.

Among the PV panels, c-Si modules hold almost a 95% share of the global PV production. The steady increase in efficiency and the continuous price reduction has made other technologies competitive with the c-Si. However, there is still a drive to incorporate research and development to reduce the price of the module for higher profits; decrease impurities, grain boundaries, and dislocations; create environmentally friendly waste disposal techniques; and manufacture thinner wafers using advanced material properties. An improved version of mono c-Si with back layer passivation, passivated emitter and rear cell (PERC) technology, offers increased performance and efficiency as compared to mono c-Si panels. PERC module production was as low as 1 GW in 2014. It increased to 64 GW in 2018 due to domination in the market, with an expected output of 168 GW by 2022.

Tandem solar cells consist of stacking perovskite solar cells on top of silicon, and they have a reported efficiency of more than 40% with a three-cell arrangement. These cells find applications in space and are difficult to fabricate due to the high cost of material, and hence are not market competitive. Perovskite solar cell technology, similar to third-generation solar cells, can attain conversion efficiencies of more than 20%. Under laboratory conditions, the technology provides good efficiency and lower cost but fails to provide reliable stability. Research is ongoing to find alternatives for the use of electrodes and various doping techniques to enhance the prospects of commercialization. Bifacial solar cells increase the total generation by producing power from both sides. These cells provide efficiency of more than 20% using a laser-doped selective emitter on a mono c-Si cell.

Various innovative projects are in the prototype stage for the PV market. Some of these technologies include the floating PV (FPV), solar trees, building-integrated PV, solar carports, solar PV-thermal systems, solar-powered desalination units, and agrophotovoltaics. The transition of existing water bodies to sustainable power plants using floating PVs creates an additional contribution to the current green energy revolution. This technology reduces evaporation and algae growth and decreases PV operating temperatures and, subsequently, the cost of solar power generation. So far, China holds the largest share of the PV market in the world and has deployed FPV in the country as a bidding scheme that is eligible for a feed-in tariff supported for 20 years. In 2019, the government sought an installation of FPV bids of 820 MW capacity across China by 2021. The increased capacity illustrates the current demand for FPV in the country. Another competing solar market in the world, India, noticed a 45% reduction in bid prices for FPV tenders during 2016–2018. During 2019, the government called for FPV bids for 2 GW capacity, of which almost 1.70 GW are in the developmental stages. Nearly more than 50% of the total FPVs are based in Japan, accounting for a cumulative capacity of 130.59 MW. The country has deployed the largest and smallest FPV plants with capacities of 13.70 MW and 460 kW at Yamakura and Aisai City, respectively. South Korea has initiated deploying the largest FPV plant in Jeonbuk province with a size of 2.10 GW, which could supply power to 1 million households and reduce carbon dioxide (CO₂) emissions by 1 million metric tonnes. The USA has so far installed 9 MW of FPVs with the largest project in New Jersey with a capacity of around 4.40 MW. Figure 1.8 illustrates the present global scenario of deployed FPV projects (Umanadh, 2020).

Solar carports are practically tall, ground-mounted PV panels that cover parking areas. The structural design, which includes frames, foundations, roofs, and PV systems, need attention when designing a carport. Structures such as T-frames, V-frames, and portal frames are commonly used along with monopitched, duopitched, barrel-arched, or beam roofs to generate energy. The carport can use four types of foundations (i.e., helical screw piles, concrete piles, concrete pads, or above-ground ballast) and its foundation selection depends on the ground conditions and the structural capacity. The efficiency of PV technologies is continuously evolving, and its choice requires the utmost care for the design. However, polycrystalline, monocrystalline, and thin-film technologies are widely used based on the local site. Apart from providing shade to the vehicles parked under the carport, the carport also generates electricity. The generated power, after integrating with a charging system, helps to charge electric vehicles and could decrease running costs. With the additional support of battery storage systems, the unit can be used after daylight hours.

The majority of desalination plants across the globe are powered by fossil fuels and are not sustainable. Most desalination plants use either thermal or membrane-based technology to produce drinking water. The membrane-based process does not require heat, and the integration of non-conventional energy sources is possible. The coming decade will see a hike in the deployment of membrane-based desalination technologies. This increase is due to the reduction in the price of PV-related auxiliary equipment and the increased demand for desalination. The thermal desalination process requires heat and electricity. Other solar technologies, such as PV-thermal and concentrating solar power, can generate thermal energy as a by-product while producing electricity. The Chtouka Ait Baha seawater reverse osmosis-based desalination plant in Morocco (Kettani and Bandelier, 2020), with a production capacity of 275 000 cubic meters (m³)/day powered by solar energy, supplies water at an acceptable cost of around US$1/m³. The public subsidies compensate for the difference between the selling and cost price of desalinated water. This amount fluctuates between 20% and 30% of the estimated cost of the desalinated water.

An innovative way of using solar power, solar trees are an energy generator similar to a tree in which the solar panel serves as a leaf. The Council of Scientific and Industrial Research (CSIR)–Central Mechanical Engineering Research Institute (CMERI) has developed the world's largest solar tree in West Bengal, India, with an installed capacity of 11.50 kWp to generate 12 000–14 000 units of power (Mishra et al., 2020). The solar tree has 35 panels, each with a 330 Wp capacity, and could save almost 10–12 tonnes of CO₂ as compared to conventional fuel systems. The solar tree can cater to farming operations such as high-capacity water pumps, e-tractors, and e-power tillers to make agriculture an energy-sustainable practice.

Solar shingles, technically known as building-integrated photovoltaics (BIPV), are roof materials similar to asphalt or slate that generate electricity. As technology improves, BIPV will become a popular option in the marketplace. The pleasing appearance; requirement of the small installation area; cheaper, easy reinstallation; and availability of various sizes and styles makes BIPV technology different from conventional solar panels. The bulkiness of ordinary PV panels has caused many homeowners to give up interest in generating energy from standard modules. However, there are new building materials, which open new possibilities for architectural solutions. Solar tiles manufactured from quartz glass are available in ground glass, slate, Tuscan, and texturized forms, which are more reliable, durable, and efficient than ordinary solar panels. Bitumen-based roll roofing coverages come with a battery option and reduce the electric connections. Usage of solar batteries as a façade panel on walls makes for innovative, aesthetic, and attractive buildings. Sticking thin-film solar batteries on glass windows is another option; however, the technology lags with lower production. Solar glass is applicable where roof space is limited and can maintain the heat during winter. PV glazing reduces the glare and enhances the temperature insulation.

Solar skins are a novel PV technology that uses selective light filtration and reflects the minimum amount of light to pass through and allows the majority of the illumination to flow through the PV cell. PV panels imprinted with a custom design are called solar skins, which work with selective light filtration, where the reflection of some portion of the illumination takes place. The technology matches graphically with roofing materials such as shingles and tiles. This innovation allows for a thin printable layer on the panel surface, which helps the owners to fix the panels similar to the roof and allows color customization. The downside of solar skins is that they come at a higher cost as compared to traditional panels.

Solar fabric is another revolution in energy production, as researchers are developing the technology to incorporate solar power in fabric. By embedding solar filaments into shirts or winter coats, the technology could keep people warm, power mobile phones, and supply the energy required. The challenge is to make a microsized solar fabric to fit into advanced breathable clothing in huge quantity. In 2017, the University of Tokyo and the research institute Rikagaku Kenkyūjo (RIKEN) collaborated to develop an ultrathin PV device that could be fitted to fabrics and be machine-washable, stretchable, and waterproof (Jinno et al., 2017).

Solar PV panels also act as a noise barrier when installed on highways, railways, and roads, where they absorb traffic noise and generate energy. These barriers act as a physical obstruction between the noise source and the receptor, where it attenuates the noise level near to the receptor. The barriers reflect the noise to the highway where it is fixed as stand-alone walls. The installation of solar cells as a noise barrier is technically possible; however, the technology lags because of higher cost and lower efficiency. These systems do not block the noise entirely and reduce the traffic noise by only one-half. Switzerland deployed the first PV noise barrier system in 1989 (Asanov and Loktionov, 2018). However, the unique mounting of these systems requires a larger land area for power generation than conventional PV systems. Land use along highways; absence of adequate codes, standard protocols, and interconnection guidelines; and the shortage of efficient noise barriers add to the hindrance of adopting the technology.

Since the beginning of the 20th century, non-conventional energy sources have become a vital part of research and development among researchers. Despite the innovative technologies that have emerged in the past decades, most developing nations have prolonged the transition to renewable energy sources. Fossil fuels have contributed to CO₂ emissions and increased global warming. The majority of countries have shown reluctance to accept renewable technology due to various categories of barriers (Painuly, 2001), including an overreliance on fossil fuels, technical barriers, political barriers, sociocultural barriers, economic barriers, geographic and ecologic barriers, and market barriers.

The usage of coal acts as a barrier to renewable energy development. Coal contributes one-third of the energy supply and provides almost 40% of the power generation worldwide. Replacing coal is a difficult task, as the transition requires a lot of infrastructure changes, which in turn results in a lot of cost and time. Its wide availability as an abundant source and its efficiency in producing a considerable amount of energy makes it very difficult to replace fossil fuels with other renewable energy sources. Most nations prefer a cheaper and more economical method to improve the economy by reducing production costs. Given that coal is the more affordable alternative and the availability of already-established coal plants, the development of new non-fossil fuel plants is very costly to the economy. The workforce required for the coal industry, which produces more power, is significantly less as compared to the renewable power industry, which has intermittent or less power. Hence, a majority of countries hesitate to shift from existing power plants to non-conventional power plants.

Technical barriers include insufficient technology and the absence of sophisticated infrastructure to support renewable technologies. The lack of qualified professionals to train, operate, and manage the non-conventional energy structures, especially in rural communities, negatively affects the willingness to adopt these technologies due to fear of failure. Geographic location also plays a vital role, as the PV systems are feasible only in particular areas, and they face challenges from other technologies suitable to the specific geography. Also, adopters worry about systems not functioning during the rainy season and avoid buying PV systems due to lack of knowledge. The lack of information among the supply side and the adopter side further hinders the acceptance of the technology. Poor connectivity to the grid increases the transportation cost and transmission losses, as the generation and consumption points are far away. Hence, the majority of investors fear investing in the technology. Insufficient operation and maintenance of the auxiliary components and lower reliability of the technology reduces confidence among consumers to support and adopt the non-conventional energy technology. Developed nations import the technologies and, hence, the servicing or repair of the auxiliary components require imported spare parts and professionals, which eventually results in the temporary stoppage of the energy supply. As a result, many consumers prefer fossil fuels, which are readily available and reliable. Some of the PV capacities offered by the government are unaffordable by low-income groups. Hence, the applicability of the technology needs to be modified to accommodate the PV capacity in smaller proportions to benefit lower-income markets.

The technology faces another serious threat in the near future as the panels installed in the early stage of the energy boom are coming to an end of their expected lifetime, and these panels will eventually get dumped in landfills. These panels lose their productivity when their life span reaches around 25 years, as specified by the manufacturer. To address the forecasted global PV waste, recycling solar panels is a smart option so that the decommissioned PV panels can be refurbished and redeployed. Recycling not only provides an efficient way to retrieve valuable elements from solar waste but also delivers a greener environment with less energy used to recover raw materials. The research and development work concerning solar PV recycling has already begun in countries such as Japan, the USA, India, Australia, and Europe. However, the majority of the research work consists of retrieval of glass and rare elements from the disposed PV modules. The recycling of the PV module consists of removing the sandwich layer and exposing it to various methods to detach and extract different materials from the dumped modules. Hence, the three categories of recycling strategies of end-of-life PV modules (Xu et al., 2018) are physical separation or disintegration, PV material separation, and extraction or purification of the materials. Figure 1.9 shows the probable PV module recycling techniques of PV technologies (Xu et al., 2018).

There is limited awareness about the environmental and economic benefits of PV recycling technologies due to the preliminary case studies. Although recovery of the elements is beneficial, the energy needed to retrieve the precious metals from the discarded PV panels is more substantial than gathering, dismantling, and retrieving the modules. Although the recycling plants are not profitable, the recycling cost of PV panels is low (Faircloth et al., 2019). There are studies that show that the profit obtained from selling the recycled content of CIGS solar panels is higher than the recovering price. However, for c-Si and p-Si solar modules, the earned amount is less than recovering the cost of solar panels. Despite the monetary gains obtained from reselling the recycled products and the environmental benefits of recycling, companies prefer disposing in landfills to recycling due to the lower initial cost of dumping (McDonald and Pearce, 2010). When comparing the potential benefits of recycling the CIGS panel with the CdTe panel, the latter is more beneficial for recycling due to the presence of a reduced quantity of precious elements in the CIGS panel. Considering the environmental loads, the recovery of metals in the case of CIGS panels does not seem commendable like CdTe modules (Rocchetti and Beolchini, 2015).

The capital investment cost, incentives, and subsidies provided by governments and economic status are the significant parameters that decide the price of non-conventional energy technologies. The cost of any innovation decreases with time and can change based on the location. Economic barriers usually relate to the higher cost of the PV modules, the auxiliary components, installation rates, and operation and maintenance costs. The higher installation cost of PV systems compared to other conventional or non-conventional sources of energy acts as a barrier. Hence, it is more likely that people will adopt lower investment options. To increase the profit generated from renewable power sources, investors also prefer the lower investment cost. The higher initial expenditure of investment for non-conventional energy sources becomes a hindrance for the deployment of these technologies. Also, developing nations depend on imported goods and technology from developed countries, and it adds extra costs to the existing power scenario.

The economic condition of a country significantly affects the adoption of renewable technology. Rural and low-income communities in developing nations often cannot afford the prices of the solar PV systems. The cost of the new technologies are not competitive enough to overtake conventional systems. Hence, the investment in the form of incentives and subsidies from the government are essential as they would enhance the commercialization of PV technologies. However, in a feeble economic situation, banks are unwilling to provide adequate support for investments in PV systems. The shrinking economy also causes a lower demand for electricity and thereby decreases the interest in PV systems. Sometimes political instability in a country weakens economic growth or the government is attempting to expel foreign nationals, which reduces future investments in PV technology. Also, insufficient credit facilities to buy sustainable technologies and the larger interest rates on the credit facilities act as barriers to PV development.

Some countries still offer subsidies for fossil fuels and create an unnecessary race for renewable technologies. The competition attracts ordinary people to conventional energy, as the grants are more than renewable sources. Long-term financial funding is an adequate solution to get rid of the biased approach toward traditional sources. Banks are usually only interested in investing in large-scale plants, as the incentives provided by the government for these plants are higher than the incentives for small- and medium-scale projects. The broader interest rate for short-term projects makes it difficult to break down the project funds. Sometimes, investors are not willing to invest, which makes financing more difficult due to the lower electricity consumption in households and reduced electricity fees.

Being an intermittent source of energy (solar as well as wind), the geographic and weather conditions of a country also need consideration during deployment of a PV project. The geographic restriction acts as a barrier to energy development. Rapid growth in the human population and natural resource consumption create concern as to whether the world can sustain the available natural resources. As a result, the cost of the renewable sources increases and they become highly expensive for energy production, which eventually makes consumers unable to afford it. This unaffordability causes a downturn of non-fossil fuel power production in some areas.

Insufficient regulatory frameworks to encourage the development of non-conventional energy technologies also create a barrier for PV technologies. To attract private investors, transparent policies and legal frameworks are needed considering the nature of the renewable energy structures. Enabling the frameworks to develop a concrete and robust atmosphere to encourage investments eliminates the barriers and ensures profit. Also, the regulatory standards improve the adoption of PV technologies by reducing the technical risks that come with investing in projects. However, policymakers have been slow to regulate renewable energy, lowering the interest of private companies to invest in non-conventional energy projects.

Implementaion of the policies is essential based on the current market which includes energy auctions, integration of PV technologies with non-conventional energy sources and timely completion of the PV projects. Community-shared solar projects help the development of financial arrangements and overcome the financial burdens by allowing the consumers to purchase or lease a part of the shared PV system. These business models, in turn, assist in the development of a PV system in the residential market, stabilization of power prices, and power bill savings. Integration of the policies in the system and urban and social levels are essential to encouraging the planning and coordination of the renewable projects. The system level consists of an extension of the current infrastructure using a microgrid or super grid to enhance the interconnection among the nations while transporting the energy generated from the PV system. As the energy source is intermittent, reliable forecasting of the weather conditions using artificial intelligence improves the accuracy of the system and reduces the uncertainty in power generation. The social-level policy involves the incorporation of the local people throughout all stages of project development for a community-based sustainable PV project. Integration of the PV systems in urban building planning, such as rooftop PV systems, solar shingles, solar carports, and BIPV systems, maximizes power generation.

Strengthening policies by mobilizing financial investment, economic diversification, and knowledge sharing is essential to receiving the maximum benefits of an energy transition. The growth of the energy sector directly affects the economy of the country. Encouraging research and development activities and sharing the research results with private entities would benefit society. Awareness among consumers, enabling a competitive atmosphere, increasing public investment in the renewable sector, and creation of jobs supports the energy sector in leading the economy. Incorporation of green bonds, carbon pricing, and revenue recycling measures would also assist in the energy transition. These revenues could be used for further advancement of the existing infrastructure and diverting the money to education, medical care, and other facilities. Incorporation of renewable energy subjects at the school and college levels could develop skills, improve job opportunities, and reduce unemployment.

Market prices for PV systems remain high and are too expensive for many consumers. The higher production cost of non-conventional energy sources and the availability of the cheaper fossil fuel options attract consumers and create market competition for non-renewable technologies. The unavailability of business models to support renewable energy technologies prevents the conversion of small-scale PV projects to large-scale or commercial plants. Subsidies are given more effectively to conventional fuel sources, which results in an unfair priority over non-conventional sources. The market for PV technologies has to be promoted by governments to obtain the maximum benefit of the renewable applications in the government market, government-driven market, and the loan and cash market. The input requirements of PV plants, such as land and water, complicate the addition of PV capacity. The regulatory frameworks associated with land acquisition and getting clearance certificates from local governmental bodies adds to the insufficient market base.

PV technology and solar optimization have achieved several milestones in all sectors, including cell structure, panel efficiency, durability of the module, fabrication technologies, and orientation. However, the industry faces severe barriers, including enhancing cell efficiency, panel performance under various operating conditions, and manufacturing costs. The different hybridizations enhance technology efficiency only up to 20%–30%. Advanced technologies have improved the applications of PV and resulted in emerging PV technologies. The valuable findings have led to the rapid development of PV production, especially in the renewable power industry.

Based on the Paris climate agreement, non-conventional energy sources are a potential solution for sustainable energy transformation worldwide. Despite the quick access and fast deploying nature of the technology, PV plants face decelerated growth in some countries. Eventually, this will result in hampering the development of the PV sector over the next few decades. Mitigation of the potential barriers, including policy, technology, social, and economic, would boost the deployments and could provide increased energy transformation at a global level. Deployment policies need to be taken care of while designing the plant and choosing the site layout. Investments play a critical role and, hence, the long-term, transparent, and secured target gets more attention from the public. The continuous adoption of policies based on the market conditions, implementation of community- and third-party-owned business models for innovative financial programs, and corporate sourcing mitigate the deployment barriers to some extent.

While framing the integration policies, it is essential to incorporate urban plans and construct new buildings that consider the public during the various stages of development, such as site selection, construction, operation, and maintenance of the PV systems. The investment for the installation of PV plants, engaging the people by providing job opportunities at the site, and sharing the economic benefits provides sustainable development of the plant. The government can aim for industrial policies that help economic diversification so that deployment and investment in PV research happens with public support. Creating awareness among consumers, encouraging companies to initiate projects related to PV systems, and development of a competitive atmosphere accelerate the process. Issuing green bonds, carbon pricing, and precious metal retrieval through recycling will help in mobilizing investment in the renewable sector. The government can use financial gains for new deployments, and budget allocation for health, education, and other sectors. The commercialization of technology requires added skill training and scientific knowledge. This addition could be possible with the incorporation of sustainable subjects at the academic degree level, which will facilitate employment as well as provide a skilled workforce for the sector.

The authors would like to thank the director of CSIR–NGRI, Dr. V. M. Tiwari, for permission to publish this book chapter (NGRI/Lib/2020/Pub-183). The authors thank Dr. E. V. S. S. K. Babu for his encouragement and support and also thank him for providing the necessary facilities to complete the book chapter from institutional projects: MLP-6406-28 (EVB) and GEOMET (MLP-0002-FBR-2-EVSSK).