Effects of solar photovoltaic technology on the

Effects of solar photovoltaic technology on the environment in China

Liqiang Qi & Yajuan Zhang

Environmental Science and Pollution Research ISSN 0944-1344 Volume 24 Number 28 Environ Sci Pollut Res (2017) 24:22133-22142 DOI 10.1007/s11356-017-9987-0

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Author's personal copy Environ Sci Pollut Res (2017) 24:22133–22142 DOI 10.1007/s11356-017-9987-0

REVIEW ARTICLE

Effects of solar photovoltaic technology on the environment in China Liqiang Qi 1 & Yajuan Zhang 1

Received: 7 February 2017 / Accepted: 21 August 2017 / Published online: 31 August 2017 # Springer-Verlag GmbH Germany 2017

Abstract Among the various types of renewable energy, solar photovoltaic has elicited the most attention because of its low pollution, abundant reserve, and endless supply. Solar photovoltaic technology generates both positive and negative effects on the environment. The environmental loss of 0.00666 yuan/kWh from solar photovoltaic technology is lower than that from coal-fired power generation (0.05216 yuan/kWh). The negative effects of solar photovoltaic system production include wastewater and waste gas pollutions, the representatives of which contain fluorine, chromium with wastewater and hydrogen fluoride, and silicon tetrachloride gas. Solar panels are also a source of light pollution. Improper disposal of solar cells that have reached the end of their service life harms the environment through the stench they produce and the damage they cause to the soil. So, the positive and negative effects of green energy photovoltaic power generation technology on the environment should be considered. Keywords Solar photovoltaic . Environmental benefit . Environmental problem . Pollution charge

Introduction Energy problems continue to restrict economic growth; presently, the main global energy sources, such as coal, oil, and Responsible editor: Philippe Garrigues * Liqiang Qi [email protected]

1

Environment Science and Engineering School, North China Electric Power University, Baoding 071003, China

natural gas, provide non-renewable energy (Xu et al. 2010). Fossil fuel, including coal, oil, and natural gas, is a limited resource (Shafiee and Topal 2009). Non-renewable energy is becoming increasingly scarce and is subject to strict environmental standards. Thus, efficient methods of using renewable energy are being developed globally (Fan 2011). Solar energy, which is abundant, inexhaustible, widely distributed, and pollution-free, has been eliciting considerable attention (Dehghan et al. 2014 and Rath and Marder 2007). The application of solar energy is represented by solar photovoltaic technology. This technology employs abundant solar energy and involves a safe and clean power generation process (Slocum et al. 2011). The extensive application of this technology can effectively reduce the greenhouse effect (Huang 2010). Solar photovoltaic has many advantages, such as low cost of equipment operation maintenance, absence of regional restrictions on installation, and low cost of transmission lines (Theocharis et al. 2005). The proportion of solar energy in the energy structure remains low throughout the world (Rath and Marder 2007), but the future goal is for renewable energy, represented by solar energy, to gradually replace traditional fossil fuel (Espey 2001 and International energy agency 2010). The photovoltaic (PV) has been one of the best renewable energy sources, having the least negative impacts on the environment (Solangi et al. 2011; Santos et al. 2014; Ndiaye et al. 2014; Verso et al. 2015; Moosavian et al. 2013). Governments have established a series of laws and regulations to support the solar industry, and scientific workers are pursuing a more efficient and economical solar photovoltaic technology with the aim to increase the proportion of solar photovoltaic in the energy structure (Elizabeth et al. 2011and European Commission 1999). However, the negative effects of solar photovoltaic technology have not been considered sufficiently and even ignored. The process of solar photovoltaic produces waste gas (Turconi 2013), which is difficult to eliminate, and wastewater

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pollutions (Kaygusuz 2009, Kang 2011 and Xiong et al. 2010). A solar photovoltaic system that has exceeded its useful life becomes waste that pollutes the environment. The source of pollution in a coal-fired power plant is mainly the process of power generation. By contrast, solar photovoltaic technology mainly involves the process of producing photovoltaic modules (Piemonte et al. 2011); the volume of waste emissions from generating photovoltaic modules is less than that from coal- and oil-fired power plants.

Environmental benefits of solar photovoltaic technology Advantages of solar photovoltaic technology The largest source of greenhouse gas emissions in China is coal-fired power plants. Therefore, reducing the number of coal-fired power plants and increasing the proportion of renewable energy would significantly mitigate global warming and effectively reduce greenhouse gas emissions (Zhang et al. 2012). Coal-fired power generation produces large amounts of ash, dust, sulfur dioxide, nitrogen oxide, carbon dioxide, and other pollutants, and waste gas must be processed before emission (You and Xu 2010; Wojdyga et al. 2014). Filters can remove dust, but a dust collector consumes large amounts of auxiliary power, and the equipment investment is large. Coal-fired power plants employ the mainstream technology of wet limestone–gypsum method to remove sulfur dioxide. However, the method consumes large quantities of limestone and produces sulfur-containing wastewater and a large amount of gypsum solid waste (Feng et al. 2014). The cost of nitrogen removal is also high (Sun et al. 2014), and the current technology is not yet mature. In addition, decarburization measures are currently unavailable. Coal-fired power plants produce large amounts of carbon dioxide and carbon monoxide into the atmosphere daily. Flue gas emissions that conform to standards could still contain a small amount of pollutants. Flue gas that accumulated over a long period has negative effects on the atmosphere and should not be ignored. Environmental pollution caused by coal-fired power plants is a serious issue. The raw materials required in thermal power generation using coal resources are becoming increasingly scarce. Thus, the use of solar energy as a new type of energy is being developed worldwide. Water and fossil fuel are not utilized, and pollution is not produced in the process of power generation through solar photovoltaic technology. Thus, a significant amount of capital for environmental protection is saved. Furthermore, solar photovoltaic technology does not involve mechanical rotation without auxiliary power and does not produce noise pollution (Fu and Cai 2009). This technology can also be utilized independently without a grid connection. Wires, telephone poles,

Environ Sci Pollut Res (2017) 24:22133–22142

and transmission facilities are not required, installation costs are reduced, and the technology can be operated in any suitable location. Solar photovoltaic components installed on the roof of a metope can be utilized as building materials. Consequently, the use of construction materials is minimized, the construction cost is reduced, and environmental protection is improved. Solar PV is the direct conversion system that converts sunlight into electricity; it does not need the help of machines or any moving devices. It is an inexhaustible energy source (Parida et al. 2011; Hosenuzzaman et al. 2015). Solar photovoltaic equipment can be installed on roofs, desert areas, and remote areas and is not subject to regional restrictions (Chen 2014; Grossmann et al. 2013). Therefore, land resources can be utilized for other meaningful projects. A thermal power plant is usually built near a downtown area to save on electricity transmission, but its presence adversely affects the environment. Strong wind power has geographical limitations, and biomass power generation requires considerable land space. Hydroelectric power causes hundreds of square kilometers of land to be submerged and thus destroys the ecological environment (Guarino et al. 2012). Solar photovoltaic technology provides clean energy and does not cause land, environmental, and ecological problems. Solar photovoltaic technology provides clean renewable energy; does not cause land, environmental, and ecological problems; and conforms to the concept of sustainable development unlike traditional power generated by coal-fired power technology.

Comparison of environmental losses Solar photovoltaic technology, a clean power generation technology, also discharges pollutants into the environment (Sun et al. 2011). To measure the cost of greenhouse gases and pollutants, we apply previous results from studies (Zhang et al. 2012) using the damage cost method to estimate life cycle cost. Not surprisingly, results vary widely among different studies. The Energy Research Institute in China carried out a study to estimate the cost based on the results from the World Bank and EU separately. The study revealed large differences by an order of magnitude. For example, the cost of SO2 varies from 1000 to 100,000 yuan/t (Gao 2010). Therefore, we choose a more reliable and relatively lower estimation from the Ministry of Environment Protection and the National Statistics Bureau as a reference for our policy study (2004 green GDP accounting of China). The average damage costs of typical pollutants under solar photovoltaic and coal power generation technologies, respectively, in China are shown in Tables 1 and 2. The environmental damage caused by solar photovoltaic and coal-fired power is shown in Fig. 1.

Author's personal copy Environ Sci Pollut Res (2017) 24:22133–22142 Table 1 Solar power damage to the environment

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Pollutants

Environmental value (yuan/kg)

Emissions(g/kWh)

Environmental damage (× 10−3 yuan/kWh)

References

CO2

0.023

64.35

1.48

Sun (2004); Zhang et al. (2012)

SO2

6.320

0.32

2.02

Zhang et al. (2012)

NOx

6.320

0.17

1.07

Zhang et al. (2012)

CO

0.360

0.01

0.004

Sun et al. (2011)

TSP

2.750

0.09

0.25

Zhang et al. (2012)

Ash

0.300

5.00

1.50

Sun et al. (2011)

Residue

0.250

1.36

0.34

Sun et al. (2011)

Total

6.66

For greenhouse gases, we set the damage cost of CO2 equivalent to 0.023 yuan/kg, according to some relevant studies (Wei and Zhou 2003). For CO, ash, and residue, we set the damage cost as 0.36, 0.30, and 0.25 yuan/kg, according to some relevant studies (Sun et al. 2011 and Sun 2004). Charge standard calculation method using the state development planning commission of the People’s Republic of China promulgated on February 28, 2003 the Bdischarge levy standard management method^. Environmental value is equal to the ratio of charge standard and compensation rate. The environmental cost of sulfur dioxide is 6.00 yuan/kg in the pollutant standards of the electric power industry (Sun 2004). The rate of carbon dioxide in the national pollution charge standard is 0.632 yuan/kg. The compensation rate of the environmental value is approximately 10%. So the compensation rate in Table 3 was calculated at 10%. From Tables 1 and 2, the total environmental damage caused by solar photovoltaic technology is 6.66 × 10−3 yuan/kWh, and the total environmental damage caused by coal-

Table 2 Coal-fired power damage to the environment

fired power generation technology is 52.16 × 10−3 yuan/kWh. This result indicates that although solar photovoltaic causes environmental damage, the effect is less than that of coal-fired power generation technology. Therefore, solar photovoltaic technology contributes to a sustainable environment. The environmental cost of solar photovoltaic generation is less than those of coal power, gas power, nuclear power, hydropower, biomass power, and other power generation technologies; its impact on the environment should be considered. A positive approach is required to develop a more reasonable method that minimizes the adverse effects of solar photovoltaic technology on the environment and for solar photovoltaic technology to be utilized as soon as possible.

Problems in the process of solar photovoltaic Solar cells include monocrystalline, polycrystalline, and amorphous silicon solar cells.

Pollutants


Emissions (g/kWh)

Environmental damage (× 10−3 yuan/kWh)

References

CO2

0.023

1024

23.55

Sun (2004);

SO2

6.320 6.320 0.360 2.750

0.59 0.80 0.12 0.19

3.73 5.06 0.04 0.52

Zhang et al. (2012) NOx CO TSP

Sun (2004) Sun (2004) Sun (2004) Zhang et al. (2012); Sun (2004)

Ash Residue Total

0.300 0.250

52.29 14.26

15.69 3.57 52.16

Emissions of SO2 and NOx are the value after desulfurization–denitration treatment

Sun (2004) Sun (2004)


Environ Sci Pollut Res (2017) 24:22133–22142 25

VRODUSRZHU FRDOILUHGSRZHU

20 15 10

Residue

Ash

TSP

CO

NOX

SO2

0

CO2

5

The production rate of silicon trichloride is low, and plenty of poisonous silicon tetrachloride by-products, as well as hydrogen chloride and chlorine gas, are produced. Solar photovoltaic equipment production causes wastewater and air pollutions. Many photovoltaic enterprises have adopted a simple pollution treatment technology because of the processing cost and technological level restrictions involved. Several small businesses discharge pollutants directly without treatment. Wastewater pollution

Fig. 1 Environmental damage (× 10−3 yuan/kWh)

Polycrystalline silicon solar cells are widely utilized because of their photoelectric conversion efficiency and cost factors. This article mainly discusses the environmental impact of polycrystalline silicon solar cells. The pollutant emission process is shown in Fig. 2.

Environmental impact of the production of solar photovoltaic equipment The production of solar photovoltaic equipment includes manufacturing crystalline silicon, producing solar batteries, and assembling a solar photovoltaic power generation system. Crystalline silicon enterprises, which account for a large portion of the photovoltaic industry, cause serious environmental problems. These enterprises consume large amounts of energy, cause high pollution, and involve a low level of repeated construction. Polysilicon production technologies mainly include the Siemens, improved Siemens, and silane pyrolysis methods. In the domestic production of polysilicon, enterprises mostly adopt the Siemens or improved Siemens method. Improved Siemens method involves the conversion of silicon metal into silicon trichloride; silicon trichloride is then restored into polysilicon through hydrogen reduction.

The production of crystalline silicon solar cells involves the use of chemicals, such as acid and alkali, phosphoric acid, hydrofluoric acid, and sodium hydroxide. These chemicals are then utilized for silicon wafer surface corrosion, velvet preparation, and other processes to remove phosphorus silicon glass (Yu et al. 2008). The use of chemicals inevitably produces alkali and organic wastewater that contain fluorine and silicon-containing chromium. Wastewater contains high concentrations of suspended solids. Currently, precipitating agents and flocculants can dispose wastewater that contains fluorine. Chemical and biological methods can remove the most toxic and harmful substances in the treatment of wastewater sewage. However, residuals could remain in sewage treated by silicon and fluorine materials. Although the pollutant concentration rate in processed sewage is extremely low, the pollution caused should not be ignored just because the crystalline silicon solar cell industry is booming. Polluted wastewater containing chromium and fluoride is discussed below. Moreover, wastewater will be produced because panels have to be cleaned with water to maintain performance. Wastewater that contains chromium mainly consists of hexavalent and trivalent chromium compounds. The toxicity of hexavalent chromium is 100 times higher than that of trivalent chromium (Jin 2008a, b). Chromium inhibits the growth of crops, and using wastewater that contains

Table 3 Environmental value Pollutants

Pollutant equivalent charge standard (yuan)

Pollutant equivalent value (kg)

Charge standard (yuan/kg)


SO2 NOx CO TSP Ash

0.60 0.60 0.60 0.60 –

0.95 0.95 16.70 2.18 –

0.632 0.632 0.036 0.275 0.030

6.320 6.320 0.360 2.750 0.300

Residue

–

–

0.025

0.250

Charge standard calculation method using the state development planning commission of the People’s Republic of China promulgated on February 28, 2003 Bdischarge levy standard management method^; environmental value = charge standard/compensation rate

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Fig. 2 Pollutant emission process

Wafering

Cleaning

exhaust

Texturing

HFǃNOX

Phosphorus diffusion

Cl2ǃHCl ①

Plasma etching

HFǃCO2 ǃ SiO2 ②

Wastewate

H+ǃF ˉ

ˉ

2-

NO3 ǃCrO4

Remove phosphorus silicate glass

plate antireflection coating

SiH4ǃNH3ǃH2 borane silane ③

screen printing

organic waste

contacting

chromium to irrigate farmlands reduces crop yield and hardens the soil (Gupta et al. 2010). Chromium accumulates in plants and enters the bodies of animals and humans through the food chain. Hexavalent chromium in the body can cause diseases, such as rhinitis, respiratory ailments, digestive tract disorders, and corrosion of the skin and internal organs (Smith 2010). Chromium contained in wastewater is a dangerous pollutant that can enter the body through air, food, and water (Tan 2003). The maximum allowable concentration of total chromium according to drinking water regulations is 0.05 mg/L; the maximum allowable concentration of hexavalent chromium is 0.01 mg/L (Zhang 2000). Long-term drinking of water that contains chromium causes skin cancer. The treatment

HFǃNOX

①4POCl3 + 3O2 → 2P2O5 + 6Cl2↑ 2P2O5 + 5Si → 5SiO2 + 4P↓ ②SiF4 + 2H2O → SiO2 + 4HF ③3SiH4 + 4NH3 → Si3N4 + 12H2↑

methods for wastewater that contains chromium include physical, chemical, and biological methods; chemical precipitation is one of the most widely used methods (Xia and Fu 2012). However, chemical precipitation generates hazardous waste sludge produced by hair waste. The process is also complex and expensive, and improper handling can cause secondary pollution. Wastewater with fluoride mainly originates from silicon cleaning and silicon battery production. Several enterprises, in their pursuit of economic benefits, discharge silicon directly and ignore the national integrated wastewater discharge standards of fluoride wastewater (primary and secondary fluorine concentration emission cap of 10 mg/L) (Wu 2012). Fluorine


can enter the body through drinking water. Potable water standards require that the fluoride content be less than 1 mg/L (Ma and Hu 2011); long-term exposure to high levels of fluoride causes serious health issues (Balasubramanian and Umarani 2012), including dental fluorosis, osteoporosis, bone sclerosis, skeletal fluorosis, and tumor development (Lei et al. 2012). Fluoride in wastewater must be treated before discharge to meet the national discharge standards. Waste gas pollution Pile system and the production of phosphorus silicon glass produce acid gas, such as hydrogen and nitrogen oxides. Phosphorus diffusion diffuses waste gas represented by chlorine gas, including hydrogen chloride gas. Plasma etching produces etching waste gas, including hydrogen, carbon dioxide, and silica. The plasma-enhanced chemical vapor deposition (PECVD) process produces PECVD waste gas, which is mainly composed of hydrogen and nitrogen, without the reaction of borane and silane fetor. Silkscreen printing and sintering produce printing and sintering waste gas. Examples of gas hazards include chlorine, hydrogen chloride, and hydrogen fluoride. Silicon tetrachloride produces caustic and toxic colorless or light yellow liquid smoke and is deliquescent. It is a hazardous waste, and indiscriminate dumping of this waste can severely pollute the surrounding water, soil, and air. Dumping silicon tetrachloride on soil could leave the soil bare, and exposure to low concentrations of this hazardous waste could cause diseases. Silicon tetrachloride in damp air generates silicate and hydrogen chloride (Chen et al. 2010). Numerous local and international companies utilize silicon tetrachloride to generate fiber, organic silicon compounds, and white carbon black. Several enterprises implement silicon tetrachloride reduction to generate original polysilicon chemical hydrogen silicon (Ye 2010 and Ivanov and Trubitsin 2011). The issue of silicon tetrachloride processing has yet to be resolved because of market demand limitations and cost constraints. The current treatment technology for silicon tetrachloride recycling is still in its infancy stage, and the recycling cost is high. The problem of processing silicon tetrachloride has become a technical bottleneck in the development of photovoltaic power generation technology. Chlorine is one of the important pollution control means in China. Chlorine is a yellowish green gas with a strong excitant odor and lively, strongly oxidizing, corrosive chemical properties (Li et al. 2007). Chlorine in water generates strongly corrosive hydrochloric acid and hypochlorite that cause equipment corrosion (Hu 2005). Chlorine is extremely harmful, and the general factory chlorine content must not exceed 1 mg/m3. Low concentrations of chlorine gas can endanger human health and affect the growth of plants and animals (Sanchez 2013). The interaction between chlorine and carbon monoxide


generates toxic phosgene. Mixing chlorine gas with combustible hydrocarbon ether produces an explosive mixture. Polysilicon companies adopt the comprehensive utilization of chlorine by mixing chlorine and hydrogen to generate hydrogen chloride gas and allowing hydrogen chloride gas to react with silicon dioxide to manufacture polysilicon materials with hydrogen–silicon. However, cost and secondary pollution problems must be considered in the comprehensive utilization of such material. Hydrogen chloride is a colorless gas with an irritating smell and often forms a hydrochloric acid fog (Ding 1997). Hydrochloric acid mist with a strong corrosive effect corrodes metal equipment and building surfaces (Cha and Wolpert 2002). Its corrosion damage on cultural relics is worrisome. Trace amounts of hydrogen chloride cause coughing and bosom frowsty in humans, and exposure to more than 1000 ppm of hydrogen chloride would endanger people’s lives. Hydrogen chloride corrodes plant leaves, turns leaves into yellow, and causes plants to wither and die. Hydrogen chloride is extremely dangerous. A practical recycling method that can not only reduce the damage to the environment but also save resources and generate economic benefits should be developed. Hydrogen fluoride waste gas, a type of acid gas produced by the production of fabrics with soft nap, is one of the main pollutants in the atmosphere. When hydrogen fluoride comes into contact with water vapor, a strong acid or hydrofluoric acid is formed. Hydrofluoric acid corrodes bare buildings and has an extremely strong corrosion effect on silicate materials (Mikeska 2000). Hydrogen fluoride can also affect human health and destroy the ecosystem (Ahmad et al. 2012; Fornasiero 2001). Borane and silane are flammable substances that can cause explosion in air. Borane is highly toxic and ignites easily when it comes into contact with oxidants, such as oxygen and halogen. The chemical property of silane is that it is highly active; this substance can spontaneously ignite even at small amounts. Therefore, PECVD exhaust gas is extremely unsafe. Waste gas from the production of solar cells requires a purification treatment to meet emission standards. Acid diffusion and etching waste gases can be processed with an acid mist purification tower (lye-spraying exhaust). A silane burn tower is available for PECVD waste gases, such as silane and borane; boron trioxide, water vapor, and silica are produced after burning. Post-combustion matter requires filter processing. Printing and sintering waste gases can be treated through activated carbon adsorption and adsorption processing with silica gel or a molecular sieve. Other forms of pollution Producing photovoltaic solar panels requires the use of numerous solar PV glass. The significant characteristics of the glass


industry include high energy consumption and high pollution. Glass is manufactured by heating, melting, and cooling raw materials, such as quartz sand, soda ash, feldspar, and limestone (Li 2005). Powder materials can cause dust pollution during processing; thus, many glass factory workers suffer from silicosis (Leung 2012). Glass production generates harmful gases, such as sulfur dioxide, nitrogen oxide, and hydrogen fluoride, and several types of wastewater, including acidic wastewater and wastewater containing phenol, tar, fluoride, and heavy metals (Zhao 2006; Xing 2000). The emission of these pollutants is directly related to human health problems. PV glass must be of good light-admitting quality; thus, leaded glass is utilized. However, lead can enter and harm the human body. Glass production also inevitably produces noise and solid waste pollutions. The production of solar photovoltaic equipment causes other forms of pollution. The machinery and equipment utilized in the production process create noise pollution. Manufacturers can utilize low-noise equipment or noisereduced equipment with acoustic isolation to reduce noise pollution. The production process inevitably produces many forms of solid waste, which should be recycled or delivered to appropriate departments for proper processing and disposal. Solar photovoltaic power generation systems in installation/ construction and operation stages affect the local ecological environment and natural landscape (Frantzeskaki et al. 2002; Gekas et al. 2002). Problems in the solar photovoltaic process Light pollution from solar photovoltaic equipment Most people ignore the light pollution caused by solar photovoltaic equipment. To improve the strength of a photovoltaic device, the photoelectric conversion element should be protected, and good permeability to light must be achieved. The surface of photovoltaic modules requires super white glass with a thickness of 3.2 or 4 mm (Xiong 2012). Photovoltaic glass produces a reflection effect with light reflectivity of approximately 4%, and its reflectance is maximum for infrared light with a wavelength greater than 1200 nm (Wang 2012). Reflected light on the surface of the glass causes light pollution. Light pollution can affect ecological balance. Light pollution caused by photovoltaic components can lead to an extremely high local temperature, which in turn generates indirect heat pollution. Moreover, light pollution could affect the physical and mental healths of people. Its impact is mostly on the human eye, and its influence on psychological health is minimal (Xie 2013). If PV modules are installed on the side of a road at an inappropriate installation height and angle, the reflected light will directly meet the eye and affect the vision of drivers on the road. As a result, the probability of a traffic accident will increase. Therefore, the

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abovementioned problems must be considered in the design and installation processes. Light pollution has become increasingly prominent in modern society and has elicited considerable research attention; however, no unified standard on detection technology exists, and effective management and preventive measures are lacking (Li et al. 2013). Research institutions can address light pollution problems caused by solar panels by studying low-reflectivity photovoltaic glass. In addition, solar panels can affect the Earth’s exposure to light and thus indirectly affect the atmosphere. Panel recycling is an option, and that is already the practice with some PV technologies such as CdTe panels (Cyrs et al. 2014; Rocchetti and Beolchini 2015). High power generation cost of solar photovoltaic technology Although the operating cost of solar photovoltaic technology is low, the cost of electric power generation is higher than the cost of coal-fired power generation because of the large initial investment and low power generation efficiency in many areas (Yahyavi et al. 2010). Although the cost of solar photovoltaic declines yearly, photovoltaic power generation has a disadvantage in terms of price compared with conventional energy or other clean energy power generation technologies. Solar photovoltaic has not been widely utilized mainly because of the high electricity cost involved. Compared with traditional energy, solar energy has less impact on the environment. The global energy crisis also makes the application of solar photovoltaic technology particularly important. Different countries are actively searching for means to reduce the cost of solar photovoltaic to utilize this technology as comprehensively as possible. Considering that silicon prices account for a large proportion of the cost of a solar photovoltaic system, reducing the price of silicon will substantially reduce the power generation cost. An advanced technology can be adopted to reduce the processing cost of silicon materials (Yaws et al. 1980), and thin silicon can be utilized to produce solar modules and consequently reduce the cost of power generation. A scientific and advanced solar photovoltaic technology developed through extensive research will reduce costs year by year (Dereli et al. 2013). However, the thermal power cost increases yearly as coal production decreases. The costs of solar and thermal powers are expected to reach the maximum by 2017 (Ma et al. 2010), and the proportion of solar photovoltaic generation will continue to increase in the field of electric power. Problems on waste solar batteries The lifespan of solar photovoltaic equipment is approximately 20 years, and a solar component that has exceeded its lifespan becomes solid waste. Several parts are considered dangerous


solid waste and potentially harmful to the environment; however, the environmental impact is difficult to measure. If silicon, lead, cadmium, phosphorus, and flame retardants are not reasonably treated or recycled, these compounds will generate an adverse effect on water, soil, air, and human health (Ni et al. 2014). Currently, the handling of waste solar photovoltaic equipment lacks an organized system. Traditional processing methods, such as burning of electronic products and extraction processes, may cause severe secondary pollution (Huang et al. 2009). The composition of solar cells is similar to that of electronic products; thus, the environment surrounding the areas where these electronic products are manufactured is in a poor state. The soil is barren, and water is undrinkable and unsuitable for irrigation. Many types of poisonous and harmful materials exceed air standards, and the pollution caused is irreversible. Garbage is a resource at the wrong time and place, and waste solar photovoltaic equipment is no exception. Adopting appropriate methods of recycling useful resources, such as heavy metals, plastic, and glass, can not only reduce environmental pollution but can also generate certain economic benefits. Most photovoltaic devices require a storage battery with a short life (Glavin et al. 2007). Battery pollution has been fundamentally solved; the remaining environmental problem to be addressed is reasonable recycling of waste batteries. Participants in the recycling of waste batteries are mainly self-employed individuals and small factories that have low environmental protection awareness. If governments do not establish strict recycling mechanisms, the personnel involved in the process of recycling waste batteries could cause serious secondary pollution to the environment under the lure of economic benefits. Lead pollution is the leading cause of waste battery pollution (Lee 2012). Only a quarter of lead batteries are recycled, and those that are not recycled pollute the air, water, soil, and food. Lead is a highly toxic substance that can enter the human body through the respiratory system, digestive system, and the skin. Exposure to excessive amounts of lead can reduce the body’s immunity and affect intelligence; it also poses a serious threat to children. Lead is non-biodegradable, and its presence in the food chain can harm humans. Therefore, advanced technology and equipment must be established to improve battery production and recycling. Governments should also implement strict policies for the battery industry to protect the environment. To standardize and rationalize the waste recycling of solar photovoltaic equipment and reduce the negative effects on the environment, recycling units should improve their environmental protection consciousness and attempt to be a socially responsible enterprise. The government should create policies that support and guide the development of solar photovoltaic.


It is worth mentioning that the last generation of photovoltaics, which has reached competitive performances in comparison to silicon, could solve most of the environmental problems (Parisi et al. 2014; Bravi et al. 2011).

Conclusion and suggestions The positive and negative aspects of solar photovoltaic technology, a novel technology, should be comprehensively considered. Solar energy is abundant, and its depletion is unlikely. The generation of solar photovoltaic systems does not cause any type of pollution and requires no energy consumption. Solar photovoltaic is not subject to regional restrictions; thus, land resources can be saved. However, non-green issues also exist in green solar energy technology. The production of solar photovoltaic equipment produces wastewater, waste gas, and solid waste. The recycling system for solar equipment that has reached their life expectancy does not have a reasonable mechanism. Indiscriminate disposal of such equipment can seriously pollute the environment. To make solar energy a real green energy, the following aspects should be considered: 1. Improving the environmental protection consciousness and capacity of independent innovative enterprises, actively developing green production technology, and reducing pollution in the process of producing solar photovoltaic equipment; 2. Processing pollutants in strict accordance with pollution emission standards to reduce environmental damage; 3. Increasing the penalties for pollutant emission and shutting down enterprises with extremely high pollution levels; 4. Improving the mechanism of waste solar battery recycling; and 5. Establishing reward systems for individuals who contribute to environmental protection. The current environmental and cost-related problems in solar photovoltaic technology can be resolved with the development of science and technology. Renewable energy represented by solar energy power generation technology will dominate the future energy structure because of several factors, including increasingly scarce fuel sources, strict environmental standards, increased government support, reduced cost, and unlimited resources. Acknowledgements This work was supported by the National Natural Science Foundation of China (Grant No. 21376072) and the Fundamental Research Funds for the Central Universities (Grant No. 2017MS140).


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