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Image Credits: shutterstock.com/Jenson
At present solar cells generate about 1.7 percent of the world’s power. Significant improvements have taken place in the materials used and the production processes. However, some environmental challenges persist, which must be overcome before solar energy may be used to represent a source of truly clean energy.
Most environmental issues with solar power stem from the production process. This begins with quartz mining and refining to metallurgical-grade silicon, involving the high consumption of fossil fuel. Further refinement involves the use of hydrochloric acid, and the final products include liquid silicon tetrachloride and polysilicon. Each ton of polysilicon is manufactured at the cost of three to four tons of these poisonous byproducts.
Silicon Production – Ecofriendly?
In most cases, however, silicon tetrachloride is recycled to polysilicon, a more energy-efficient method of silicon production than obtaining silicon from raw silica. This equipment costs million of dollars, which has led to many operators choosing to discard the silicon tetrachloride instead. When silicon tetrachloride is exposed to water it releases hydrochloric acid which causes acidification of soil as well as the emission of toxic fumes. This problem can be solved, by using the right recycling facilities. In the future, with the use of ethanol rather than chlorine-based compounds as the source of polysilicon, it may well be a non-issue.
Semiconductor Cleaning
Toxic chemical compounds are used to clean the semiconductor wafers that make up the photovoltaic (PV) cell. These include hydrofluoric and sulfuric acid. This cleaning step is essential to remove damage and produce the right surface texture. However, hydrofluoric acid is deadly to an unprotected individual, being capable of corroding tissue and decalcifying the bones. It needs to be handled and disposed of with extreme care. The use of sodium hydroxide instead is a potentially safer alternative, since it can be treated and disposed of more easily, and poses lower health risks to workers.
Toxic Chemicals
In addition, some materials used to build the solar cell, such as gallium arsenide and cadmium telluride need careful recycling, to avoid contamination of the environment. However, these are rare and relatively costly, which gives manufacturers a financial impetus to recycle them. Another option is to use zinc sulfide rather than cadmium sulfide in thin film PV cells.
Another hazard is the production of silicon dust during the manufacturing process, which is regulated by law. Lead content in the solder is a further source of pollution if these products are sent to the landfill or for incineration, but many manufacturers are considering the use of lead-free solder.
Many of these issues can be obviated by switching to thin-film solar cell technology, using semiconductor layers deposited on a glass substrate (or on metal or plastic). This prevents the need to cut silicon ingots into wafers, thus avoiding waste, and bypassing the processing required to make a conventional PV cell, such as melting, drawing and slicing. Instead, one glass plate enters the process at one end and leaves the other end of the process as a full-fledged PV cell.
Land Use
Another set of issues has to do with land use for solar energy production. While rooftop solar panels are capable of producing power enough for the building on which they are installed, this is not the case when solar energy is generated on a large scale as is required for a power utility. Here the inefficiency of solar energy collection makes excessive land use a must. In most cases up to 10 acres of land must be covered with solar panels to generate a single megawatt of power. When this extent of land must be made available by clearing forest, or virgin territory, wildlife is likely to be impacted by the loss of habitat, while the soil quality also suffers from the rooting out of plants. These long-range environmental impacts must be taken into account while assessing the cost of the installation and the generated power.
Excessive Water Use
Water use is also significant, since water is required to cool the plant, during the processing of various components, and control of air pollution, besides cleaning during solar panel installation and use. Yet this water utilization is much lower than the amount required to cool energy plants based on fossil fuel or nuclear power.
Is Solar Power Generation Worth It?
Another issue involves the relative shortfall of energy production when the power required to manufacture solar power components and that generated by the solar power plant is compared.
The majority of PV plant equipment is supplied using fossil fuel-based power generation, which is linked to greenhouse gas emission and the production of other environmental pollutants.
More pollution occurs during the transportation, installation and maintenance of the equipment. Finally, disposing of panels once their useful life is over poses a tremendous challenge and legislation must be put in place to ensure manufacturer responsibility for taking back and safely disposing of these products.
However, the greenhouse gas emissions linked to solar power generation at all stages is estimated to be less than 0.2 pounds of carbon dioxide equivalent per kWh power (CO2E/kWh) generated. This is very low compared to the 0.6 pounds CO2E/kWh that is produced by natural gas, and up to 3.6 CO2E/kWh released with coal, over its lifetime. Finally, the energy used to generate solar energy is usually paid back within six months to two years.
Will Newer Developments Solve the Problem?
Newer technologies like single-walled carbon nanotube (SWCNT) PV cells which have 28 percent efficiency in solar energy capture can reduce environmental impacts compared to monocrystalline silicon. These tubes, however, are likely to disperse in the environment at any stage in their lifecycle, and may then bind heavy metals like uranium in the neighborhood. As they are very small, they may form colloids with water, which then pass through the soil into water and even into biological systems, causing negative health impact.
For many reasons, therefore, the effects of solar energy on the environment must be carefully assessed when a solar power plant is to be set up. The overall impact of increasing solar energy use is likely to be positive based on the current state of knowledge.
Sources and Further Reading
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