Solar energy has long been touted as better for the environment than fossil fuels. Considered as one of the ‘green’ sources of energy, it has a chance to become mainstream within the next decade. Increasingly, however, there are fears that production of solar cells might release more hazardous pollution than fossil fuels would. Confirming these fears, Chinese authorities recently suspended production at a solar panel factory after protests by residents who blamed the plant for creating air and water pollution. In India, on the other hand, the Union Ministry of Environment and Forests (MoEF), which issues environmental clearances to all projects across the country, has exempted solar photovoltaic (PV) power projects from falling under the ambit of environmental clearances. After all, the reasoning goes, isn’t it ‘cleaner’ to harness the power of the sun? The obvious answer is, “Yes,” but only when the right manufacturing processes are followed.
By Richa Chakravarty
Reasons for pollution
Manufacturing: Solar panel manufacturing generates a number of effluent gases that contain contaminants such as silane, trichlorosilane, dichlorosilane and hydrochloric acid (HCL), apart from producing chemicals like silicon, cadmium compounds, germane and polyvinyl fluoride, all of which are hazardous to the environment and to people who are exposed to them. This manufacturing process also involves raw materials that have to be mined—quartz sand for silicon cells and metal ore for thin film cells. Next, these materials have to be treated at different stages (in the case of silicon cells, these include purification, crystallisation and wafering). Finally, these upgraded materials have to be manufactured into solar cells and assembled into modules. All these processes produce air pollution and heavy metal emissions, and they consume energy which brings about more air pollution, heavy metal emissions and also the release of greenhouse gases. Given the scale at which solar manufacturing is anticipated in India, there is going to be an enormous release of hazardous chemicals and gaseous substances, enough to pollute the environment.
Industry’s response: However, industry experts and researchers have noted that solar cells produce far fewer air pollutants than conventional fossil fuel burning power plants. Making PV cells requires potentially toxic heavy metals such as lead, mercury and cadmium. It even produces greenhouse gases (GHG), such as carbon dioxide, that contribute to global warming. Still, researchers found that if people switched from conventional fossil fuel burning power plants to solar cells, air pollution would cut down by roughly 90 per cent.
According to Raghunandan, vice president, Engineering, Kotak Urja Pvt Ltd, “Solar PV cells record the lowest emission statistics of 32 tonnes per GWhr of electricity generated, which is the lowest of all the conventional and non-conventional energy sources. With coal sources emitting a whopping 960 tonnes per GWhr, solar PV cells stand as the lowest emitter of greenhouse gases among all. These emission figures of the solar industry are only due to the energy consumption during the manufacture of value chain components.”
Research conducted by Brookhaven National Laboratory, New York, recommends cadmium telluride as one of the most promising PV technologies. But cadmium is one of the worst heavy metals. Still researchers found that even when comparing direct emissions from the production of cadmium telluride cells with coal power plants, toxic emissions were 300 times lower.
Several studies have been done to compare GHG emissions of various power generation mechanisms and all have found that renewable sources of power exhibit much less GHG emissions compared to fossil fuels. Wind, nuclear and hydropower have always emitted the least amount of GHG over the lifecycle of electricity generation, PV being next, is still 4–6 times better than coal and gas based systems.
Disposal: The amount of toxic chemicals used to make solar panels that produce solar energy create a potential environmental issue. For solar power to be truly green, industry must reduce and eventually eliminate the use of toxic materials and develop environmentally sustainable practices. Also, manufacturers must take responsibility for the lifecycle impacts of their products by testing new materials and processes, adopting more recycling technologies, and designing products for easy recycling. PV modules, for example, contain substances such as glass, aluminium and semiconductor materials that can be successfully recovered and reused, either in new PV modules or other products.
Despite the volume of waste being small at present, industry has to be cautious in opting for recycling processes in order to prevent environmental damage. PV Cycle, a European voluntary PV recycling initiative, estimates that there will be 35,000 tonnes of PV waste by 2020. However, thankfully, companies like First Solar and SolarWorld have already introduced recycling schemes for thin film and silicon modules.
Industry’s response: Industry experts feel that for thin film technologies, the biggest concern is safe disposal of hazardous materials. However, manufacturers are opting for all the preventive measures to ensure safe disposal as most of them use fluorine based recipes for chemical processes to mitigate GHG emission.
Impact on depleting water resources
The other aspect of environmental degradation by solar power is that vast installations of solar power plants will create immense pressure on already depleting water resources. This is because solar thermal generation requires a large volume of water to cool the steam. Also, water is needed in large volumes to wash solar panels as dust accumulation can affect the efficiency of solar panels, especially in dry areas like Gujarat and Rajasthan. These are states that have not only initiated solar power projects but have also huge installations lined up.
Industry’s response: Experts believe that there is an urgent need to attend to this problem since water is a scarce resource. Thus, there is a need to lay down normative water use and management standards for solar plants.
Solutions to curb PV linked pollution
Though solar cells are far from being a zero emission technology, this does not mean that PV solar energy should not be promoted. Environmental protection is a global concern, thus manufacturers should pay attention to how can they work on reducing or curbing the pollution levels by following international standards and protocols when a system’s total carbon footprint is calculated. Here are a few solutions.
Using the abatement system: Semiconductor, PV and LCD manufacturing processes produce hazardous solid by-products and waste gases, as we have already pointed out. These processes produce a mixture of toxic, reactive, ignitable or corrosive gases. In order to curb environmental pollution, hazardous gases need to be treated before being released into the atmosphere or water systems. There are a wide range of solar cell technologies, in some of which the basic constituent materials are really hazardous. The same may not be applicable for all or other different technologies. The unutilised, non-consumed or unreacted gases (for example, silicon based technology, which uses gas) are passed through an abatement system, which can work with the ‘dry’ or ‘wet’ method. This would help in neutralising the effects of harmful toxic gases.
Explaining the process, Biju PC, manager, sales and marketing, Emmvee Photovoltaic Power Pvt Ltd, says, “In case of the dry process, the flammable gases are burnt with an external supply of gases like LPG or methane and form a non-reactive ash. Here, the product is an oxide of silicon which can be re-used in the brick or glass industry. In case of the wet method, it requires an external aid of other chemicals along with a mixture of water, which forms a non-reactive slurry of silicon oxide. Thus, through these processes other constituent gases also get converted into non-reactive/non-toxic gases with a very minimal quantity of nitrogen oxides. All these are released into the atmosphere following due industrial and pollution control authority norms. Similarly, during the manufacturing process of solar modules, all fumes that are emitted are passed through an abatement system and in the process get neutralised.”
Using solar panels to produce solar panels: A better strategy would be to use already available solar panels to produce more solar panels. Experts believe that the ecological burden of solar panels can be halved if 100 per cent of the energy required by the factories could be delivered by solar power.
Opting for green manufacturing processes: There are various solar companies that fall under the category of ‘zero emission’ and ‘green category manufacturer’, as permitted by the Pollution Board. Emphasises Raghunandan, “We have inhouse generation of solar power to back up the electricity requirements. We do not have any chemical processes involved in our manufacturing. But yes, packing is a major concern and we are working on it to reduce the emissions. For this, we have developed recyclable packing designs, which allow all our packing materials to be recycled 100 per cent. Thus, by improving the packing methods and complying to standards, one can drastically reduce the use of wood and paper.”
Opting for alternative cell technology: Crystalline cell technology has got several alternatives, which are far better than conventional process technologies in terms of GHG emission. Laser assisted processes and dry etching are prominent examples. Laser has become an indispensable tool for thin film PV module production. With most thin film materials, the layer scribing steps required for monolithic integration cannot be performed with the same flexibility and precision using any other process. This is why laser technology has been a key part of thin film development for over two decades. There are several laser based processes which are currently used in solar cell manufacturing or which have a high potential to be implemented in series production in the future. Among these are laser edge isolation, laser fired contacts, metal/emitter wrap-through and laser doping. These technologies come at a cost in terms of capex and also the watt/area produced. Many companies are using these technologies on a commercial scale for volume production.
As more companies begin to develop efficient solar energy collection technologies and higher purity manufacturing systems, the price of solar energy will become more competitive. However, solar energy’s economic and environmental benefits could be wiped out if thin film manufacturers do not design, install and maintain pollution control systems to reduce harmful effluents from the gases released. In such a scenario, we will be only trading one set of problems for another.
Two sides of the coin
There are always two sides to a coin—while solar energy is considered the safest and most cost effective renewable energy, its production process is energy intensive. However, at the cell level, the pollution is very minimal and at the module level the pollution is negligible or near zero. According to industry experts, overall, emission per tonne is the lowest among all the energy sources.
Opines Raghunandan, “If civilisation has to move into the 22nd century, the 21st century has to be the century of clean power. Else, we will all see devastation in the next 50 years. It is better to invest in solar power before we run out of fossil fuels.” As per recent estimates, coal availability on a global average is expected to last only 60 years. The switch to solar energy is inevitable, so as to save this planet and leave a cleaner world for future generations.
MoEF notification welcomed by solar players
The Ministry of Environment and Forests (MoEF) notification in May 2011 has clarified that no environmental clearance is required for solar PV power projects. The notification came in after the Ministry of New and Renewable Energy (MNRE) took up this issue with MoEF.
The notification stated that solar PV power projects are not covered under the ambit of EIA notification, 2006, and no environment clearance is required for such projects.
Although the environmental experts are concerned about this move, solar players have all the reasons to rejoice. In the absence of such clearance, banks or other financial institutions have always been apprehensive about lending to these developers. Hence, the industry has welcomed this clarification, as it will help developers to get funding as well as complete their projects in time. However, projects coming up in forest areas will have to apply for forest clearance from MoEF.
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