Solar Energy

PV cells

  • Hydrofluoric acid: Manufacturers rely on hydrofluoric acid to clean the wafers, remove damage that comes from sawing, and texture the surface to better collect light. Hydrofluoric acid is a highly corrosive liquid which requires extreme care when handling, and it must be disposed off properly.
  • Silver: The point of concern in the manufacture of solar panels is that the silver content used in the module is leftover and is considered a dangerous waste. Silver salts and silver itself are very harmful to human body, causing damage to multiple organs or even death. Producing these panels in high quantities could also lead to the depletion of silver resources. According to scientist G.J.M. Phylipsen’s book Environmental Life-cycle Assessment of Multicrystalline Silicon Solar Cell Modules, a PV contribution of five percent of the current world electricity production would require about fifty percent of current silver production.
  • Volatile organic compounds: Extra cares should also be taken to prevent accidental emissions of Tetrafluoromethane (CF4) as well as solvents and other volatile organic compounds during the various manufacturing steps of panel i.e. fluoride nitrate, sulphur dioxide (SO2) which is toxic to humans, CO2 which affects global warming and isopropanol and solvents which support photochemical ozone formation at the ground level and are also toxic to humans.
  • Land: Large scale of land are required to install a solar farm, and it is usually done by clearing land, which in turn affects native vegetation and wildlife in numerous ways and has an adverse ecological impact and can affect the rainfall and the drainage of a region. In space constrict place like Singapore, whereby land itself is a very precious resource, such installation have to be carefully planned and carried out.
  • Water: Parabolic troughs and central tower systems use steam plants to generate electricity, which generally use water for cooling. Increase in water demand can strain available water resources, which water is another precious resource that are very costly to produce despite surrounded by sea. While the use of chemicals at solar facilities i.e. dust suppressants, dielectric fluids, herbicides could result in contamination of surface or groundwater and also impact soil, water and air resources.
  • Silicon Dioxide: While solar energy can be generated using a variety of technologies, the vast majority of solar cells today start as quartz, the most common form of silica (silicon dioxide), which is refined into elemental silicon. The quartz is extracted from mines, putting the miners at risk of lung disease silicosis.
  • Polarized light pollution: A concentrated beam of light may injure or kill birds and insects that come into contact with it.
  • Low efficiency: Organic solar cell only converts 12-15% of the sunlight power into electricity
  • High initial costs: The cost of starting up solar technologies, especially those using PV panels, is relatively high, which means the cost of electricity is higher than that derived from fossil fuels, at least at first. All costs must be paid at the start, when the technology is installed. That said, improved technologies and increased use of PV panels continues to drive down costs. And because the sun is a free electricity source, solar technologies can pay for themselves over time.
  • Recycling: Whether it is possible to recycle the materials of used panels is one in numbers of question concerning scientists nowadays. As we mentioned above, materials using in manufacturing PV cells are toxic, after used, if it is released to the environment without recycling, our living area can be contaminated. There is only a small dumping area in Singapore. But the solution is not that easy! The problem is there are a huge varieties of solar panels and the number of need-to-be-recycled panels is so small that if we build a recycling factory, it will not worth the money. As a result, no investors put their money in this field because their benefit is not assured.

Thin film PV cells

Gallium arsenide/Cadmium telluride: Today’s dominant thin-film technologies are cadmium telluride and a more recent competitor, copper indium gallium selenide (CIGS). In the former, one semiconductor layer is made of cadmium telluride; the second is cadmium sulfide. In the latter, the primary semiconductor material is CIGS, but the second layer is typically cadmium sulfide. So companies’ uses compounds containing the heavy metal cadmium, which is both a carcinogen and a genotoxic, meaning that it can cause inheritable mutations.

Arsenic in solar cells

Benefits

Compared to silicon, Gallium Arsenic (GaAs) has low thermal conductivity, direct band gap, high electron mobility and high saturation current, and has highest efficiency of 28.8%.

  • Low temperature conductivity: GaAs resistance respond poorly to increase in temperature. Comparing between silicon and GaAs, we see their distinct difference

Silicon: 1.3 W cm-1°C-1

GaAs: 0.55 W cm-1 °C -1

Low resistance is favored to reduce energy loss as heat. The low increment in resistance due to increase in temperature of GaAs favors the condition where temperature of solar panel rises due to constant exposure to the sun.

  • GaAs has direct bandgap, unlike silicon which has indirect band-gap. This means GaAs requires less energy for current to flow whereas silicon either requires higher energy, or needs phonon assistance for current to flow.
  • GaAs also has higher electron mobility and high saturation current. As electrons repel one another, an increase in electron would force other electrons to move away from each other. Eventually, it will reach a stage where the whole structure is so saturated with electron movements that the current cannot increase further; this is known as the saturation current. And GaAs favors a higher saturation current that it’s counterparts.

Incorporating arsenic into the structure of solar panel to improve its efficiency. Increasing the efficiency of solar panel is important because all solar panels have a lifetime, and it’s important that the harnessed energy is higher than the energy needed to produce it in the first place by a significant amount. However, the price to pay for higher efficiency is the use of harmful elements such as arsenic, which can cause lungs, skin, kidneys, liver and heart diseases.

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