CO2 emissions from renewables: solar pv, hydrothermal and EGS sources

Geothermal and solar pv are future energy sources, as both these renewables draw energy from natural heat sources i.e. the Earth and the Sun. While geothermal energy utilizes Earth's heat for power generation and for direct applications, like space cooling and dehydration, solar energy captures the Sun's energy and converts the energy to electricity through solar pv cells. The quartz required to manufacture solar cells that can generate 1 MWe weighs about 10 tons, and the manufacture of pv cells involves two important stages: metallurgical grade silicon (MGS) and electronic grade silicon (EGS). In the first stage an amount of 1756 x 10(6) kg of CO2 is released, and a similar amount of CO2 is released during the conversion of EGS to ingots. The total CO2 emissions during the lifecycle of a solar pv cell are about 3312 x 10(6) kg. This is far higher than a geothermal energy source, which emits about 450 g/kWh. According to the International Energy Agency (IEA), under the sustainable development policy proposed for adoption to mitigate CO2 emissions, nearly 54 x 10(9) cells are required to meet the generation target of 14,139 TWh. Of solar pv and geothermal energy sources, geothermal energy is the best option under this policy scenario to mitigate CO2 emissions and to control global temperatures. In addition to the emissions related to the manufacture of solar pv cells, solar panels and solar cell waste management are of great concern. Globally the generation of solar panel waste will be of the order of 78 million tons (Weckend et al. 2016). Countries involved in the manufacture of solar pv cells will emit considerable amounts of CO2 from this source in addition to coal-based thermal power plants. Solar pv cells may not emit CO2 during the generation of electricity, but during their life time emissions are considerable. Therefore, solar pv cannot be considered a zero-emission source.