Greenhouse Gas Equivalent
The environmental impact of solar energy is not very simple to define. And one quantitative measure, the most common and most convenient, is the greenhouse gas (GHG) emission caused by its production. Researchers estimate that with current technology, PV equipment produces 46 gram/KWh of energy produced by it when averaged over the life cycle of this equipment. In other words the GHGe of PV is 46g/KWh. What this means is that the mass of GHG produced by all processes involved in the production and use of PV panels and balance of the system, divided by the total PV energy in KWh produced by the system, is 46 gram/KWh averaged over the complete life cycle of the system .
GHGe of solar thermal is currently estimated at 22 g/KWh. Also, it is expected that with improvement in processes, and use of more solar energy in the production processes, the GHGe will reduce to 15g/KWh. The current and future figures for solar energy compare very favorably with a combined cycle Gas power plant which has GHG equivalent of 400 to 600 g/KWh. Oil power has GHGe of 893g/KWh; and coal power, 513-994 g/KWh. Nuclear, wind, and hydro power have much smaller footprints than even solar thermal power. You can find more here: https://sinovoltaics.com/learning-center/basics/can-solar-energy-reduce-greenhouse-gases/Other Effects
In addition to direct GHG effect of solar equipment production, there are other factors:
• Toxic Metals: Manufacturers use Cadmium in thin film PV panels, but the amount is about 5-10 g/m2 of panel. GHG effect is in micrograms /KWh which is negligible if proper care is taken. Lead is part of the solder. The GHG equivalent is negligible, and in any case, lead is not a necessity for soldering.
• Threat to Birds: This can come from high power beams CSP if a bird crosses its path.
• Land Use: The estimated Footprint of rooftop PV is at 0.59 m2.a/MWh compared with 7.9 for large scale PV; and 9, and 16 for large scale CSP using dishes and towers, respectively. For coal power the land use foot print is quoted at18 m2.a/MWh, which is very large.
For more details read here: https://www.ucsusa.org/clean_energy/our-energy-choices/renewable-energy/environmental-impacts-solar-power.html#.XBD0hnQzbIUConclusion
It is clear that solar energy has much less GHG effect than fossil fuel and deserves to be called ‘clean’. Further, one should remember that the GHG foot print of solar power will suffer where the average solar insolation is low, because the output will be low.