Environmental impact of solar power

Unlike fossil fuel based technologies, solar power does not lead to any harmful emissions during operation, but the production of the panels leads to some amount of pollution.
One megawatt solar power can save 88,932/5 tons of a year, 24,678,630,000,000/17 btus of energy, 6,855,175/1,122 tons of , 296,440,000 gallons of , (equal to 741,100 trees)
=== Greenhouse gases ===
The Life-cycle greenhouse-gas emissions of solar power are in the range of 22 to 46  g/kWh depending on if solar thermal or solar PV is being analyzed, respectively. With this potentially being decreased to 15 g/kWh in the future.
Alsema, E.A.; Wild - Scholten, M.J. de; Fthenakis, V.M.
Environmental impacts of PV electricity generation - a critical comparison of energy supply options ECN, September 2006; 7p.
Presented at the 21st European Photovoltaic Solar Energy Conference and Exhibition, Dresden, Germany, 4–8 September 2006.
For comparison (of weighted averages), a combined cycle gas-fired power plant emits some 400-599 g/kWh, an oil-fired power plant 893 g/kWh, a coal-fired power plant 915-994 g/kWh
 or with carbon capture and storage some 200 g/kWh, and a geothermal high-temp. power plant 91-122 g/kWh.
 The life cycle emission intensity of hydro, wind and nuclear power are lower than solar's as of 2011 as published by the IPCC, and discussed in the article Life-cycle greenhouse-gas emissions of energy sources. Similar to all energy sources were their total life cycle emissions primarily lay in the construction and transportation phase, the switch to low carbon power in the manufacturing and transportation of solar devices would further reduce carbon emissions. BP Solar owns two factories built by Solarex (one in Maryland, the other in Virginia) in which all of the energy used to manufacture solar panels is produced by solar panels. 
A 1-kilowatt system eliminates the burning of approximately 170 pounds of coal/, 300 pounds of from being released into the atmosphere, and saves up to 105 gallons of consumption monthly.Solar Energy Facts
The US National Renewable Energy Laboratory (NREL), in harmonizing the disparate estimates of life-cycle GHG emissions for solar PV, found that the most critical parameter was the solar insolation of the site: GHG emissions factors for PV solar are inversely proportional to insolation.NREL, Life Cycle Greenhouse Gas Emissions from Electricity Generation, NREL/FS-6A20-57187, Jan 2013. For a site with insolation of 1700 kWh/m2/year, typical of southern Europe, NREL researchers estimated GHG emissions of 45 ge/kWh. Using the same assumptions, at Phoenix, USA, with insolation of 2400 kWh/m2/year, the GHG emissions factor would be reduced to 32 ge/kWh.David D. Hsu and others, Life Cycle Greenhouse Gas Emissions of Crystalline Silicon Photovoltaic Electricity Generation: Systematic Review and Harmonization, 2011.
=== Energy payback ===
The energy payback time (EPBT) of a power generating system is the time required to generate as much energy as is consumed during production and lifetime operation of the system. Due to improving production technologies the payback time has been decreasing constantly since the introduction of PV systems in the energy market.
 In 2000 the energy payback time of PV systems was estimated as 8 to 11 yearsAndrew Blakers and Klaus Weber, "The Energy Intensity of Photovoltaic Systems", Centre for Sustainable Energy Systems, Australian National University, 2000. and in 2006 this was estimated to be 1.5 to 3.5 years for crystalline silicon PV systems and 1–1.5 years for thin film technologies (S. Europe). These figures fell to 0.75–3.5 years in 2013, with an average of about 2 years for mono- and multicristaline PV and CIS systems.Jinqing Peng, Lin Lu, Hongxing Yang, Review on lifecycle assessment of energy payback and greenhouse gas emission of solar photovoltaic systems. In: Renewable and Sustainable Energy Reviews 19, (2013), 255–274, Fig. 5, .
Another economic measure, closely related to the energy payback time, is the energy returned on energy invested (EROEI) or energy return on investment (EROI),C. Reich-Weiser, D. Dornfeld, and S. Horne. Environmental assessment and metrics for solar: Case study of solfocus solar concentrator systems. UC Berkeley: Laboratory for Manufacturing and Sustainability, 8 May 2008. which is the ratio of electricity generated divided by the energy required to build and maintain the equipment. (This is not the same as the economic return on investment (ROI), which varies according to local energy prices, subsidies available and metering techniques.) With expected lifetimes of 30 years,Service Lifetime Prediction for Encapsulated Photovoltaic Cells/Minimodules, A.W. Czanderna and G.J. Jorgensen, National Renewable Energy Laboratory, Golden, CO. the EROEI of PV systems are in the range of 10 to 30, thus generating enough energy over their lifetimes to reproduce themselves many times (6-31 reproductions) depending on what type of material, balance of system (BOS), and the geographic location of the system.Joshua Pearce and Andrew Lau, "Net Energy Analysis For Sustainable Energy Production From Silicon Based Solar Cells", Proceedings of American Society of Mechanical Engineers Solar 2002: Sunrise on the Reliable Energy Economy, editor R. Campbell-Howe, 2002.
=== Cadmium ===
One issue that has often raised concerns is the use of cadmium in cadmium telluride solar cells (Te is only used in a few types of PV panels). Cadmium in its metallic form is a toxic substance that has the tendency to accumulate in ecological food chains. The amount of cadmium used in thin-film PV modules is relatively small (5-10 g/m²) and with proper emission control techniques in place the cadmium emissions from module production can be almost zero. Current PV technologies lead to cadmium emissions of 0.3-0.9 microgram/kWh over the whole life-cycle. Most of these emissions actually arise through the use of coal power for the manufacturing of the modules, and coal and lignite combustion leads to much higher emissions of cadmium. Life-cycle cadmium emissions from coal is 3.1 microgram/kWh, lignite 6.2, and natural gas 0.2 microgram/kWh.
Note that if electricity produced by photovoltaic panels were used to manufacture the modules instead of electricity from burning coal, cadmium emissions from coal power usage in the manufacturing process could be entirely eliminated.CdTe PV: Real and Perceived EHS Risks
=== Birds ===
Some media sources have reported that solar power plants have injured or killed large numbers of birds due to intense heat. This adverse effect only applies to concentrated solar power plants however, and some of the claims may have been overstated or exaggerated.
==References==
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== Further reading ==
* Smaller, cheaper, faster: Does Moore’s law apply to solar cells? Scientific American analysis
* Herders Strap Solar Panels To Donkeys To Harness Solar Power To Light Their Manyattas (February 2015), K24 TV (Kenya)
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