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The key environmental impacts associated with significant adoption of solar energy are the land area required, impacts due to the production and disposal of the solar collectors, and impacts associated with increased requirements for energy storage. As an indication of the scale of production that may be necessary, the IEA BLUE Map scenario projects a need to install, each year until 2050, an average of 215 million m2 (about 86 mi2) of solar panels world-wide to meet the 4,750 TWh/year of solar electricity generation they project will be needed to displace a portion of fossil-fuel-generated electricity [4]. This is in addition to concentrated solar thermal power plants.

In the U.S., the average amount of peak solar energy that reaches the surface is on the order of 1 kW/m2. For photovoltaic (PV) systems, conversion efficiency is typically no higher than about 20%, so each m2 of PV could produce no more than about 200 W of power. When combined with the changing azimuth of the sun over the course of a day, it is reasonable to assume that the net energy produced per m2 would be roughly 1 kWh. Turner estimated 0.63 kWh/m2/day of electricity from flat plate collectors of 10% efficiency, and also estimated that the actual area would be twice that amount for infrastructure (supports, power lines, access, etc.) [49]. Higher efficiency collectors or tracking collectors would further reduce the amount of area required per kWh. Displacement of 1 GW of peak power would therefore require about 5 million m2 (about 2 mi2) of land area. Much of this surface area is currently located on rooftops in distributed generation systems, which reduces the amount of land surface that would need to be dedicated to PV collectors [4]. This approach may change as new PV technologies are developed that would be more effective in central solar facilities, but it is likely that both systems integrated into buildings and central facilities will have a role in future PV generation.

An additional environmental issue is the production process and the materials needed to produce PV cells. Work at the National Photovoltaics Environmental Research Center at Brookhaven National Laboratory has identified a number of environmental risks associated with life cycle production and use of PV power systems [50, 51]. A key concern is the use of cadmium-tellurium (CdTe) compounds in PV systems and the potential for increased Cd emissions in the mining and refining of Cd and the manufacture, utilization, and disposal of PV modules.

Some of the other hazardous materials present in PV manufacturing include arsenic compounds, carbon tetrachloride, hydrogen fluoride, and hydrogen sulfide, lead, and selenium compounds [52]. These compounds can be released in the event of fires, either at the manufacturing site or at PV installations, although there is some disagreement with respect to whether they would be released in a residential fire scenario [53, 54].

Disposal of used PV modules provides another route for introduction of hazardous materials into the environment. Fthenakis states that recycling is technologically and economically feasible, and estimates that there would be minimal environmental impact if such recycling and recovery is conducted properly [55].

The IEA, through its Photovoltaic Power Systems Programme, has recently started a task to evaluate the health and safety issues associated with PV production and use, including life cycle emissions estimates ( task12.htm). Much of the information in life cycle assessments is quite dated, as pointed out by de Wild-Scholten and Alsema, particularly given the advances in the semiconductor industry over the past decade [56]. Studies by Moskowitz and Lawrence et al. [57-59] are well over 15 years old, and do not account for changes made in PV production in the intervening time since. Recently, the U.S. Bureau of Land Management announced its efforts to develop a Programmatic Environmental Impact Statement to evaluate solar energy development on federal lands. This effort will involve evaluating the environmental impacts of tilting PV and solar-thermal systems in six states in the western U.S. [60].

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