3.8.1 Environmental impact and safety
The environmental impact of photovoltaic energy is probably among the lowest of all electricity generating systems.
This is because:
- In normal operation PV energy systems emit no gaseous or liquid pollutants and no radioactive substances.
- Crystalline silicon PV cells contain only minuscule quantities of dopants such as boron and phosphorus. (However CIS or CdTe modules include very small quantities of indium, cadmium and tellurium, so there is a slight risk that a fire in an array might cause small amounts of toxic material containing these elements to be released into the environment.)
- PV modules have no moving parts, so they are also safe in the mechanical sense, and they emit no noise.
- The electrical hazards of a well-engineered PV system are no greater than those of other comparable electrical installations.
PV arrays do, of course, have some visual impact. Rooftop arrays will normally be visible to neighbors, and may or may not be regarded as attractive, according to aesthetic tastes. Several companies have produced special PV modules in the form of roof tiles that blend into roof structures more unobtrusively than conventional module designs.
PV arrays on buildings require no additional land, but large, multi-megawatt PV arrays will usually be installed on land specially designated for the purpose, and this will entail some visual impact.
Environmental impact and safety of PV production
The environmental impact of manufacturing silicon PV cells is unlikely to be significant – except in the unlikely event of a major accident at a manufacturing plant. The majority of PV cells are made from silicon, which is not intrinsically harmful.
When small amounts of toxic chemicals are used, such as the cadmium used in manufacturing some PV modules, manufacturers need to follow standard practices to ensure containment of any harmful chemicals in the event of an accident or plant malfunction.
PV arrays are potentially very long-lived devices, but eventually they will come to the end of their useful life and will have to be disposed of – or, preferably, recycled. Most European manufacturers are beginning to recycle PV modules at the end of their working lives under the auspices of the voluntary ‘PV Cycle’ initiative. Draft EU regulations on PV module recycling under the EU’s Waste Electrical and Electronic Equipment (WEEE) directive are in preparation.
Energy balance of PV systems and potential materials constraints
A common misconception about PV cells is that almost as much energy is used in their manufacture as they generate during their lifetime. In the early days of PV production, manufacturing processes were very energy-intensive, and the efficiency of the cells was relatively low, leading to low lifetime energy output. But with modern PV production processes and the use of thinner cells with improved efficiency, the energy balance of PV is now much more favorable. The use of materials with low embodied energy in PV array support structures can also improve the overall energy payback time of PV systems. Recent research (Fthenakis et al., 2009) suggests that the time taken for a PV array to produce as much energy as used in its production, i.e its energy payback time, is approximately 1.8 years for monocrystalline and polycrystalline PV, and 1.1 to 0.8 years for cadmium telluride PV, in southern European conditions.