What is the environmental impact of photovoltaic (PV) solar panels?

As with any industrial product there is an environmental impact associated with solar Photovoltaic panels. The main areas of potential concern are:

  • The energy required to produce them, particularly the photovoltaic cells
  • What happens to them at the end of their lifetime
  • Toxic and other potentially harmful materials used or created in the production of PV panels/cells

However, it is important to take these issues in context. All electronic equipment can cause these concerns, and whereas many electrical goods are only designed to last for a couple of years, PV panels are expected to last for at least 30 years (here at CAT we have some that are 15 years old and still functioning well). Furthermore, PV panels are used in place of other sources of electricity which have a much greater environmental impact per unit of electricity generated.

The question of energy and carbon payback is answered separately on our website here.

The main component of most PV modules is silicon, which isn't intrinsically harmful, but parts of the manufacturing process do involve toxic chemicals and these need to be carefully controlled and regulated to prevent environmental damage.

Making monocrystalline panels tends to result in more waste, as they are made from slices of silicon ingots - leaving offcuts, etc. However, this waste can be used to make polycrystalline or multicrystalline PV modules, constructed of 'mashed up' silicon. Thin film silicon reduces the volume of material needed by spraying a thin layer of silicon on to a surface, so has the potential to reduce impacts and waste.

A report by the Silicon Valley Toxics Coalition lists a number of potentially damaging chemicals used in the manufacture of PV cells. There are several different types of PV technology and each of them use different processes to manufacture, but some of the common harmful chemicals involved in crystalline PV cell manufacture are:

  • crystalline silicon is made using silane gas, the production of which results in waste silicon tetrachloride which is toxic. It can be recycled into more silane gas but has the potential to cause harm
  • Sulphur Hexafluoride is used to clean the reactor used in silicon production. If it escaped it would be a very potent greenhouse gas. It can also react with silicon to create a range of other compounds.
  • a range of other chemicals used for cleaning the silicon and cells

There is also lead and small amounts of aluminium and silver in the electronics. The use of lead-based solder would lead to pollution problems if items are sent to landfill or incineration. Manufacturers can use lead-free solder, and some already are.

It is important to note that the same materials are in other electronic goods such as computers and TVs - so we need to develop ways to control them and address potential problems anyway, outside the solar industry.

Some kinds of PV panel contain Cadmium, which is an extremely toxic metal. It is not banned (for example by EU regulations), as when it is in the form of cadmium telluride (CdTe) it is a stable non-metallic substance and is not soluble in water. The melting point of CdTe is 1050 degrees C, so accidental domestic fires would not pose a risk. Industrial fires may reach higher temperatures, but tests have shown that the molten CdTe remains contained in the PV module. It is also worth noting that one NiCd battery contains 2500 times as much cadmium as a thin film CdTe PV module, and the production of 1kWh of electricity in a coal fired power station will emit 360 times more cadmium (as air pollution) than is needed in each CdTe solar module per kWh produced. Cadmium is essentially a waste product, as it is only collected as a by-product of zinc mining and manufacture.  So it will still need to be dealt with in some way, whether used in PV modules or not.

One area that does need to be developed is the recycling of PV equipment at the end of its life. PV panels are being phased in to WEEE (waste electrical and electronic equipment) legislation, governing the disposal of electronic equipment and making the manufacturer responsible for the eventual disposal or recycling. There are already some voluntary takeback schemes run by some of the companies involved. It is important that adequate legislation is introduced before there are large quantities of PV panels to be disposed of.

A group of manufacturers and distributors of PV panels have come together in the PV CYCLE scheme, which aims to reach recycling rates of 80% by 2015 and 85% by 2020.

This Ethical Consumer report and this report from the silicon valley toxics coalition both attempt to compare the environmental credentials of different PV manufacturers.

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