Sustainable solar

Solar power is one of the world’s most sustainable forms of electricity generation, known globally for its zero carbon emissions and rightly earmarked as one of the key technologies needed to combat climate change. Solar is also on a tremendous cost reduction curve, the International Renewable Energy Agency reports that between 2010 and 2017 the cost of solar projects fell by 73%. This represents a cost reduction unprecedented in the history of electricity production technologies. Solar is also socially sustainable. Solar employed more people than the coal, oil and gas industries combined in 2017 in the US and accounted for almost 40% of the workforce in the electricity sector. Solar, therefore, succeeds in meeting all three pillars of sustainability: environmental, economic and social.

A recent study commissioned by the German economy ministry and carried out by the University of Stuttgart noted the existence of cadmium and lead in silicon-based solar panels and suggested these could seep into the water cycle if the panels are not properly disposed of at the end of their lifetime. Cadmium and lead are indeed still present in the pastes used to produce solar cells and panels and it would be foolish to ignore this fact. It would, however, be equally foolish to conclude that these traces of heavy metals make solar panels unsustainable. The industry is working hard to eliminate them and to ensure that all panels are disposed of correctly. We must also not forget the considerable amounts of heavy metals emitted every year by the fossil fuel industry.

First, lead. The typical amount of lead in a solar panel is around 10 grams, a very small amount when you consider that an average panel weighs about 18 kilograms. Most solar panel companies do still use lead in their products, but heavy metal free alternatives exist and as their cost comes down, so their uptake increases. Indeed, the International Technology Roadmap for Photovoltaics, drawn up by industry in 2018, anticipates lead-free pastes to become widely used in the mass production of crystalline silicon cells, the most common cells used in commercially available solar panels, by 2020.

The use of lead in panels is compliant with European chemicals legislation, which restricts the use of pastes containing lead. Panels that are permanently installed in a defined location are excluded from this restriction, but the regulation will be reviewed again in 2021, by which time the use of cadmium and lead will have significantly reduced in solar.

Long life

Moreover, compared to other electronic and electrical equipment, solar modules have a relative long lifetime of up to about 30 years and so, as a recently developed market, current waste streams are still small, less than 1% of the installed base. We will see an increase in this waste stream in the next 15 years and in Europe we already have a legal framework under which producers are responsible for organising and financing the management of their products at the end of their life.

Solar panels belong to the class of electronic equipment which meets the highest collection (85%) and recycling (80%) rates in the EU. Using conventional recycling processes, rates up to 90% have been reached for silicon solar panels. A pilot project in Italy, which uses an innovative process based on mechanical and chemical treatments to recycle silicon solar panels, achieves very high recycling rates of 94% to 99%. Such techniques could be developed on an industrial scale as the quantity of solar waste increases. And our sector is not stopping there. We are also working tirelessly to improve the economics of panel recycling by bringing high value materials back into the supply chain. Key research and development topics include the full recovery of glass sheets and of high purity silicon/cells and valuable metals.

Cadmium, meanwhile, is present in some thin-film panels in the form of cadmium telluride, a chemically stable compound that can be recycled. This is a toxic compound, though it is not carcinogenic, and its presence in solar panels also complies with EU chemicals legislation. Cadmium can be recovered for re-use or effective sequestration at relatively low costs, resulting in a high-purity recovered material. Indeed, state-of-the-art facilities achieve recycling rates of up to 90% of the semiconductor material and 90% of glass used in those products.

Coal and heavy metals

A final word must go to comparing solar with coal. It is important that concerns about the use of heavy metals in solar technologies are put in the context of what the world has experienced, and is still experiencing, from the burning of this fossil fuel. Coal power plants are among the largest industrial sources of emissions of heavy metals such as mercury, lead and cadmium. In terms of air pollutants, coal plants in the US are responsible for 42% of the country’s mercury emissions. On a yearly basis the US coal fleet emits 41.2 tons of lead, 4.2 tons of cadmium, in addition to arsenic, carbon monoxide and volatile organic compounds, according to the US Union of Concerned Scientists.

There is no getting around it, solar does use some heavy metals. The industry recognises this and is working to reduce their use and improve the recyclability of panels and all elements of the solar system. Solar is a sustainable form of electricity production and we cannot beat climate change without it. We must therefore make sure that scare stories based on a selective set of facts do not dampen the enthusiasm of consumers or policymakers for solar or any other renewable technologies.

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