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September–November 2023

The sustainability conundrum of photovoltaics: unravelling the energy and GHG emissions debate

‘What’s the point of photovoltaics?’ a former colleague challenged me recently. He argued that the energy consumption and greenhouse gas (GHG) emissions during solar panel production outweigh the lifetime benefits of zero-emissions energy. Similar arguments are made against electric cars and other carbon-friendly technologies. Intrigued, I embarked on research that yielded unexpected outcomes.

A 2016 Nature Communications paper (vol. 7, article 13728) shed light on a potential break-even point between the disadvantages and benefits of photovoltaics, projecting it to fall somewhere between 1997 and 2018 – a rather long period. Yet definitive evidence of this elusive point and whether we now enjoy net positive benefits for energy or net GHG emissions remains unproven.

One crucial unstated assumption in the paper is the sole use of fossil fuel energy for making solar panels. Presently, in China, the major producer of solar panels, 12% of the energy consumed from the grid is renewable energy, insufficient to tip the balance towards a ‘net positive’ status. Additionally, energy-intensive processes in the silicon supply chain in China still rely solely on cheap coal energy and diesel fuel.

What we can say, with certainty, is that where fossil fuels are used in the production of solar panels, there will be a side product of local pollution. China wears all this pollution and we, the importers of their solar panels, get all the clean energy without the pollution. By importing solar panels from China, we are effectively exporting our emissions from the offset energy production, at least until China is using 100% clean energy to make solar panels (which won’t be any day soon).

A good way to look at a solar panel is that all the energy and GHG emissions are invested up front. Thereafter, it’s all upside. There are two main measurables that affect the net energy and GHG position: solar efficiency and solar panel longevity. The higher the solar efficiency and the longer the solar panel life, the more energy that is generated relative to the original investment in energy and GHG emissions during production. Weather matters too, of course.

Higher solar efficiencies have continuously been sought by the manufacturers of solar panels for decades, and at ever low costs of production. Longevity of solar panels has also improved over time, with solar panel product warranties now typically being for 25–30 years. However, just because solar panels are warrantied for such long periods doesn’t mean that they are used accordingly. In fact, in a recent market survey some colleagues found that the typical installed life of a solar panel in Australia may be as low as eight years. This, ironically, is because of the continued improvement in solar efficiencies and costs. Effectively, after eight years one might find that solar panels have doubled in output power, and that they are such relatively low cost that is it worthwhile to discard old panels and install new ones. This is viable because much of the cost of installing solar systems is not the solar panels but other upfront costs such as site costs, grid access and power system connectivity.

Addressing the present state of solar panel R&D, efforts concentrate on combating the impending efficiency limit for single-junction silicon devices. This situation compels researchers to consider two options for improvement: either change the substrate materials (impractical due to the established silicon infrastructure) or develop dual-junction devices that capture a broader solar spectrum.

It is possible, of course, that improving efficiencies simply exacerbates the solar panel lifetime problem by continually making it economically viable to replace working solar panels well before their practical end of life. This problem could be overcome by addressing the recyclability of solar panels. The silicon in solar panels represents a very high energy cost when first produced; if the silicon could more easily be recycled, then much of the upfront energy cost for making solar panels could be avoided.

However, the current solar panel design makes the recycling of silicon very difficult; the weathertight encapsulant essentially glues all the components together, making it difficult (expensive and energy intensive) to extract the silicon, free from the other components. If solar panels were only warrantied for 8–10 years, it is feasible to imagine solar panel designs that would not need encapsulant, and that would allow easy recycling of the silicon.

Of course, if most of the energy used to make solar panels were renewable, then the net energy and GHG emissions problem would solve itself. However, this is only likely to happen if the solar supply chain is replicated outside of China (to create diversity in approaches to manufacturing) and solar panels were taxed on their carbon footprint, inclusive of end-of-life considerations.

Ian A. Maxwell is a visiting professor in the Faculty of Engineering and IT at University of Technology Sydney, who started his career as a physical polymer chemist. Ian is also the chair of a number of high-tech start-ups.

Andrey Moisseyev/iStockphoto

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