SOLAR CELLS became a serious industry around 2000, when an exponential expansion in their installation began. Since then, they have gone on to make up a whopping — or rather, minuscule — 2 per cent of the global energy market.

They are, however, scheduled for continued extreme growth over the coming years, with the most dramatic predictions forecasting that their share of the energy market could increase to 50 per cent by 2050.

If it were possible to satisfy the entire world’s energy needs with solar power, (this is thought impossible because of the ways some energy must be used and stored) an area approximately the size of Spain would need to be totally covered in solar panels.

Although that target is enormous, it is a specific aim — all that is needed is the manufacture of the required panels. And the panels are being made: hundreds of gigawatts-worth of cells are being manufactured per year.

Around 95 per cent of solar panels used in the EU are made in China, although solar cells are also fabricated in many European countries — except Britain. (This is perhaps not surprising given the relative importance in Britain of wind relative to solar, but it makes the country unusual in its manufacturing capacity.)

Solar cells rely on a phenomenon called the photoelectric effect. In this effect, a material absorbs a photon (a light particle), causing an electron to jump out of the material it is in and leave behind a vacancy. The electron then flows away in another material.

In solar cells, many electrons are stimulated at once, and the flow of multiple electrons constitutes an electric current — one that has been produced by light alone. The solar cells currently being made are silicon solar cells. In this design, the material that pops out electrons is a slab of silicon. Silicon is an extremely abundant material; as silicon dioxide it is the main constituent of sand and many rocks.

However, there are problems with silicon solar cells: their theoretical efficiency is believed to be capped at around 27 per cent (compared to 64 per cent for a steam engine), and the material is expensive to mine and purify, which is exacerbated by the thick layer of high-purity material that is required for each solar cell. To top it off, these slabs of silica are rigid, brittle and opaque, limiting their use on flexible semi-transparent fabrics and plastics.

But silicon isn’t the only material that solar cells could be manufactured from. The front runner for some time has been “perovskites.” These materials have been in development for less than 20 years but have already overtaken silicon cells in the lab in terms of efficiency. Efficiency in solar cells is important, but like any single number can drive unbalanced innovation. The magic of rapid gains in perovskites has won over many solar researchers.

But efficiency isn’t the only important thing. Perovskites are also deposited as a super-thin layer, which can be flexible and semi-transparent, and are cheap and easy to manufacture. Unfortunately, researchers haven’t yet worked out how to stabilise them against degradation by exposure to air or water, which is generally agreed to be their biggest limitation with respect to silicon cells.

However, perhaps more importantly, the layers contain lead, making them highly toxic. The most recent proposal for the use of perovskites is the use of tandem cells, where a perovskite layer is tightly bonded within a complex sandwich of materials, all tightly glued together. The potential efficiency gains are high, but the design is complex, and durability remains an issue.

Moreover, what was a safe silicon panel becomes a toxic hybrid. So far, perovskite solar cells have remained firmly in the lab. Despite the claims for their potential, there’s a strong case for more research into lower efficiency non-toxic technologies like organic pv-cells.

This issue of degradation is a significant problem that remains to be faced by the solar cell industry as a whole. The lifespan of regular silicon solar cells is 20-25 years, although they become significantly less efficient before this length of time.

In fact, for many solar farms, it makes sense to replace the panels before the end of their useable life in order to keep the production levels high. Though that lifespan is large compared to a device like a mobile phone or computer, it means that the first large-scale solar cells that were installed 25 years ago are coming already to the end of their useable life.

That means they all need replacing, and soon. Solar cells can be recycled, but it is expensive — and currently much more expensive than dumping them in landfills. One of the main issues is the glue that binds all the layers of a solar panel together. The whole panel must be crushed up and stripped in order to disentangle the different components.

One of the more valuable components in solar panels is silver, which is used as a conductor to get the electrons flowing out of the silicon panel. As demand for solar panel parts eats up more of the world’s mined silver (in 2023 it was already 14 per cent of global silver use), this is likely to become a bigger problem.

Silver mining in itself is a serious environmental issue. There is the potential to swap silver out for a less precious metal, though recycling-watchers point out that this would also reduce the economic viability of solar panel recycling, so would increase solar panels going to landfills. The development of easily renewed and/or recycled solar panels using green technologies is the only answer.

The green transition, where it is finally affecting power production, is developing large-scale industries at speed — more money was invested last year in solar than any other energy infrastructure. But energy transitions still take time and produce new problems to solve. The material investment in solar panels, if they continue to be produced and simply dumped at this rate, is vast.

Though research is growing into new technology and recyclability for future panels, the transformation of the industry relies on this research being put into practice. Though any reduction in fossil fuel use is to be celebrated and pursued, the new industries are not immune from the same issues as those they replace: high energy costs, high waste, and lack of sustainable planning for the materials that they use.