Season 6 - L’avion solaire

Episode 2 - Is it as green as it seems?

Time is marching on, and despite some unbearable heat peaks here and there, summer 2023 continues to be pretty grey. But nevertheless, we’re going to continue talking about solar power, and solar aeroplanes. As we saw in the previous episode, the solar plane is an aircraft covered with solar cells, which turn its engines or its propellers. Better still, to compensate for the inevitable nightfall, it uses the daytime to charge lithium batteries so it can fly without stopping. It’s a marvel of tech and innovation that has solved two of the main issues with aviation: how to fly autonomously and the alarming levels of greenhouse gases it emits. Except, this technology has its own set of problems.

To be clear - we’re not going to put solar energy on trial here. Abundant, renewable, free and with no impact on biodiversity or the climate, it’s probably the most virtuous of all energies. The problem lies rather in the method and the tools we use to exploit it. As documented by Greenpeace, the manufacture of voltaic cells leads to significant silicon emissions and pollution. The NGO states that the panels are easy to recycle, especially if they’re bought and disposed of in Europe, where there are strict regulations.

Then there are the lithium batteries, since solar planes will only be able to fly in direct sunlight. It's no secret that the extraction of this metal – the price for which rose from $5,700 at the end of 2020 to more than $60,000 at the end of 2022 – has been described as an ecological disaster waiting to happen. Mainly because of its water consumption. In Chile’s magnificent Atacama Desert, an American company and one from Chile run the extraction of 26% of the world's reserves. However, in 2022, the Chilean company SQM declared that it was pumping 400,000 litres of water per hour to power the lithium factory. Per hour. That is 9.6 million litres of water per day, 67.2 million litres of water per week and nearly 3.5 billion litres of water per year. Unsurprisingly, the inhabitants and the surrounding nature in the area are already suffering.

It’s not only solar aeroplanes that drive up demand for photovoltaic cells and lithium batteries. It would be wrong and dishonest to say otherwise. However, there is a problem of scale. The Solar Impulse 2 has 17,000 solar cells and four lithium batteries, which isn’t much in the scheme of things. Despite having the wingspan of a Boeing 747, it can barely carry its pilot in a tiny cabin. We’re not doing the calculations ourselves, but it’s clear that if it were to carry 580 passengers – as a 747 can – it would need many more photovoltaic cells and lithium batteries. Got a number in mind? Keep it there, and now multiply it by the 42,710 new planes that will be roaming the skies by 2040. It’s a monumental figure.

Even under these conditions, it’s quite possible that the solar plane will be much less polluting than its kerosene equivalent. Although being realistics, it’s unlikely that there will be solar-powered Boeing 747s in our time. For Gérard Feldzer, engineer and president of Aviation Sans Frontières, if medium and long-haul aircraft do eventually use solar energy, it will be through a hybrid propulsion system, with hydrogen for example. And we know that is very far from planet friendly. Fortunately, there’s a small glimmer of hope in the darkness, as the solar aeroplane could be useful in a different context.

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