In 2019, during the ESA Power Workshop, engineers confronted the dilemma of limited solar power for spacecraft. Unable to boost the Sun’s intensity or enlarge solar panels indefinitely, they turned their attention to a clever workaround: making panels thicker. By layering micron-thick substrates atop one another, they effectively expanded the solar spectrum captured by each panel.  

Imagine panels boasting up to eight layers of exotic substrates, each widening the spectrum they could ‘see’. Out of the total available sunlight energy of 1.4 kW/m2, typical panels received only around 250 W/m2, assuming full spectrum absorption. However, real-world conditions usually yield only 20-30% efficiency.

Six layers can see more of the solar spectrum than a single layer, capturing light from a wider window - from UV to Infrared
Six layers of material represented by the different colours of absorption windows

The maximum achievable conversion in an ideal system is 472 W/m2, yet even with these advancements, panels remain bound by the Shockley-Quiesser limit. Moreover, the addition of each layer escalates the risk of failure; a single malfunctioning layer can render the entire stack inoperative.

Each layer demands more rare earth metals, with the mined material being about 50 times more voluminous than the layers themselves. When we consider the cumulative raw material requirements for all the photovoltaics of a CubeSat, or a constellation like Starlink with thousands of satellites, the environmental impact becomes substantial. Factor in the mining methods, such as acid leaching and the generation of Naturally Occurring Radioactive Material (NORM), and the sustainability of this approach is in question.

While we cannot alter the Sun’s output or endlessly augment panels, we can enhance the amount of light they receive. And this is where lasers enter the picture.