Solar paint approaches commercial use

Under the general rule of what works for automotive often works for marine, a new solar paint has been adopted by Mercedes Benz to help extend the driving range of their electric cars.

Pulse has reported on this type of coatings technology before, but until quite recently the most promising advances were restricted to the laboratory. Now it has been perfected enough to become an option, offering the ability to recharge the vehicle’s battery even when the car is unused and isolated from the grid. So long as sunlight is falling on the car’s body, electricity is being generated. Clearly, this type of tech can also be used afloat, and there has already been some flirtation with the idea by some forward looking boat builders.

The secret to the breakthrough is in the way the coating is layered. The actual generation is done by nanotechnology, tiny particles called quantum dots. Based on colloidal synthesis, where metal salts are dissolved in a solvent and heated to form tiny, semiconducting crystals, these particles make up the active layer of the coating. By adding a suitable and complementary pigment, you can have any colour you like. Underneath this ‘paste’ of quantum dots, thinner than a human hair, is a second layer, tasked with spiriting the charge away to an energy converter that directs the stabilised current into the battery. A top layer is also added to the coating, this one intended to allow light to pass through, but also to protect the quantum dots from damage and UV degradation. According to Mercedes Benz, the photovoltaic layer is around 20% efficient, comparable with a standard solar panel, but researchers suggest they could go on to be 11% more efficient still. With the existing technology, an 11m2 surface area, about the average coverage of an SUV, could add another 12,000km of driving range per annum. However, this figure is based on a series of ideal conditions in Stuttgart, Germany, so Mercedes says it could be even higher, citing a possible 20,000km in Los Angeles, for example.

But would it work on a boat? Very probably. On a car, no-one will be clambering across the hood or trunk, unlike the deck of a boat, but the protective layer should still allow for some gentle footfall. Areas of the hull and topsides that don’t see any abrasion could also be coated, allowing the boat to catch reflected light from the water’s surface, too, much as tandem cells do with a base layer or perovskite.

This type of solar paint is one of three types currently being developed for the harnessing of renewable power. As already mentioned, perovskite has a role to play as it can harness extreme ends of the light spectrum for power generation. The mineral, discovered in 1839 and named after the Russian mineralogist Lev Perovski, can be turned into a liquid, and can even be sprayed onto glass surfaces or incorporated into clothing as printed inks. Another type of solar paint uses a newly discovered substance, synthetic molybdenum-sulphide, to split moisture in the air into hydrogen and oxygen, allowing the hydrogen to be tapped off for use in renewable fuels. The white pigment, titanium oxide, is also key to the moisture splitting process.

The good news about the quantum dot technology likely to be deployed by Mercedes Benz is the cost. In a feature in Solar Review, an extract from a research paper by Susanna Thon states “There are two advantages to colloidal quantum dots. First, they’re much cheaper, so they reduce the cost of electricity generation measured in cost per watt of power. But the main advantage is that by simply changing the size of the quantum dot, you can change its light-absorption spectrum.”

More about the new Vision Iconic car and its solar paint can be found at: https://www.mercedes-benz.com/en/design/concept-cars/vision-iconic/