Invisible power plant

Soon ready for series production: how car paint can generate electricity

(Bild: Mercedes-Benz)

A new type of paint is set to transform cars into rolling photovoltaic systems. Mercedes is conducting intensive research into this technology - and into a new generation of power electronics for the high-voltage battery. The common goal: more efficiency, more range.

PV modules on the car roof or on the entire body: several car manufacturers have already tried to use this concept to generate electricity while driving and parking. Ultimately unsuccessful - or with very manageable returns in relation to the effort and costs involved. The Mercedes development department is now making a new attempt. No longer with conventional solar cells, which are brittle, prone to breakage and difficult to process. Instead, they are using a coating that is applied to the entire car body and generates electrical energy when exposed to light. According to Mercedes, the efficiency is over 20 percent and therefore roughly on a par with silicon panels.

The electricity-producing paste is applied to the sheet metal or plastic parts of the electric car to a thickness of just five micrometers - considerably thinner than a human hair. One square meter weighs only 50 grams. On top of this surface is a new type of nanoparticle-based paint coating that allows 94 percent of the sunlight to pass through to the solar layer.

Power for 12,000 kilometers per year
The technicians hope that the car will be ready for series production in the next few years and expect the solar paint to offer considerable advantages in terms of charging costs, charging time and range. The EQXX experimental vehicle with its almost 1.9 square meter solar roof is already providing initial experience. Ideally, this produces enough electricity to cover a distance of 25 kilometers over the course of a sunny day.

Unspectacular, but effective: the solar paste is simply applied to the body panel - 5 micrometers thin.

(Bild: Mercedes-Benz)

There would be space for up to eleven square meters of the energy-generating coating on a current midsize SUV. And this surface could "produce energy for up to 12,000 kilometers per year under ideal conditions" in Stuttgart, for example, according to optimistic reports from the development laboratories. However, it is clear that the respective yield depends crucially on geographical location, sun intensity and shading. In any case, not much electricity is likely to flow when the car is parked in an underground garage.

The energy generated by the car when moving or stationary can be used directly for driving or fed into the high-voltage battery. When parked at the wallbox at home, energy generated by the car could be used for vacuum cleaners and refrigerators or fed into the home power storage system using vehicle-to-home (V2H) technology. What else speaks in favor of the solar paste is that it does not require rare earths or silicon and contains only non-toxic and readily available raw materials. It is also recyclable and can be produced much more cheaply than conventional solar modules.

Developing the battery revolution
In parallel with solar paint, Mercedes is researching the next generation of electrical inverters. This is because, according to the engineers, the current series connection of battery cells with hardware-based converters has a whole series of drawbacks. For example, the output voltage depends on the current state of charge, each cell is charged and discharged identically and the weakest battery cell determines the overall performance of the battery when driving, charging and recuperating.

Still a dream of the future: programmable micro-converters regulate the current flow of each individual battery cell.

(Bild: Mercedes-Benz)

If the Mercedes engineers have their way, this will soon be a thing of the past. They are relying on programmable micro-converters to regulate each individual battery cell. As things stand, the software-based helpers make it possible for each cell to provide a constant 800 volts, regardless of its state of charge or age. This ensures better efficiency, faster charging, less heat generation and longer ranges. The new technology also saves a considerable amount of installation space, giving designers more freedom in the conception and design of future electric cars.