Bringing space solar back to earth



We touched on it in the February edition of pv magazine, but can you remind us of the long history that Webasto has had in developing and producing solar roofs for the auto industry?

Our work in solar started 33 years ago; Webasto worked with Audi to introduce a small solar roof system. It started with 21 solar cells at a size of 105 mm x 105 mm, and the efficiency was below 15%, but the features and functionality were awesome, and there was a lot of testing to prove the concept. Audi did testing in Morocco and they realized the functionality of the solar was great because all of the plastics within the car stood up much better under the Saharan sun. That’s because the car’s HVAC fans [heating, ventilation, and air conditioning] were powered with solar, so there was a continuous lowering of temperature, meaning the plastics didn’t release so many agents and didn’t age as fast. We’ve since produced more than 350,000 solar rooftop units all based on this history.

That was a kind of proof-of-concept for the solar roofs. How have things progressed since, in terms of the volume of demand?

We started production of the solar roofs in the year 1990 and the feature was sold until 2018. What we are now realizing is that the automotive industry is getting more and more interested in the topic. Our colleagues in Korea introduced a 200kW solar system for the [Hyundai] Ioniq 5, for example.

We are in the middle of a development project and we have the start of production at the end of this year for a 300W solar system – the world’s biggest solar roof for a vehicle. We started in 1990 with 30W and now we are at 300W in the product power output, which shows what happened in the solar business.

That points to the power output increase, but cost reduction has also been a major achievement of the solar industry. How does that impact what you’re doing with solar roofs for the auto industry?

Let’s say the costs are the same, but you get a factor of 10 times more power – it’s a rough estimation, but it fits. At Webasto, the first solar cells we bought were €20/Wp. Now we are on a significantly lower level.

I have a personal vision that there is a way for [very high-efficiency] III-V semiconductor materials to follow this price decrease, and in this the auto industry is going to be really important. While standard solar costs €0.20 ($0.23)/Wp, III-V semiconductors cost €100/Wp. But this is because the global III-V industry has a global manufacturing output of around 1MW. And we can easily scale that quantity up by orders of magnitude with a single [auto solar rooftop] project, which could cause a dramatic price decrease.

In this way, Webasto really holds the key for disrupting the III-V market. In conjunction with a car company, a serious project can easily have 50,000 to 100,000 units. That will mean 300W+ rooftops, and it would be amazing for the cost of III-V materials. We see a huge potential in high efficiency solar cells.

III-V solar semiconductors are used in space applications, where cost isn’t a factor. But as you say, the volume of demand is tiny. So, are you saying that solar rooftops for cars could actually change this?

I think it’s time for serious disruption and to have a new energy source on a different cost level. It really is getting the space solar back on earth.

That is a genuinely exciting vision. Looking at EVs in more detail, at present they are integrated into the car’s low-voltage power system. As with the Audi project more than 30 years ago, it seems like you argue that this is a far from trivial contribution, is that right?

We like to emphasize comfort; in the premium car segment in Europe comfort is what is sold as a luxury. Therefore, there is demand for solar energy for the cooling systems. We have done some studies with Denso, the big HVAC company, where it has been shown that solar energy can reduce the power draw of an HVAC compressor in a car by around 40%. This means more efficiency, reducing the size of the HVAC system, saving weight and extending the range of the car.

What about moving towards the high voltage system – the electric power train?

300W is delivering an amount of energy that starts to get interesting. The moment the cars are consuming per kilometer around 250Wh, and when you are installing a roof panel with 300W peak power, you can see that you are able to power the car, the solar really is moving the car.

There are definitely some challenges. During parking for instance, there is the challenge of how to get the energy into electric architecture. Other challenges include, from a safety standpoint, the need to double protection for high voltages, and getting all the solar energy into the battery cells.

But when you think that now there is a Toyota Prius with a solar roof with 860W peak power, it’s just amazing, and you see the numbers: 9,000 km a year powered by the sun in Australian conditions.

And while here in Europe everyone is complaining that we don’t have sun, but 1,200kWh/m2 of irradiation is a lot and can sum up to between 5-15 km per day; and that certainly provides good cover for the standard consumer on the daily commute.

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