Solar roofs on electric vehicles: step toward climate-neutral future

News13-10-2023

A consortium of researchers and Flemish industry partners has successfully integrated high-efficiency solar cells into curved glasses for solar roofs of electric vehicles, resulting in increased efficiency gains (6%).

This article previously appeared in Dutch in Engineeringnet.

Solar panels can no longer be ignored. You see them mainly on south-facing roofs or in solar parks, the latter sporadically floating. And this is a positive evolution, as the EU’s renewable energy target was raised in March to 45% by 2030, double the current European level of 22%.

At the same time, sales of electric passenger cars are growing exponentially, and the auto industry can play a key role in reducing global CO2 emissions (with a goal of a one-third reduction by 2030). In fact, electric vehicles emit up to three times less CO2 than fuel-engine vehicles. Those emissions can be further reduced as the electricity supplied becomes more carbon efficient.

A synergy between the two can already be seen on the market: the integration of solar cells into the roof of an electric car, allowing the car to partially recharge itself in an environmentally friendly way. An efficient “solar roof” can increase driver comfort, reduce dependence on the primary battery and relieve strain on the power grid.

In other words, less frequent charging and longer battery life (given that the depth of discharge is reduced). In current passenger cars, however, such solar roofs have limited power output. Thus, the additional driving range is only a few kilometers (e.g., Toyota Prius Prime, Karma Fischer Revero, Hyundai Sonata). More efficient solar roofs are still under development or involve high costs, making further research essential.

Synergie tussen markten

Er is al een synergie tussen beiden te zien op de markt: de integratie van zonnecellen in het dak van een elektrische auto, waardoor de auto zichzelf op een milieuvriendelijke manier deels kan opladen. Een efficiënt ‘zonnedak’ kan het comfort van de bestuurder verhogen, de afhankelijkheid van de primaire batterij verminderen en het elektriciteitsnet ontlasten.

Met andere woorden: minder vaak opladen en een langere batterij levensduur (gezien de diepte van ontlading verminderd wordt). In de huidige personenwagens hebben dergelijke zonnedaken echter een beperkte vermogensoutput. Zo is het extra rijbereik slechts enkele kilometers (bijvoorbeeld Toyota Prius Prime, Karma Fischer Revero, Hyundai Sonata). Efficiëntere zonnedaken zijn nog in ontwikkeling of gaan gepaard met hoge kosten, waardoor verder onderzoek essentieel is.

New generation of high-efficiency solar panels

As part of an imec.icon project, a consortium of Flemish companies and research partners focused on this issue. The SNRoof project (Solar multi-junction cells iNtegrated in 3D curved ROOFs of electric vehicles) investigated the reliability and safety of a new generation of high-efficiency solar panels for application in curved glass car roofs. This also took into account aesthetics, which is not unimportant in the automotive industry.

“Combined with next-generation solar cells, solar roofs on trucks are not far away” Jonathan Govaerts, imec/UHasselt/EnergyVille.

In addition, this “multi-wire” configuration allows parallel switching of solar cell circuits, maximizing the energy production of the cells with different orientations to the sun (due to the curved surface) and thus achieving energy gains in the shade. As a result, compared to more conventional interconnections, this innovative interconnection leads to an efficiency gain of 6%.

Extra possibilities

But the possibilities extend further. The consortium looked at the addition of additional optical coatings, which could increase efficiency even further, while reducing heating of the solar panels and cabin. The latter increases passenger comfort and reduces air conditioning consumption.

Moreover, the integration of promising tandem cells has also been demonstrated, combining the electricity production of silicon on the one hand and perovskite solar cells on the other. Automation of the (originally manual) production process of the “multi-wire interconnection films” has also been achieved, allowing future innovations to be implemented in a cost-efficient manner in these glass solar panels.

Flexibility

“Further scale-up is absolutely necessary,” said Jonathan Govaerts, project coordinator and senior researcher at imec and UHasselt within EnergyVille. “But what makes this project so special is the proof-of-concept for a wide range of applications.

The flexibility of the developed “multi-wire” interconnection in integrating solar cells in different surfaces and various configurations is impressive. Combined with the next generation of solar cells, solar roofs on trucks are not far away, and what’s more, this technology also opens the door to other applications, such as, for example, integration into metal hoods, lightweight structures or challenging architectural shapes.”

Seamless integration

While the current grid arrangements of solar panels will not disappear from the streetscape anytime soon, they are only a beginning. The SNRoof project opens the door to a seamless and organic integration of solar panels into our environment, unobtrusively striving for a climate-neutral future.

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