Solar energy is already used in hybrid cars, such as the Hyundai Sonata, which can recharge up to 60% of the battery every day through its solar roof. Credit: Hyundai.

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The main automotive companies are testing new models of electric cars with photovoltaic panels that bring the dream of the solar car seems close. The implementation of solar energy in transport goes further and is already tested from trains to airplanes, but it still has important challenges ahead.


The unveiling of an experimental Toyota Prius with photovoltaic cells incorporated into its roof, hood and rear window is one of the most recent signs that the commitment to solar energy has also reached the transport sector. One of the ideas gaining the most traction is to use electricity generated from the sun's rays to boost the driving range of electric cars. But beyond that, there are also those who dream of using this clean energy source to power trains, planes and ships. While some innovative designs have materialised in the real world, others still dwell in the land of possibilities. Through some examples we review where the transport sector is at with regard to solar energy.

The idea being developed by Toyota, which is working on the project with the manufacturer Sharp and the prestigious Japanese public research centre NEDO, is to harness solar energy to increase the cruising range of electric vehicles and thus make them more energy efficient and have less environmental impact. This is not the first time the Japanese automotive giant has attempted this. A decade ago it added a solar-panelled roof to a Prius model, but at the time it didn't seem like a mature idea. Later, in 2017, it released in Japan a version of the same car with integrated photovoltaic cells, albeit with rather limited capacities.

Now the Japanese carmaker has made further advances and claims to have developed an electric model that has high-efficiency solar cells (34%) that is able, when parked, to store in its battery enough solar energy to provide 44.5 kilometres of extra range a day (up to 56 km when the vehicle is being driven). In the Prius previously sold in Japan, it only managed 6.1 km. Early last July, Toyota announced that it was ready to begin public road trials with this prototype and evaluate its benefits "based on improvements in CO2 emissions reductions and convenience," as well as "the number of times a vehicle requires recharging."

Increasing the paneled surface increases the autonomy of the electric car, allowing self-loading, with greater efficiency and less impact. Credit: Lightyear.

The issue of range

Not everyone is sure that betting on solar energy in the car sector is the best option. Among those who have expressed doubts is visionary Elon Musk, who is concerned that the available surface is not sufficient to take significant advantage of this clean source. Others, in contrast, are more in line with Toyota. Its competitor Hyundai, for example, has just launched in the South Korean market a hybrid Sonata model with a solar roof, an addition that would allow it to recharge between 30% and 60% of its battery each day and, with six hours of daily recharging, increase the distance travelled by 1,300 kilometres per year.

In Europe, too, some companies are following suit. This Dutch company claims to be developing an electric and solar model with a range of more than 700 kilometres that will be available in 2021 at a price of 149,000 euros. Then there is this German start-up, which claims to have already received more than 10,000 orders for a car based on the same type of propulsion and also available in two years, but "perfect for day-to-day use" and in pre-sales at a price of 25,000 euros.

Ricardo Guerrero Lemus, member of the International Energy Agency and professor at the University of La Laguna (Tenerife), believes that in the field of solar cars, "there is still some way to go, but it is clear that [this option] will begin to be introduced soon, not as an independent solution, but to provide energy to the batteries of electric vehicles." In his opinion, "any contribution of solar energy should be welcomed because we will need less plug-in time to charge the battery."

The NEDO research centre stated in a study published last April that in Japan it is considered that there will be a market for photovoltaic systems in cars starting from 2030, suggesting that something is still missing. But the work of engineers and industry specialists is intensifying nevertheless. In addition to the increased range, one of the advantages that solar energy can bring to cars is the increase in "comfort inside the vehicle," because it can contribute to supplying functions such as air conditioning or lighting, according to Guerrero. On the other hand, he points out that "the main difficulty is the price of the multi-unit solar cells, which in this case should be flexible and even colourable."

Solar energy is also being integrated into aviation. An example is the Solar-Impulse II, that went around the globe using mostly photovoltaic energy. Credit: Solar Impulse.

Sunlight to power buses, trains and airplanes

The idea of powering vehicles with sunlight is intriguing not only to some car manufacturers, but also to developers of other means of transport. At different latitudes, there have already been several attempts to turn this vision into reality. There is this Ugandan company, which has produced a prototype solar bus. In other countries, such as India and Australia, photovoltaic panels were applied to the roofs of some trains (in the former country as an integration with diesel propulsion, while in the latter so that solar is the only source of energy).

Only a few weeks ago, a railway project was also announced in the United Kingdom. It is a pilot project to experiment with a "solar railway farm," i.e. a rail line located in the south of England connected to a trackside solar farm that feeds some elements of the network such as signals and lights. Its developers believe that it is the first step towards creating railway infrastructure capable of supplying trains with photovoltaic energy directly and thus reducing the need to use fossil fuels.

The integration of solar energy has also been tested in the nautical sector and in aviation. In this latter case, among the projects that have generated the most media impact is the Solar-Impulse II, an aircraft largely powered by solar energy that between 2015 and 2016 completed the first round-the-world flight, traveling across some sections at night thanks to the energy stored during the day. Also noteworthy is the AirBus Zephyr S, an unmanned aerial vehicle powered by solar energy and designed as a "pseudo-satellite" able to remain in flight at about 21,000 metres for months at a time and perform tasks of "visualization, detection and connectivity." The vehicle has already aroused particular interest from the UK government, the company explained.


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Tungsteno is a journalism laboratory to scan the essence of innovation. Devised by Materia Publicaciones Científicas for Sacyr’s blog.

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