Running on Sunshine: A Case Study on Solar Electric Vehicles

BatteryBits Editors

Published in

BatteryBits (Volta Foundation)

8 min readApr 3, 2021

This story is contributed by Pooja Vadhva

Recently, there has been much hype surrounding solar-powered electric vehicles (EVs) such as the Tesla Cybertruck and the futuristic Lightyear One. How much range is achievable on solar power alone?
Solar EVs could revolutionize urban cities by allowing vehicles to rely less on the grid and reducing the need for charging infrastructure.
This article provides a case study of solar EVs in developing countries.

A solar panel electric car

“A van, because you have a big flat area, that’s actually where solar starts making a little more sense…even if the apocalypse happens, you can still drive it around. ” — Elon Musk’s thoughts on the potential for a deployable solar roof to enable the Tesla Cybertruck and electric van to be grid independent.

But how realistic is this?

Solar Range

Elon Musk has suggested that a solar roof can provide roughly an additional 50 km of range per day. Although Musk has hinted at a solar roof option for the Cybertruck, the most premium solar car being launched this year is the Lightyear. Dutch startup Lightyear strives towards sustainability by maximizing drive efficiency and solar yield and seeks to achieve one lightyear of kilometers powered by solar by 2035. The company claims to have 1000 solar tiles fitted across the bonnet and roof of the EV which enables their soon-to-be-released EV to achieve a range of 725 km, with the solar panels providing an additional up to 70 km per day (assuming a completely sunny day). The solar panels are able to provide that much range due to the car’s extremely efficient design, consuming 83 Wh per kilometer on the Worldwide Harmonised Light Vehicles Test Procedure (indication of energy consumption under realistic driving conditions), a third to a half that of a typical EV, with what it claims to be the most aerodynamic five-seater designed to date. The integration of 5 m^2 of solar panels around the streamlined vehicle body is especially impressive, considering that the dimensions of a typical car roof measure 1.5 m in width by 2–3 m in length. With its sleek, futuristic look, the Lightyear One provides considerable additional range thanks to its solar panels, reducing the need to spend any time or money at a charging station.

At $170,000, however the Lightyear One does not come cheap. For this price, you could buy a state-of-the-art EV and install enough solar panels on your house to power both your EV and household appliances. In addition, it assumes around 5.5 hours of “maximum yield under ideal solar conditions” which can be challenging depending on the climate you live in.

Solar cell efficiency

Solar panels for EVs have to be designed to withstand vibrations, weather conditions including hail and snow, and debris during driving whilst being extremely thin and flexible to fit around the aerodynamic design of the vehicle. Unlike typical residential installations, the relatively flat angle of the panels on the roof of the car are not optimal for capturing sunlight, accounting for a roughly 30% loss in energy generation. To maximize charging your vehicle from solar power, you have to park your car directly under the sun which could be difficult if you have an underground or covered space.

With the maximum theoretical limit for silicon solar cells at 30%, most widely available commercial silicon solar cells exhibit an efficiency of ~20–25%. While multi junction solar cells have efficiencies of 40–50%, these tandem solar cells typically require vacuum processes making them commercially prohibitive. While Lightyear claims to manufacture panels encased in safety glass so strong that a person can walk on them without any fractures, it is unclear whether these panels will remain this robust during the lifetime of the EV.

Hyundai has joined in on the solar panel game with its hybrid car, the Sonata only for Forbes to point out that its panels provide only 2 miles of additional range per day even when parked in the sun. On the other hand, for countries that lack charging infrastructure, solar EVs could be highly beneficial and enable EV adoption while the grid infrastructure scales up over time.

Comparison of solar panel efficiency of Hyundai hybrid care and rooftop

The German start-up Sono Motors provides hope for a more practical solar hybrid EV. You cannot miss this car with 248 solar cells plastered around its body. Albeit less flashy than the Lightyear, it provides an additional 33 km of charge per day, at a much more reasonable price of $28,500. With the reduced cobalt content in its batteries, Sono makes the case that its cars are a more ethical purchase.

But are solar cars for everyone or it is a technology meant only for sunnier countries? Consider the global solar energy generated in kWh/m^2 per day. With a 5 m^2 array of solar cells providing 215 W/m^2, the Lightyear One generates almost 6 kWh of energy per day, assuming a nominal 5.5 hours of peak solar daylight for a range of 70 km. This 5.5 hours of peak solar daylight corresponds to 2000 hours of annual sunshine, suggesting that much of northern Europe and Canada may not receive the full benefit of 70 km/day. Many of the developing nations in Asia, Africa and regions in South America, however, both exhibit high solar insolation and have unreliable and underdeveloped grid infrastructure, ideal conditions for solar panel EVs.

Solar panels in Asia case study

Could solar EVs make financial sense in south and southeast Asian markets where solar output is high? In India, one of the key reasons for poor EV uptake is the lack of charging infrastructure. The Indian government aims to build 2,600 EV charging points by 2023, in contrast to the 38,000 charging stations currently installed in the UK , which has 1/20th of the population. Perhaps the likes of Lightyear or a Cybertruck do not make financial sense here, but what about a low cost, small EV: a rickshaw? For example, a low-cost solar 3-wheeler (similar to a rickshaw) designed by an Australian high school student to transport pregnant women to the local hospitals in Zimbabwe shows the promise of solar mobility solutions.

An electric rickshaw with solar panels integrated into the flat roof could be ideal for sunny Asian countries, although the additional 40 kg of panels must be considered when calculating the mileage. A case study suggests that 560 W of 20% efficient solar panels can output 1.9 kWh per day in New Delhi, given 3.7 hours of daily sunshine and 10% shading loss. Since the solar e-rickshaw weighs less than the Lightyear EV, assuming a 56 Wh per kilometer efficiency (e-rickshaw with a 4.8 kWh battery pack and 85 km range) an additional range of ~32 km per day is achieved. Contrasting an e-rickshaw to a solar e-rickshaw, it takes ~5 years to recover initial capital cost due to solar panels and within 7 years a saving of £466 (650 USD) is made using the solar e-rickshaw due to the cost savings in refueling. A solar e-rickshaw may be a reliable solution for countries with poor electrical infrastructure. It may also help reduce emissions, since many Asian countries still rely heavily on coal and other non-renewables for their electricity.

The solar e-rickshaw circuit diagram and electronic components

Solar EVs do not have to be limited to e-rickshaws. As of 2020, the Ministries of Power and Renewable Energy, Heavy Industries and Finance in India are planning on providing subsidies to solar cars for automakers who can manufacture this technology. Automaking giant Mahindra & Mahindra has already acquired a solar panel patent for its cars and a consumer vehicle may be arriving soon.

Charging frequency of solar EV and current EV on market

Summary and Outlook

In sunny developing countries where grid infrastructure is poor or non-existent, a low-cost solar EV can make economic sense as shown by the case study of the solar e-rickshaw, with consumer vehicles yet to come. For those not living in a high insolation area, is the extra range still worth the cost? With the Cybertruck solar option predicted to cost an extra £4k (5.5K USD), the cost savings might not justify the purchase, but the charging time saved might. Depending on the users’ charging behavior, people in large cities living in flats may end up waiting until the battery of their EV is almost flat before using public charging locations as they do not have access to home charging so cannot top up overnight. Having solar panels could provide additional charging and keep the battery pack at a higher state of charge (SoC), reducing battery degradation and increasing the lifetime of the EV. For developing countries lacking grid infrastructure, solar EVs may serve as a key enabler for adopting EVs as the grid ramps up over time to meet this demand. Moreover, solar EV adoption could become more popular as solar cell prices continue to drop and even today, solar EVs provide benefits in countries with an underdeveloped grid. Perhaps someday EVs running solely on sunshine will be possible for those in sunnier locales.

Acknowledgements

Thanks to Tim Suen, Linda Jing, Eric Zheng, and Nicholas Yiu for reviewing portions of the draft of this article and providing helpful feedback.

Pooja is currently a PhD student at the University College London researching solid electrolytes to enable high energy-density lithium metal batteries. Her work focuses on fabricating thin-film solid electrolytes, cell testing and failure characterization using X-ray methods such as X-ray computed tomography. Prior to her PhD she interned at Jaguar Land Rover modelling cell cycling behavior in the advanced battery team. She has also worked with an electric scooter company, SKUTE designing battery packs for petrol to electric scooter conversion in Bali. Her interests lie in industry developments within the electric vehicle battery sector, helping to advance battery technology from laboratory stages into commercialization.

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