• Skip to primary navigation
  • Skip to main content
  • Skip to primary sidebar
  • Skip to footer
  • Subscribe
  • Advertise

Power Electronic Tips

Power Electronic News, Editorial, Video and Resources

  • Products
    • Power Supplies
    • AC-DC
    • DC-DC
    • Battery Management
    • Capacitors
    • Magnetics
    • MOSFETS
    • Power Management
    • RF Power
    • Resistors
    • Transformers
    • Transistors
  • Applications
    • 5G
    • AI
    • Automotive
    • EV Engineering
    • LED Lighting
    • Industrial
    • IoT
    • Wireless
  • Learn
    • eBooks / Tech Tips
    • EE Training Days
    • FAQ
    • Learning Center
    • Tech Toolboxes
    • Webinars & Digital Events
  • Resources
    • Design Guide Library
    • Digital Issues
    • Engineering Diversity & Inclusion
    • LEAP Awards
    • Podcasts
    • White Papers
    • Design Fast
  • Video
    • EE Videos & Interviews
    • Teardown Videos
  • EE Forums
    • EDABoard.com
    • Electro-Tech-Online.com
  • Engineeering Training Days
  • Newsetter Subscription

Cars powered solely by solar energy? Sure…but with a very big “but”

October 26, 2022 By Bill Schweber

Lately, I’m seeing a lot of cases where solar power is posited as the energy solution for “everything.” And why not? It’s free and ubiquitous, and it feels good to say you are using it. I recently read a column by someone (sorry, I couldn’t find it afterward) about the easy practicality of cars powered entirely by solar power.

To be honest, I couldn’t tell if the author was serious or just being sarcastic, as he said there’s no reason you can’t just put a solar panel on the roof of your electrified car and drive away happily. Oh, yes, you might need a battery for night or cloudy times, but that’s it. The author even speculated that the lack of such cars was a conspiracy by the big auto companies and their suppliers….well, you get the picture.

The reality is that it is a conspiracy, but one promulgated by the laws of physics as we know them. The harsh reality is that even if the efficiency of solar panels and all the intermediate electronics was 100%—and they are not, by quite a factor—there isn’t enough solar energy falling on the Earth’s surface per square meter to power a car in any meaningful way.

A quick look at the numbers tells the story. The solar constant of impinging radiation at the top of Earth’s atmosphere is about 1.4 kW/m², and it’s all further losses from there. Reflection at the top of the atmosphere and back to space due to clouds, atmospheric particles, or bright ground surfaces (such as sea ice and snow), plus further absorption in the atmosphere by water vapor, dust, and ozone, all combine to attenuate this (Figure 1). In the end, only about 1 kW/m2 is available for the PV cells—that’s under ideal conditions at solar equinox and when the PV cell is normal to Sun’s angle. [Note: other very credible sources place the amount of solar power reaching the Earth’s surface at about 340 W/m2; that’s a somewhat significant difference likely due to “correction factors” which I haven’t had time to resolve. But it doesn’t significantly change the point of my argument that follows.]

Fig 1: Only a small fraction of the Sun’s power reaching the Earth is available at the Earth’s surface due to various “loss” mechanisms. (Image: NASA Earth Observatory)

Looking at the various losses in the photovoltaic cells, inverters, motors, and other circuitry, you’d be lucky to get roughly around 50 W/m2 of useable power. That’s not much in terms of doing real physical work, such as moving a car at any speed.

Of course, the real issue is the constant “energy versus power” balance related to energy harvesting. First, remember that the terms “energy” and “power” are often used interchangeably in casual conversation by non-engineers and engineers alike; they are distinctly different but closely related physical parameters.

How so? Energy is the ability to do work, while power is the rate at which energy is collected or used. Mathematically, power is the time derivative of energy, while power is the time integral of energy. In practice, in any energy-harvesting scenario, you collect energy when it is available—often in erratic and unpredictable spurts—and you spend it as needed in the form of power at a rate that is required to do the work. It’s like saving your coins in a piggy bank until you have enough to spend all at once on that shiny new toy or gadget.

So, can you power your car via solar power alone? Absolutely yes, as long as you don’t plan on going anywhere for extended idle periods while the car’s battery stores up energy collected by the PV panels on the roof, at most a few square meters. You might have to wait weeks for enough energy to be collected and stored to go even a few kilometers at a reasonable speed—and that ignores other car functions such as heating, safety functions and features, headlights and other essential lights, and more. Of course, if you park in the direct Sun to collect maximum solar energy, you’ll have a very, very hot car that will likely need air conditioning; yet another power drain.

The harsh reality hasn’t stopped some folks from trying. As ambitious as it sounds, a few companies are working on cars that charge via such panels (they also include an onboard charger for conventional EV charging as well). These vehicles are not the ones you may have seen for the well-known Australian World Solar Challenge, which has been running for over 30 years with three classes of cars (Figure 2), none of which are even close to “street legal.”

Fig 2: The Australian World Solar Challenge has been running every two years since 1987; its entrants are one-of-a-kind and nowhere near street legal. (Image: Australian World Solar Challenge)

Among the companies working on viable solar-powered cars are Lightyear (based in the Netherlands) with their Lightyear One (Figure 3). It has about 50 square feet of solar cells (4.6 m2) and four lightweight electric motors (one in each wheel) to minimize weight and extend range, rather than a single motor and gearbox.

Fig 3: The Lightyear One looks somewhat like a conventional sedan, but it is capable of fully self-contained solar charging. (Image: Lightyear)

The Lightyear One prototype claims a range of more than 440 miles (700 km) on a full charge; a full day in the Sun provides a range of a little over 40 miles (64 km). If you are wondering, “how much does it cost?” and “when will it be available?” the answers are “$175,000” and “next year.” Before you say, “that’s crazy”, the company claims that more than 160 vehicles have already been reserved in Europe, with most of them paid for upfront (US sales are planned for a later time).

Another developer of these solar-powered vehicles is San Diego-based Aptera Motors Corp. with the Luna, a two-person, gull-wing, three-wheeled vehicle (Figure 4). With about 24 square feet (2.2 m2) of solar cells, they claim a range of up to 40 miles after a full day of charging in the summer sun; the 350-V battery pack is supposed to be good for 250 to 1,000 miles on a full charge depending on pack capacity, which can range up to 700 W-hr), whether from solar or grid.

Fig 4: The Aptera Luna is a three-wheel solar-powered vehicle that claims a 40-mile range on a full day of optimum charging. (Image: Aptera Motors Corp.)

As for price, they say they’ll be delivering a version with a 400-mile range to US customers next year, with prices for a basic model starting at $29,800—significantly less than the Lightyear One. They are classifying it as a three-wheel motorcycle rather than a car to avoid some of the regulatory mandates, such as airbags. (They say that in most states in the US, such vehicles do not require a motorcycle license, only a regular driver’s license.)

In addition to the lower rolling resistance of three wheels versus four and extremely lightweight due to the use of highly advanced composite materials, Aptera claims one of their keys to success is drag coefficient (wind resistance) which is about half that of conventional vehicles. This is critical as drag, and its associated losses increase with the square of the vehicle’s speed.

These solar-only cars raise some interesting questions: Are they just expensive toys for those who only need to go a few miles per day with minimal load? Are they only available for longer trips or cloudy days for those with another vehicle? Rather than look to park in the shade, will owners of these vehicles look for sunny spots (and as the Sun moves, the shade moves as well) and avoid parking garages? Will people accept vehicles that lack standard safety features (many are mandated), as well as comfort features which are now standard such as heat and air conditioning (yet parking in the Sun to maximum charging can really heat up the interior)?

The something-for-almost-nothing mindset of solar-only/mostly cars clearly has infected many bloggers and commentators on both sides of the story (see References). Some suggest charging your vehicle via your rooftop panels is a viable option, but my question is, “what else could you be charging with those panels?” Some say, “what’s the big deal? Why can’t it be one?” as well as those who deflate this sort of wishful thinking, no matter how well-intentioned.

Related EE World Content

What battery chemistries are used in grid-scale energy storage?
Battery Management Systems: Effective ways to measure state-of-charge and state-of-health
Battery pole and busbar connectors for energy storage systems
Signal transformers for BMSs sport high isolation, working voltages
Rugged connectors designed for automotive BMS and inverters
Next-gen BMS goes wireless, with proprietary protocol and functional safety compliance
Photovoltaic high-power fuses designed to UL 248 and IEC 60269 standards

References

Charging

  • Bike Rumor, “#Vanlife: Can you charge an electric vehicle with rooftop solar panels?”
  • World Economic Forum, “Solar charging your car is possible, researchers say. Here’s how”
  • Solar Edge, “Meet the World’s First EV Charging Solar System”
  • SolarMax Technology, “Guide to Charging Your Electric Car with Solar”
  • Com, “Charging Your EV With Solar Panels and Using IRA Incentives To Bring Down the Cost”
  • EE Times, “Where Solar Might Fit Into EV Charging Equation

Solar Radiation & Power

  • Wikipedia, “Solar irradiance”
  • of Energy, Office of Energy Efficiency & Renewable Energy, “Solar Radiation Basics”
  • NASA Earth Observatory, “Earth’s Energy Budget”
  • University of Calgary, “Energy Education”
  • University of Oregon, “Solar Energy Basics”

 

You may also like:


  • Battery Management Systems: effective ways to measure state-of-charge and state-of-health

  • Inverters for green energy systems

  • Under the hood of PV inverters

  • Next-gen BMS goes wireless, with proprietary protocol and functional safety…
  • PVs
    Solar systems’ maximum power point trackers

Filed Under: Automotive, EV Engineering, Featured

Primary Sidebar

Featured Contributions

Meeting demand for hidden wearables via Schottky rectifiers

The case for vehicle 48 V power systems

GaN reliability milestones break through the silicon ceiling

Developing power architecture to support autonomous transportation

What makes SiC tick?

More Featured Contributions

EE LEARNING CENTER

EE Learning Center

EE TECH TOOLBOX

“ee
Tech Toolbox: Internet of Things
Explore practical strategies for minimizing attack surfaces, managing memory efficiently, and securing firmware. Download now to ensure your IoT implementations remain secure, efficient, and future-ready.

EE ENGINEERING TRAINING DAYS

engineering
“power
EXPAND YOUR KNOWLEDGE AND STAY CONNECTED
Get the latest info on technologies, tools and strategies for EE professionals.
“bills

RSS Current EDABoard.com discussions

  • Lightbox circuit help
  • Battery sensing circuitry for coin cell application
  • Replacement of the rectifier diode with a MOSFET transistor?
  • differential amplifier with active load
  • How can I get the frequency please help!

RSS Current Electro-Tech-Online.com Discussions

  • Telegram Based Alarm - Sensor cable protection
  • using a RTC in SF basic
  • 100uF bypass Caps?
  • Lightbox circuit
  • how to work on pcbs that are thick

DesignFast

Component Selection Made Simple.

Try it Today
design fast globle

Footer

EE World Online Network

  • 5G Technology World
  • EE World Online
  • Engineers Garage
  • Analog IC Tips
  • Battery Power Tips
  • Connector Tips
  • DesignFast
  • EDA Board Forums
  • Electro Tech Online Forums
  • EV Engineering
  • Microcontroller Tips
  • Sensor Tips
  • Test and Measurement Tips

Power Electronic Tips

  • Subscribe to our newsletter
  • Advertise with us
  • Contact us
  • About us

Copyright © 2025 · WTWH Media LLC and its licensors. All rights reserved.
The material on this site may not be reproduced, distributed, transmitted, cached or otherwise used, except with the prior written permission of WTWH Media.

Privacy Policy