Solar Cars — In Depth

Solar cars may soon become one more benefit of falling battery prices and the concurrent rise of fossil fuel costs. Since solar cars do not burn fossil fuels, they may reduce carbon dioxide emissions per vehicle by 43-54%. Recent advancements in battery efficiency may be the residual element that make solar cars ubiquitous. Until such a time, however, the small surface of a car limits the amount of energy that can be used to propel a car and its systems through solar power.

Since solar cars must be light and efficient, those that are constructed from ultralight composites are preferable, as they save weight. Prototype solar cars demonstrate the need for even more safety, technology, and — oh, yeah — design that’s a little bit more appealing to the average consumer.

Converting the sun’s energy through solar cell technology

The sun can power a vehicle when solar energy is converted into electric energy. Today, this conversion is usually obtained through photovoltaic (PV) cells, but new hybrid perovskite solar cells (PSCs) may surpass the conventional low-efficiency and stability that limits PV technology.

Sunlight is comprised of particles called photons. As both particles and waves, photons are responsible for refraction and diffusion. Some interesting characteristics about photons are that, as of what we know now, their frequency is independent of the influence of mass, they don’t carry a charge, and they can be a form of energy that is transferred or converted to other types of energy. It is that process of conversion that creates the photoelectric effect that makes solar power possible. When photons strike solar cells, they create a flow of electrons, resulting in electric current.

When exposed to sunlight, an arrangement of PVs produces power, but many other components are needed in order to conduct, control, convert, distribute, and store the energy produced in conjunction with PVs. These components can include a DC-AC power inverter, battery bank, system and battery controller, auxiliary energy sources and, sometimes, a required appliance. A balance of system hardware is needed, too, which involves wiring, overcurrent surge protection and disconnection devices, and other power processing equipment.

A PV system often uses batteries to store the energy it produces and to later supply that energy to electrical loads, such as at night or in cloudy weather. Batteries also supplement PV systems when they are near to their maximum power point, to power electrical loads at stable voltages, and to supply surge currents to electrical loads and inverters.  A battery charge controller keeps the battery from overcharging or overdischarging.

Less common than PVs but possibly more striking is recent research around inorganic-organic hybrid perovskite solar cells (PSCs). Cost effective, efficient, and possessing photostability, PCSs may change the way we think of solar cells. Dr. Seok at the Ulsan National Institute of Science and Technology in South Korea and a research team have studied how PSCs, a mixture of organic molecules and inorganic elements within a single crystalline structure, can work together to capture light and convert it into electricity. With unique crystal structures consisting of two cations and one anion, they can be fabricated more readily and inexpensively than silicon-based solar cells, due to their flexible and rigid substrate. PSCs reaching a photovoltaic efficiency of 22.1%, comparable to that of single crystalline silicon solar cells (25%), may, indeed, be the go-to solar cells of the future.

How a solar array creates enough energy to power a solar car

A solar array consists of hundreds of solar cells that convert sunlight into electricity. In order to construct an array, cells are placed together to form modules, which together build into an array. For an array to be able to power a solar car, one of the following configurations is generally used.

• Horizontal: Good for low latitudes; offers little interaction with the wind;
• Vertical: Free standing or integrated sails harness wind energy;
• Adjustable: Tilting the axis to increase power when the sun is low or to the side;
• Integrated: Covering every available surface with solar cells;
• Trailer: Retrofitting existing vehicles with little stability and may also include the batteries or drive motor;
• Remote: Mounting at a stationary location instead of the vehicle.

A selection of solar arrays to power a car involves a geometric configuration of optimal power output, aerodynamic resistance, and vehicle mass. Additional considerations can often include the surface area of a vehicle, degree of cooling of the cells and shading of the riders, mounting and encapsulation, and overall efficiency of the solar cell.

World Solar Challenge offers design and function inspiration for solar cars

The World Solar Challenge is an event created to offer universities and research institutes a venue in which they can design then race solar cars across 1878 miles of hot, dry Australian landscape. In 1982, two entrepreneurs, Hans Tholstrup and Larry Perkins, wondered if their home-built solar car, “Quiet Achiever,” could cross Australia from west to east. Success! The results inspired Tholstrup to prod others to explore the boundaries of sun-powered transport. With assistance from a major sponsor, the South Australian Tourism Commission, the World Solar Challenge continues today as a showcase for the development of advanced automotive technology and the promotion of alternatives to conventional vehicle engines. The event is held every three years.

Solar cars typically are low in profile, need a proven charging system, and contain a supplemental battery pack. Today, while solar cars push the limits of energy efficiency, they also can inform everyday vehicle technology.  World Solar Challenge cars must utilize no more than six square metres of solar panels as they test and promote the solar cars through an “ultimate synergy of nature, motion, and innovation.”

The three classes of World Solar Challenge entries are:

• Challenger Class: These tend to be smaller and sleeker with improved driver vision. They involve lateral thinking to meet the conflicting needs of maximizing the solar collection area, minimizing aerodynamic drag, meeting requirements for driver vision, and other design requirements.
• Cruiser Class: Entrants must work with specifications of payload, energy consumption, and, quite importantly, a subjective element of practical aesthetic design that would appeal to consumers around the world.
• Adventure Class: This is non-competitive and allows cars built for previous editions of the event to run again, usually with new team members. It can also be used as a catchment for those who, while meeting the exacting safety standards, may not have quite made full compliance with the latest requirements.

Many memorable solar cars have emerged from the World Solar Challenge:

The first World Solar Challenge took place in 1987, with winning entry, GM’s “Sunraycer” hitting an average speed of 42 mph. Ford Australia’s “Sunchaser” came in second.

The 2007 World Solar Challenge became the fourth successive victory for the Dutch Nuon Solar team in the challenge class, averaging 55.97 mph under new, more restrictive rules. The Belgian Punch Powertrain Solar Team’s “Umicar Infinity” placed second.

In 2012, a high school student and his mentor from Adelaide, Australia helped to design a solar-powered car to transport pregnant women in Zimbabwe to a local health clinic. They came up with a low-maintenance, solar-powered, three-seat vehicle that was capable of traversing difficult terrain.

“Stella,” a solar car with a real lack of aesthetic design appeal, first appeared in the U.S. in 2014. Students from the Eindhoven University of Technology in the Netherlands originally built the solar-powered vehicle as an entry in the World Solar Challenge race,  A more recent version comes with the claim that it produces more energy than it uses, has a range of 621 miles on a full charge, and can reach a top speed of 77.6 mph. Stella demonstrated that technology that had once been directed to the race track could also be applicable to the consumer market with combined performance and specialized innovation. It can discharge energy back into the grid, so it’s got the potential to be a prototype for other solar-powered vehicles that provide a mobile source of renewable energy.

The last time the World Solar Challenge was held was 2015. Here are the highlights of that event:

Challenger Class

1st Nuon Solar Car Team “Nuna 8” (The Netherlands) average speed 91.75
2nd Solar Team Twente “Red One” (The Netherlands) average speed 91.63
3rd Tokai University “Tokai Challenger” (Japan) average speed 89.41

Cruiser Class

1st Eindhoven “STE2” (The Netherlands). Total Score: 97.27 points*
2nd Kogakuin “Owl” (Japan). Total Score: 93.61 points*
3rd HS Bochum “Sunriser” (Germany) Total Score: 82.91 points*

Mainstream solar vehicle technology advances — with nearly mainstream solar cars close by

The 2010 Toyota Prius advanced solar automotive development with is solar-powered cooling system. With ventilation that was a separate function from the motor, the vehicle worked concurrently to maintain interior vehicle temperature and pointed us to the possibilities of solar cars of the future. In just the last month, moreover, Toyota has announced that its new Toyota Prius plug-in hybrid, called Prius Prime in the U.S., comes with a full length solar panel on the roof that helps recharge the car’s lithium ion battery when the car is parked. It also powers such things as air conditioning, power steering, power windows, and interior lighting while the car is being driven.

In 2015, Envision Solar International won a statewide contract from the State of California to provide EV ARC™ products to California state departments and other state and local agencies or entities. Envision Solar was proud to be able to announce, “This means that many CA government workers and employees will now be able to charge their electric vehicles with sunlight at their workplaces!”

The “Immortus“ is a limited edition bespoke solar electric sports car with on-board storage capacity. Inspired by the world portrayed in post-apocalyptic movies, the Immortus is designed to exhibit a toughness that no other car has: endurance. The ability to run on the power of the sun and store the energy for later use make it a car of significant endurance.

In conclusion

We may still be a good way off from a viable, commercially produced solar powered car. But solar cars have a lot of positives. Their panels work silently, so they don’t contribute to existing road noise pollution. They don’t create greenhouse gases, they use free solar energy, and they may be able to free us from dependence on foreign oil. Solar power has the potential to become a viable source of renewable energy for vehicles. We just need a bit more time, research, and innovation.

Photo credit: desertdutchman via Foter.com / CC BY