World Solar Problem: How Far In A Solar Automobile?

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Solar energy is a great source of renewable energy, but it always had its limits. At best, only 1,000 watts / m2 are available on the earth’s surface on a sunny day, and the limited efficiency of solar panels further reduces this. It’s such a small amount that solar panels in passenger cars have been limited to minor tasks like maintaining batteries and running low-power fans.

However, where some see an impossibility, others see an opportunity. The World Solar Challenge is a competition designed to show the true potential of solar powered transport. Now, 30 years after its inception, what was previously impossible is being achieved by multiple teams in less than a tenth of the original time. To keep the competition on their toes, the rules have evolved over time, repeatedly pushing the boundaries of what is simply possible with sunlight. This is not a standard transport. This is a technical challenge. How far can you go with a solar car?

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The Quiet Achiever, pictured here on its 1982 cross-continental journey, was the forerunner of the World Solar Challenge.

The event was preceded by a Hans Tholstrup, a Danish born adventurer with a passion for sustainability and alternatives to fossil fuels. Working with Australian touring car legend Larry Perkins and his brother Garry, the trio built a solar-powered vehicle called The Quiet Achiever. In 1982, the light vehicle drove 2,518 miles from Perth to Sydney in just 20 days, all in sunlight. The feat received a lot of public attention and led directly to the first run of the World Solar Challenge just 5 years later.

The inaugural competition was put together in 1987 in collaboration with the South Australian Tourism Commission. At the start there were 13 participants, 6 of whom reached the finish line. General Motors won the event with Sunraycer, completing a course from Darwin to Adelaide in just 44 hours and 90 minutes. He beat Ford Australia’s runner-up start by almost 23 hours.

Initially every three years, from 1999 every two years. In a few years, over 50 teams have joined the race on the starting line, although many are retired due to falls or mechanical problems ending their race. Participants come from different countries around the world to take part in the race. For the past three decades of competition, automakers, tech companies, universities, and even colleges have competed. Team sponsors often come from high-tech industries dealing with technologies relevant to such applications. Having a company on board that can supply highly efficient solar panels or a light, powerful motor can go a long way.

The race runs from Darwin in the Northern Territory to Adelaide in South Australia. The race ends with the participation of all participants in Victoria Square for the closing ceremony.

Over the years, the race has evolved as new technology has emerged. The regulations for the maximum area of ​​solar panels have been tightened as the modules have become more efficient over the years. This helps keep costs down as the latest and greatest solar panels don’t come cheap. Other regulations focus on limiting on-board energy storage and ensuring a level playing field among competitors. Competition vehicles drive on public roads and must therefore comply with speed limits and road traffic regulations.

As average speeds have increased over the years, the rules have changed to put a practical emphasis on practicality as well. The aim is to help competitors develop vehicles that are closer to something that can be used on the road. The competition now includes the cruiser class for multi-passenger vehicles rated on factors such as ease of entry and the total number of passenger kilometers traveled during the journey.

It’s all about efficiency

The Tokai Challenger, which was built by students from Japan Tokai University, won the event in 2009. Note the extreme, optimized design that aims to minimize air resistance.

Similar to traditional motorsport, the regulations of the World Solar Challenge have shaped the design of competition vehicles. With limited energy available, efficiency is critical in all aspects of design. A competitor who is able to capture the most energy and convert it into forward motion is best able to bring home victory.

On the electrical side, the first problem is getting as much energy as possible from the available sunlight. Installing the highest efficiency solar panels available is only part of the equation. The teams often tilt their solar panels so that they are perpendicular to the rays of the sun after the end of the journey at 5:00 p.m. in order to make the most of the light available before sunset. In order to squeeze the last drop out of the cells, the maximum power point tracking hardware is used to keep the solar cells in their optimal operating range. Motors and controls are designed similarly, with an emphasis on using as little energy as possible to drive the vehicle.

In 2013, the cruiser class for solar vehicles was introduced, which is intended to carry several passengers.

Perhaps the biggest influence on the exterior design of these vehicles is aerodynamics. When driving for hours at a speed of up to 130 km / h, air resistance plays a major role in energy efficiency. Reducing drag to the bare minimum is key, as single occupant Challenge class vehicles often come with nosedive designs with knife blades. Wheels are often equipped with airfoil shrouds to allow them to cut through the air. In the past, with most designs, drivers have been in near-lying or lying positions to minimize their contribution to the profile of the vehicle. In recent years, however, the seating positions have been changed to a more natural upright position to better resemble a road vehicle. Entries in the cruiser class tend to have more uncompromising designs in this area as they are necessarily bulkier and larger in order to accommodate multiple seated passengers. However, they continue to aim to minimize drag wherever possible, even if streamlined knife-edge designs are not practical in this class.

Mechanical efficiency is also key to building a competitive vehicle. Rolling resistance must be kept to a minimum and specially designed tires are used to pursue this goal. It is also important to ensure that bearings, chains, and belts are properly selected and maintained to avoid undue losses in these areas. Paying attention to such small details can have serious repercussions as you travel thousands of miles, especially when there is so little energy available.

Look to the future

As teams continue to build cars to overcome existing challenges, the rule set continues to shift to push the boundaries further. For 2021, regulations will change again to focus on driver comfort and dynamic stability of competitive vehicles and to include new safety features such as daytime running lights. All of these changes affect performance, from changing aerodynamics to adding new power to the vehicles. However, it is precisely this challenge that forces teams to innovate and adapt their designs in order to create better, more powerful solar cars than ever before. While we don’t expect solar panels to become the standard for passenger cars anytime soon, save for a major change in our sun, the event still serves as a useful showcase and testing ground for the best of solar and electric propulsion technologies.

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