February 4, 2015

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How to develop a light-weight, cost-effective solar powered car

Through this blog, I would like to propose a basic idea for designing and developing a light-weight, cost-effective single seater solar car, and also discuss the various technologies involved  in this project, which  offers great scope for innovation in the use of renewable energy. The model I am proposing is technologically advanced and environment friendly with good potential to become highly sustainable in the automobile industry.   

THE CAR

Steering

In steering, the design chiefly rests on reliability and efficiency. The steering system is precisely aligned because even the smallest misalignment can cause significant loss and increase tire wear. I suggest the use of a Rack and Pinion type of steering system.

Suspension

The object of employing suspension is obviously to cushion the vehicle.  It should be soft enough to protect the car and solar array from unnecessary jolts, and firm enough to provide a stable ride.  A good suspension will also ensure that the wheels stay in contact with the surface of the road by controlling bounce and re-bound.  A spring allows movement, and a shock absorber or damper prevents oscillation. I suggest that we use a double wishbone suspension for the front wheels and a trailing arm in the rear.

Transmission

By using hub motors and a motor controller we can eliminate the entire transmission system. As the vehicle will be rear wheel steered, the need for a differential is also eliminated. Without the transmission system, the car becomes much lighter.

Tires and Brakes

In early racing events, bicycle wheels and tires were commonly used because of their light-weight, low rolling resistance (minimal friction). These wheels and tires were generally overloaded when supporting the weight of a solar car, which affected the performance and safety of the vehicle. Fortunately, the popularity of solar car racing has prompted some tire manufacturers to construct tires designed for solar cars. Bridgestone Ecopia 16 inch, 185/60 solar car tires are best suited for the challenge.

A split hydraulic system on all 3 wheels can be used as the braking system. A manual hand-brake would also be required as a safety measure.

Chassis

The primary challenge in developing a good chassis lies in maximizing strength and safety while minimizing weight. Every extra pound requires more energy to move. This means that teams must strive to minimize weight especially in the chassis. However, safety is more important and the chassis must meet stringent strength and safety requirements. Generally, there are three types of chassis used in solar cars:

  1. Space frame
  2. Semi-monocoque or carbon beam
  3. Monocoque

The solar powered vehicle should have a chromoly framework and the body should be fabricated either with carbon fiber (if it is economically feasible) or fiber reinforced plastic.

Above: Isometric view of the chassis; Below: Upper surface design

Electrical System

At the heart of any solar powered vehicle is the electrical system.  This comprises the batteries and power electronics that control and manage the power that enters and exits the system/solar arrays.

Solar Technology

A solar cell is made up of a thin sheet of ultra-pure monocrystalline silicon. The roof of the car involves a solar array consisting of hundreds of photovoltaic solar cells converting sunlight into electricity. In order to construct an array, PV cells are placed together to form modules which are placed together to form the array. Larger arrays can produce over 2 kilowatts - a power of roughly 2.6 hp.

When sunlight hits the solar panels, photons (or light particles) energize the electrons within the panel, and the electrons move from layer to layer of the solar cells. This energetic movement between the layers generate the current which will drive the car.

Battery Technology

The electrical current is transferred to the electric motor (brushless or brush depending on the cost and the weight) of the solar car when it is in motion. When the electric motor is switched off, the current charges the battery pack. Power from the battery comes into play when conditions are not sunny. The battery pack is usually an assemblage of Lithium Ion cells or Lead Acid (whichever is more cost-effective or light) - technology similar to the cells which power our cell phones or iPods. A typical battery pack can be fully charged in about 20 hours using only the solar panels or in 3 hours using a 220 V power outlet.

Transmission of Electric Power

Solar cars do not have a transmission system like normal cars. Power to the motor is controlled by two components called Motor Controllers and Power Trackers. Motor Controllers are fitted on the wheel and their job is to transfer DC power from the batteries or solar panels into AC electricity for the motor. Manipulating the speed of the motor is done by simply setting the frequency of the AC output.

Power Trackers correct the current to maintain at a suitable level and boost the voltage when energy is to be used to charge the batteries. Continuous calibration and adjustment is necessary as power output in solar panels varies with the changes in sunlight, temperature and other factors.

COST ANALYSIS

Suspension

Steering

Brakes and Tires

Chassis and Manufacturing

Solar Array and Motor

Total Cost:  INR 23,52,909

CONCLUSION:

So, what have we achieved?

  • Low cost: Solarix (the car) can be manufactured within INR 25 lakhs, which is much cheaper than the current solar cars. Solar cars of top companies cost well above a Crore in Indian rupees.
  • Efficient use of the available energy by using better power electronics.
  • Light weight: The total weight of the car would be around 200 kgs (un-laden). Although this is much higher than other cars, through better technology and design we can reduce the weight further. By using a hub motor instead of the normal motor, the weight of the entire transmission can be eliminated.

REFERENCES:

  1. http://solarcar.engin.umich.edu/
  2. http://www.infinitepower.org/newfact/new96-811-No6.pdf
  3. http://www.petrolprices.com/green-technologies.html