The SolarX solar car: part 2

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Energy will flow from the sun, the brakes and even the shock absorbers in the SolarX solar car. Clint Steele describes the power train in part 2 of our series on the car’s design.

The main function of a solar car is, not surprisingly, to convert solar energy to torque at the driving wheels so that the car can travel at speeds that make it a practical driving option.

Power flow

The biggest difference in a solar car’s power system, compared to a conventional car, is in the flow of energy and the recapture of that energy. In a standard petrol car, the power flow is pretty much one way: fuel engine transmission.

In this solar car, however, there’s an additional flow, with power reclaimed via regenerative braking. This is common to most electric vehicles.

There’s also one more power flow in the SolarX. In most cars (electric or non-electric), energy is lost in the suspension system as it dampens the car vibrations. Shock absorbers can reach up to 180 °C as they dispel this energy as heat. This sounds high, but the actual amount of energy is usually not enough to warrant the effort of regenerative shock

absorbers. This is not the case here—the power used by the car is so small that the suspension units will make a significant difference. Thus, the team working on the suspension are also developing a regenerative shock absorber.

Power management

In a standard car, the power is delivered as needed: fuel is delivered to the engine or the current is drawn from the batteries when required.

However, the sun is an energy source that can’t be controlled in such a way. If the batteries are fully charged and the vehicle is at a speed that needs a relatively small amount of power, any excess energy falling on the solar cells is lost. And, in fact, this extra energy needs to be managed, to avoid damaging the batteries. This is another unusual aspect of managing the energy flow in this solar car.

Figure 1 shows the major components and the layout of the power system that ultimately converts sunshine to tractive effort. The subsystems are discussed below.

Energy storage

Most electric vehicles on the market today rely on lithium battery technology. For the SolarX car, the design team is investigating a hybrid energy storage system consisting of traditional lithium ion batteries coupled with supercapacitors.

Supercapacitors have superior power density, much higher than that of chemical batteries, which means they can be lighter for the same peak output power capacity.

A series of high-power car stops and starts will cycle a battery enough to shorten its life. By using supercapacitors to take these peaks, the life of the battery can be extended considerably.

This is not a concern in solar car racing, which is the pedigree of this car, but it is in road cars.

One of the challenges of this project will be managing the flow of electricity to each of the batteries and capacitors as desired.

Read the full article in ReNew 127. Read Part 1 of the article here.

 

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