Solar cell science has been around since the late 1800s, but the application of the science didn't appear in our daily lives until the 1950s when the first solar panels where mounted on roof-tops. As the technology becomes more efficient at converting sunlight into power, the more options we have available to us. With solar cells reaching a 20 percent sunlight-to-power conversion rating in 2010, solar powered cars are becoming science fact, not science fiction.
Solar Array
Solar cells, photovoltaics, are responsible for all power generation from sunlight. Cells are made from a thin piece of monocrystalline silicon that has a chemical reaction to sunlight, producing electricity. Individual solar cells can produce up to 0.5 volts at around 3 amps during peak sunlight exposure. If you have 1000 cells wired into an array, using a serial wiring method, your total output would be 500 volts. You won't have to worry about the power output from the array being too much, the power tracking unit will convert the array output power to match the system requirements.
Batteries
Solar arrays provide the raw power for the system but batteries are needed to provide the smooth, sustainable power needed to operate the motors for the car. Variations in power due to driving under a shaded area would greatly reduce performance if the motors were directly wired to the solar array. If you need 72 volts for your system, you will need six 12-volt batteries wired in a series. Batteries with a high amp-hour rating are the preferred choice because of longevity. Types of batteries for solar cars can be lead-acid, Nickel-Cadmium and Lithium-Ion.
Motors
Motors for a solar car are usually DC, brush or brushless magnet motors. Power is supplied to electro-magnets inside of the casing. The electro-magnets surround a drive shaft that is also strongly magnetized. Both magnetic pieces are polarized in the same manner, naturally making the two parts try to separate. When power is applied to the electro-magnet, it forces the drive shaft to turn, in an attempt to oppose the "pushing" effect. The amount of power that is supplied determines how fast the drive shaft turns.
Power Controls
Monitoring and controlling the power system is vital for the performance and endurance of the solar car. Power tracking units will control the flow of power from the solar array to the batteries and to the motor controllers in some cases. Motor controllers regulate how much power is supplied to the motors depending on the throttle input from the driver. Motor controllers also synchronize the two or four drive motors so they always have matching drive velocity.
Instrumentation
The state-of-charge meter is the most important instrument on a solar car. The meter provides information on remaining battery power, amperage draw, overall system voltage and sometimes can estimate time remaining on batteries at the current rate of use. Most batteries will read as normal when not under load, so voltmeters are installed on individual batteries to display real-time voltage while the car is in use. A speedometer is the only other real-time instrument used on a solar car, not necessarily to gauge how fast you are going, but to stay within a set margin for maximum endurance.
Considerations
Solar cars must be lightweight, aerodynamic and have a large enough surface area to accommodate the solar arrays. Eliminating as much weight and drag on the car is important because the batteries can only operate the car for so long before they will need to be recharged; the more efficient the car is, the more endurance it will have. Solar arrays can only fully charge the batteries while the car is not in use. Three hours or more may be needed for a full solar charge or the use of a 220 volt power outlet.
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