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Strategy

The basic strategy for optimum performance for a solar car in a race like The World Solar Challenge is to drive the car at a fixed speed, being the maximum speed that you can sustain throughout the race.

We assume a solar array with a peak power of 1000W (which matches Sungroper fairly closely). For the purposes of simplicity, we ignore weather (clouds and wind), hills, control stops, other power usage (like electronics, telemetry, etc), and efficiency (of the motor and the batteries).

Ignoring weather, the input solar power rises rapidly from sunrise (because the solar array is pointed directly at the sun) until 8AM when the car starts moving. The solar power drops immediately to around 400W and then rises slowly to its peak power in the middle of the day before dropping back to around 350W at 5PM when the car stops. The power then jumps immediately up to around 900W as the array is pointed at the sun and then drops off until sunset around 7PM. The curve looks something like this:

The output power going to the motor should be constant (since the speed is constant). To figure out what it should be, we simply sum the input power available in a day, which is roughly 9.25kWh, and divide by the time spent driving (9 hours) to get a power of roughly 1027W.

We assume the battery charge will be zero at the end of the days racing (5PM) and thus can calculate the charge in the battery charge at any time of the day. We now know the input power, output power, power to/from the battery and the battery charge for all times of the day, which gives us a graph like this:

All numbers are Watts, except for Battery Charge which is Wh.

Now all that remains is to see how fast you can travel with the available power (1027W).

The raw data is: