How do solar powered cars use the energy generated by the solar panels?
The simple answer is that when there is both sunshine and a charged battery, both can be used simultaneously.  Any combination is possible with the right control electronics, so it will differ depending on what the manufacturer wants to happen.  The battery will always be the more powerful unit, so when solar panel and battery are both available, the solar panel will probably be used to supplement the battery power, so the battery will not discharge as quickly.  Charging and draining simultaneously doesn't even make sense, but alternating between them can.  For example, regenerative brakes charge a battery but then the battery drives the motor after braking has ended.
In a solar powered car with a battery, a few hours parked somewhere will charge batteries enough to get to the next parking lot, maybe.  The difference between battery capacity and solar cell capacity is that big, and it always will be because the biggest limitation is the amount of energy the sun delivers per square metre, not the efficiency of solar panels.  If all solar panels became 100% efficient tomorrow, electric cars would still need batteries, and the sun would still go down at night.