It is possible to "power" a laptop using solar power, but it will not be cheap and you will be at the mercy of the weather since overcast and cloudy days will significantly decrease the amount of solar energy that can reach the solar panel.
Here is video for the PowerAdd 40w solar charger which costs $200m. However, 40w may not be enough to charge the laptop's battery while you are using it because as stated before, clouds can cause actual power to fluctuate. A better solution is probably the 60w version which sells for $320. Why is it so expensive? Well, it is portable and includes a voltage regulator. Alablcho provided a link to a solar panel, but you still need to purchase a voltage regulator to make it usable, otherwise you...