Electric bikes are fairly powerful and therefore need to store about 200-500 watt of energy in their batteries to travel the desirable range. More powerful electric bikes usually come with bigger batteries. Electric bikes are not stationary and are therefore in need to mount or transport solar panels. Of course one could mount a panel at home and work if this is the main use of the electric bike.
Some companies now offer roll-up solar panels from 25 to 75 watts of output. Three of those solar panels in series will provided the now common 36 volts used in most electric bicycles and could recharge your e-bike while at work. The solar panels roll up small enough to place on the rear rack including the charge converter. Non roll-up panels are more efficient but are not that easily transported, they might require to be installed at home or/and work. There are prototype bicycle trailers like the Bob motor trailer which have an electric motor, batteries and fold-out solar panels - all mounted on the trailer. (Call us for a quote) This is a very neat solution that can be un-hooked from the bicycle in 5 seconds if not needed.
The size of the solar panels depends on the amount of time you have available and the size of the batteries you need to charge. It is usually recommended to use batteries larger than needed for one trip, it allows you to ride on some of yesterday's sunlight in case you need to run home early or the sun has not been out at all. Most solar panels now do not need direct sunlight to work but will not quite run at 100% capacity on a cloudy day.
Running a bike on sunlight is hip, green, fun and more and more common and affordable. Many larger manufacturers are looking into mass-producing these panels for use with electric bikes. NYCeWheels in New York City is in the process of adapting the system to a line of electric bikes including the line of eZee bikes, Giant Twist, A2B Motor Bike, and BionX electric bike conversion systems.
The solar charged electric bike might be one small answer to our current energy problems.