I think in tropical countries where we have moderate solar irradiation all year around, it is possible to power heavy vehicles by solar energy, of course with good energy storage mechanism. For example, a solar powered bus was unveiled in Uganda recently. http://www.bbc.co.uk/news/world-africa-35458465 ; http://www.chimpreports.com/uganda-manufactures-first-solar-powered-bus-in-africa/

Dear colleague Fidelis Abam,

Have a nice time and good day.

Indeed, the problem of solar energy is the low output power, so for Ex. a solar panel of 215 watt output has dimensions of 165 cm X 95 cm approximately so the heavy based PV transportation like truck it will may be possible but with bigger  dimensions or with traditional dimensions but but with limited hours of operation (4-6 hrs) in case of supported by batteries with the next design; the output will be from batteries and the solar panel will recharge the batteries. The reason if we take in mind 735 watt (one horse power) need to to 3.5 solar panel from the mentioned size with total area (165x3) X(95x3). the truck may need for a machine with 60 horse so the total area will be ( (165x3X60) X(95x3X60) so you can imagine the needed area.

I think the mentioned Ugandan bus (from the answer of Dr. Ssennoga Twaha) is limited to a operation hours and impossible to work all the day. At South Valley Univ, Qena Egypt we design a solar car with 6-8 operation hours (photo attached). So, i think the traditional truck is difficult nowadays to be PV held per day but only for limited operation hours.

yours

A.Eldenglawey

Vehicles can be powered by solar however it may be impractical for a HD Truck As solar energy relies upon surface area and reserve power.

From the reality perspective; what may be far more feasible is to design and introduce hybrid trucks which run on electricity with a fall back to diesel these hybrid vehicles may then be sustainably powered/recharged using solar power banks which  rely upon banks that have enough power source stored to meet demands.

Dear Colleagues

Thanks for all your your find  contributions

Fidelis, there is a major problem with powering mobile objects with solar energy, and it is related to the 'three halves' power law. The irradiation intercepted by the object is proportional to its area (linear length squared), while it's mass and therefore power requirement to move is proportional to its volume (linear length cubed). So the bigger the object, the less it will be able to move. Animals get round this by eating plants which grow over a very wide area, so they can tap into solar energy incident on land a million times their own area, and the problem is solved. Sadly, vehicles can't easily do this. But I wish you well in your endeavours. The vehicle must be wide and long, very light, and have very low rolling resistance. This is not a heavy truck, unfortunately.

 Thanks Tony for your scientific illustrations I do hope for scientific break through.