hybrid electric semi trucks

I had a weird idea the other day. 

There are lots of people that are stressed about how shipping stuff in trucks uses a lot of fuel. 

Now that we are seeing things like the tesla vehicle that can go 250 miles on a charge .... and they can be charged with a solar panel array ......  I wonder if a semi truck could have solar panels mounted on the top of the truck and on top of the trailer.  Maybe during a sunny day, that would be enough power to keep the rig going down a freeway.

Most class-8 trucks ("tractor trailer", "18 wheeler", "semi truck") with a full load get about 6 miles per gallon of diesel.  Some with aerodynamic improvements get 7 to 8.  Maybe a hybrid could get 16.  And maybe with all the solar panels, it could get 500 mpg or better at noon on a sunny day. 

My understanding is that trains are even more economical.  And I'm pretty sure they are already diesel/electric hybrids.  So then it just becomes a matter of adding solar panels. 

I dunno, just a crazy thought.  I haven't done any actual math.

along these lines ....

solar car race:  http://video.google.com/videoplay?docid=143192687118710102

Paul,

If these solar cars weigh about 300 pounds (est.) driver included and they average 15" in length, completely covered in solar cells, then how long would a solar vehicle have to be in order to carry the average net/gross load of a class A semi?

A direct proportion would not take into consideration the net load of the semi or any increase in power required to power a vehicle of this length but as Bill Nye says, Consider the following:
15 foot solar car/300 pounds=0.05
38,000 empty semi truck with referigerated trailer x .05=1900 foot long solar powered semi without load.

Again, this is not even considering the larger solar truck needing more solar cells for it's mass.

You began with an optimum milage rate. Most full sized semi's only get about4 to 5 mpg, loaded or empty.

You have a good point though. I think solar, combined with wind would be excellent for sea going vessels though.

In the days of sail, a schooner, employing 15 to 30 sailors would only carry the equilivant of one semi's net payload, and this took months to make oceanic crossings.

SS

The solar racers were storing power throughout the day.  And they had to obey the speed limits. 

Once the semi truck is moving, and if you can do aerodynamic stuff to offset wind resistance, then it would seem that your primary fuel expenditure would be in maintaining speed.

The advantage with the semi is the flat roof combined with so much less wind resistance to mass.  A semi truck would get less wind resistance than 40 hybrid cars even though it would weigh about the same (wild guess).  Maybe 10 times less wind resistance per mass?

Paul,

You bring up some good points.

I saw some Class B straight trucks on the internet that were hybrids. I believe it was in England. I only remember that they were a bright green. Also, I recall a comment that the solar charger worked even in England. Class B trucks spend much of their time in traffic or at a delivery location where they could be charging their solar powered system.

Some things to consider:
Keep in mind that my knowledge from a practical standpoint, not an engineer's. I tried the occupation a couple times and racked up about 4 years experience driving mostly Iowa to Seattle and back on I-90. My dad did it for 48 years and only retired last March due to an accident.

Engine speeds are constantly changing to address the grade of the roadway. These trucks don't only just get up to speed, they are continually struggling to maintain their speed.

There is the concern that much of the drag on a semi-truck is actually from side wind. Most people only consider the frontal area when addressing this. Aerodynamic adjustments can overcome some of this, to the point where they create other problems or cause issues due to the system's complexity.

As a hybrid, using wheel motors that charge batteries while braking would be a great first step. Trucks generate a tremendous amount of resistance to deceleration. The engine retarders and "Jake-Brakes" really waste much of the forward energy.

Equipment failure is common, mostly in the current drive-train and the braking systems. The DOT is forever inspecting braking systems due to the concern of wear, neglect, and failure. It would be wonderful if the heavy trucking industry could get away from friction brakes.

Considerations as to weight of components and their distribution are a big factor. Also, how they perform on ice, snow, rain, and in the mountain passes must be considered. It would be difficult to charge the system if there were snow on top of the solar collectors. There are times when there is 1/4" of ice on a semi due to freezing fog. I would estimate 21 days per year or more for a truck on northern routes.

Over-the-road heavy trucks see some of the harshest environments. Electrical and pneumatic equipment fails often at sub-zero temperatures. Diesel fuel systems begin to fail if the fuel temperature gets below 28 degrees F. The source of keeping the fuel warm is the heat of the engine. This can be augmented by the use of electrical resistance heaters on the fuel lines.

I have been in blinding snowstorms, just trying to get off the highway to somewhere safe, and having to drive very slowly. This caused my engine temperature to drop to about 100 degrees, which would not warm my fuel enough to burn correctly.

Some trucks are driven 20 hours per day.

Constraints
To properly evaluate this topic, one would have to work within the constraints of the subject vehicle.

From memory, a standard class A semi truck is limited to 102 inches wide maximum (not including mirrors) and 65 feet in length.

It can have up to 12,000 lbs. on the steering axle, and up to 20,000 lbs. on a dual wheeled single axle, or 34,000 lbs. on a pair of axles less than 10 feet from eachother, not to exceed 80,000 combined configuration. To simplify, use an example of a standard semi with a steer axle, two dual drive axles close to each other and two trailer axles close to eachother.

You should be able to load 12,000 on the steer, 34,000 on the drive, and 34,000 on the trailer axles maximum, respectively. It is quite a chore to make it come out correctly when loading a trailer. Mess it up and you get to pay a fine at the scale house and get workout in having to move it by hand to correct it.

A wonderful aspect of reducing the fuel consumption would be not having to carry the weight of the fuel. My trucks had a 275 gallon capacity at about 8 lbs per gallon. That is 2200 pounds one could reduce in tare and apply to net.

A crude guideline for making this technology profitable:
The trick is that a current technology semi, say hauling perishables, would need to be able to haul a net load of 42,000 pounds almost 5 days a week for up to 48 weeks per year in order to turn a profit.

Silverdale Slug

And it seems it now exists