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Solar panels for conventional vehicle fuel saving

Solar panels for conventional vehicle fuel saving

(OP)
Wouldn't putting solar panels on top of the trailer portion of a truck save enough fuel to be economically viable by taking load off the alternator/generator? Even 1 or 2 mpg savings in a long haul truck that spend most of the time in the sun anyway should add up for a vehicle like that, no?

RE: Solar panels for conventional vehicle fuel saving

Do you intend to fully disengage the alternator during your trip?  If so, what happens when the sun goes behind a cloud?  Plan on having enough stored energy?  A big diesel will eat up an uncharged battery in a heartbeat.

Dan - Owner
http://www.Hi-TecDesigns.com

RE: Solar panels for conventional vehicle fuel saving

Most of the alternator load is lighting - which isn't used when the sun is shining.

So you'd need storage.

Storage is heavy.

 

RE: Solar panels for conventional vehicle fuel saving

PV panels would seem to be viable to perform air conditioning work; the compressor could be electric and feed from the alternator if no sun available.  

The problem I see is that the tractor and the trailer are usually owned by diffferent people, neither of which has a financial incentive to help the other.

RE: Solar panels for conventional vehicle fuel saving

see if you can make the economics work for a refridgerated trailer.  if not, then forget it.
 

RE: Solar panels for conventional vehicle fuel saving

Typical trailers I see are not even maintained well enough such that the brake lights work.  Generally they light randomly in a non-symmetrical fashion, if at all.

Now you want to put several thousand dollars of fragile plates on top?

RE: Solar panels for conventional vehicle fuel saving

And they hit bridges all the time.  Would scrape all those expensive solar panels right off.

RE: Solar panels for conventional vehicle fuel saving

Would give the kids throwing rocks off overpasses something to aim for.

----------------------------------------

The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.
 

RE: Solar panels for conventional vehicle fuel saving

Expecting "Even 1 or 2 mpg savings" is hopelessly optomistic, given that the typical semi gets 5 to 8 mpg loaded, maybe 9 empty.

Consider this in the context of what it might take to get 10% to 40% better mpg in a light truck or SUV.  Or divide the expectation by at least 10.


Norm

RE: Solar panels for conventional vehicle fuel saving

"A big diesel will eat up an uncharged battery in a heartbeat."
Just to clarify, it depends on the engine. A tier I or earlier diesel only needs electricity to start and hold the fuel shut-off solenoid. Modern diesels on the other hand are a different story, with ECU's and such.

And I agree with Norm, 1-2 mpg is overly optimistic. They don't even get that with the super low resistance wheels.

ISZ

RE: Solar panels for conventional vehicle fuel saving

Or look at it this way.

For an extreme upper limit, estimate 1000 W / m2 incident and 10 % efficiency.  A long hauler towing triple trailers has (as an upper limit) 3 x 8.7m x 2.4m of space available, or a little less than 63 m2.

This sets the upper limit output at 630 W, which is 0.84 hp.  Compare that to the aerodynamic drag power requirement for a for a standard (single) tractor trailer, which Google puts at >100hp.

So, the highly optimistic upper limit of savings is <1%. Reality would be only a fraction of that.

For a single trailer, I don't think 200+ W will even help much with refrigeration.

A turbine on the top could churn out some real hp while cruising down the interstate though.

RE: Solar panels for conventional vehicle fuel saving

Good catch!  100 W / m2 gives 6.3 kW and 8.4 hp as an upper limit.  Still not an encouraging uppper limit.  I believe in school we used 250 W / m2 as a typical 24/7 average for fixed installation, which immediately cuts the average to 2.1 hp, unless we target daytime drivers in sunny locals.

Any idea what the actual hp required is for a semi cruising at highway speed?  

22% cells don't sound like the typical low cost production units, but then this isn't my field.  If 22% were available and appropriate for mounting on autos, 20 m2 on a trailer top would kick out 2.5 kW (3.34 hp) per trailer using your figures.  Not a trivial amount, probably sufficient for some cooling purposes.

There aren't any electric semis to get handy figures for... but another way to look at the concept is if you could squeeze 4 m2 of the same dandy cells on top of a car, you would get (500 W * 8 hr) 4 kW-hr in a sunny 8hr day at work.  Thats enough for 1/4 a 16 kW-hr charge in a Chevy Volt, or maybe 10 miles based on the 25-50 mile advertised electric range... If you were rolling for the same 8 hours, you would have extented your range by the same 10 miles while travelling approximately (8 hr * 50 mph) 400 miles, which means a 2.5% range / efficiency increase.

RE: Solar panels for conventional vehicle fuel saving

A highway-speed HP requirement of 150 or more would not surprise me.  Anything under 100 would.

15 lbs rolling resistance per ton times 40T would be 600 lbs, which at 88 ft/sec = 96 HP.  Aero drag is roughly the same at that speed.


Norm

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