Brand new here...
I hope someone has thought to put solar panels on the roof of those semi-trailers.
Also, for the solar roof panels.
Is there a thought of using Google, Bing or a direct satellite image of a potential client's roof and generating both a feasibility plan and bid? The dimensions (particularly the roof pitch) ought to be available via the local county or MLS data.
“I hope someone has thought to put solar panels on the roof of those semi-trailers.”
The only people who’ve though this are those that haven’t done the math. The ones that have done the math know it’s a silly idea.
Ask yourself this question: “Under ideal conditions, how much power could solar cells on the roof of the trailer generate?” This is an easy question to answer— just look up the surface area of the top of a trailer, the amount of energy in sunlight, and the efficiency of modern solar cells.
@Dramsey (November 17, 2017)
<< “Under ideal conditions, how much power could solar cells on the roof of the trailer generate?” >>
Well, enough to save significantly on AC, if the contents must stay cool.
@ddodge, Quote: "Is there a thought of using Google, Bing or a direct satellite image of a potential client's roof and generating both a feasibility plan and bid?"
Oh, like Project Sunroof? The one that Google already has?https://www.google.com/get/sunroof#p=0
Solar on the trailers would not be a Tesla thing, and they are selling the Truck, and customers can hitch up any trailer.
Solar could not be only on the top, but also on the sides for additional capacity.
What makes this a non issue is the newly announced MegaChargers at truck stops. They will charge up a depleted battery in 30 minutes, while the driver grabs a meal. Just filling up a diesel truck takes 15 minutes, while the driver needs to stand there and wait to take on hundreds of gallons of diesel. Using the MegaCharger will actually save the driver some time.
They usually update their log books while grabbing a meal or shower.
Something glossed over is the bigger issue of 18 wheelers with bad brakes. Not unusual for trucks to overheat their brakes on long downhills, with heavy loads. They want to keep the wheels rolling, and often push their brakes past the time that they need servicing. Many highways have emergency run off areas where run away trucks can bail off the highway into gravel filled traps. The trucks sink into the gravel and are brought to a halt. Expensive to get them towed back out, but that is how they deal with overheated brakes.
The Tesla will simply use regenerative braking to slow the trucks on down hills, while putting additional electrons back into the battery to extend range.
Many communities ban the use of compression "Jake Brakes" due to their loud noise. The Tesla solution is much more elegant.
Getting rid of smelly, polluting Diesel trucks would be welcome by most of the traveling public.
"Well, enough to save significantly on AC, if the contents must stay cool."
Hm. OK, let's do the OP's work for him. Trailers come in several standard sizes but I'll start with the largest, which is 53 feet long and 102 inches wid:
That's just over 450 square feet, or 41.85 square meters. What the heck, let's call it 42 square meters.
As we all know, maximum solar flux at sea level is a kilowatt per square meter, or 150-200 watts by the time you suck power from PV cells. We'll go with the higher figure, 'cause PV cells keep getting better, right? 200 watts per square meter times 42 square meters is 8.4 kilowatts.
And that's where I stop; I can't easily find data on the air conditioners used on refrigerated trailers. But I imagine even a couple of kilowatts would help, so I'll agree with your assertion.
Uncle Paul +1
Additionally the other point is how much slow accelerating trucks, gum up traffic. With trucks being able to essentially accelerate as fast or nearly as fast as the avg car, this will help in keeping traffic moving.
If you put solar cells on the semi, then the CD goes way down, and you burn more fuel. In addition they are almost never pointed at the sun, and the power drop off is really quick. Optimized stationary solar makes far more sense.
Tesla does not own or make the trailers and putting solar on the trailer adds all sorts of logistical complications. Again on a flat top trailer the panels would be 20 to 30 degrees off of optimum, greatly reducing the power output. Further reductions would be caused by dirt buildup and you'd need to clean these roofs quite often.
Here's an in-depth analysis for the Model S, where the payback is about 115 years! https://teslatap.com/articles/solar-vehicle-roof-analysis/
The trade-off in additional weight is probably not worth what little energy would be produced.
@Dramsey, that is peak, at high noon, near the equator. Even forgetting higher latitudes and poor angle, that is a daily average of 46 kWh or an extra ~115 miles of range per day, for a truck that is going to be driving ~700 miles a day. I guess that actually isn't too bad, unless the poor angle and higher latitude effects become significant.
I have not heard whether Tesla plans on making the trailers, but it would be very advantageous to have regenerative brakes on the trailer, not only from an energy perspective but also from a safety standpoint. Brakes controlled by the truck's computer would aid a lot in preventing a jackknife.
@psusi - All the factors make 46 kWh solar generation assumption a bit crazy. But even at 46 kWh, the semi is rated at 2 kWh/mile, so at most 23 miles, not 115 miles. My rough guess is you'd be very lucky to get half of that in the USA under normal conditions - or 11.5 miles of range assuming a 12 hours of sun every single day. For those in rain/snow/clouds, the number goes to zero.
@TeslaTap.com, what? 2kWh/mile? Wow. With the insane low drag coefficient Elon boasted about, I assumed it would not be that much worse than the 315 Wh/mi a Model X gets. I figured around 400. 2000 is crazy bad.
FYI, I used the annual average output of 5.5 Wh per day per nameplate Watt that I typically see for solar installations here in Florida.
A MS is ballpark 300kwh per mile highway and let's say 5000ish lbs so 7 times as much energy to move 16times more weight doesn't seem bad if you have two brain cells to rub together
@Psusi the drag coefficient doesn't mean the total wind resistance. A bigger front truck with the same drag coefficient as a smaller front Roadster will have a proportionally bigger resistance to overcome. AFAIK.
@Dramsey to finish off what you're saying about the economics of solar roof top semi-trailer. ... if the truck roof can make 8.4kW when the sun is straight up in perfect conditions... then we should multiple that by about 5 hours of "perfect" sunlight (the day is longer, but it's also getting increasingly less power on either side of noon). Let's say 50kWh can be generated in perfect conditions.
That's a lot. Kind of. The truck has a 1000kWh battery pack so that works out to give about 20 miles of range when travelling in the middle of the day. And when recharging is 7c/kWh, to save 50kWh, then over a year it's $1300 saved.
Regardless of AC, it'd be hard to make that big a solar array on a truck pay for itself. AC can use a small portion of the 1MWh battery.
@wipster It would not make sense to put regenerative brakes on the trailer, because there are four motors to turn kinetic energy into stored electrical energy on the truck, plenty enough to slow the entire truck. Since Tesla has already solved the jackknifing problem without involving the trailer why add the complication and expense of involving the trailer?
@Homebrook... Semis do have brakes on the trailer though already... which I suspect are used frequently but not as much as the tractor brakes.
But I'm not sure how much they're used. Nor whether a trailer could be made to not use them.
Okay learned a little. The Trolley brakes seem to be more like parking brakes, which can be used for a hill start with a truck, and parking - but are there to hold the trailer in position while the tractor backs into it to connect. There is a lever to pull for them. Many drivers use it as a normal brake to save money, using it at very low pressure so it doesn't lock the wheels, as this can extend the life of the tractor brakes at the expense of the trailer brake (that they don't own or need to pay for servicing on).
When a truck slows down the weight moves forward and puts a lot of pressure on the tractor back wheels. It takes weight off the back trolley wheels (hence losing traction and sometimes jackknifing). So all good for the Tesla truck.
It's possible I'm searching for the wrong thing, but seems like having regen motors on the back trailer wheels is unnecessary.
Drag=.5*(velocity squared)*(air density)*(coefficient of drag)*(frontal area)
So Model S has a drag area og 6.2 sq ft. A semi trailer is 13.6 feet high and 8 feet wide so the frontal area is about 109 sq ft or 15 times a Model S!
@TT, Quote: “If you put solar cells on the semi, then the CD goes way down, and you burn more fuel.”
That’s pretty ridiculous, @TT. It’s putting smooth flat material on a smooth flat surface. There would be no change to the CD or aerodynamics.
There is very little smooth flat surface on the semi. A tiny strip on the top. So if you make all the surfaces flat for solar cells, it would be like converting the semi into a brick. There are a couple of small vertical panels on the side between the semi and the trailer that are flat, but I doubt you could generating much power from the poor orientation. One side would always be out of the sun as well. Can you point to where you expect to put solar cells on this image?
I suppose you could cover the entire top above the windshield to glass, and add solar cells, but most cells would get zero sun at least 50% of the time. The expense of that complex curved surface in glass and cells is likely many times that of a flat panel.
Tesla does not sell the trailer, which does have a flat area, but we're talking about the Semi that Tesla produces.
@TeslaTap, Oh, I didn't even notice you had changed the subject to talking about solar panels on the semi rig. No one else here was talking about that, so it never occurred to me that's what you were talking about. People were talking about panels on top of the long flat roof of the trailer.
@Rocky - I sort of see that now :) Hard to get everyone on board with the proper terminology. The Semi is the Tesla powered portion. The Trailer is provided by other vendors and frequently the Semi owner and trailer owner are not the same.
For example, a trucker who owns/leases the Semi portion (Tesla or others), will contract for a job of hauling someone else's trailer and contents to another location. There are companies that own it all, such as UPS, FedEx and Walmart.
@TeslaTap, Sorry, my response sounded a little accusing. I should have still noticed that in reading more carefully, that you were not referring to the trailers. So of the two things, neither is useful:
1. The rig doesn't have enough area to be useful for solar.
2. The trailer is an interesting thought experiment to calculate numbers, but can't ever actually happen because trailers are 3rd party.
@Rocky - No problem - you summarized the issues better that I did!
Walmart, Loblaws, and Moving services are likely to own both tractor and trailer. I imagine many fleet purchases would - though not my area of expertise.
Whereas Fercam is hauling those standard sized shipping containers.
Still the power generated would mean the money would be better spent on a slightly bigger battery. Or go all out with a removable?) battery slab under the trailer for long hauls.