October 05, 2014
FedEx Going With Diesel Electric Drive Trains

Constant speed diesel engines can recharge the batteries in Federal Express delivery trucks.

FedEx is working with Wrightspeed, the Silicon Valley-based company founded and run by Ian Wright, who helped create Tesla in 2003. Wright is still all about electric mobility, but his new company doesnít make cars. It makes electric powertrains to be dropped into existing vehicles. And itís sold 25 of them to FedEx for a pilot program.

Read the whole thing. Sounds promising.

As battery costs decline higher capacity batteries can be used and the ratio between precharged grid power to diesel will rise. This allows a very gradual shift from oil to assorted grid electric power sources.

What I would be curious to know: how much electric power could be generated from thin film solar panels installed on the roof of a deliver truck? I say thin film because the panels would weigh less. Recently a new record was set for CIGS thin film PV: 21.7%. Could a few panels on the roof of a delivery truck make much of a difference?

Share |      Randall Parker, 2014 October 05 08:32 PM 

Cyril R. said at October 6, 2014 2:36 AM:

Well... lets put some rough numbers on that. For a 1 TEU size truck you might be able to squeeze 14 m2 of solar panel on that roof.

With a panel efficiency of 20% (optimistic for cheap enough panels) and 1000 W/m2 peak you get 14*0.2*1000 = 2800 Wp.

Unfortunately laying panels flat means you can expect only 10% capacity factor realistically (especially when you consider time in garage etc).

So we might only get an average of 280 Watt. Not much for all the trouble. Typical average consumption during driving would average at least 100x that.

My guess is the added weight of the panels largely or completely offsets the 280 Watts average you get.

Regarding weight, thinfilm isn't much lighter than crystalline. Active material is a small portion of the weight. Weight is dominated by encapsulant, structural backing etc. Likely this would be heavier for a truck than stationairy installation because of vibration issues, shock and the like.

bob sykes said at October 6, 2014 4:34 AM:

You did notice that a diesel engine is supplying the power, didn't you?

The unsolvable problem with both solar and wind is that they are intermittent. The typical capacity factor for wind is about 10% and for solar around 20%.

Batteries are also a problem, mainly because they have very low energy storage densities, which have not changed materially since the days of Volta and Galvani. The available densities would have to increase by factors of 10 to 30 to become comparable to gasoline and diesel. And then there is the charging time: hours vs. minutes.

Solar and wind have a few very limited applications where the power demand is small and a steady supply is not important. Even then, connection to a conventional power grid is preferable unless the application is too far from the grid for an reasonably cheap hook-up.

What stands between solar and wind is not only economics but physics and chemistry. They will never be major players, and Tesla is a prime example why: very long charging times, very short driving radius, equivalent gasoline mileage of about 35 mpg, and higher CO2 emissions than gasoline/diesel.

Engineer-Poet said at October 6, 2014 6:43 PM:

The engine burns diesel fuel, but the article claims it's actually a gas turbine.

Small gas turbines do not have particularly good efficiency (the 60 kW Capstone hits just 30%; diesel engines are much better), but operation only at optimal power and the use of grid power and regeneration apparently outweighs that factor.  I would have gone with something like a 2-liter VW diesel with an alternator taking surplus power from the turbocharger, but the gas turbine would be lighter and maybe there wasn't the weight budget for a diesel.  I can't argue with success.

Brett Bellmore said at October 7, 2014 3:21 AM:

A solar panel on the roof is a good feature for keeping your car battery charged when you're not driving, or even powering a fan on a hot day to keep the interior of your car ventilated. But the contribution to energy needed for propulsion is trivial.

I wonder to what extent this decision was driven by economics, and to what extent it is a PR stunt? (Or worse, management wasting the company's money for ideological reasons.) A lot of things get done in the areas of 'renewables' and 'alternative energy' that make no real sense in the cold light of economics or engineering.

Engineer-Poet said at October 7, 2014 9:38 AM:

The economics of plug-in hybrids are quite good.  Battery-electric propulsion delivers power at an energy cost equivalent to about $1/gallon fuel.  There's also the effect on the balance of vehicle systems.  Regenerative braking practically eliminates wear on the service brakes, so there are substantial cost savings there.

Wolf-Dog said at October 7, 2014 11:29 PM:

According to this article, the South African company Sasol is producing liquid fuels from coal at $45 per barrel. The United States has enough coal to meet all its liquid fuel needs for at least a century. The only complaint is that coal to liquids manufacturing creates more CO_2 emissions, but by planting a lot of bamboo trees (which grow 1 meter per day), and by fertilizing the oceans with iron, we can absorb all the CO_2.


Every day 120 000 metric tons of coal are transported to a plant at Secunda, near Johannesburg, where they are converted into 150 000 barrels of oil a day.
The plant belongs to one of South Africa's success stories, Sasol, the parastatal company that invented and perfected the technology for making petrol and diesel from coal.
Sasol's main plant in the province of Mpumalanga - the only commercial coal-to-liquid plant in the world - produces about 150 000 barrels of synthetic fuel a day and meets about 28% of South Africa's annual fuel needs.
Coal-to-liquid (CTL) technology makes economic sense only in a world of high oil prices: synthetic fuels become economically viable when oil prices reach $50 a barrel. As a result, Sasol has come of age. Until 2003, oil prices averaged $25 a barrel, making $45-a-barrel liquid coal economically prohibitive, but today oil prices hover at $70-a barrel, so the demand for CTL technology is booming.
Worldwide liquid-coal production is expected to rise from 150 000 barrels a day in 2007 to
600 000 in 2020 and 1.8 million barrels a day in 2030.

Nick G said at October 8, 2014 10:03 AM:

I have the impression that the dimensions of the most common semi's on the road in the US are 2.6M width x 14.6M long (8.5'x45'). That's 37.8 sq meters, so I would think 30M sq would be doable. At 20% efficiency that's 6kW peak power - that's not nothing. Even if it's only 5% of cruising power consumption, truckers will take the contribution.

PV is now standard on Australian RVs.

PV is much cheaper than diesel: if diesel costs $3.50 per gallon, holds 40 kWhs of energy, and we get 30% efficiency, then that's about $.30 per kWh. PV panels are under $.70 per kWp. If they're installed when the truck trailer is manufactured, it should be installable for $1.50 per kWp. With 10% capacity factor that's $.12 per kWh - much cheaper.

Weight's a much smaller factor with regenerative braking.

PV has gotten much cheaper than diesel only recently, so it will take a while, but I expect PV to become standard on all commercial transportation eventually.

Cyril R. said at October 9, 2014 4:42 AM:

NickG, please consider the first two things:

1. This is a BIG truck you're assuming (not a delivery truck that is the subject of this article). Such a truck would typically be running at 0.4 liter/km fuel consumption, very roughly some 400 kWt, so think 120 kWe at 30% efficiency (guess).
2. 6 kWp is only at best a yearly average of 0.6 kWp. 10% capacity factor would be difficult enough considering horizontal alignment, bad angle and inclination, plus occasional shadow and shades, increased dust from the road and having flat laid panels... etc.

With these assumptions if the truck runs 1/3 of the time it would need an average of 40 kWe and you're giving it 0.6 kWe average of solar input. So think 1.5% fuel savings.

Now consider the last factor:

3. The solar panels add weight. 30 m2 of efficient panels would be around 600 kg. Lumping around more than half a ton extra weight is going to cut into your measly 0.6 kWe. You can cut that to maybe 200 kg with thin film, but you lose so much output due to poor efficiency that it isn't worth it. I would not be surprised if lumping along an extra half a ton of cargo costs you more than 0.6 kWe in fuel equivalents, in which case the whole scheme becomes energy negative.

I know solar on trucks can be made to work with ridiculous assumptions, but any reasonable numbers would clearly show this is a marginal game, more for PR purposes (even if you think PV is cheaper than diesel) than actual meaningful fuel consumption improvements.

Much more interesting are investments in drive train efficiency and lightweight construction. In stead of investing 10000 dollars in this solar setup you could invest the 10000 dollars in a state of the art engine and get much more than 1-2% fuel savings. Please consider also that fuel prices are largely taxes and that capital is worth a lot for transport companies so consider a high interest rate on the panels (ie no 20 year paybacks).

Unsurpringly solar is pretty much useless for big things that go (semi trailers, ships, aircraft). This should be obvious even to a child.

Cyril R. said at October 9, 2014 10:01 AM:

Ok I checked the marginal energy required for road trucking, it appears to be around 2 MJ/ton-km.

So to lump half a ton of solar panels with you means you must expend 1 MJ/km extra. That's 0.3 MJ/km of useful work at 30% diesel to work.

If the average truck speed is 20 m/s then it takes 50 seconds for a km, so 0.3 MJ/50 = 6 kJ/s.

In this example even if the solar system generates at full peak output of 6 kWe, it only generates enough energy to lump itself along. But it generates not 6 but 0.6 kJ/s on average. The truck is going to have a "capacity factor" of a lot more than 10%!

This scheme is energy-negative, even with lighter solar panels.

Cyril R. said at October 9, 2014 10:16 AM:

"Weight's a much smaller factor with regenerative braking."

For long distance trucking, this is not really true. Very little energy is lost in breaking for most trips. Weight is an issue because of rolling resistance, not so much breaking. The rolling resistance is there all the time.

Small city delivery trucks gain much more by regenerative breaking, but they also have little surface area for PV.

Ronald Brak said at October 9, 2014 6:17 PM:

Gluing lightweight semi-flexible solar panels to vehicles isn't that uncommon in Australia. At the moment it is generally done by either by people who use their vehicles for camping or tradespeople who want a convenient power source. I presume that at some point commercially produced electric vehicles will come with solar PV as an option. Using the roof or body of the car as backing for the PV will save on both weight and cost. However, while the marginal cost per watt will be low, setting up the production line and getting the process right will not be cheap, and so we may have to wait a while for it to become available. But given that private passenger cars are only driven an average of about 40 kilometers a day here, with a Leaf like energy consumption of one kilowatt-hour per 5+ kilometers driven, solar PV on cars could power a significant portion of a car's kilometers. At $1 a watt and a 10% capacity factor and 10% discount rate, electricity from car PV would be much cheaper than grid electricity in Australia. At a more realistic figure of 30 cents a watt is used instead, electricity from car PV should be cheaper than current grid electricity prices anywhere in the United States.

Stephen said at October 9, 2014 7:21 PM:

Cyril said: Much more interesting are investments in drive train efficiency and lightweight construction. In stead of investing 10000 dollars in this solar setup you could invest the 10000 dollars in a state of the art engine and get much more than 1-2% fuel savings.

Agree, its odd they're investing so much money just to achieve fractional gains when, for the same investment, they can buy better powertrain components and get double digit reductions in fuel consumption.

I smell a tax dodge.

Cyril R. said at October 9, 2014 10:58 PM:

@ Ronald Brak. If my numbers are remotely accurate, solar on vehicles is energy negative. You'd do this for camping if the alternative is not having any power at all, but you're using more energy to lump the panel along than it generates. Especially because camping typically involves long distance travel to the camping site.

Also, the Leaf already comes with a solar panel spoiler option. It generates perhaps an average of 0.05 kWh/day based on this discussion:


So you need perhaps 7.5 kWh to drive your 40 km (more kWh needed if you want aircon/heating). So that's 1/150th the power you need. Say you put ten of those things on the roof rather than one on the spoiler. Then it generates 1/15th the power needed. But again, you have to add the energy needed to lump the weight along.

Figures I've seen for thin films are not impressive. They weigh 3-4x less than rigid plat plates, but efficiency of commercial products is poor so you only get a factor of 2 or so in weight per Watt reduction plus very little power. Simply sticking the panels on the roof means the roof is going to get very hot so you need more aircon; further deteriorating net energy of this scheme (if weight based energy consumption doesn't do it in already).

I disagree that 1/150th or even 1/15th the power is "signficant". Its 0.66% or 6.6% respectively. Well in the margin of error for mileage from the car itself (depending on driving habits, consumption of aircon etc). This is NOT significant, it is feel good technology.

Cyril R. said at October 9, 2014 11:25 PM:

As for price, the nissan leaf solar panel spoiler option appears to be $300 or so. For 10 Wp. $30/Wp. $300/average Watt.

Like I said before. Solar enthusiasts like NickG or Ronald Brak can use ridiculous assumptions to try and make solar work. But they're not even telling you the whole story...

This solar panel car is something that works only in the mind of enthusiasts. In the real world, it doesn't work.

Ronald Brak said at October 10, 2014 5:35 AM:

Cyril R., are you aware that the cost of standard solar panels is now under 50 cents a watt?

Cyril r said at October 10, 2014 5:50 AM:

Cost of panels is irrelevant. Price for actual pv in car is $30/wp. There are major costs involved in integrating pv in cars. It does not matter anyway because pv provides tiny savings even if free.

Ronald Brak said at October 10, 2014 6:58 AM:

Cyrul R., do you think that PV on cars will always be about $30 per watt?

Cyril R. said at October 10, 2014 8:14 AM:

Ronald, its easy to see how it will be much cheaper than $30/Wp. Covering more of the car (in a more serious attempt than the tiny leaf spoiler panel gadget) would easily net a factor of 2 reduction, another factor of 2 from mass manufacturing... quite plausible. Maybe it can be done for $5-7/Wp eventually.

But I don't think it is all that important what it will cost. Its such a small contribution to the car energy needs...

If you could cover the whole car with a solar paint that is 100% efficient, and do it cheaply, then it gets very interesting. This does not appear to be technologically plausible though (not to mention violating second law of thermodynamics).

Ronald Brak said at October 10, 2014 1:52 PM:

So Cyril, you think that in the future it will cost maybe 10-14 times to put PV on a car than what it currently costs to put it in a module? But done on a large scale wouldn't putting PV on a car roof cost less than putting it in a standard module as the backing that supports the PV is "free" since generally speaking the car has to have a roof anyway?

Cyril R. said at October 11, 2014 12:38 AM:

Ronald, if you are interested in large scale solar thinfilm cost, the Topaz Solar Farm using First Solar Cd-Te modules costs about 2.5 billion for 550 MWp.


Around $5/Wp. If this project were initiated today it would probably be around $4/Wp as First Solar has cut costs since.

I'm not sure why you keep talking about the production cost of the module. This is just one part of a PV system.

In any case this is all a minor point. The major point is that little energy is to be had from putting solar on cars and if you think solar is a good idea then don't put them on cars.

Once (or if) cheap solar paint with ultra high efficiency is available the calculus can change for electric cars (once the PV becomes a major or nearly all of the power source, the battery size can be reduced which is very attractive).

Ronald Brak said at October 11, 2014 2:31 AM:

Cyril, First Solar thin film was about 60 cents a watt last year. And there is no need to use CdTe PV. Silicon PV works just fine. Why do you think in the future it will cost 10-14 times at much to put solar PV on a car than it currently does to put it in a module?

Cyril R. said at October 12, 2014 5:34 AM:

Ronald, first off as I mentioned twice already, the cost of the solar panel is just one part of the cost of a solar system. See this graph:


Most of the cost reductions have been at the module level, but the other costs now dominate, and they are much more stubborn in terms of learning curves for cost reduction. As you can see some costs are actually going up (like BOS and administrative).

There are many costs in mobile applications that stationairy solar panels aren't burdoned with. Mostly have to do with robustness. Also an EV solar system is very small (at most 500 Wp) so doesn't get the economy of scale that a rooftop system (of say 5000 Wp or more) can have. Smaller systems have more non module costs than bigger systems so that makes it worse.

I am simply looking at what is on the market today, and it is a Nissan Leaf solar panel of $30/Wp. I am not a dreamer that listens to unsupported mantra about penny solar systems that leave out most of the actual costs. I simply look at what is available on the market today. If you have a problem with that, we just have to agree to disagree.

Ronald Brak said at October 12, 2014 1:14 PM:

Cyril, The average cost to install rooftop solar in Australia without subsidy and before our 10% Goods and Services Tax is about $1.86 US a watt. This is about 2.7-3.8 times larger than your suggested price of 5-7 dollars a watt to put PV on a car. Why do you think it will be so much more expensive to install solar on a car than on a roof? What do you think will make solar on cars in the future cost multiples of what it currently costs to put solar on roofs?

destructure said at October 12, 2014 5:40 PM:

One day, solar and electric will make sense. Then all the enthusiasts will say, "See! See! We told you it was better. It just took 25 years for everyone else to realize it!" No. It's not better. But in 25 years it may be. LOL

Ronald Brak said at October 12, 2014 6:56 PM:

Destructure, I recently put solar on my parents' roof. It cost under $2 US a watt before our Renewable Energy Target subsidy was applied. At that price and using my 9% discount rate it produces electricity for well under half the cost of purchasing electricity from the grid. (The marginal cost of electrity from the grid for my parents is about 25 US cents a kilowatt-hour.) Using my parents' 5% discount rate it produces electricity for less than a third what it costs from the grid. No need to wait for solar electricity to make sense, it already does.

Cyril R. said at October 13, 2014 8:45 AM:

Ronald, as I explained already the car PV system is small so has higher cost per Watt than a rooftop system. Also the cost of making PV things last potholes and the like is considerable.

As for taxes, I don't know what world you live in where you don't consider tax in the price of stuff, but on planet earth where I live, everything is taxed.

If PV on rooftops is $2/Wp then how come Nissan is charging $30/Wp? Give your brain a chance.

And at the risk of repeating myself for the ump-teenth time now, it does not matter what PV on cars costs because PV on cars can only provide a small fraction of car traction energy. It is not a deal maker or deal breaker. The main thing is to go electric and get the electricity to charge the car from a clean source, nuclear being far more suited than solar because of reliability and time of delivery issues (my car is not at home during the day so a home PV system for charging the car is strictly pointless and only makes sense with hocus pocus accounting tricks such as net metering which involves burning fossil to charge the car and call it net metering for greenwashing reasons)

destructure said at October 13, 2014 9:38 AM:


I said, "One day, solar and electric will make sense." Since electricity is already ubiquitous in homes, it should have been obvious that I was talking about cars. Solar and EV cars don't make sense either from economics or practicality. That's why almost no one uses them.

I'm not sure what kind of discounts you're talking about but it sounds like subsidies. Subsidies aren't free. And it irritates me that people sponge off others then spout off about how affordable something is. If it's so affordable then why do you need subsidies?

Cyril R. said at October 13, 2014 10:07 AM:

Destructure, discount rate is an economics term for interest rate.

However solar does require subsidies in a properly functioning market. This is because the true value of solar is the value of fuel saved in powerplants, about 3 cents per kWh. Solar is too unreliable to power countries but it can save a very small amount of fossil fuel at great cost as proven by Germany.

Ronald Brak said at October 13, 2014 3:33 PM:

Cyril, we already have solar PV on caravans, RVs, and other vehicles and as far as I am aware it does not appear to suffer from major problems, so I don't think that solar PV for mobile applications will cost multiples of solar PV for stationary does, when done on a large scale. I also think it will cost considerably less for a car manufacturer to put PV on a car than it does to install PV on a roof. The reasons I think this are the body of the car provides structural support for the PV so no aluminium frame or backing is required, no inverter is required as DC power is fine, no racking or clips or screws are required, and the roof or other part of the car becomes the panel so there is no extra labour cost after that to install it. Additionally there is no sales work needed as it is a feature of a car and not something that's sold and it would all be done in a factory meaning there isn't the expense of driving out to people's houses with tools and panels.

Ronald Brak said at October 13, 2014 3:40 PM:

Destructure, sorry for misunderstanding you.

Cyril, the value of point of use solar, or rooftop solar as it's often called, is that it saves households and businesses the retail cost of electricity which tends to be significantly higher than three cents a kilowattt-hour.

Engineer-Poet said at October 13, 2014 4:16 PM:

The retail cost of electricity has the infrastructure and demand charges mostly rolled into the per-kWh rate.  Unbundle those, and both the threat to utilities and the profitability of PV simply go away.

Engineer-Poet said at October 13, 2014 4:18 PM:

Residential and small-commercial rates, that is.  Large commercial consumers are mostly unbundled already.

Stephen said at October 13, 2014 4:54 PM:

In my neck of the woods, the transmission line owner (by definition a monopoly) is imposing a penalty on homes with solar. It's argument is that they still have a fixed expense to maintain the transmission line 24/7 even if the home owner only uses it for a fraction of that time.

Essentially their saying, go 100% solar or don't do it at all.

destructure said at October 13, 2014 5:55 PM:


Materials science will be the game changer. -IF- that battery fulfills its potential it could tip the balance sooner rather than later. Though I've learned to be skeptical. Someone is always touting the next supposed breakthrough that will revolutionize solar. electric, etc. While I've no doubt tremendous breakthroughs have been made they've never quite tipped the balance for total cost of ownership. Eventually it will. Then the floodgates will open. No one will be happier than me to have... POWER! UNLIMITED POWER!!!


Nick G said at October 14, 2014 10:52 AM:


A few thoughts.

Let's look further for energy per ton-km. The large majority of highway truck power consumption is aerodynamic: just moving the air out of the way, and some of the rest is drivetrain losses which are not strongly proportional to load. I'd guess that the percentage of power that goes into flexing tires is less than 20% of the 120kW figure you calculated above. That suggests that a truck carrying, say, 40 tons is using less than 24kW per 40 tons, or 300 watts per half-ton.

I'd suspect that cells integrated into a truck roof would weigh and cost significantly less than panels meant to be mounted onto a freestanding support structure. Certainly most conventional Balance-of-system costs would disappear: no frame or inverter, cheap assembly line installation, integrated wiring, no permitting, etc.

It's silly to compare the cost of the Nissan toy PV to something with far greater scale.

Trucks operate primarily in daylight, because their operators are designed that way by evolution, and commercial vehicles are operated a large percentage of days in the calendar So, the average production would be substantially higher than 10% of peak.

Finally, I agree that there are much lower hanging fruit. Nevertheless, PV generated power is much cheaper than diesel generated power, and there are very substantial "hotel" loads for all commercial vehicles which PV could at least partially supply. Ancillary benefits like the value of increased range and reduction of idling (now mostly illegal) also help. It doesn't matter if it's a small percentage of total power - it's still valuable. And, as vehicles become more efficient, PV's percentage contribution will grow.

I'd say that it's only a matter of time before PV expands into almost all commercial vehicles.

Nick G said at October 14, 2014 10:56 AM:


If fossil fuels were free of pollution, then the utility argument about indirect costs would make sense. But, until coal is eliminated from the grid, solar deserves all the rate-based support we can give it.

Cyril R. said at October 15, 2014 5:54 AM:

@ Nick G. Your point is theoretically valid but info is inaccurate.


Looks like a reasonable ballpark for sake of argument is that the rolling resistance is roughly half the total power need.

So my figure of 2 MJ/tonne-km for weight based marginal energy usage is a bit high but not much. Typical value given is 2.5 MJ/tonne-km nominal so if we take half that it is 1.25 MJ/tonne-km for the marginal weight based energy consumption.

A half ton PV system would cost you some 0.6 MJ/km. At say 500 km/day this is 300 MJ you need to lump the panels along. This is much, much larger than the amount of energy you would produce with PV on even a double trailer; you have to think in the ballpark of 100 MJ for a sunny day, likely half that on average for most locations where truck travel is intensive. That's with efficient panels.

So you make 50 MJ but you need 300 MJ and that assumes 100% PV electric to traction efficiency!!

If thin films say triple the power density per Watt you're still not anywhere near where you need to be.

So your argument that we will soon see PV on semi's is still not backed up by the numbers. Sorry Nick. Wish it wasn't so.

Cyril R. said at October 15, 2014 5:58 AM:

"It's silly to compare the cost of the Nissan toy PV to something with far greater scale."

Correct. That's why I think the price could be that much lower than $30/Wp. Probably a halving on size economy plus another halving in integration and mass manufacturing cost cutting, and we're down to $7.5/Wp. Then with further panel cost reductions maybe it can be done for $5/Wp.

The problem I have is with enthusiasts who oversell solar by saying it cost $0.5/Wp. Solar is more expensive than this in reality. More importantly, solar is NOT a useful contribution to the energy needs of a car and it is even energy NEGATIVE for trucks and other long distance mobile apps. Saying otherwise is proof of innumeracy in energy metrics.

Cyril R. said at October 15, 2014 6:07 AM:

"It doesn't matter if it's a small percentage of total power - it's still valuable."

I could not possibly disagree more. This is symptonomous of our current energy policy of "every little helps". No, every little DISTRACTS from the big problems of energy consumption and scale that we all must face. We are bleeding all over the floor and heading for collision with reality, and you argue, with your time and intellectual capacity wasted, that a little aspirin pill is a good remedy.

Every BIG helps. Leave the little stuff alone. Its not worth your attention span and the time, money and resources spent on it can be better spent on BIG things.

Cyril R. said at October 15, 2014 6:13 AM:

"But, until coal is eliminated from the grid, solar deserves all the rate-based support we can give it."

Yet another statement I just have to oppose 100%.

Solar deserves no support. It is an unreliable power source for the grid that has found useful niches in offgrid applications that do not need further subsidies or other support. It is already good where its good at, and throwing more money at it will not make it do things it can't such as powering countries and using this as an excuse to not build nuclear plants.

This is reality. Germany has gone this way, arguing that solar deserves limitless support and must have limitless priority in selling to the grid (even when there's no power demand). We've seen the scars. Germany has failed to cut fossil consumption, has failed to cut CO2 emissions, and is setting a bad and contagious example, a poison pill that many other countries have now swallowed whole.

France has taken a different path. They realized solar and wind are not suited to powering countries, even when they would be cheaper. France realized that a modern economy needs a reliable and energy dense energy source. Exactly the two attributes that wind and solar lack.

Cyril R. said at October 15, 2014 6:21 AM:

"I'd suspect that cells integrated into a truck roof would weigh and cost significantly less than panels meant to be mounted onto a freestanding support structure."

I'd suspect that would be a good way to heat up sensitive cargo excessively.

PV needs a heat sink. This is mostly the back of the panels. It is why they are mounted some distance off your roof, typically.

If you heat sink is the inside of the trailer, that trailer is going to get hot. This will not be acceptable for many cargos, such as food, and if you need more airconditioning to offset the heat load then that will further destroy the output (which is already deeply energy negative).

Any air cooling structure on the top is going to increase air drag and so this approach also results in increased energy consumption.

Whereas insulating the PV from below would add cost and increase panel temperature that reduces efficiency and lifetime.

Nick G said at October 15, 2014 3:49 PM:

That chart for rolling resistance just shows the relationship between speed and fuel consumption. We can tell that it's not useful because there's *no* relationship between aerodynamic drag and payload.
I certainly agree that there are lower hanging fruit. But eventually, PV on commercial vehicles is inevitable.

Ronald Brak said at October 15, 2014 4:53 PM:

Cyril, solar PV may have an albedo of about 0.1. If the PV is 20% efficient then 22% of the light energy absorbed will converted to electrical energy. This means that about 70% of the light energy hitting the PV ends up as heat. Generally speaking this is better than a car that is painted red. There seem to be plenty of red cars on the roads today. There are even some black ones. I presume the drawbacks of having a red or black vehnicle must not be that great and so the drawbacks of having solar PV on a car, with regards to heat absorbed, will not be that great either.

Engineer-Poet said at October 15, 2014 6:03 PM:
until coal is eliminated from the grid, solar deserves all the rate-based support we can give it.

Nick, I can't believe you're making such an elementary mistake.  Solar only deserves support IF it is displacing coal (and gas) from the grid... and it's not.  PV and wind are being used as excuses to shut down nuclear and run gas-fired backup plants instead.  Germany and Denmark are heavy coal users.

If solar isn't actually pushing FFs off the grid, it's a waste of money we should be spending on nuclear instead.

Engineer-Poet said at October 15, 2014 6:05 PM:
A half ton PV system would cost you some 0.6 MJ/km. At say 500 km/day this is 300 MJ you need to lump the panels along.

I just did a bit of digging and found a flexible Renogy solar panel (RNG-Bend-100D) which is rated at 100 W(peak) and masses 2 kg.  If you can get a capacity factor of 0.4 out of it during road operations (daylight), that's 20 W per kg or 20 kW/ton.

If you need 1.25 MJ/ton-km for propulsion, you would need to be running at about 60 seconds per km (60 kph) to break even.  Faster than that, the panels couldn't produce enough power to overcome their own induced rolling resistance.

Ronald Brak said at October 15, 2014 9:30 PM:

Obviously PV does not weigh as much as modules mounted on roofs otherwise solar powered drones and aircraft would never get off the ground. The pdf on solar powered flight by the Royal Aeronautical Society gives the watts for kilogram for various kinds of PV back in 2008:


PV - watts per kilogram
Crystalline Si 350/1000
Amorph. (α-Si) 4400
3-jnct. α-Si 5000
CIGS 3000
CdTe 2000
GaAs (Ge sb.)270
GaAs (inv mt)3000

Cyril r said at October 15, 2014 11:59 PM:

Ronald your figures exclude substrate and encapsulant and are for very expensive aerospace cells.

Cyril r said at October 16, 2014 12:16 AM:

Ep a 50 wp/kg panel would average 5 w/kg over the year. 5 kw per tonne. 3600 times 24 times 5 is 432 mj/day/tonne panels. But you need say 1 mj/tonne/km to overcome the weight. So if the truck travels over 400 km it becomes an energy negative affair. Double semis easily do more than 400 km/day. Nick g is totally wrong.

Cyril R. said at October 16, 2014 1:55 AM:

Here's a solar panel that is light weight and efficient enough to be useful for cars and trucks:


The panel costs $400/Wp for a 5 kWp system. So $2 million for a truck.

Cyril R. said at October 16, 2014 3:00 AM:

"That chart for rolling resistance just shows the relationship between speed and fuel consumption. We can tell that it's not useful because there's *no* relationship between aerodynamic drag and payload. "

The relationship between rolling resistance and payload is well known; as is the fuel consumption per tonne-km for varous modes of transport. From this you can estimate things nicely.

But even if I use your figure of 20% rather than 40% (ie 0.5 MJ/tonne-km to lump the panels along) and use E-Ps higher power density thin PV, you need to expend 250 MJ/day to lump the panels along 500 km, of the generated 432 MJ/day available. Assuming 90% efficiency of PV to traction, there's 389 MJ available. So you waste (250/389) = 64% of the energy to lump the panels along. This is silly economically and energetically. If you put the panels on stationairy applications, you generate 50% more power and waste none in parasitics. So you end up generating 4-5x more net energy with a stationairy panel. That's such a waste, if you believe PV is useful, then for Pete's sake don't put it on long distance mobile apps.

Nick G said at October 17, 2014 8:05 AM:


We still haven't found real data to show the marginal energy needed to move an additional kilo of weight on a truck. The numbers we typically see for fuel consumption per tonne-km are typically averages which include everything. For instance, IIRC a train uses very roughly 1 litre per 200 tonne-km. Well, that's an average: metal wheels on rail use very little power for flexion. Trucks will use more, but we really don't have data.

The weight of vehicle-integrated PV won't be the same as building or field mounted PV. The theoretical minimum weight is in the range of a kilo per kW (and not for expensive satellite 3-junction cells, either). So, there's enormous room for weight reduction where desired. I haven't been able to get good data on vehicle-integrated PV weight, but I suspect it's rather less than 20 kilos per kW.

If you have a chance to dig these up, that would be great.

I looked a bit at the albedo of trucks and shipping containers. It does look trucks are almost always painted white or silver, so temps do seem to be a real consideration. OTOH, shipping containers are typically painted dark colors, so not so much for them. I'd guess that truck-integrated panels probably want to be insulated from the interior, with small aluminum fins parallel to the direction of travel to largely eliminate drag. OTOH, it looks like the albedo of PV, effectively around .4 (googling finds a nominal .2, to which you have to add the power conversion level of about .2), is probably not significantly different from that of shipping containers, so inter-modal containers are probably ok.

As for Germany and France: Germany simply hates nuclear. If you're a nuclear enthusiast, you just have to accept that. Germans are willing to burn more coal in order to get rid of nuclear. It's probably not optimal from our POV, but there it is. France, of course, went for nuclear because they wanted nuclear weapons. They're now building out wind power pretty strongly, and de-emphasizing new nuclear build a bit.

Solar is real, and useful. Of course a carbon tax would be far more optimal, but in the meantime we have to accept what we can get, like tariffs that favor low-GHG power sources.

Cyril R. said at October 17, 2014 12:46 PM:

"We still haven't found real data to show the marginal energy needed to move an additional kilo of weight on a truck."

We have the nominal figure of 2.5 MJ/tonne/km for road truck transport. We have a decent guestimate of 40% rolling resistance. So for arguments sake 1 MJ/tonne/km is decent. Double semis would have a greater proportion of rolling resistance so if anything I'm being conservative here.

The relationship between rolling resistance and weight is very simple. Its proportional, within reasonable ranges.

From these two we can be sure enough that lumping in a ton of weight costs an extra 1 MJ/tonne/km of diesel. It isn't rocket science Nick.

"The weight of vehicle-integrated PV won't be the same as building or field mounted PV. The theoretical minimum weight is in the range of a kilo per kW (and not for expensive satellite 3-junction cells, either). "

Yes, if you want a fragile, disposable, single mission type solar cell that has nil protection from the environment. This isn't it. Its a high duration, industrial grade, mobile app. Its shaking its ratcheting, its serious. You don't apply a bit of glue and hope it sticks. It has to last 10+ years in a really tough application. The active semiconductor material is very fragile.

We haven't talked about power electronics, cabling weight etc. that all add up more.

A kilo per kW IS the expensive 3 junction Spectrolab module state of the art. Actually its a lot less than that on the systems level. More like 300 W/kg.

"As for Germany and France: Germany simply hates nuclear. If you're a nuclear enthusiast, you just have to accept that."

Why? I must accept night and day and the realities of near zero solar output in winter. These are realities of nature. The reality of Germany is no reality at all, it is a bubble.

But I don't really care about Germany. I'm perfectly happy with them boiling in their own misery a bit more. They aren't cooked yet, clearly. But Germany's anti-science anti-nuclear stance is contagious. It is affecting other countries that are copying it much like people mimick serial killers. Except there'll be considerably more deaths and damage from Germany type energy policy copying than copying of serial killers.

"Solar is real, and useful. "

Solar is useful in markets where no support is needed - remote terrestrial and space applications. Throwing money at it for grid connected applications won't help at all, it is fooling yourself. Solar is so unreliable it needs vast amounts of fossil backbone (not "backup" as the euphemism goes, but "backbone"). This is exactly the wrong direction to take right now. We simply can't waste any more time and CO2 emissions in these distractions and excuses for continuing the anti-science, anti-nuclear position that has gripped the modern world.

Lets say I am wrong, and, at the limit, PV on trucks costs next to nothing and weighs nothing. Thats absurd. But even then, it will only provide less than 1% of the traction energy for the double semi long distance traveller. It is a total marginal game, even if it works energetically and economically.

Yet you and me and others have wasted hours of our lives in debating it. Meanwhile how much CO2 has been emitted?

Nick G said at October 17, 2014 10:11 PM:

Hhmmmm. 2.5MJ/tonne-km, for a 30 ton truck covering 100kM in an hour would be 7.5GJ/hour. That's about 2.1 MW. That sounds over powered for your average semi.

Nick G said at October 17, 2014 10:30 PM:

For our US readers, that's 2,800 horse power. A semi might cruise with 160.

Cyril R. said at October 18, 2014 12:59 AM:

Nick G, that's thermal figures. 2800 thermal horses so maybe 900 real horses. Which doesn't sound all that odd to me for a massive behemoth of 30 tonnes moving at 100 km/h in realistic driving conditions.

Plus you're stretching the numbers as 100 km/h is too fast, no way you are going to do this on average doing long distance with a 30 ton truck!!! 80 km/h average speed would be more reasonable. Also 30 tonnes is stretching things. I found a source that basically confirms my figures.


Table 2-2, 26 ton articulated diesel, 60 km/h, appears to have an asymptote (ie marginal energy use per ton of added weight) slightly below 1 MJ/tonne/km. This assumes only 60 km/h which is slow and it assumes a 100% good road surface. You'll quickly get to 1 MJ/tonne/km with some back/connection roads and 80 km/h.

And that's the best figures you get - all the lighter diesels and especially lighter gasoline trucks have woeful energy consumption, the light gasoline truck for instance appears to asymptote towards 3 MJ/tonne/km (and it has muchless surface area for PV).

I'm not sure why you keep arguing over this point. We have already established that, even if PV has zero parasitic energy consumption and costs next to nothing, it would only save 1% of the truck fuel consumption. Its fooling around in the margin.

What are you trying to prove here Nick?

Cyril R. said at October 18, 2014 6:30 AM:

Lets do a limit analysis on the useful power created to prove the point again.

The light weight solar panel that E-P suggested isn't particularly efficient, but lets say it was, at a space age 30%.

This means you fit around 10 kWp on a double semi trailer.

This would generate a yearly average of some 25 kWh/day, 90 MJ/day.

Lets say there is no energy needed at all to lump the 10 kWp system along.

We have 90 MJ of electricity at our disposal.

At 600 km/day and a total energy consumption of 1 MJ/tonne/km (efficient truck!) and 30 tonnes load, we need 18000 MJ of diesel. That would be about 6000 MJ of work. Say we can convert the 90 MJ of solar eletricity to work at 100% efficiency. Lets assume the truck is always loaded fully for all distance travelled.

Now with these absurdly optimistic, and even second law violating, assumptions, we have 90 MJ of the 6000 MJ we needed. We have generated a feeble 1.5% of our power need despite using every optimistic space age solar technology that doesn't exist in any reasonable quantity and price.

Clearly this is utterly marginal even with future advanced technology.

Engineer-Poet said at October 18, 2014 9:20 AM:

With improved aerodynamics, semi-trucks have been demonstrated to be capable of 13 MPG.  At 140,000 BTU/gallon, that's 7 MJ(th)/km, or about 2.8-3 MJ of work.

A free 30 km per day isn't huge, but it's not trivial either.

Cyril R. said at October 18, 2014 9:35 AM:

E-P, I'd like a source for this. I've read about 10 MPG trucks but they were under 30 tonnes load.

One thing is that semi's aren't always loaded with the full 30 tonnes or so. The realities of logistics are such, that many km are with zero load which really cuts into average fuel consumption. Many km are also with part load. That's just the market and logistics.

I really like to stress also that the previous post I made is with ridiculous other assumptions such as zero reduction from parasitics (weight of the solar installation) and 100% PV electric to traction, not to mention 30% efficiency.

Using more reasonable (but still futuristic) figures: 7 kWp solar, 60 MJ/day. 90% PV to traction = 54 MJ net. Minus parasitics (lumping all the weight around, assuming much ligher panel than today), down to 45 MJ/day net.

@ 3 MJ/km (again realistically you have to consider the logistics of things where some km are without load and some part payload etc. that would increase this) we need 600 * 3 = 1800 MJ of work.

We get to provide 45/1800 = 2.5% of your traction energy.

That IS trivial. The growth in transport over the next few years will offset ALL of these savings.

That is why we need to think about 90 and 95% cuts. Fooling around with the 1% and 2% plans is no good. I'm sure you agree because you quoted me on your website (which by the way is excellent, my compliments).

Engineer-Poet said at October 18, 2014 11:04 AM:

I mis-stated the 13 MPG figure.  The demo run actually achieved 13.4 MPG.

Yes, small cuts are silly.  We need to aim for 100%, so we can settle for 90%.  I averaged 350 MPG on my last tank of gas, which is close enough to a 90% cut from my previous car (a diesel) that all I need is a de-carbonized electric grid to be good.

However, that doesn't mean that integrated solar on a semi-trailer is worthless.  Consider reefer trailers.  They usually carry diesel or propane to run the refrigerator unit.  These units run 24/7 when the trailer is carrying goods, even when parked.  Off-loading some of this to PV power saves a fairly expensive fuel, so it may be economic.

Cyril R. said at October 18, 2014 11:32 AM:

It may be economic but if it is 0.1 or 1% of the problem then what are we talking about?

By the way your ref shows a single trailer not double. This would be more like max. 15 ton than 30 ton payload. So 13 MPG for 15 ton, this is already 2x the value I calculated. So we are down to ~1% of traction energy.

Engineer-Poet said at October 18, 2014 2:29 PM:

Standard highway weight limit for semis in the USA is 80,000 lb, so 30 tons payload more or less.

Nick G said at October 19, 2014 3:24 PM:


Let me say it one more time: there are other lower hanging fruit. Cheap PV is new, and the transportation industry is conservative. So, PV won't be the first thing implemented., by a long shot. We can expect better aerodynamics, hybridization, and perhaps most importantly a move to rail.

So, why are we debating this? Well, first, because Randall asked.

2nd, because long-haul trucking is the worst case. UPS Local delivery trucks drive at much lower speeds and will be electrified first - they might use 25% as much power per ton-mile - that might raise your figure to a 10% contribution. Trains use 1/3 as much power per ton-mile, and container ships use 10% or less.

3rd, PV keeps getting cheaper, and oil keeps getting more expensive. Oil looked cheap early in it's life, but now we're recognizing enormous indirect costs: pollution, climate change, oil wars, etc. PV can now produce power for $.10-.20 per kWh, while the real price of oil is probably $2/litre, which means that power generated from oil costs about $.60 per kWh. So, PV is exploding in places that rely on oil-generated power, like Hawaii.

Oil is expensive, dirty and risky. It's time to kick the habit in every way possible.

Cyril r said at October 23, 2014 2:51 AM:

Nick you are wrong. Long haul truck has lowest energy per ton. Please read the ref i provided for you. Pv on trucks is utterly marginal. Pv on trains is utterly marginal. End of argument.

Auster said at October 23, 2014 4:26 AM:

Maybe I missed it, but the capital costs of electric drivetrain are 3x normal diesel drivetrain, but the fuel saving from switching to electric with diesel range extending generator was not mentioned. That would be the relevant offsetting savings that would be important to know for deciding if the economics work.

The main issue with lithium ion batteries is poor energy density (about 7% as energy dense as a tank of gasoline, at best) and this is unlikely to change much (150 years of batteries and density has improved about 1.5% per annum). Tesla's gigafactory may be able to get lithium battery costs down closer to materials costs of c. $225 per kWh, which would make the economics better for EVs, but still with lousy range. The onboard range extender is what wright is doing here for trucks, and while not green or sexy, it does work. Route-based vehicles that return to a depot at night are also prime candidates for electric drive trains because they can use high speed equipment to recharge large batteries overnight.

Cyril R. said at October 24, 2014 1:59 AM:

"So, why are we debating this? Well, first, because Randall asked."

And we have provided a robust answer that has been repeated to you and others several times now: PV is utterly marginal as an energy source for long distance freight transport, of any kind.

"2nd, because long-haul trucking is the worst case"

Wrong, long haul has the lowest energy use per ton. Please read the ref I provided for you.

"rd, PV keeps getting cheaper, and oil keeps getting more expensive. "

Irrelevant. PV can cost nothing and would still provide less energy than a few more years of economic growth. The advantage has utterly evaporated by the time you're done installing all the panels on all the freighters. Total non-policy.

The real problem is in enthusiasts like Nick G and Ronald Brak. Very enthusiastic and sympathetic people, very likeable, but totally naive. They are trying to make a technology do something it can't. Photovoltaics is a useful technology, for instance for sattelites and remote terrestrial powering of small loads, but there are many things it can't do, such as powering long distance transport, industry, and entire countries. It is good to be enthusiatic about clean energy technology, but don't let that become an uncritical eye piece where all you can do is cheer at all solar applications. Sometimes you run the numbers and the numbers don't support your ideas and worldviews. I know this is hard, but you have to get over it. Some ideas just don't work. Move on.

Engineer-Poet said at October 24, 2014 6:23 AM:
long haul has the lowest energy use per ton.

Wrong metric.  The proper metric is "average watts per ton while in service".  Long-haul is a worst-case scenario because of the high speed and thus high per-ton losses to rolling resistance.  Local transport, such as delivery service, has a completely different profile.

Brandon said at October 24, 2014 11:41 AM:


Cheap oil is here to stay: http://online.barrons.com/articles/SB50001424053111903536004579459323209921860

You idiots and your shitty electric cars are toast.

Engineer-Poet said at October 24, 2014 2:10 PM:

Oil will only be cheap if people have no money to buy it.  Motor fuel consumption has been falling YoY in the USA.  This means that it's obviously too expensive for the public to go on driving sprees.

I've averaged 125 MPG since late April of 2013.  Petroleum prices matter very little to me.  This will become true for more and more of the public as time goes on and vehicles electrify.

Brandon said at October 24, 2014 5:27 PM:

Gas prices have mattered little to you because you parasites have been subsidized up the ass by taxpayers for your shitty electric cars. We're not going to take it anymore.

Engineer-Poet said at October 24, 2014 8:08 PM:

I'm supposedly eligible for a subsidy for my Fusion Energi, but I've not been able to collect it.  As a taxpayer you have no business complaining to me about anything.

Brandon said at October 24, 2014 9:14 PM:

Cut the bullshit. You're still leeching off the subsidy, since the subsidy programs help create the demand for the car companies to put out the electric shitmobiles.

Engineer-Poet said at October 24, 2014 10:27 PM:

"Shitmobiles"?  I'll have you know that my Fusion Energi is the smoothest, quietest, most luxurious vehicle I've ever owned (when it's not buzzing up a hill on the gas engine).  I can easily get mileage in the high 40's even after the traction battery is drained beyond EV-only levels.  If I'm off the Interstates I can average in the low 50's minimum, depending how I want to drive.  In local travel I do without liquid fuel entirely.  This lowers the price of petroleum for you.

Brandon the dumb troll
Takes cheaper gas and complains
Ungrateful bastard

Since the USA supplies most of the cost of keeping the sea lanes open to the Persian gulf, the full cost of gasoline is several times the pump price.  You're the one who gets the subsidy.  Own up to it.

Brandon said at October 25, 2014 10:19 PM:

No, the US subsidizes foreign users of Mideast oil abroad and people who drive electric pieces of shit domestically. We need to end the subsidies and drill at home, off-shore, and in our hemisphere.

Cyril R. said at October 27, 2014 11:08 AM:

" Long-haul is a worst-case scenario because of the high speed and thus high per-ton losses to rolling resistance. Local transport, such as delivery service, has a completely different profile."

This only matters for the PV self consumption from its weight, but not for the total PV energy that can be gained. The total will be much worse for small delivery because of higher MJ/ton total.

Its a moot point anyway. We've established that PV is not going to be a significant powerhouse for commercial freight transport, even if the PV weighed nothing and was more efficient. That's the main thing here, but people keep dartling around the main point with sideshows and other diversionairy tactics.

Engineer-Poet said at October 27, 2014 3:25 PM:

No, Cyril.  A local delivery truck has a much lower power expenditure per ton-hour than the OTR semi.  A panel on a truck that's sitting curbside generates power without costing anything to move it.  A truck creeping in traffic has very low power expenditure; if it's being blasted by sunshine, a PV roof can generate much more power than is required to carry it around.  A 15 m² box roof, getting 800 W/m² of sunlight and converting it at 25% generates 3 kW.  That's a significant amount of power, well in excess of the typical demands of air conditioning.  3 kW is probably sufficient to creep in traffic indefinitely.

Just because the OTR semi isn't suitable doesn't mean it has no place.

Cyril R. said at October 28, 2014 12:46 PM:

3 kWp = 0.3 kWe average, year round for a flat roof in average solar conditions.

You are entitled to believe that 300 Watts is a lot of power. You are also entitled to believe that aircon is a big power consumer for a commercial delivery truck. Its a free country.

But, when you're in a more serious mood, we can perhaps have more useful discussions.

Cyril R. said at October 28, 2014 12:56 PM:

"Just because the OTR semi isn't suitable doesn't mean it has no place."

Oh, but my position is that PV has a very good place on all vehicles. Its very good greenwashing you see, cheaper than running expensive adds all the time, a very visual way to show you're "doing something" even though you're only reducing fuel consumption 1-2% and next year's growth in your or someone else's transport business will completely offset the savings.

I can definately see this happening. Though fake solar panels would be much cheaper for the transport company and would have similar environmental improvement as the real panels so aren't much more of a scam than the real deal.

Nick G said at November 7, 2014 2:18 PM:


Clearly, the key issue is that you don't think solar has *general* value. This is incorrect.

Solar is far cheaper than oil-generating power, which is still a big factor in many places. I've seen an estimate that about 10% of overall world oil consumption is still for power generation, in places like Japan, Saudi Arabia, Hawaii, Chile, China, India, etc., etc. That's a large part of why solar is growing so fast. One example: the US military is installing solar aggressively, to make it''s mobile and stationary assets more resilient, and reduce the "long tail" of millitary operations. And, of course, all of the "house" power generation in mobile vehicles adds up. 10-20% reductions in fuel consumption and range in commercial vehicles would not be something that any sane commercial fleet manager would just ignore.

Now, here's a key question: do you agree that Climate Change is an important risk? If you don't, I can understand your skepticism - we have lots of coal and gas. But, if you agree with the scientific community that Climate Change represents a real and very expensive risk, then you should agree that low-CO2 sources eliminate an important external cost of fossil fuels.

Engineer-Poet said at November 9, 2014 4:58 AM:
3 kWp = 0.3 kWe average, year round for a flat roof in average solar conditions.

But your delivery truck isn't operating "year round in average solar conditons".  It is operating mostly during daylight hours, exactly when PV is producing.  There are places where it would probably be a lousy idea (cloudy Seattle), but others where it would be a good one (Tucson).

You are entitled to believe that 300 Watts is a lot of power.

Off by an order of magnitude:  3 kW (just over 4 HP), not 300 watts.  Generating 3 kW during a stop would be sufficient to run the A/C and put something in the hybrid battery.  Just shutting down the engine saves considerable fuel.

You are also entitled to believe that aircon is a big power consumer for a commercial delivery truck.

IIUC, cabin aircon for passenger vehicles consumes up to a couple of horsepower (depending on engine speed).  If you can generate twice that much at a small weight penalty, it's energy-positive.

The Unisolar 136 watt peel-and-stick panel is 7.7 kg.  Most of that is probably packaging that would be eliminated if integrated with the box roof.  Guesstimate 1 kg active stuff, 7.4 kg/kW, 22.2 kg for a 3 kW installation.

At 1.25 MJ/tonne-km rolling resistance, this panel would require 28 kJ/km to push it.  This is about 9 seconds of its nameplate output.  Since no box truck is ever going to travel a kilometer in 9 seconds or less, it's a safe bet that such panels would be strongly energy-positive.

PV has a very good place on all vehicles. Its very good greenwashing you see

It has the potential to be much more than that, especially because it's offsetting refined petroleum.

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