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Solar powered trucks?



Generative AI enables more powerful engineering tools, which make groundbreaking projects more feasible and economically viable; and this will spark a new wave of innovation within hardware products. What crazy ideas will come to fruition? Solar powered vehicles? What about these fuel-thirsty heavy trucks that storms the roads every day? Today, approximately 96% of the trucks in EU are powered with diesel [1]. What a truck today, or any vehicle with a combustion engine for that matter, actually strives for is to in the most efficient way possible convert the chemical energy from hydrocarbon molecule chains to mechanical energy, in order to move a mass from A to B. The problem is that this procedure is really hard to perform efficient, most of the energy in the fuel ends up being wasted as heat to the surroundings in the combustion process. From the energy available in diesel/petrol fuel, only about ~30-40% of the chemical energy can be converted to mechanical energy (tank-to-wheel) that we can use to do some actual work with. And oh, there's another not so good thing about breaking these hydrocarbon molecule chains under high heat and pressure in combustion engines, the carbon reacts with oxygen in the air and forms carbondioxide (CO2). At the same time, the nitrogen in the air also reacts with the oxygen and forms nitrogen oxides (NOx). I will not go into details about the increased environmental risks that comes with adding billions of tons of CO2/NOx in the atmosphere every year, so let's just assume that maybe it's not such a good idea in the long run. But if we can't use these great high energy hydrocarbon molecules to power trucks, what can we use instead? Well, we have a big fusion reactor in the sky, what about that one? It shows up every day too! But can we use it to power all medium/heavy vehicles in all of Europe without any significant technology breakthroughs? Is it possible? Let's find that out!

I will divide the study into 8 parts:

1. Energy network and truck design

2. Number of medium & heavy vehicles

3. Energy consumption

4. Solar panel area

5. Batteries

6. Battery production

7. Solar panel production

8. Conclusions

1. Energy network and truck design

First, let's think about how the energy network and trucks should be designed. Solar panels generates power in the form of electricity, so an electric powertrain in the truck is probably the best choice. Since the power/weight ratio for solar panels is low, and trucks have a small surface area compared to its power need, it's not possible to generate enough power to drive the truck if we place the solar panels on the truck. "But what about these flexible lightweight solar panels? Can't we use them to create a solar wrap that covers the whole truck?" you may ask. Well, let's look a bit closer on that.

Figure 1: Flexible solar panel [2].

The largest tractor + trailer combination in EU is about 25.25 m long, 2.6 m wide and ~2.7 m high, which equals to a surface area of ~216 m2 (neglecting area under the truck). Flexible solar cells are usually less efficient than "traditional" solar cells and generates about ~80 W/m2 during full sun light, so covering every single square meter of the truck would result in a power generation of 80 * 216 = 17 280 W = ~17 kW. If the sun would shine on all of the truck at the same time, that is. A few sides will always be in the shadow or facing the sun with a bad angle and we also can't cover windows etc. with this solar wrap. So a more realistic number would probably be ~4-5 kW during full sun light at most, and that's only a few percentage of the trucks average power consumption.

It's probably a better idea to extract the energy from the sun somewhere else under optimal conditions, and transfer the energy to some energy storage system in the trucks instead. A suitable solution could be to have distributed solar parks which provides power to charging stations, where the trucks can charge and store energy on board.

Figure 2: Illustration of energy network.

How should we store the energy on board on the trucks? Well, we mainly have two alternatives if using technology available today: large amount of batteries or hydrogen+fuel cells+small amount of batteries. If we would like to use the energy generated from the solar cells as efficient as possible, only batteries is the way to go. Using only batteries has a 2-3 times higher efficiency from grid to wheels compared to using hydrogen and fuel cells. And since the sun doesn't shine all the time (and to have enough power flow to the charging stations), we would also need an energy storage system between the solar panels and the charging stations, so let's use batteries (big mega-batteries) here as well.

2. Number of Medium & Heavy Vehicles

As for 2015, there were 13 048 717 medium and heavy commercial vehicles on road in Europe (6 243 377 in EU, 160 171 in EFTA and 6 645 169 in Russia, Turkey and Ukraine) [1]. The definition of medium in this case is a Gross Vehicle Weight (GVW) between 3.5 - 16 tons and the definition of heavy is a GVW above 16 tons.

 Figure 3: Vehicle data from ACEA [1].

The average number of medium & heavy commercial vehicles between 2011 - 2015 averaged ~13 122 455. It's likely that we can expect some growth on number of vehicles in the future, but let's use the average in this study. The registration mix between medium and heavy trucks/buses in EU-28 is shown in the figure below.

 Figure 4: Vehicle data from ACEA [3].

And a closer look on the truck mix:

 Figure 5: Vehicle data from ACEA [3].

Figure 4 shows that the large majority of new medium & heavy commercial vehicles registrations in EU-28 is trucks and buses over 16 tons (~77%). If we just look on the trucks, ~86% is trucks over 16 tons where the majority is long-haul tractor trucks (Figure 5). But note that Figure 3 includes all medium & heavy commercial in all of Europe, and Figure 4 and 5 just shows data from EU-28. To simplify things a bit, and to introduce a margin of safety in our upcoming calculations, let's assume that all 13 122 455 vehicles in Europe are heavy trucks/buses over 16 tons (this is of course an exaggeration).

3. Energy consumption 

The force needed to move a vehicle at constant speed needs to be equal to the sum of the resistance forces acting on the vehicle, which are: air resistance, friction force between the wheels and the ground and internal forces in the powertrain (when driving on flat ground). The size of these resistance forces depends on how aerodynamic the truck is, its weight and tires, the surface it's driving on and the design of the powertrain. These parameters will set the trucks power need and energy consumption. But during a driving cycle, trucks are also accelerating and deaccelerating, and all the additional power needed to accelerate are not being received when deaccelerating. Every time time you press the brake pedal in a diesel vehicle, you are decreasing the vehicle's kinetic energy by converting some of it to heat in the brakes = energy waste. This is therefore an additional power loss that needs to be considered. Also, some additional losses from road gradient also needs to be included. But instead of doing theoretical calculations of energy consumption, let's study actual real-world fuel consumption of trucks on the road in EU. Figure 6 below shows the average fuel consumption for heavy-duty trucks in EU.

Figure 6: Fuel consumption [3].

As it can be seen in the figure above, the average fuel consumption ranges between 35-37 l/100km for trucks in EU, with a higher density area around ~36 liters/100km. Other studies have also shown similar results, where the fuel consumption ranges between 34-36 liters/100 km in 2015 [3][4][5]. Keep in mind that this is average fuel consumption for trucks on the road in 2015, were the majority of trucks probably were produced in the years 2005-2015. The energy density for diesel is ~35.8 MJ/liter (~9.9 kWh/liter) [6], which means that 36 liters/100km equals to 36*9.9 = 358 kWh/100 km, or 3.58 kWh/km. But this is the energy extracted from the tank, not the energy that's being used to move the vehicle (due to losses in the combustion process and rest of the powertrain).

The efficiency of the powertrain differs drastically between a diesel and an electric powertrain. A diesel powertrain mainly consists of an internal combustion engine, gearbox and central gear/s. The efficiency for a heavy-duty diesel engine is often greater than the smaller ones used in passenger cars, mainly because higher pressures are used in larger engines, which means that an efficiency over 40% can be reached [7], but let's use 40% in this example. Let's also assume a total transmission efficiency (including gearbox and central gear/s) of ~90% [8][9]. An electric powertrain consists of batteries, a AC-DC inverter, one or more electric motors and a small gearbox. The gearbox in electric cars is usually an one-step gearbox to increase the torque output at the wheels and increase the operational frequency of the electric motor. For a truck, it's reasonable to assume that at least a two-step gearbox could be needed (one low and one high range gear). This, however, is not a must, but it could give some advantages on high torque output at low speeds and increased operational efficiency of the electric motor/s during the full drive cycle. But in any case, a gearbox for an electric powertrain would most likely be smaller and simpler, probably also without any central gears (if using electric axle drive). This would probably lead to higher efficiency compared to the total transmission in a diesel powertrain, so let's use 95% here. State-of-the-art Li-Ion batteries have a round-trip efficiency of ~85% (incl. climate system), AC-DC inverters has an efficiency of ~95% and electric motor can be operated with an efficiency of around ~95%. [10]. The total efficiency and energy need per km for both powertrains then results in:

Figure 7: Efficiencies and energy need.

With the efficiencies stated above, the total efficiency for a diesel truck results in ~36% and for an electric truck in ~73%. We know that the truck consumes ~3.58 kWh/km of diesel from the tank, so we can calculate the trucks energy need at the wheels by simply multiplying 3.58 kWh/km with 36% and get ~1.29 kWh/km. If we assume that the energy need for the electric truck at the wheels is equal to the diesel truck's, we can simply calculate the energy need from a electric DC power source by dividing the energy need of 1.29 kWh/km with the total efficiency of 73% and get ~1.77 kWh/km. But we need to adjust this number a bit. As mentioned above, when a diesel truck breaks, it uses the disc brakes to convert the decrease in kinetic energy to heat (wasted to the environment). But when an electric truck breaks, it can use both the disc brakes and the electric motor/s as breaks (often referred to as "regenerative breaking"). This is possible because electric motors can also be used as generators if run "backwards", and this means that some of the trucks kinetic energy can actually be converted back to electrochemical energy in the batteries. The amount of energy that can be regenerated depends on the driving cycle, an energy decrease up to ~25% is often encountered [10][11], but let's use 20% in this study. This means that the energy needed from the source instead is 1.77 * (100%-20%) = 1.41 kWh/km. If we assume an average velocity of 70 km/h, the average energy consumption at the wheels of ~1.29 kWh/km is equal to a power of:

1.29 kWh/km * 70 km/h = ~90.2 kW

Yes, the electric truck is heavier due to the extra weight of the batteries, but at the same time it can be designed more aerodynamic due to the decreased need of cooling compared to a diesel truck. That's why the Tesla Semi can have a drag coefficient similar to a Bugatti Chiron sports car (along with some other aerodynamic improvements on truck and trailer). Therefore, we do the simplification here and assume that the power need at the wheels to move the two trucks is approximately the same.

Ok, so now we know how much energy one truck consumes per kilometer, but what about in one year? The majority of heavy trucks drives under 500 km per day (~80%), a typical tractor + trailer truck in Europe drives about ~130 000 km per year on average (~356 km/day) [13][14]. This means that the energy consumption for an electric truck during a day is equal to:

1.41 kWh/km * 356 km/day = ~504 kWh

And for a full year:

1.41 kWh/km * 130 000 km = ~183 935 kWh = ~184 MWh

And, as mentioned before, the number of trucks on road in all of Europe is approximately 13 122 455, which give a total energy consumption of:

184 MWh * 13 122 455 = 2 413 675 930 MWh = ~2414 TWh

4. Solar Panel Area

Now when we know how much energy all trucks in Europe consumes in a year, we can calculate how large area of solar panels that would be needed to generate all this energy. Sunlight has a power intensity of approximately ~1000 W/m2 (depends a bit on where on earth you are), and state-of-the-art commercial solar panels has an efficiency of ~18-20%. Since the power output from solar panels depends on the sun, we need to store the energy generated somewhere in order to be able to provide energy 24/7 and on cloudy days. As mentioned before, I'm going to assume that we use mega Li-Ion batteries here, which has a charge/discharge efficiency of ~85%. Solar panels generates electricity in the form of direct current (DC), which we can use to directly charge the mega-batteries with. And if we assume this solar panels -> mega-battery -> charging station -> truck network (Figure 2), we don't really have a need to convert the electricity to AC at all. Therefore, we can cut some AC-DC/DC-AC conversion losses. In reality, however, some DC-DC conversions would be needed to convert the voltage along the power chain, but let's assume that these are included in the Li-Ion battery round trip efficiency in this study. The total power that the solar panels delivers to the charging stations would then result in:

1000 W/m2 * 18% * 85% = ~153 W/m2

The average number of sun varies a bit depending on which country in Europe you look at, below are some annual average hours of sun for cities in Europe (based on last 30 years).

Lisbon, Portugal: 2799 h

Ljubljana, Slovenia: 1712 h

London, United Kingdom: 1410 h

Luxembourg, Luxembourg: 1630 h

Madrid, Spain: 2769 h

Milan, Italy: 1914 h

Minsk, Belarus: 1758 h

Moscow, Russia: 1721 h

Munich, Germany: 1709 h

Odessa, Ukraine: 2183 h

Oslo, Norway: 1668 h

Paris, France: 1662 h

Prague, Czech Republic: 1668 h

Pristina, Kosovo: 2123 h

The annual average hours of sun for the cities stated above is ~1900 h, that's equals to sunny days ~65% of the year with 8 hours of sun each day. With this information, we can calculate the energy produced per m2 every year:

153 W/m2 * 1900 h = 290 700 Wh/m2 = ~291 kWh/m2

Now, we can calculate the total area of the solar panels needed provide the trucks with energy:

(2414 * 10^12 Wh) / (291 * 10^3 Wh/m2) = 8 302 978 774 m2 = ~8303 km2

This would also mean a peak power output of:

153 W/m2 * 8 302 978 774 m2 = ~1270 GW

If we picture the area as a square, the sides in the square would be equal to:

sqrt(8303 km2) = ~91 km

To get a better understanding of how big area that is, let's put it in perspective to the land area of Europe.

Figure 8: Required solar panel area.

The red square in Germany represent the 8303 km2 required to provide all trucks in Europe with energy (~2.5% of total land area in Germany). But it's not practical to have all the solar panels at the same place, so let's randomly distribute them, just to give a better understanding of how large of area it actually is:

 Figure 9: Required solar panel area, distributed.

In reality, these solar panel parks should be distributed even further and placed on strategic places, instead of just randomly distribute them as I have in Figure 9. And that's it. That's the area of panels needed to power all the trucks in Europe with only the sun.

5. Batteries

In section 3 we calculated an average energy consumption for the electric truck to be 1.41 kWh/km. It's likely to assume that this number will drop in the future due to improved vehicle design, but in an attempt to increase the reliability of this number, let's study the energy consumption of some existing electric trucks:

Volvo FL

GVW: 16 tons

Range: 300 km

Battery capacity: 300 kWh

Energy consumption: 1.00 kWh/km [15]

Tesla Semi

GVW: 36 tons

Range: 483 km/805 km

Battery capacity: Less than 604 kWh/1006 kWh

Energy consumption: Less than 1.25 kWh/km [16]

Freightliner eCascadia

GVW: 36 tons

Range: 400 km

Battery capacity: 500 kWh

Energy 1.38 kWh/km [18]

Freightliner eM2

GVW: -

Range 370 km

Battery capacity: 325 kWh

Energy consumption: 0.88 kWh/km [18]




Earlier we did the approximation that a heavy truck in Europe on average drives ~130 000 km per year, which equals to ~356 km per day. Suppose that the trucks on average have a range of 400 km (remember, the majority of heavy trucks drives under 500 km per day). And the only thing needed to drive a longer distance is just a stop for a recharge, the driver needs to take a break now and then anyway. To provide this range with an average energy consumption of 1.41 kWh/km without the need of recharging, a battery capacity of 400 km * 1.41kWh/km = ~566 kWh would be needed. Note that this is a simplification, because in reality the batteries would favorably be used in a shorter range than 0-100% to extend their life time. For 13 122 455 trucks, that would be:

13 122 455 * 566 kWh = 7 426 695 168 kWh = ~7.4 TWh 

And that's it for the truck batteries. But we also need to store the energy generated from the solar panels somewhere, and as earlier stated, we're using batteries here as well. These mega-batteries would need to be able to store a buffer of energy to cover peak hours (when the power output from the solar panels are lower than the output from the charging stations) and energy consumption during a series of cloudy days with decreased energy generation from the solar panels. But keep in mind that the sun matches the charging demand quite well. Most of the trucks drives during the day when the sun is up, and stays at rest during night when the sun is down. Also, contrary to what people might think, solar panels do actually generate power during cloudy days too, even when it's very cloudy. The power capacity, however, drops to about 10-25% of the power generation during a sunny day, depending on how cloudy it is [19][20]. Suppose that be mega-batteries on average needs ~48h of energy storage capacity to have enough buffer to cover charging during peak hours and some charging at night and on cloudy days. Earlier we calculated the energy consumption of all trucks in Europe for a full year, we can use that number to calculate the the average energy consumption for two full days:

2414 TWh * (2 / 365 ) = ~13.2 TWh

So the mega-batteries would need to be able to store ~13.2 TWh of energy and the batteries in the trucks 7.4 TWh of energy. This gives a total battery capacity demand of:

13.2 TWh + 7.4 TWh = 20.7 TWh

This sounds like a lot! But is it possible produce batteries of this size? And how large and heavy would they be? Suppose that we use a similar chemistry for these mega-batteries as for the Li-Ion batteries in the trucks (Like Tesla do in their Powerpacks). State-of-the-art Li-Ion batteries have an energy density of up to 265 Wh/kg on cell level [21] and up to 207 Wh/kg on module level (data from Tesla Model 3 [22]). For the trucks, this would mean a battery pack weight of:

566 000 Wh / 207 Wh/kg = ~2734 kg = ~2.73 tons per truck

On a cell level, the weight of the truck battery packs and the mega-batteries would result in:

One truck: 566 000 Wh / 265 Wh/kg = ~2136 kg = ~2.14 ton

All trucks: 2.14 ton * 13 122 455 = ~28.0 million tons

Mega-batteries: (13.2 * 10^12 Wh) / 265 Wh/kg = ~49.9 million tons

Total battery weight (cell level): 28.0 mil. tons + 49.9 mil. tons = 77.9 million tons

What about the size of these mega-batteries? The cells would have to be placed in modules, which would have to be placed in a housing with cabling, integrated cooling and protection to the environment. Tesla's Powerpacks are equipped with all of this, so suppose that we build this mega-batteries with a large series of Tesla's Powerpacks.

Figure 10: Tesla's Powerpack installation in Australia [23].

Tesla's Powerpack is designed for infinitely scaling and each Powerpack contains 16 Li-Ion battery modules with which together can store 210 kWh of energy. With this number, we can calculate how many Powerpacks it would take to cover a capacity of 13.2 TWh:

(13.2 * 10^12 Wh) / (210 * 10^3 Wh/pack) = 62 979 150 packs = ~63 million packs

One Powerpack is 0.822 m wide, 1.308 mm long and 2.185 high, which gives a volume of ~2.35 m3 per Powerpack [24]. With 61 million Powerpacks, this would equal to a total volume of:

61 159 752 * 2.35 m3 = 147 954 371 m3

Which would be equal to a total ground area of:

147 954 371 m3 / 2.185 m = 67 713 671 m2 = ~67.7 km2

Which only is ~0.82% of the required solar panel area, which is too small to even illustrate in Figure 8 (or about half the size of Walt Disney World resort in Florida [25]). If we would picture this area as a square, the sides in the square would be:

SQRT(67.7 km2) = ~8.2 km

6. Battery production

Commercial Li-Ion batteries that currently have the highest energy density have a Lithium-Nickel-Cobalt-Aluminum: NCA (ex: Tesla Model S), Lithium-Cobalt: LCO (ex: Apple Iphone), Lithium-Magnesium: LMO (ex: Nissan Leaf) or Lithium-Nickel-Manganese-Cobalt: NMC (ex: Tesla Powerwall) cathode chemistry [26]. All of these elements is found in earth's crust, and we can rank them according to how common they are in the crust [27]:

 Rank Abundance in earth's crust (ppm)

1. Aluminium: 3 ~82 000

2. Manganese: 12 ~1000

3. Nickel: 24 ~90

4. Cobalt: 32 ~25

5. Lithium: 33 ~20

As it can be seen above, lithium and cobalt are the rarest ones among these elements. So is there even enough Lithium and Cobalt on earth to produce 77.9 million tons of Li-Ion batteries? Well, first of all, not all of the 77.9 million tons are lithium and cobalt. Tesla uses about ~0.200 kg/kWh of lithium and 0.06-0.09 kg/kWh of cobalt in their batteries [28][29][30]. This would mean that it would take:

0.200 kg/kWh * 20.7*10^9 kWh = 4 130 463 340 kg = ~4.13 million tons of lithium

And

0.06 kg/kWh * 20.7*10^9 kWh = 1 548 923 753 kg = ~1.55 million tons of cobalt

I'm using the lower part of the cobalt interval because the trend goes to reducing cobalt in batteries. For example, Tesla has reduced their cobalt content with ~60% over the last 6 years, and claims that they will fully eliminate cobalt in their battery chemistry in the future [31]. But do we really have this huge amount of lithium and cobalt in earth's crust? The crust is like a thin layer that covers the earth's surface, like the peal on an apple. It varies in thickness and is less than 1% of earth's mass, about ~0.5% some estimates have shown [32]. The earth weighs about 5.97 * 10^24 kg [33], so 0.5% would then be: 0.005 * 5.97 * 10^24 = ~2.82 * 10^19 kg. Using the ppm values stated above for cobalt and lithium this would result in 564 970 billion tons of lithium and 706 213 billion tons of cobalt. So we need about 0.0000007% of all lithium and 0.0000002% of all cobalt available to produce all the batteries we need. And beyond that, the oceans also have an additional ~230 billion tons of lithium. But these numbers are based on rough estimates, and it's also a question of how much of the available cobalt and lithium that we can access and extract. The point is, there is more than enough lithium and cobalt on earth to electrify the whole planet. That's not the bottleneck here, the bottleneck is production.

Even if there are a lot of lithium and cobalt on earth, the amount that we currently excavate is relatively very low. The production of lithium in 2017 was about 43 000 tons, of which ~46% was used for battery production, and the global reserve of lithium is estimated to be ~16 million tons [34]. The production of cobalt in 2017 was about 110 000 tons, of which ~50% was used for battery production, and the global reserve is estimated to be ~7.1 million tons [35]. Most of the cobalt is received as a by-product in nickel/copper production. Also, cobalt production is often associated with political risks since a large part of the production takes places in politically unstable areas such as the Democratic Republic of Congo (by far biggest producer, ~58-65% of the cobalt market) [36][37]. So there is enough excavated lithium and cobalt to produce the amount of batteries needed, but the yearly production would not cover it, a significant amount from the reserves is needed. But what about the battery production?

This is where things starts to get really tricky. Estimates of the global battery production for xEVs is shown in Figure 11 [38].

 Figure 11: Estimated battery production [38].

As it can be seen in the figure above, the yearly battery production is far less than we would need to produce the ~13 million 566 kWh packs + 13.2 TWh mega-batteries. The battery production forecast above shows a growth rate starting at ~79% to level out at ~6% in 2024-2025. Even if we would assume that the growth rate would remain at ~6% after 2025, it would take ~25-27 years to produce the battery capacity we would need, if we somehow could manage to use 100% of the production (which of course is not realistic). The batteries needed for just the trucks would however take far less time to produce. The point is, the battery production capacity is the largest drawback to in a short period of time reach a solar based energy generation/consumption system for all heavy trucks in Europe. At least if we choose mega-batteries as the choice of energy storage. But that doesn't mean that it's outside the ability of humanity to actually achieve. Remember that production just aims to to meet the demand, and the production estimates aims for meeting the estimated future demands. And until a couple of years ago, before this electric vehicle boom era, the production estimates was far lower for 2015 and forward, and the market for new players didn't look as attractive as today. But today there's another story, where future demand estimations are extremely high which makes the market looks more attractive and new players entering the market can really help to strongly increase the production in a relatively short period of time.

7. Solar Panel production

The base material in solar cells is by far Silicon. And silicon is the second most common element in earth's crust after oxygen [27], which means that there's absolutely no shortage of that. However, silver is also used in solar cells due to its conductive properties. And silver is far less common on earth compared with lithium and cobalt. In fact, the concentration of lithium in earth's crust is 286 greater than silver's (Silver has a concentration of only ~0.070 ppm in earth's crust [27]). I will not go in-depth on silver production, but the trend shows a strong decrease for silver usage in solar cells over the last couple of years. For example, the average silver content in solar cells has decreased with ~68% between 2007 and 2016, and estimates shows that today's number will be cut in half before ~2028 [39]. Silver in solar cells is basically only used for its conductive properties, which makes it likely that it can be replaced with other conductive materials like copper or aluminum in the future.

The solar industry is growing extremely fast. The compound annual growth rate (CAGR) over the last 15 years was above 40%. In 2017, the global solar production was between 90 - 95 GW [40], and as mentioned earlier, we would need ~1270 GW. If the production would continue to increase in the extreme rate of ~40% it would take ~10 years to reach an annual production of ~2750 GW (Roughly, it depends on how the power output is defined). So a ramp-up in production is also needed on the solar side to create the mega solar parks needed to power all trucks in Europe with solar power.

8.Conclusions

The real question I wanted to investigate with this study was not to see if a mega-solar park/battery system like this was producible today, but if it's something that lays within the ability of humanity to achieve in the near future. A transition to a renewable way of producing and consuming energy is extremely important (and inevitable in the long run), but it's nothing that can be achieved over a single year.

But is it realistic to power all trucks with only solar? Well, a mix of renewable sources would make a lot more sense to increase the robustness of the system. But it would most certainly be possible to only use solar and store the energy in big batteries, as I've showed in this article. However, the bottleneck that prevents us from achieving this in the very near future is the production capacity of solar panels and batteries. But one important fact that people needs to understand is that there's no shortage of battery metals in earth's crust, we have barely scratched the surface yet! And there's a big difference between mining coal/oil and metals, because unlike fossil fuels, metals are recyclable (very close to 100% recyclable). This means that when enough metals are extracted to satisfy a certain industry, the metals can just be recycled in a recycling loop (yes, some material is lost in the recycling process but it's a relatively small amount). This fact in combination with the large amount of metals available in earth's crust (and oceans for lithium) makes the availability of battery metals close to infinite as far as humanity is concerned. So to favor fossil fuels by using the "what about battery materials, is that really sustainable?" argument is really a weak argument. One should not mix up battery material availability with current battery production pace.

Keep in mind that the exact numbers in this article should be taken with a grain of salt, but they should at least be in the ballpark of a realistic estimation. It's highly likely that we will see some improvements trucks' energy consumption and solar panel efficiency in the future, which will give an even smaller required solar panel area and battery weight/volume. But further investigations are of course needed to increase the reliability of the results in this study. However, the most important thing with a study like this is to investigate what is actually possible and not possible for humanity to achieve, to find inspiring things to strive for in the future. Big trucks powered by the sun may sound impossible to some people, but is it really? These kinds of questions are healthy to ask, and the answers lays in the underlying physics and facts, not in biased newspaper articles with catchy headlines. And if you feel skeptical about the results in this article and think it appears to be "electric-vehicle biased", please do the math yourself. The more people that look into the facts and physics behind sustainable energy solutions the better.

Ref:

[1] Europe Automobile Manufactures Association (ACEA), Report on Vehicles in use Europe 2017 (https://www.acea.be/uploads/statistic_documents/ACEA_Report_Vehicles_in_use-Europe_2017.pdf).

[2] https://www.adafruit.com/product/1485

[3] The International Council on Clean Transportation (ICCT), European Vehicle Market Statistics 2016/2017 (https://www.theicct.org/sites/default/files/publications/ICCT_Pocketbook_2016.pdf)

[4] Future measures for fuel savings and GHG reduction of heavy-duty vehicles, Umvelt Bundesamt, Texte 32/2015. (https://www.umweltbundesamt.de/sites/default/files/medien/378/publikationen/texte_32_2015_summary_future_measures_for_fuel_savings.pdf)

[5] Explanatory note: Comparing US and EU truck fuel economy, Transport & Environment 2015. (https://www.transportenvironment.org/sites/te/files/2015_06_Comparing_US_EU_truck_fuel_economy_explantory_note_Final.pdf).

[6] https://en.wikipedia.org/wiki/Energy_density

[7] P. Roura, D. Oliu How energy efficient is your car?, Am. J. Phys. 80, 588 (2012) (http://physics.oregonstate.edu/~giebultt/COURSES/ph313/ppt/carefficiency.pdf)

[8] http://www.meadinfo.org/2008/11/gear-efficiency-spur-helical-bevel-worm.html

[9] "Maskinelement" By K.O. Olsson Liber, (2006)

[10] "Design Of Rotating Electrical Machines" By J. Pyrhonen, T. Jokinen, V. Hrabovcov (2008).

[11] B. J. Varocky. Benchmarking of Regenerative Braking for a Fully Electric Car, Report No. D&C 2011.002, January (2011) (http://www.mate.tue.nl/mate/pdfs/12673.pdf)

[12] G. Solberg, The Magic of Tesla Roadster Regenerative Braking, June 29 (2007) (https://www.tesla.com/blog/magic-tesla-roadster-regenerative-braking

[13] The International Council on Clean Transportation (ICCT), Overview of the heavy-duty vehicle market and CO2 emissions in the European Union, Dec 1 (2015) (https://www.theicct.org/sites/default/files/publications/ICCT_EU-HDV_mkt-analysis_201512.pdf)

[14] http://inconvenienttruck.eu/the-economics-of-trucks-industry/

[15] Volvo FL specs: https://www.volvogroup.com/en-en/news/2018/apr/news-2879838.html

[16] Tesla Semi specs: https://www.tesla.com/semi?redirect=no

[17] Einride specs: http://www.einride.tech/

[18] eCascadia/m2 specs: https://electrek.co/2018/06/07/daimler-electric-semi-truck-ecascadia-tesla-semi/

[19] Solar power on cloudy days: https://cleantechnica.com/2018/02/08/solar-panels-work-cloudy-days-just-less-effectively/

[20] Solar power on cloudy days: https://www.solarpowerrocks.com/solar-basics/how-do-solar-panels-work-in-cloudy-weather/

[21] Li-Ion batteries: https://en.wikipedia.org/wiki/Lithium-ion_battery

[22] Tesla Model 3 batteries: https://insideevs.com/tesla-claims-model-3-battery-has-highest-energy-density-of-any-electric-car/

[23] Tesla's Powerpack installation in Australia: https://internetofbusiness.com/tesla-powerpack-worlds-largest-battery/

[24] Tesla Powerpack: https://www.tesla.com/powerpack?redirect=no

[25] https://sv.wikipedia.org/wiki/Walt_Disney_World_Resort

[26] Battery cathode chemistry: http://www.visualcapitalist.com/critical-ingredients-fuel-battery-boom/

[27] Abundance of elements in Earth's crust: https://en.wikipedia.org/wiki/Abundance_of_elements_in_Earth%27s_crust

[28] Tesla Battery chemistry: http://www.visualcapitalist.com/critical-ingredients-fuel-battery-boom/

[29] Tesla Battery chemistry: http://www.benchmarkminerals.com/panasonic-reduces-teslas-cobalt-consumption-by-60-in-6-years/

[30] McKinsey & Company, Lithium and Cobalt - A Tale of Two Commodities , June (2018) (https://www.mckinsey.com/~/media/mckinsey/industries/metals%20and%20mining/our%20insights/lithium%20and%20cobalt%20a%20tale%20of%20two%20commodities/lithium-and-cobalt-a-tale-of-two-commodities.ashx)

[31] https://www.theverge.com/2018/6/21/17488626/elon-musk-cobalt-electric-vehicle-battery-science

[32] Mass of earth's crust: http://loki.stockton.edu/~hozikm/geol/Courses/The%20Earth/Content%20Web%20Pages/Kim/crust.htm

[33] Mass of earth: https://en.wikipedia.org/wiki/Earth_mass

[34] U.S. Geological Survey, Mineral Commodity Summaries, January (2018) (https://minerals.usgs.gov/minerals/pubs/commodity/lithium/mcs-2018-lithi.pdf)

[35] U.S. Geological Survey, Mineral Commodity Summaries, January (2018) (https://minerals.usgs.gov/minerals/pubs/commodity/cobalt/mcs-2018-cobal.pdf)

[36] Cobalt production: https://investingnews.com/daily/resource-investing/critical-metals-investing/cobalt-investing/top-cobalt-producing-countries-congo-china-canada-russia-australia/

[37] https://www.cobalt27.com/cobalt/about/

[38] Berylls Strategy Advisors, BATTERY PRODUCTION TODAY AND TOMORROW, March (2018) (http://www.berylls.com/wp-content/uploads/2018/03/20180323_Studie_E-Mobilitaet_EN.pdf)

[39] Silver in solar cells: https://www.pv-magazine.com/2018/07/06/amount-of-silver-needed-in-solar-cells-to-be-more-than-halved-by-2028-silver-institute-says/

[40] Jäger-Waldau, A. PV Status Report 2017, Luxembourg: Publications Office of the European Union (2017) (http://publications.jrc.ec.europa.eu/repository/bitstream/JRC108105/kjna28817enn.pdf)

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