Could we use solar power for transportation?

I often hear that installing wind and solar power doesn't help with our oil import problems, because we don't use oil for electrical generation anymore. I think that's not thinking far enough "outside the box".

So, do renewables help with our problems with oil?

Yes, solar power should be an important part of our transportation solution portfolio.

Transportation needs to be electrified, and all forms of existing transportation have power-hungry electrical systems, which draw power from the engines. PV can provide electricity more cheaply than can gasoline/diesel engines functioning as generators¹.

We could reduce transportation fuel consumption by aggressively deploying PV on planes, trains, ships and automobiles. Let's discuss the hardest case, flying.

1st, Manned non-commercial planes that run on PV² exist right now, and PV can certainly provide "hotel" electrical consumption (lighting, instruments, etc) on commercial aircraft. Planes travel above the clouds, and mostly during the day, which raises the "capacity factor" - the % of time the PV would generate power. The surface area of a plane could be maximized with trailing surfaces and longer wingspans. Taking the surface area of a large existing plane, one might generate 5% of overall energy needs using 20% efficient current commercial technology.

PV efficiency is likely to rise to something close to it's theoretical 66%, tripling the % that it can provide, while energy requirements are likely to fall: In the long term, design changes can reduce fuel consumption by 70%: "CAMBRIDGE, Mass. — In what could set the stage for a fundamental shift in commercial aviation, an MIT-led team has designed a green airplane that is estimated to use 70 percent less fuel than current planes while also reducing noise and emission of nitrogen oxides (NOx). source

The combination of 3.3x the PV output and 1/3 the energy requirement brings the PV % up to perhaps 50% of energy needs.

Finally, the remainder of the power could come from fuel (SOFC, hydrogen, etc) cells, which make much more sense for aviation than for personal transportation because infrastructure requirements are much easier to deal with (there are a relatively small number of airports). It's perfectly possible aviation will go to fully electric drivetrains.

Lets look at shipping, starting with the Emma Mærsk . With a length of 397 metres, and beam of 56 metres, it has a surface area of 22,400 sq m. At 20% efficiency we get about 4.5MW on the ship's deck at peak power. Now, as best I can tell it probably uses about 10MW at 12 knots (very roughly a minimum speed), 20MW at 15 knots, and 65MW (80% of engine rated power) at 25.5 knots (roughly a maximum). So, at minimum speed it could get about 45% of it's power for something close to 20% of the time, for a net of 9%. Now, if we want to increase that we'll need either higher efficiency PV, or more surface area from outriggers or something towed, perhaps using flexible PV. You could add a roof, or you could incentivize 10% of the containers to be roofed with PV - they could power ships, inter-modal rail, inter-modal trucks...

Here' a fun example of a boat that's 100% PV powered, and here's another.

Rail would be relatively easy, as most trains are driven by electric motors. A straightforward solution would be to build PV into the roofs of shipping containers, which could be plugged into ports on both trains and container ships.


¹ $3 gasoline in a car translates to $.30/kWh (there are about 35kWh in a gallon, of which the most efficient generators can extract about 10), which PV can beat handily. $2 diesel or jet fuel translates to $.10/kWh (there are about 40kWh in a gallon, of which the most efficient diesel engines can extract about 20). That would require PV that cost $2 per peak watt, which the best existing PV modules can provide. Balance of System costs (structures, wiring, inverters, installation) would be greatly reduced by building panels into rolling stock as part of the manufacturing process. Inverters wouldn't be needed, as power would feed directly into vehicle electrical systems.

We can expect diesel to rise in price, while PV will continue to fall.

² This may look very far from a practical solution, with it's small single-person manned capacity and it's very wide wingspan, but these guys are trying something very hard: continous powered flight during the night. They're trying to solve a problem that's much harder than commercial daytime aviation from Chicago to New York.

How quickly will we move to electric vehicles?

As you probably know, I think we should find replacements for oil ASAP. In particular, we should move to electric vehicles. Lately we've seen solid progress towards EVs, in the form of the Nissan Leaf and Chevy Volt. OTOH, GM plans to ramp up the Volt slowly to not get ahead of demand, and other car manufacturers are moving more slowly.

So - why aren't we moving more quickly to EVs?

I think there are a few things going on:

Oil's price has been higher than the price for substitute fuels for most of the last 40 years, but the margin has varied enormously, and it has only been clearly very high just in the last several years;

Industrial/commercial users are more price sensitive than residential/personal users;

Substitution takes a while ("capex lag");

Transportation is harder to replace than stationary uses, due to the secondary cost of energy storage (mostly in the form of batteries);

EVs are competitive with $80 oil, and far cheaper when you include external costs (security, "conventional" pollution, CO2, etc, etc) , but external costs are only internalized for a small minority of consumers, who are willing to recognize and factor in those costs even without subsidies, credits, fuel/carbon taxes, etc. External costs are extremely important: If those things weren't a problem, we wouldn't be worrying about HEV/PHEV/EREV/EVs. Heck, web sites like The Oil Drum etc wouldn't exist;

OPEC knows they face dangers from substitutes, and will keep prices in their current range as long as they possibly can. Effective fuel prices will stay moderate unless there is another price breakout, or governments rustle up the courage to internalize costs; and

A substitute needs to be much better than the status quo (rather than just competitive) to replace it quickly;

So.....the transition to EV/PHEV/EREVs will be kind've slow for a while.

Won't another wave of high gas prices cause a recession, that will prevent people from buying EVs?

EREVs are here now. Suggesting that high gas prices will cause recession, and that no one will notice and do anything about it, seems highly unrealistic to me. You may object that's already happened, and I'd reply that's only partially true. OTOH, the part that is true is why we're seeing a CAFE that's rising sharply; the Volt and Leaf vehicles; and an EV credit of $7,500.

If we were to see another oil price shock, I think we could expect to see the transition from ICE to EV accelerate very considerably.

Keep in mind that one of the major causes of oil-shock induced recessions is consumer uncertainty, as they delay their purchase, and wait to decide whether to buy something with better mileage. Well, I think another oil shock will push people off the fence: they'll start buying EREVs and EVs, and they'll have a much better reason to replace their old vehicles than they've had for a very long time.