I told my brother-in-law that I had previously worked on car engines but now work at a solar company. He then said, “Oh really? Can you make a solar-powered rocket car? I want that.” (Sure, buddy…) Is he really in the market for the sustainable Batmobile? Like the majority of Americans, he buys used cars that burn gasoline. He’d be happy to use renewable fuel if it was cost-effective and available. If my brother-in-law is willing to compromise on the rocket engine, maybe we can still figure out how to do solar-powered cars.
There are a number of ways to power a car with solar energy. Putting solar panels on the roof of a car unfortunately won’t generate enough power so generating power with a stationary plant and using storage is required (Sono Motors would disagree). Generating electricity with a solar plant and then using the power to drive an electric car is one way. Biofuels, like ethanol, might be considered solar fuels, except that a substantial amount of fossil energy is typically used to produce them, so the energy is only partly solar energy. A solar plant could be used to make hydrogen by driving an electrolysis plant, and the hydrogen could be used in a fuel cell vehicle like Honda’s Clarity Fuel Cell Vehicle (FCV). Finally, solar plants could be used to make hydrogen and carbon monoxide feedstocks to make synthetic gasoline or diesel fuels, which could be used in a normal car. Oh yeah, a solar plants could also be used to make hydrogen, which could be liquefied and stored in a tank on a car and then burned in a rocket engine. (Rocket cars do pose other challenges like projecting hot exhaust and driving in reverse.)
Rather than talking about one car, more interesting questions are how to power a large number of cars, say half of the vehicle fleet, with solar energy and how to get there quickly. What is the easiest strategy to get solar-powered vehicles to become widely used?
The first point about automotive power trains is that the fuel and the engine need to work well together. Indeed, gasoline and the spark-ignition engine have evolved together over the last hundred years. If a solar fuel is going to work, it needs to work with a solar fuel engine. In addition to large solar fields converting sunlight, one of the following scenarios is needed:
A) A new engine that works with already available fuel infrastructure,
B) A new engine and a new fuel with all of the required infrastructure, or
C) A new fuel with new infrastructure that works well with existing engines.
Electric vehicles are an excellent example of a “new engine” that works with an existing fuel: electricity (Strategy A). Solar plants or any other power plant can feed electricity to the grid, and inexpensive charging stations can be used to recharge electric cars. The main issue with this strategy for making solar-powered cars ubiquitous is that it is slow, simply as a result of the sheer scale of the vehicle fleet. There are about 270 million passenger vehicles in the U.S., and only about 17 million new cars were sold in 2018. So, roughly 6% of the fleet gets replaced each year. In 2018, 360,000 electric vehicles were sold in the U.S. This is about 2% of total new car sales, and that represents replacing just 0.1% of the total vehicle fleet. Besides convincing people to buy new-technology cars, people just don’t buy new cars that often.
If getting a new engine car into the fleet is slow, pursuing a strategy of using a new engine and a corresponding new fuel is even slower and harder (Strategy B). A concept like producing hydrogen with a solar plant and then running cars off hydrogen in a fuel cell would require 1) the vast adoption of new, expensive vehicles and also 2) the capital investment of duplicating all of those gas station, tanker trucks, pipelines, etc. with hydrogen infrastructure. The green car market is getting competitive too. Any new fuel cell vehicle market entrants will have to convince green-minded shoppers not to buy one of the many available electric car models that can be charged at many charging stations and probably also at the owner’s house. It may be a winner-take-all scenario for the green car market between fuel cell vehicles, electric vehicles, and other green cars.
The best strategy is to introduce a solar fuel that utilizes both the existing vehicle fleet and the existing fuel infrastructure. That way all you have to do is make the fuel. Although this is no mean feat, it is only one third of the system of fuel production, fuel distribution, and fuel consumption. More importantly, it is much faster because there is no delay waiting for new cars to trickle into the vehicle fleet. What this looks like is a large-scale solar plant that generates some kind of feedstock that is converted into a drop-in replacement for gasoline or, for the heavy truck sector, diesel fuel. The first stage of introduction would be a feedstock that is blended into one of the process streams at an oil refinery to back out some amount of crude oil or perhaps contributing solar hydrogen to replace a refinery’s hydrogen production.
An example to follow is the biofuels industry. U.S. oil imports were growing quite high in the 1990s so the government incentivized biofuel production and consumption. During the 2000s, ethanol consumption in the transportation sector consequently shot up by a factor of 10 to around 4% of the total transportation energy consumption. A normal engine cannot operate properly on straight ethanol so most ethanol was blended into gasoline at fraction of up to 10%, which a normal spark ignition engine can accept. Blending is done far from the consumer, and the average motorist does not have much choice but to use the gasoline with ethanol in it. The introduction of ethanol has been fast and effortless on the part of the consumer. A solar feedstock might follow a similar path.
The sexiest way to do a solar car would be a solar-hydrogen-fueled rocket car. However, this would be just one, expensive car. The fast way to get to a fleet of solar cars may be through the oil refinery. Detailing how this can start, and why we haven’t seen activity in this space comes next.