Boldly Go!

What will become the new standard for cars after we run out of fossil fuels? This post will assess the viability of the following alternatives:

Ethanol/Bio-diesel
Compressed Air
Hydrogen
Super-capacitors
Electrochemical Batteries
Fuel Cells

Ethanol/Bio-diesel:

Ethanol and bio-diesel have energy densities comparable to gasoline and diesel.  Ethanol requires inexpensive modifications for it to work in your car, and if you have a diesel truck it takes no modifications to use bio-diesel.  In Brazil, ethanol makes up 40% of the automobile fuel consumed, and most cars sold in Brazil can use gasoline or ethanol.

Why did I group ethanol and bio-diesel?  People incorrectly pit these fuel standards against each other.  If we make the switch we are going to need all the bio-fuel we can get.

In the bio-diesel corner: soybeans produce more bio-diesel per acre than corn does ethanol, bio-diesel is less pollutant, and diesel engines last longer and waste less fuel. In the ethanol corner: can be grown much more widely because it’s derived from corn or even weeds, and more cars use gasoline so it’s easier to adopt.  In kin with gasoline and diesel, ethanol and bio-diesel cater to different needs.

Advantages:

1. Compatible with current vehicles, slight modifications needed for Ethanol.
2. Renewable.
3. The technology is already highly developed

Disadvantages:

1. Expensive and time consuming to create.
2. Would drive up the cost to eat by competing with food production for farmers
3. While much better than oil, burning ethanol and bio-diesel causes pollution

——————————

Compressed Air:

Official MDI Site

It seats three, has a max speed of about 68 miles per hour, and gets about 125 miles on a tank. Oh… and it costs about two bucks to refill it. It’s pretty hard to beat two dollars for every 125 miles. An air compressor comes inside the car, so you can refill the air tanks by plugging it into a wall outlet. Technically the air is only a way of storing the energy, so it’s an alternative to a battery powered car.

Advantages:

1. Light weight engine is optimal for fuel efficiency
2. No inherent pollution
3. No large battery that goes bad and needs to be repurchased
4. The energy is transported via powerline

Disadvantages:

1. Compressed Air has a bad energy/volume ratio
2. Lacks the oomph of gas and batteries, making it unsuitable for faster/larger vehicles
3. Compressed air tanks explode somewhat easily

——————————

Hydrogen:

It seems to work well for rockets.

Iceland has a fleet of 33 hydrogen powered school buses, and eventually hopes to power many vehicles using hydrogen.  Because you have to use more energy then you get to extract hydrogen, hydrogen is a battery option for transporting Iceland’s geothermal energy.  Currently, the cheapest way to make hydrogen is through steam reforming which uses fossil fuels.

You can also get hydrogen from water, but you will never really be able to run your car on water. While water is a viable hydrogen source, an outside energy source is needed to extract the hydrogen from water. The process of separating hydrogen from water (2 H20 → 2H2 O2) and burning hydrogen (2H2 + O2 → 2H20) are exact opposites of each other. So any energy gained by one process would be lost in the other according to the first and second laws of thermodynamics. In fact, since it can’t be a 100% energy efficient system, you end up with significantly less usable energy. An outside energy source is needed, and the outside energy source is the true source of power.

However, a hydrogen from water system could be a very good way of storing energy that comes from another source.  It is possible and one day it may even be practical for a factory or home that is getting extra power from an external source to extract hydrogen for car use.  If the machinery needed to convert water to hydrogen were light weight, a system similar to what is being with the air powered car could be developed.  You could fill the tank with water, plug the car into your home, and wait for it to convert the water to hydrogen.  But while it’s already possible to separate hydrogen from water at home, it’s much more energy efficient at a factory.

Advantages:

1. High energy density.
2. Extremely abundant. Hydrogen is in almost everything.
3. It’s possible to have water as a waste product.

Disadvantages:

1. Splitting hydrogen bonds isn’t energy efficient
2. The cost. The fuel and vehicles are expensive to make.
3. Technology isn’t well developed

——————————

Super-capacitors:

Unlike batteries, super-capacitors can be recharged almost indefinitely without going bad.  But they also have a bad energy density, making them less suited for vehicles and more suited for factories.  However, China has started using super-capacitor buses.  The energy density of super-capacitors has been improving with time.  One day they might become good enough to power smaller vehicles.

Advantages:

1. Can be recharged without going bad, which cuts down on expenses and pollution
2. Currently recharges much quicker than batteries.
3. Little energy is lost when storing energy from an outside source

Disadvantages:

1. Low energy density makes it unsuitable for small vehicles.
2. Low energy density means significant energy is lost transporting its own weight.
3. It might never be possible to make super-capacitors that have a high energy density.

——————————

Electrochemical Batteries:

An electrochemical battery is different than a fuel cell battery. A fuel cell has a reactant like hydrogen that is consumed and needs to be replenished. An electrochemical battery is a closed system where the reactant isn’t used up and the battery just needs to be recharged. Adaptability-- can use grid power-- efficient transportation. Much easier to switch to on a grand scale.  Will it become the new standard? The Tesla Model S sure looks promising.  But, the batteries of the Tesla cars cost a small fortune and they need to be replaced every few years.

Advantages:

1. Can be charged using any energy source including wind, nuclear, and solar power
2. Electrochemical Battery technology has been actively developed for a long time
3. Transporting the fuel is cheap, fast, and only requires powerlines and a wall plug

Disadvantages:

1. Low energy density when compared to liquid fuels
2. Batteries go bad and can be expensive to replace
3. Not as environmentally friendly as super-capacitors or compressed air

——————————

Fuel Cells:

Fuel cells should be looked at as an alternative way of storing liquid fuel, rather than as an alternative to batteries.  Technically fuel cells do not store charges from an external source.  Fuel cells convert the reactant inside of them into electricity and the process uses up the reactant.  So fuel cells need to either be replaced, or refilled like a gas tank.  While fuel cells have a better energy density than electrochemical batteries, they lack other advantages.  Fuel Cells can’t be charged by powerlines, so cost is involved with creating and transporting a liquid fuel.

Advantages:

1. Can utilize a variety of fuels
2. Better energy density than electrochemical batteries
3. Efficient at transferring chemical energy into electricity

Disadvantages:

1. Lack the energy density of liquid fuels like bio-diesel and ethanol
2. Expensive to make and expensive to refuel
3. Would require large infrastructure changes to create and deliver the fuel

The Verdicts:

1. The best fuel option is: biofuel in a combustion engine

Besides Ethanol/Bio-diesel and Fuel Cells, the new standards listed are battery options rather than alternative fuel options.  Ethanol and bio-diesel have higher energy densities than fuel cells, would be easier to switch to, and are currently much easier to mass produce.  So it seems unlikely that we would switch to fuel cells over ethanol and bio-diesel.

——

2. The best battery option is usually: Electrochemical Batteries.  However, there are important niches where compressed air and super-capacitors are the better choices.  Hydrogen is the worst battery option and will not be used significantly.

Super-capacitors are efficient at transferring the energy, and they are the most reusable.  But because of their low energy density they lack the ability to provide much power.  If super-capacitors were to become significantly more energy dense they would be the best battery option, but after 60 years of developing them this has failed to be the case.  They are currently the best option for large vehicles like city buses that don’t have to go fast or far, but they are ill suited for anything else.

Compressed air can be used in small and large vehicles, and the battery will never go bad.  However, because compressed air has low energy density the air powered vehicles have to be incredibly light weight.  There are questions about the ability of these cars to pass crash tests, since there has never been a car light weight enough to get over 100mpg that has passed a north American crash tests.  Another problem with compressed air is that the more you compress the air to increase energy density, the less efficient compressed air is at storing energy.  This is because the more it’s compressed the more energy it takes to continue compressing it  Despite these issues, compressed air looks promising for small, light weight vehicles that don’t have to go far..

Hydrogen has the highest energy density.  But the high energy cost of splitting hydrogen bonds makes it the least efficient way of storing energy.  It could be produced much more efficiently in a factory setting than in a home, but that would give it the same disadvantages as other liquid fuels except intensified.  Hydrogen takes up four times the volume of gasoline to provide the same amount of energy, so it would be expensive to transport.  Neither transporting it as a fuel or producing it in the home is as energy efficient as the other battery options.

Electrochemical batteries are the only battery option besides hydrogen with a high enough energy density to allow the size of cars we currently drive go far and get there fast.  Electrochemical batteries beat out hydrogen because they are a more efficient way of storing energy, and electric cars are cheaper to make than hydrogen cars.   They have disadvantages to both pocketbooks and the environment when compared to compressed air and super-capacitors.  But compressed air and super-capacitors still aren’t options for allowing us to continue to drive family cars long distances, making  electrochemical batteries the most appealing option.

——

3. Electrochemical batteries are a better option than biofuel

Battery powered cars are better for the environment, and it is also much more cost effective to refuel a battery powered car than it is to refuel a gas powered car.  But, the expense of electric cars with oomph like the Tesla needs to continue to drop.  From a car manufacturing standpoint, it will be easier to switch to ethanol/bio-fuel cars.  But from an energy transport standpoint, it will be easier to switch to electric cars.  When fuel shortages start to become a problem, the cheaper operation costs and ability to utilize any fuel source will be more important than the ease of switching to ethanol/bio-diesel cars and the superior energy density of gas.  With only a 7.4% energy loss from factory to wall socket, it’s more energy efficient to burn fuel at a factory and turn it into electricity than it is to physically move the fuel.

——

4. Electrochemical cars will dominate, but there will be other cars too

While I think the electrochemical batteries will be in the average car of the future, I don’t think they will dominate cars the way gas powered vehicles have.  Super-capacitors, air cars, and gas powered vehicles will still probably have niches.  The citizens who are really concerned about the environment might be driving air powered cars which are more environmentally friendly, but can’t go fast and can only go short distances.  Super-capacitors also look like they will be the superior option for large, slow transport vehicles that will last a long time without maintenance.  And for years to come, gas will probably remain the best option for both large, fast moving vehicles like semis and for race cars that need to be able go 200+ mph.  Of course, new technological discoveries could throw what makes sense in the present out the window.