In January, California Governor Jerry Brown called for a 50% reduction in oil consumption by 2030. This throws the gauntlet directly at the feet of the oil industry and challenges their persistent dominance over transportation. Transitioning millions of vehicles off oil will not be easy, but as the Governor said, “Taking significant amounts of carbon out of our economy without harming its vibrancy is exactly the sort of challenge at which California excels.“ While petroleum-funded pressure groups continue to claim that there is no problem, and we couldn’t do anything about it even if there was, recent research has shown that California can transform its energy economy and dramatically reduce the environmental impacts of transportation.
This raises an obvious question: If we’re going to halve oil use, what will our cars run on? Most experts agree that the internal combustion engine will yield its throne to the electric motor, which converts stored energy into motion without wasting much of it as heat. Electric motors also don’t lose as much energy to friction, due to fewer moving parts, and don’t need to run as many pumps, compressors and fans; most electric motors used in vehicles run cool enough that they don’t even need a radiator. The superior torque and wide range of useful speeds in electric motors eliminate the need for a heavy, complicated transmission system. Taken together, these features can allow electric vehicles to travel more than three times as far per every unit of energy as their gasoline equivalents.
The question is what will push an electric vehicle’s electrons through the wires? The two leading contenders are batteries and hydrogen fuel cells. Battery powered vehicles have a significant head start on their fuel-celled counterparts; first generation hybrids, like the Toyota Prius had small batteries, to capture energy from braking and use it to reduce the load on the gasoline engine. Over time, batteries in hybrids have gotten larger and provide more of the energy that moves a vehicle from the electric grid. Many more models of pure electric vehicles (EVs) have been introduced recently, which use electricity as their sole source of energy.
Hydrogen fuel cells, which generate electricity by reacting stored hydrogen with oxygen from the air, are a less mature technology that has not yet been widely deployed. There are still cost and performance problems to resolve and only a handful of fueling stations exist. Several projects are under way to build hydrogen fueling networks in big cities, where automakers might target an initial roll-out of hydrogen vehicles. By clustering the vehicles and fueling stations into a small area, manufacturers can attain the critical mass necessary to smooth the transition to hydrogen for vehicle owners. Supplying hydrogen to fueling stations is also a critical question. At present, most hydrogen is produced from natural gas, which is a fossil fuel. Hydrogen can also be made by splitting water molecules apart using electricity, but this process is inefficient and expensive at present.
The Big Question
If we want to achieve the kind of emissions reductions necessary to prevent the worst effects of climate change, the passenger vehicle fleet will have to almost entirely switch to EVs. If so, where will the electrons get their push? Over the next decade at least, batteries’ head start will likely keep them in the lead; over the long run, the contest is more even.
Batteries are, at present, cheaper than fuel cells and have some efficiency advantages. Creating hydrogen by electrolysis loses about 30% of the input energy as heat and generating electricity from that stored hydrogen in a fuel cell loses almost as much, though technological improvements may be able to improve upon this. Charging and discharging battery is generally more efficient than making hydrogen; lithium ion batteries (currently the dominant type) return 80-90% of the energy that goes into charging them.
If efficiency is the battery’s strong suit, capacity is the fuel cell’s. Batteries increase capacity by adding more cells and electrolyte, which adds to weight and expense. Hydrogen fuel cells can increase capacity by simply expanding the size of their hydrogen tank, which is usually lighter and more cost-effective than an equivalent increase in battery size. This has important implications for certain applications which need more energy and longer time between refueling, like long-distance trucking. Batteries may not be practical for hauling fifty tons of freight several hundred miles at a time, but a hydrogen fuel cell could be. Hydrogen fuel cells also typically require less time to refuel.
Size vs. range for several electricity storage systems. Fuel cells can generally achieve longer ranges than similarly sized batteries.
A lot depends on how much range people really need. Studies have shown that even comparatively low battery ranges, like 20 miles, can allow as much as half of all driving to occur without needing to recharge or change driving habits. If you increase the range to 60 miles, this number goes up to around three-quarters. The Nissan Leaf currently has around an 80 mile battery range. So, for most drivers on most days, the extra range of a hydrogen fuel cell might be unnecessary. But many drivers want the option of taking longer trips, even if they don’t often use it.
It’s Not Just About the Cars
The deciding factor may be in how each of these technologies interacts with their fueling infrastructure. In batteries’ case, they will pull energy from the electrical grid, which increasingly draws from a diverse and intermittent pool of renewable sources. Solar panels provide a lot of energy for a few hours during the middle of the day. Wind varies during any given day and over seasons. As a result, we see variable demand and in some cases, if not managed properly, too much electricity can be as much of a problem as too little. EVs, if charged when ample renewable energy resources are available, could help smooth out the peaks and valleys in a typical day on the grid. Generally, vehicles would want to avoid charging when the demands on the grid are highest, in the early evening as people return home from work and instead draw power when the sun was at its highest or in the middle of the night, when demand is low. If electric vehicles are connected to smart chargers, which communicate with the grid and can be turned on or off to match local conditions, vehicle charging can improve the resiliency of the grid. There are also interesting proposals for letting the grid tap into EV batteries, when an extra boost is required. These vehicle-to-grid operations still have many technical and regulatory hurdles to overcome, but may further improve EVs’ contribution to the electrical grid of the future.
Hydrogen fuel cell vehicles should also have interesting and potentially useful infrastructure effects, too. The scalability of hydrogen allows for far larger tanks than those in a passenger vehicle. Hydrogen, produced during times of ample solar and wind power, allows for storage of very low carbon energy across seasons or even years. Hydrogen vehicles could contribute to this in a fashion similar to the vehicle-to-grid concept discussed above, by plugging into the grid and running stored hydrogen through their fuel cells, they could make it significantly easier and cheaper to turn energy stored as hydrogen back into electricity.
And the Winner Is:
If only it were that easy….
If you hang around sustainable energy conferences you will repeatedly hear the phrase “portfolio approach,” as in, “achieving a sustainable future will require a full portfolio of solutions, there is no silver bullet.” Transportation is no different and unless there is a breakthrough in one of these technologies, both will probably play a role in a low-carbon future. Between the substantial head start, the ability to use existing grid infrastructure and the efficiency advantages, batteries will probably supply most of the energy which moves electric vehicles around for the foreseeable future. Hydrogen fuel cells may achieve broad deployment in certain cities or along a few high-traffic transportation routes, in addition to being an important energy storage medium. As renewables dominate the grid, there will be excess electricity more and more often. Hydrogen can help absorb that excess and store it for a long period of time. A fleet of hydrogen fueled vehicles makes a future hydrogen energy system more useful and robust. The good news, for consumers, is that there will probably be a wide variety of sustainable transportation choices available to meet their needs.
During times when renewable energy is available in excess of total demand, that excess can be directed towards hydrogen production, smoothing out the net electricity supply curve. If necessary, this hydrogen could be converted back into grid electricity.
Ultimately, both hydrogen and batteries will probably become part of the overall portfolio of technologies used to address climate change. Application that needs less capacity on faster cycles probably play towards the strengths of batteries. Larger-scale demands with longer storage times match the characteristics of hydrogen. Most importantly, both technologies show immense promise as a way to break oil’s stranglehold on transportation and pave the way to a clean, sustainable future.
 Some models have a small radiator on the battery pack or charger, but not on the motor itself.
 If I may be forgiven a moment of pedantry, I would like to point out that the way many commentators express this point, “Where will the electrons come from?” is scientifically inaccurate. Power plants do not create electrons, they impart a charge to them, thereby forcing them through wires.
 References to brand names are as examples only and do not indicate any endorsement of a product by NextGen Climate America.
 Source: Battery University: http://batteryuniversity.com/learn/article/will_the_fuel_cell_have_a_second_life