There are over three million buses on the roads of cities globally. Their passengers travel 7,000 billion kilometers per year in this mode of transportation alone. Unlike personal cars, they are in constant use in stop and go traffic. And traditionally they’ve been burning diesel, so contributing a significant portion of both greenhouse gases and urban air and noise pollution
Decarbonizing them is a priority, but what will work? There are several choices, but the answer is already clear globally, although some jurisdictions refuse to get the memo.
The short list of climate actions that will work starts with electrifying everything everywhere all at once. This series is looking at electrification starting with transportation and moving through commercial, residential and industrial heat.
What are the choices?
Just as with cars, putting batteries and electric motors in buses instead of fuel tanks and engines is an obvious alternative. Buses around the world have been tied to electrical lines above roads, using grid electricity directly but with the requirement for more infrastructure costs and a busier overhead on city streets.
Then there are the liquid and gaseous fuel choices. Compressed natural gas (CNG) buses have been around for decades and obviously the purveyors of natural gas think that they are the obvious answer. Hydrogen is a favored option of many, with fuel cells emitting nothing but water, at least at the tailpipe, and it’s also a favored pathway of purveyors of natural gas. Others have tried synthetic diesel made from hydrogen and some source of carbon, yet another preferred pathway of the fossil fuel industry. And finally there’s biodiesel in standard engines.
Is there an obvious winner out of this multitude of choices, each with its own pros, cons and advocates? Yes, there is.
Battery electric buses will own this segment. Nothing else will be more than a rounding error or a forgotten option in a couple of decades.
How can we know that? Well, there are a few things which make this clear.
Let’s start with the biggest one. One big country has tried all of these different types of drive trains and fuels, and right now they have over 600,000 battery electric buses on the roads of their cities, and a few hundred or a couple of thousand of any of the others. The massive natural experiment in China has already played out. Battery electric buses are so dominant that alternatives barely exist.
Let’s characterize China a bit. It’s roughly the same size as the United States. It has greater extremes of geography and climate than most countries, with its border with Nepal running through Mount Everest, vast deserts in the west, a fully tropical climate in the south and bitterly cold winters in the north. There is no combination of topology and climate that China doesn’t have, and none where electric buses aren’t operating effectively. Arguments that conditions in any country uniquely preclude electric buses in favor of alternatives are hard to justify on any factual basis.
Why did battery electric buses win the 1.4 billion person country’s national bakeoff? A big part of it is efficiency.
What’s true for cars is true for every form of vehicle. Electric motors are the most efficient mechanism for creating mechanical energy for motion that we’ve invented. Batteries are the most efficient mechanism for storing electricity that we’ve invented.
Trolley buses, the ones with the overhead wires, are even more efficient than battery electric buses, but modern ones have batteries too, and the cost of installing and maintaining additional overhead wires eats into those efficiency costs. It’s typically only useful on the highest use routes downtown in cities. A fully battery electric system is simpler, but on the other hand requires more and bigger chargers in depots.
Hydrogen is a lot lower efficiency, whether it’s made from low-carbon electricity and water or from natural gas with carbon capture bolted on. In the first case, making hydrogen is at most 70% efficient, then loses more in distribution and storage, and then fuel cells are at most 60% efficient. In the latter case, the carbon in the natural gas accounts for 41% of the energy content and extracting it, capturing the carbon dioxide that results from the process, piping the carbon dioxide to a sequestration site and turning it into supercritical carbon dioxide for injection underground takes a lot more energy.
The fossil fuel industry is hoping that they can make hydrogen made from their products with the addition of carbon capture the future of transportation fuels and heating, but that’s only in their interest. It would be much more expensive and not that much friendlier for the climate in most cases.
Synthetic fuels made from hydrogen and some hopefully circular source of carbon like biomass are even less efficient than hydrogen, as they have all the inefficiencies of manufacturing hydrogen, add more energy losses for manufacturing the fuel, and then are burned in internal combustion engines which are typically half of the efficiency of fuel cells. And they still create urban air and noise pollution.
Compressed natural gas is obviously a problem because the carbon in it turns into carbon dioxide when it’s burned and natural gas is methane, which is a much more potent greenhouse gas than carbon dioxide. Between leaking methane and creating more carbon dioxide, it’s a non-starter, not to mention that it doesn’t address air and noise pollution. That doesn’t stop the natural gas industry from promoting it, of course.
Modern biodiesel from our waste food, livestock dung and cereal stalks is great and diverts that waste biomass from turning into methane, a real problem. But biodiesel is more expensive than diesel or electricity and biodiesel buses still have diesel engines which are comparatively inefficient and emit a lot more air and noise pollution. The biodiesel is going to be saved for segments of transportation that can’t be tied to electrical lines or use batteries. That’s a much smaller segment of transportation than most people assume, by the way, so keep reading the series.
Electric buses, all with batteries and some grid-tied, win on all counts. They have the lowest carbon fuel. They are the quietest. They are the easiest to get new fuel supplies for because it’s just electricity. They have the lowest tailpipe emissions.
Transit organizations around the world, except for some oddballs like California for historical reasons, are buying electric buses, not the alternatives. Every week sees more announcements of electric buses, although nothing on the scale of China’s existing fleet. Nigeria has ordered 12,000 electric buses from Chinese bus giant Yutong. Just like China, transit buyers globally are doing the math and choosing batteries.
When transit organizations do buy alternatives, especially hydrogen buses these days, they only do so where the countries and states they are in are subsidizing the buses, the refueling infrastructure and the hydrogen heavily. As soon as the hydrogen subsidies run out, they pivot to battery electric.
And so, another segment of transportation and our economy is electrifying. As a rule of thumb, if electricity can be used directly or via batteries for something, it’s going to be more cost effective and climate friendly than alternatives. That’s proven true for buses just as with cars. But what about trucks? That’s the next article in the series.