Fuel Cell Maintenance and the “Moving Parts” Fallacy

In the comparison between battery electric and hydrogen fuel cell electric vehicles, what maintenance looks like is actually the biggest difference between the technologies. It’s not so much comparing apples and pears; more like apples and iPhones.

For BEVs, the real issue to consider is not moving parts, but battery use and cycle life, and how taking care of the battery impacts your operations. For fuel cells, the issues are operating hours and fuel cell lifetime - and if it suits your business to invest in a hard-working, long life asset with consistent OPEX where you can manage lifetime costs. Let’s explore in more detail.

The “moving parts” fallacy

A common trope is to use the number of moving parts as a proxy for “things that can go wrong” and hence need repair or replacement and person-hours to fix. According to this metric, battery electric vehicles have fewer moving parts than a diesel so will be cheaper to maintain. Fuel cell electric vehicles have fewer moving parts than diesel, but more than BEVs, so will sit somewhere between. And so, it is claimed, BEVs are best so “please stop talking about this hydrogen thing.”

As with many other simplifications, the “moving parts” analysis is a fallacy. In a fuel cell powertrain, there is more complexity and some moving parts such as pumps and a compressor. But the important bits that might be costly don’t move, and while there are fewer moving parts than a diesel engine, fuel cell vehicles are currently more expensive to maintain. While a battery system might look simple, that’s because the complexity and “things that go wrong” are hidden inside a literal black box. So, what is really going on and what should you care about when comparing lifetime costs of zero-emission vehicles?

The black box

The architecture of a BEV is simple - we all understand it from playing with remote control cars as a kid. A battery and motor plus some power electronics and control. Few moving parts, no oil, low maintenance costs, easy peasy. For cars, this is turning out fairly well; car dealerships are worried about the lack of maintenance as it’s lots of lost revenue.

But in reality, a truck battery has 1027 moving parts! All that lithium moving in and out of the electrodes. By the laws of physics, entropy always increases, so in each cycle those lithium ions will never go back exactly as they were when the cells were manufactured.

For commercial vehicles then, the thing to worry about is the battery cycle life. How many cycles, and the management of charge and discharge so the battery is happy. If a battery system can do 2000 cycles (currently a stretch, but likely soon) to the point where it has lost 20% of capacity, that’s probably 6 years with a daily cycle.

If you need to do rapid opportunity charging in the middle of the day though, that’s another cycle so you are down to 3 years! Rapid charging also can stress the battery. Recent studies have shown that it’s no worse than a regular cycle as long as the battery system stays under 30C, but then you are really dependent on the thermal management system, especially in summer, and either charging is slowed down or a hot fast charge will dent your battery life significantly.

Do you want your operation to be weather dependent? And how much use is a loss of 20% in your range anyway? At what point does the vehicle become useless and you have to buy a new one or replace the battery? What’s your RV at 3 or 5 years?

So the real issue to consider for BEVs is not moving parts, but battery use and cycle life. Now to be clear, battery cycle life is the area that is most-improved (for car batteries) over the last 20 years - probably more than energy density - and this trend will continue for trucks. The important point from a maintenance point of view though, is that there is nothing you can do about the inevitable degradation. Please don’t try either! Opening up a battery case to try to find a dodgy cell with a voltmeter will not end well.

Maintenance is not so much not necessary, as not possible. The only repair option is to buy a new one, or rely on a cast-iron warranty. And even then there is a fairly hard stop on vehicle lifetime.

Trigger’s broom

In contrast for a fuel cell electric powertrain, there is more going on, but it’s not really the moving parts either. There is greater complexity, and there are things to maintain, but that can lead to a lower TCO as lifetime extension is possible.

Let’s start with the magic part, the fuel cell stack. There is some similarity with the battery here, although it’s operational hours to worry about, not cycles. Like a battery, there are things that can make this worse that are dependent on the quality of system design and integration.

One difference though is that the impact of degradation is in power, not energy capacity - a loss of efficiency at the top end of the power curve. In a well-designed and managed system, you shouldn’t see this, and so the degradation is mostly invisible, probably showing as a small drift in efficiency over time.

Crucially though, for some fuel cell technologies, you can also refurbish the stack for a fraction of the cost of a new system. A 25,000 hour refurbishment for a truck doing 9-hour daily shifts is a cost-effective "engine" refurbishment at 8 years for another 8.

Maintenance for the last generation of fuel cells was expensive, significantly more than diesel despite fewer moving parts. Air compressors are a wear item and chemical filters to make sure the air is clean for the fuel cell are made in low volume, and are currently pricey. But this is all to do with the current state of the supply chain. The next generations of components are designed for the job and should last for vehicle life. Chemical filters and pumps will become cheap replacement items over the next few years.

Trigger 2

So, for fuel cells the wear and tear does not impact performance much and all the bits that matter can be replaced or refurbished. For fans of Only Fools and Horses, a fuel cell system is like Trigger’s broom. At the end of life, it’s the same fuel cell, just a lot of the parts have been changed.

Maintenance is there, and there are real parts and labour costs, but compared to batteries it’s visible and consistent through life. And through maintenance, system lifetime can be extended. We expect vehicle lifetime will be longer than for diesel and so overall TCO better too, despite higher CAPEX costs.

The issues to think about for fuel cell vehicles are operating hours, fuel cell lifetime and stack refurbishment cost. And if it suits your business to invest in a hard-working, long life asset with consistent OPEX where you can manage lifetime costs.

What works for your operation? Black Box or Trigger’s broom?

There is a battery in an FCEV powertrain. But it isn't "cycled", and with the right battery choice (and this choice is important) degradation is small, doesn't affect range and the battery will last beyond the life of a truck.

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Jonna Christensen
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Ballard Motive Solutions
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