The question of whether drive technology and power generation need to be green is no longer an issue, because unless this happens the goals of the Paris Climate Accord – limiting global warming to well below two degrees Celsius (ideally 1.5 °C) – will be impossible to achieve. The only question now being discussed across the world is “how?”. Indeed, there is no clear-cut answer. What part will combustion engines play? What potential do fuel cells have? Which fuels are key?
Today, anyone looking to power a ferry, excavator or generator set often chooses a diesel engine. However, in just a few years' time the choices are set to widen, and when that happens operators will face a choice: batteries or fuel cells? Or what about an internal combustion engine that's no longer powered by conventional fossil diesel, but by renewable e-fuels such as e-hydrogen, e-methanol or e-diesel?
“The key to transforming off-highway mobility lies in the fuels,” says a convinced Dr. Daniel Chatterjee, Director of Technology Strategy & Regulatory Affairs at Rolls-Royce's Power Systems division. Thanks to modern Power-to-X processes which use electrolysis to turn green electricity into hydrogen, which is in turn processed into e-methane, e-methanol or e-diesel, an entirely new range of drive power technologies will soon emerge.
Batteries in niche applications only
The foundation for all green fuels is electricity created from renewable energy sources. The most obvious solution would be to store it directly in batteries and use it to power electric motors – as will probably soon be standard practice in passenger cars. But ships traveling long distances or dump trucks moving large loads would call for batteries of gargantuan proportions. Running a 2,000 kW diesel engine for 8 hours would need batteries weighing around 100 metric tons.
“Battery-powered electrical drives won't be able to serve many applications in the off-highway business which means they won't be able to power the largest off-highway vehicles. That's something we're pretty sure of,” said Dr. Peter Riegger, Vice President of PowerLab at Rolls-Royce Power Systems.
Fuel cells on the other hand are highly promising – both for mobile and power generation applications where high energy density and large energy quantities are required. Strictly speaking, fuel cell systems are also electric drives. The only difference is that the electric motor is driven not by batteries, but by a fuel cell. Inside the fuel cell, a controlled chemical reaction takes place between hydrogen and oxygen, producing electricity that powers the electric motor. Emissions are almost non-existent – just water vapor. The amount of heat given off is low, which is why what happens in the fuel cell stacks is also referred to as 'cold combustion'.
“In a few years' time we'll be supplying fuel cell solutions.”
“Developing fuel cell systems ready for market”
“In a few years' time we'll be supplying fuel cell solutions,” says Riegger. They promise exactly what we all need for a green future: zero-carbon mobility and zero-carbon power generation. Another major advantage of fuel cells over internal combustion engines is that they are scalable and extremely versatile in applications, meaning that if more power is needed, more fuel cell modules can be added on.
This also happens in operation: To date, propulsion power – for example in ships – is produced mainly by diesel engines whose power rating has to correspond to the vessel's maximum power requirement. Fuel cells, however – especially when combined with batteries – open new possibilities, allowing the vessel to constantly adapt the amount of power being generated to match its current power requirement, saving fuel in the process. When a lot of power is required, all fuel cells are used, and in average power demand scenarios, on the other hand, some fuel cells can simply be switched off.
Fuel cells for stationary power supplies
But propulsion is not the only use where fuel cells are a real alternative to combustion engines. Electricity generator sets are another application set to be revolutionized by them. For example, they can be used to supply climate-friendly emergency power to data centers and hospitals, replacing diesel generators within microgrids, or to provide permanent green power wherever no grid connection is available.
Rolls-Royce Power Systems unveiled its new, future-proof mtu fuel cell system for C02-free power generation at the UN COP 26 climate conference that took place in Glasgow, Scotland, in October 2021. Fuel cells are scalable and integrated complete solutions for reliable power generation in the megawatt range and are to be available as standard systems from 2025.
They shall be based on cellcentric fuel cell modules with a net power output of ca. 150 kW – sufficient for the electrical power needs of ten family households or 50 washing machines. The fuel cells will be linked and controlled using smart technology, whereby the number of modules and overall system size shall be determined by the customer's power requirement.
Combustion engines powered by hydrogen and methanol are coming
No doubt about it: the fuel cell is hugely promising as we move forward towards climate-neutral power delivery and power generation. But it is not about to usher in the end of the combustion engine. “The internal combustion engine has not had its day. Using synthetic fuels such as hydrogen, produced from renewable energy sources, it is set to remain a key technology going forward,” says Riegger with conviction. Engineers at Rolls-Royce Power Systems are currently developing hydrogen and methanol engines.
“The internal combustion engine has not had its day. Using renewably produced fuels such as hydrogen, it is set to remain a key technology.”
In the MethQuest project underway at Rolls-Royce Power Systems, engineers are currently putting hydrogen technology through its paces on a single-cylinder test stand. If the tests continue to be as promising as they have been to date, a fully configured engine will be tested on the test stand before the end of 2022. “So far, with the mtu hydrogen engine, we've mainly been focusing on stationary power applications, but we also see potential in the industrial and rail sectors,” says Riegger.
Rolls-Royce Power Systems engineers are currently working on an mtu methanol engine primarily intended for marine applications. The energy density of methanol is high in comparison with other sustainable fuels and since it is liquid at room temperature it is very convenient to store and tank. In many cases, the infrastructures in place for petrol and diesel fuels can continue to be used for methanol. Another benefit of methanol is that it is suitable not just for diesel and spark-ignition combustion engines, but also in conjunction with zero-emission fuel cells: Using a reformer, hydrogen can be produced from methanol for powering the fuel cell.
To be carbon-neutral, hydrogen must also be green
As a source of energy, hydrogen has a great future ahead of it. But if power delivery and power generation technology is to be truly climate-neutral, it must be produced from renewables. The trouble is, this 'green' hydrogen remains difficult and expensive to obtain. However, the European Union's Green Deal and international water strategies and programs could soon change that. Factories for mass production are currently being built all over the world and are having the effect of reducing costs.
But hydrogen is not set to be the only fuel with the potential to 'green up' the world's power delivery and power generation technology. It can be processed further into things like methanol – a fuel that is of particular interest to the shipping industry. It is easier to handle than hydrogen, and existing infrastructure can be used to transport it. The development people at Rolls-Royce Power Systems therefore also have their sights set on methanol-powered combustion engines. And as if that weren't all: using a reformer, methanol can potentially also be converted back into hydrogen which could then be used directly in a fuel cell to produce electricity.
The green energy revolution calls for everyone to pull together
“We're in the middle of an exciting transformation right now. Climate-neutral mobility and power generation is possible, and will come. From now on, it's all about teamwork. It's only by working together with our customers, partners and the politicians who create the framework that we can make the green energy revolution a reality,” sums up Peter Riegger.