Power Technologies: Going green

Fuel cells generate electricity by using hydrogen and oxygen

Mark Patrick, technical marketing manager for Mouser Electronics, believes hydrogen fuel cells are showing their credentials

Green is a desirable colour for most of those involved in the energy business, with clean, renewable energy becoming an ever-higher priority. Massive engineering effort is being expended and major research investments are being made into this area each year.

In the automotive industry, minds are focused on zero emission cars. Most manufacturers have electric vehicle (EV) or hybrid models. Increasingly popular, hybrids run on electricity until their charge is depleted, then switch to conventional diesel or petrol fuelled operation. With them, however, come the emissions of the much-derided greenhouse gases commonly associated with conventional cars.

On the technological front, most EV development has been based around batteries. These vehicles need to be plugged into a suitable power source to recharge their battery reserves. While electricity is increasingly produced from renewables such as solar and wind, a large proportion of its production is still reliant on fossil fuels. Access to EV charging points is also an issue and so far has seemingly put off car buyers.

There is another promising avenue for those in the automotive industry and potentially elsewhere too – hydrogen fuel cells. This has several advantages over combustion engine technology or even battery-based EV technology. Fuel cells convert potential energy held in chemical bonds directly into electrical energy, making them highly efficient. The by-products of this operation are just water and a small quantity of heat, but no actual pollutants. Also the production of hydrogen is comparatively environmentally friendly; there is very little if any pollution relating to this.

The refuelling process is rapid and more akin to filling a conventional car with fuel, rather than requiring many hours to recharge the battery of an EV, which has proved to be a serious hindrance to users. Furthermore, there are no moving parts in a fuel cell, unlike in a conventional engine. This gives them greater reliability and means that maintenance tasks are much more straightforward to execute. Finally, the range of these vehicles is closer to that of combustion engine-powered vehicles, while EVs are limited by the storage capacity of the battery.

While it may be the most abundant element on earth, hydrogen is never encountered on its own. Instead, it is always found combined with other elements such as oxygen in water (H2O), for example, or with organic compounds in hydrocarbons such as natural gas, methane and propane. Most hydrogen is currently obtained from these hydrocarbons through the application of heat, in a process known as reforming. Alternatively, an electrical current can be applied to split water into its constituent elements, which is referred to as electrolysis.

A hydrogen fuel cell consists of the following elements:

 

  • • An anode where the hydrogen enters;
  • • A catalyst that separates the hydrogen into ions and electrons’
  • • A proton exchange membrane (PEM) where protons pass, but electrons are blocked; and
  • • A cathode where oxygen is forced through the catalyst to form two negative atoms that attract the hydrogen ions through the membrane, ultimately regrouping to form water.

 

So far so good, but refuelling a hydrogen fuel cell requires pressurised hydrogen to be pumped in. This is where some problems arise in terms of automotive use. Infrastructure is expensive to install, largely because of the pressure requirements. Consequently, fuel cells are still to see widespread proliferation and as yet have only made limited headway in the automotive sector. Despite this, firms such as Toyota remain committed to the technology and are still investing heavily in on-going research.

In the meantime, there are other application opportunities that could allow hydrogen fuel cell technology to gain greater traction. Currently around 50% of trains are powered from overhead electric lines, which are expensive to install. Increasingly, it is believed that electrification will only be suitable for rail routes with the heaviest volumes of traffic.

Most other trains run on diesel, which is increasingly regarded as a dirty fuel. Trains powered by hydrogen fuel cell systems could provide an alternative. Though in an automotive context they would require large financial outlay on supporting infrastructure, here they would actually present a way of keeping the investment needed in infrastructure down.

Germany, whose government has committed to reducing CO2 emissions by 40% from 1990 levels by 2020 and to providing 80% of its energy from renewable sources by 2050, has a fuel cell-powered train project underway. The trains will run on hydrogen that has been produced from surplus energy generated by wind turbines during periods when demand for electricity is low. Two trains are undergoing trials, and service in the lower Saxony region is expected to begin later this year.

Power from the fuel cell will be used by the auxiliary and traction converters while spare energy will be stored in the lithium-ion batteries until needed, as will power from regenerative braking. The fuel cells will only operate at full power when demand is at its absolute peak.

Smart power management was also a key aspect of a pilot scheme to run a small (11m) hydrogen-powered ferry in Bristol Harbour in 2013. During the six-month scheme, the ferry operator found that refuelling was only required every four days, keeping the operation costs very low.

Sadly, a lack of UK hydrogen refuelling infrastructure led to its demise, however a much larger (35m) ferry is expected to go into service in France in 2020. Running between the islands of Ouessant and Molène – both of which lie off the western-most tip of Brittany – and the mainland, the ferry will use surplus energy – obtained from renewable sources such as wind turbines – that has been converted into hydrogen.

Another scheme for a high-speed passenger ferry and refuelling station in San Francisco Bay is going through feasibility studies, while research into providing power to berthed ships (cold ironing) from a barge-mounted PEM fuel cell on the US west coast also shows great promise.

Though installation of the infrastructure required to store and deliver the necessary hydrogen presents difficulties, there are considerable merits to using fuel cell technology as an ecologically viable source of power. Clearly, improvements in battery storage technology do not necessarily hold all the answers.

Mark Patrick is technical marketing manager for Mouser Electronics

www.mouser.com

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