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Reliable and sustainable

Date: 23rd January 2013
Topic: Monthly Features
Issue: Issue 12
Tags: fuel cells

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Backup power is a vital consideration for the resilience of a TETRA network. Sandra Saathoff considers fuel cells as a sustainable alternative to diesel generators

Whether a TETRA network is being used for ‘blue light’ emergency or first responder personnel or to enhance general communication within a geographic locale, the robust and resilient nature of the network is its primary attribute. Recent natural disasters, as well as concerns about national security, are a dramatic demonstration of the need to further improve the reliability and availability of global communication infrastructures. One can have the most highly resilient switch network and network management, but in order to have a truly resilient network, the power behind all of this advanced equipment must also provide reliability and resilience. 

One tool in the quest for ever-increasing reliability in power is the fuel cell. Fuel cells have been commercially available to communication networks for a decade, with a number of suppliers providing products globally. Within early adopters, fuel cell usage has progressed from early trials to larger rollouts providing critical backup power to several hundred sites in a single network. Globally, fuel cell adoption numbers several thousand installations.

Airwave, currently the world’s largest TETRA network, with 300 000 users, accounts for 10 per cent of the global TETRA user base. They have been using a small number of fuel cells within their network for over a year.

Gary Orman, Airwave’s head of safety and environment, commented: “For Airwave both operational excellence and sustainability are of utmost importance to us, and we see the use of hydrogen fuel cells becoming more prevalent in the future to enable us to meet our business objectives in both these areas. Providing high reliability standby power whilst reducing emissions and waste can only be a win-win situation for us.” 

Fuel cell power solutions

Before discussing how a fuel cell complements a TETRA network, we first must understand exactly how it does what it does. A fuel cell is a DC power generator that converts the chemical energy of a fuel (hydrogen, natural gas, methane, methanol, etc.) and an oxidant (air or oxygen) directly into electricity. While there are a number of fuel cell technologies available, the most common and practical technology for small to medium-sized standby power is the proton exchange membrane (PEM) fuel cell which generates electricity through an electrochemical reaction using hydrogen and oxygen. This process happens without combustion. A fuel cell operates electrochemically through the use of an electrolyte, just like a battery, but it does not run down or require recharging. It is similar to a generator in that it operates as long as the fuel is supplied; but unlike an internal combustion generator, it is simple, quiet, and clean with few moving parts. Because fuel cell systems are load-following, fuel consumption depends on the load, and equipment operating at relatively low loads can see a significant extension of runtime when powered by this technology. 

Criteria for selecting a fuel cell backup system for a specific application include power requirements, frequency and duration of outages, response time to the site, environmental restrictions and serviceability requirements. Fuel cells can and are being used as the sole backup power solution in many critical applications; however, they can also be used as an added layer of protection for a site using incumbent solutions. This concept is analogous to a layered network security architecture where each layer of security, e.g. firewalls, intrusion detection devices, etc., add to the overall network protection. Fuel cells offer rack-mounting options within an equipment shelter as well as environmentally-hardened outdoor cabinets for flexibility to meet network design parameters.

Most fuel cells being used for backup power today range from 50 watts to approximately 20 kilowatts. Based on technology available today, customer sites can be provisioned with fuel for hundreds of hours of runtime. Refuelling allows the system to run continuously as long as needed during extended outages. For sites with these relatively low power loads and outages lasting from hours to days, fuel cells can be the backup power source of choice. 

Fuelling options

Intrinsic to fuel cells is the need for fuel in order to operate. PEM fuel cells use hydrogen as the fuel to supply electricity and there are a number of options for fuelling. Traditionally, fuel cells have used hydrogen cylinders to store fuel (packaged gas). The refuelling of hydrogen cylinders is accomplished by a vehicle transporting full cylinders to the site and exchanging them for the empties. Though somewhat labour-intensive, for many locations this remains the option of choice. 

A second option is bulk hydrogen refuelling. Network operators and fuel cell manufacturers have worked with major global hydrogen suppliers, initially in the United States, to establish a refuelling model similar to the diesel/propane model. In this model, the cylinders remain on site and are filled on site by the refuelling truck. This development has broadened the market for fuel cells to address higher capacity installations and sites requiring extended runtimes of several days. 

 A third option for providing hydrogen for fuel cells is the fuel reformer. The reformer takes a hydrogen-rich carbon-based fuel, such as methanol mixed with water and, using heat and a catalyst, separates the hydrogen from that fuel in order to deliver it to the fuel cell. Because these fuels tend to be liquid, energy density is better than with gaseous hydrogen, allowing for more runtime to be stored on site in a smaller space. However, reformers introduce additional cost and complexity to the fuel cell system and can reduce the reliability of the system as a whole. Hydrocarbon fuels, because they are not simple hydrogen, also emit some pollutants during the reforming process. In locations where hydrogen is not readily available or is priced too high, a reformer may be the fuelling option of choice. 

Integrating a fuel cell into a network

One of the attributes of a fuel cell that makes it attractive for deployment in TETRA environments is that a fuel cell produces DC power. This makes it akin to a standby rectifier source, as the power provided from the fuel cell can be directly connected to the site’s DC power bus. 

In an outage situation, the fuel cell turns on automatically, providing DC power formerly provided by the rectifiers. This means fuel cells can effectively function for long reserve times as a standby power source in customer applications. Fuel cell systems are intended to operate in parallel and augment the traditional DC power system components. 

Fuel cells may easily be added to an existing network or may be designed into a new network location. They may also be combined with solar and/or wind power to provide a clean hybrid power solution in locations where the grid is unavailable or unreliable. With hot and cold weather design features, many fuel cells are capable of serving loads in a wide variety of geographical locations. 

The hallmark of the TETRA network is its reliability. This is also true for fuel cells, with some products receiving field reliability ratings of 99.9 per cent.

A viable site-hardening plan would involve combining one or more backup power technologies in parallel, increasing the availability of the site by providing a highly reliable ‘backup’ to the primary backup power source. For instance, a site that would generally run off AC power and is already equipped with VRLA batteries connected to the DC bus, for response to an AC power failure, would benefit from a fuel cell also connected to the DC bus to carry the site load and charge batteries when the batteries dip below a certain voltage at loss of AC power or in the event of a rectifier failure. The fuel cell prevents the deep level of discharge on a battery string and allows the site to operate on backup power for much longer than on batteries alone.

The BOSNet TETRA network in Germany

The BOS digital radio network (BOSNet) is the world’s largest TETRA project and will be deployed in all 16 German states during the next few years. Sascha-Wolfgang Baltruschat, the head of fuel cell implementation for the BOSNet project explained: “The Working Group ’fuel cell’ as a team in the Central Service of the Police of the State of Brandenburg, has received funding for the project W-NEA BOS BB, the first nationwide comprehensive emergency infrastructure with fuel cell technology built in a high-security radio network operation, by the BMVBS ( Federal Ministry of Transport, Building and Urban Development).” 

According to Baltruschat, the program began investigating the viability of fuel cells in 2008, doing trials in 2009 and then developing a business case for fuel cells compared to diesel generators. They determined that, while the capital cost of the generator continues to be less than that of the fuel cell, when taking into consideration the lower maintenance requirements of the fuel cell, the long term cost analysis favoured the fuel cell. Further issues swaying the case for fuel cells included the stability of hydrogen fuel over diesel, the scalability of fuel cells which allow for the ability to increase power availability as a site requires additional equipment, and the environmental benefits of fuel cells over generators. 

Baltruschat commented: “A fuel cell system is much less sensitive to temperature, has few mechanical parts and is virtually maintenance free. These characteristics and more bring the BOS digital radio higher reliability for emergency power supply in case of disaster. 

“The emission-free reaction of hydrogen and oxygen into electricity and water is another argument for the fuel cell. NOW GmbH, the national organization for hydrogen and fuel cells, hopes that with the support of this project, a pioneering step has been taken in the further development of the German fuel cell market.”

Environmental Issues

As with the BOSNet example, an increasing level of focus is being paid by corporations and nations to the environmental impacts of the products we depend upon. In the US, states such as California have set limits to the number of hours a generator can be run in non-emergency situations in order to address the emissions issue. Federal guidelines limit the amount of emissions allowed by generators. In Europe, countries including Germany have created Emissions Control Acts, which work to limit pollutants and make technologies such as generators subject to official approval. The general opinion is that this scrutiny will only increase.

Hydrogen fuel cells, as mentioned earlier, emit no pollutants. Since they very often replace diesel generators at communication customer sites, a comparison of the environmental impacts of the two can be helpful. Diesel generators are notorious for their pollutants. For example, a 50kW diesel generator falls under US Tier 2 standards and is allowed five grams of carbon monoxide per kilowatt-hour, 7.5 grams of NOx per kilowatt-hour and 0.4 grams of particulate matter per kilowatt-hour. When one extrapolates to 1000 generators providing 150 hours of runtime per year each for five years, the environmental impact becomes very clear.

A fuel cell operating on reformed methanol has significantly lower emissions than the diesel generator, but still higher than a hydrogen fuel cell, with 0.007 g/kWh of NOx, 0.17 g/kWh of CO and 0 g/kWh of particulate matter. 

Conclusions 

The issue of reliability is critical for TETRA networks. As the bar is raised in the expectation that communication be able to take place no matter what, the issue of backup power becomes paramount. When a high level of reliability can be provided by a product that also meets sustainability goals, a win-win scenario develops. Fuel cells meet both those goals and offer a compelling solution for site hardening at critical locations. 

  • Sandra Saathoff is director of marketing communication at ReliOn. Visit www.relion-inc.com



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