Backup power for mission-critical networks

Diesel and battery power dominate backup power systems worldwide. However, for mission-critical TETRA networks in Europe in particular, fuel cells are making major inroads into power support, as Vaughan O'Grady discovers

Diesel and battery power dominate backup power systems worldwide. However, for mission-critical TETRA networks in Europe in particular, fuel cells are making major inroads into power support, as Vaughan O’Grady discovers

Backup power in Europe’s TETRA networks means diesel, batteries, fuel cells or a combination of some or all of these. It is a well-established market, as you might expect — diesel, in particular, long predates the arrival of TETRA. However, the market domination of TETRA backup power supply in Europe by diesel and batteries may be shifting towards fuel cells.

One reason for this, ironically, is that mission-critical telecommunications in Europe are rarely under major threat from lack of mains power. The continent has a reliable power supply most of the time. For example, Mark Janssens, head of infrastructure at ASTRID, the government-owned operator responsible for providing communications to all Belgian public safety organisations, points out that Belgium has never suffered a lengthy power cut.

However, Europe is not totally immune to smaller-scale outages. For example, in Belgium in 2013 two incidents — an explosion in a high-voltage cabinet in Machelen, and technical problems with a high-tension line near Brussels — disrupted regional power supplies.

More recently, heavy snowfall in January caused trees to fall on power lines in the Ardennes. Ice, storms, even power lines cut by construction work, can all hit power supplies.

But it does bear repeating that power cuts are infrequent in Europe. Dantherm Power A/S, which develops clean energy backup power systems for telecom equipment suppliers, utilises hydrogen fuel cell technology from Ballard Power Systems, of which it is a subsidiary. Much of its recent focus has been on Denmark, Norway, Sweden and Finland. Jesper Themsen, Dantherm Power CEO, says: “In Denmark all power lines are underground, which means it’s a very reliable network.

Our experience is that our fuel cells will start up seven timesa year per site for small outages to support the electronics.” Norway, and other countries where power lines are overground and trees may fall on them, can experience double that rate of interruption, but it is still not a major concern compared with the very lengthy and widespread outages often suffered by developing economies.

Power backup is not cheap, however. And, as Adrian Dain, principal consultant with IT consultancy Mason Advisory, says: “It’s not just the base station that provides you withthe TETRA air interface. You also need to power your base station controllers, your transmission network, your backhaul, your network operations centre — and all of the other key components of the whole TETRA network. So if you’ve got a site supported by microwave, you might have two or three microwave hops to get the microwave transmission to thesite — you’ve got to make sure that whole string of microwave dishes is all powered up to keep [speaking] to the base station.”

Themsen adds: “I would say the further you go towards the backbone, the higher the reliability demands are [for] backup power.”

That said, TETRA networks have fairly low power requirements. However, if they are mission-critical, the operator will be obliged to spend a fairly large sum of money backing up the power the network receives from the grid (or sometimes from renewable energy if it is off-grid).

Safety isn’t the only concern. Even if they are offlinefor moments rather than hours, as Nick Smye, principal consultant at Mason Advisory, says, the base station doesn’t just come straight back online. “When the power comes back on again it’ll have to reboot and probably get synchronisation from GPS and all sorts of other stuff — so it can take a while.” Dain adds: “It is worth saying that TETRA has some, gradual, graceful failure modes, whereby even if it loses transmission it will still keep on working as a local island of TETRA coverage — and of course the handsets can speak directly to each other using direct mode operation. There are some failure modes built into the technology — but you have to have that power backup across the entire piece.”

And these days backup will usually pass the test. Storms and accidents didn’t stop ASTRID, which in the case of the January power outage even had to deal with a spike in usage.

Backup power systems have to work in any weather conditions

Of course, that is what it is supposed to do. ASTRID,like many mission-critical or emergency networks, has to guarantee continual operation: in the case of power cuts, eight to 24 hours of communications based on backup power must be ensured. In ASTRID’s case this normally means lead acid batteries for the base stations and diesel generation plus uninterruptable power supplies (UPSs) for the control rooms.

ASTRID uses lead acid batteries because, says Janssens: “Battery backup is quite cheap and works quite well.” Also, unlike other fuel sources, when the grid comes back on, batteries can be charged up and no extra handling is needed. He adds: “Solar power could be an alternative but doesn’t work at night. Fuel cells use hydrogen and diesel generators use diesel, which has to be refilled after use.”

Batteries and diesel dominate much backup power supply globally, though for critical infrastructure such as TETRA, this seems to be changing. Where very long backup is required, batteries in particular may be more challenged. They are also often heavy, need replacing more often, and may require air- conditioning where temperatures are high.

On the other hand, they won’t necessarily be the only source of power. One approach to deployment, as Martin Benke, operations director at Airwave, points out, is to diversify. “Airwave, which is now part of Motorola Solutions, typically uses lead acid batteries supported by liquid petroleum gas generators on base sites because it is cleaner than diesel and less likely to spill — important as many of our TETRA sites are in environmentally sensitive areas,” he says. “The engines also require less maintenance for the minimal run times they have. One challenge is that lead acid batteries require a constant temperature, so in areas of temperature variability we use nickel cadmium batteries; it is important to consider the total cost of ownership when selecting batteries. We use diesel- powered generators to provide backup power for our switch and network management sites.”

Batteries can recharge and are relatively inexpensive, as ASTRID’s Janssens made clear. What about diesel? Themsen agrees that: “As long as you need power for longer periods— like continuous power — diesel is low-cost fuel. Andit’s easy to repair a diesel generator.” But in limited outage environments, he says: “Where fuel cells have a play is as a backup power unit where you don’t consume a lot of hydrogen — because hydrogen is expensive.”

Another consideration is that the emissions and noise from diesel generators (most likely during monthly tests) would not be well received in urban areas, or indeed some environmentally sensitive rural areas. The Black Forest in Germany is an example. And diesel makes set-up demands. As Mason’s Smye says: “You’ll take it to site. You’ll run it for a certain time. You’ll check the temperatures. Check all the alarms are working. Fill it up with fuel.” You will also need to be aware of fuel storage regulations and procedures to avoid or deal with fuel leaks.

Also, the transition to diesel during power cuts isn’t seamless. Mark-Uwe Osswald, VP of marketing, Fuel Cell and Electrolyzer Systems at Heliocentris, a provider ofenergy management systems and hybrid power solutions for distributed stationary industrial applications, says: “In TETRA applications with a diesel generator you typically have two or four hours of batteries installed to bridge short outages because you don’t know if the diesel will start first time.”

This is one of a number of areas where using fuel cells to back up TETRA networks in Europe is likely to be more efficient. Batteries also support the start-up of fuel cells during outages but, Osswald says: “With a fuel cell system from our Jupiter product line you can reduce the amount of batteries to an absolute minimum for the start process because you know it starts. There’s no rotating machine, no mechanical energy conversion. The fuel cell system starts immediately depending on a voltage drop or based on an external start signal. It’s just a click to put the fuel cell to work.”

Themsen adds that for those who don’t want a battery for the five to ten seconds of start-up (even these small batteries require maintenance and, potentially, air-conditioning), supercapacitors can be used. “The supercapacitor solution is a standard product from Dantherm Power and usually the preferred solution for critical networks,” says Themsen.

The Heliocentris Jupiter fuel cell systems have an operational lifetime of thousands of hours. One bottle of hydrogen (50L/300 bar) can store 17 kilowatt hours of electricity — enough to operate a 2kW load for 8.5 hours. However, backup power regulations can be quite strict, so more bottles will usually need to be installed. The autonomy time required in Germany for the BOS network (the TETRA network for the police and fire brigades and security which Heliocentris supplies) is quite demanding. Osswald says: “For the critical sites they demand 72 hours.”

Unlike diesel, fuel bottles or tanks for fuel cells need tobe transported to site and replaced when used, which couldbe costly. However, some other advantages make up for the upfront cost of fuel tanks and fuel tank transport — such as reliability. Themsen says: “The fuel cell is an extremely simple device as we build it; electrochemical with almost no moving parts, much like a battery. The advantage is that it’s a battery you fuel by external fuel. And you have the ability to monitor the capacity of the fuel cells. You can do some test runs and you can monitor them — which is difficult for batteries. At the same time they don’t have the reliability issues of a mechanical device like a diesel generator.”

They are also relatively easy to install. Osswald says: “The latest fuel cell systems we provide for the BOS network are containerised solutions — a one metre times four metre container. It has two compartments: one for the fuel cell system — up to 6kW — and one for the hydrogen bottles— up to 24. This container is easy to install. You place it on a concrete foundation, you connect it electrically and then you bolt it. Then you put the hydrogen bottles in, you connect the bottles, you do commissioning tests... it can work very fast. We also offer solutions that are cabinet-based: you set up one cabinet, or you can put two or more cabinets beside each other — as many as you need depending on the power level or the autonomy time you need; it is scalable and extendable.”

Themsen adds: “Fuel cells are often up to ten times lighter than batteries for critical infrastructure and the footprint is often five times less. A fuel cell system can be installed inside the existing shelter and provides a much more compact and lightweight solution compared with a diesel generator.” In accessible areas a fuel cell installation can take as little as a half a day or one day in remote areas that may require helicopter or snowmobile access. And no air-conditioning is required for fuel cells, unlike batteries.

Whatever the backup source, regular maintenance and testing will be essential. Airwave’s Benke recommends robust testing and maintenance cycles, and issuing engineers with personal issue generators for a secondary layer of resilience.

Dantherm’s Themsen adds: ‘The systems undergo a monthly full load, full functionality self-test which ensures that possible weaknesses are discovered before failure. A message is sent to the network operating centre or service provider if anything is discovered during self-test. We often provide full service and warranty agreement on the fuel cell systems as this leaves the operator with no concerns.”

Remote monitoring systems are also used. Heliocentris uses a system called Energy Manager with its fuel cell installations; it can remotely monitor, analyse and control a site.

By comparison with fuel cells, diesel generators are dirty, noisy and big, so why are they still popular? The main reason is that they are cheaper over long periods. Certainly they have a long history in countries such as Nigeria where grid power supply has long been erratic or, in some areas, nonexistent. But for backup of TETRA networks in Europe where, as Osswald says, “very often there’s no hydrogen bottle exchange for years”, fuel cells can compete, even on price.


A Heliocentris installation for MTN, a MNO in South Africa. L-R: hydrogen tank, fuel cell and electrolyser system, and water tank 

There are, however, downsides. The hydrogen must be of good purity; impurities can degrade a fuel cell’s membrane and shorten its life. Also, bringing fuel bottles to remote areas can often be inconvenient or expensive, so fuel cells wouldbe best suited to accessible locations in regions where the supply of hydrogen can be guaranteed — although a greater take-up of hydrogen-powered cars does offer the possibility of bringing hydrogen fuelling stations to isolated areas. Having said which, some isolated regions do use fuel cells — notably in hybrid power offerings.

Motorola Solutions developed a basic design concept for a National Park APS (alternative power solutions) system to meet the requirements of the Royal Norwegian Ministry of Climate and Environment. It awarded PowerControls,a company that focuses on alternative power systems for locations without AC power, the contract to build one of the two first prototypes according to this concept. After the prototype was tested and results were concluded, Motorola Solutions awarded additional National Park APS sites to PowerControls.

Mikael Davidson, manager of design and engineering, APS at Motorola Solutions Norway, says, “The design is based on solar power, which should provide more than 50 per cent of the required kWh on an individual site and works perfectlyin Norway for seven to eight months per year. Additionally, we have installed a methanol-powered fuel cell and a diesel generator, which respectively provide the primary and secondary power during the winter period. With this concept, we meet the typical power consumption of 6,500-7,500kWh per year and can even run the site with close to no diesel consumption during the summer months, which also enables us to reduce the emissions to a minimum.”

There is also a way to deliver hydrogen without transporting it: a combined fuel cell and electrolyser system, where you generate the hydrogen on site from excess energy and water.

Heliocentris’s Osswald explains: “For sites with no hydrogen bottle availability or access — typically off-grid and primarily powered with renewable energy from sun and wind — we offer solutions with hydrogen generation on-site; we call this line GenStore, for generation and storage. You have wind, you have sun. You operate your load and you charge the batteries. You still have wind and sun available when the batteries are fully charged. You split water into hydrogen and oxygen with an electrolyser. You store the hydrogen and when there’s no wind or sun and the batteries are depleted, you operate the fuel cell from the stored hydrogen to support the load.”

While it looks more than promising in Europe, the future of TETRA backup is not necessarily entirely about fuel cells. Lead acid batteries, for example, are giving way to nickel cadmium, and in the longer term could give way to lithium ion, if issues of cost can be overcome.

But companies that offer fuel cells for mission-critical networks are, not surprisingly, very upbeat. The Ballard backup power systems were designed directly for TETRA applications and, says Themsen: “The first 120-plus units were installedin 2009 and have operated without any issues since then. For these seven years of operation with around 15,000 startups, the operator [the Danish TETRA Network] has experienced 100 per cent power availability on all sites.”

Osswald adds: “This [TETRA] is typically a sector where people don’t look for cost but the government or authorities look into other values: high availability, reliability, long autonomy... fuel cells will make more and more inroads into the TETRA and professional mobile radio environment, and costs will also come down.”