Reliable power for data and telecommunications sites

September 30th, 2014, Published in Articles: Energize

 

Fuel cells are finding increasing use in the ICT sector, both as back-up power and as primary power sources, and are proving to be an effective alternative to traditional battery and diesel generator backup systems, in a variety of applications, from small remote telecommunications sites, to large data centres.

Fuel cell technology features both quick start up and long run time, without emissions or noise, at a cost and reliability that are competitive with existing solutions. Fuel cells (FC) have several advantages over other forms power generation and energy storage used in the ICT sector.

Main advantages of fuel cells

Modularity

Fuel cells are made up from stacks, and can be combined in fairly small steps to provide a wide range of power output ratings. It is thus possible to match load requirements closely.

Size

Fuel cells are generally smaller and lighter than other systems of comparable power output.

Efficiency

FC either operating alone or in combination with reformers have a higher efficiency than other sources with comparable power output and thus emit less CO2 for the same energy generation.

Fuel types

Fuel cells can be configured to work on a variety of gaseous and liquid fuels, from hydrogen to diesel oil.

Maintenance

Fuel cells do not require regular servicing and operate maintenance free.

Storage capacity

The storage capacity of a fuel cell is dependent of the amount of fuel stored. As this is external to the FC and independent of the size of the unit itself, a range of storage capacities can be achieved with a relatively small sized unit, compared to a conventional battery where the energy stored depends on the size of the battery. This also applies to the self-recharging fuel cell where hydrogen is stored externally to the FC.

DC output

Dc power is available directly from the FC, which can be configured to give the voltage required. Telecommunications equipment operates mainly off DC, and the FC can be used to provide DC without the use of conversion equipment.

Step loads

Fuel cells however do not respond rapidly to step loads and may have to be combined with storage batteries or ultra-capacitors if step loads are to be encountered.

Remote telecommunications site application

Mobile network operators are using FC solutions in increasing numbers to power base stations and repeaters.A South African operator is reported to have more than 100 FC installations in its network, and there are a number of other operators installing trial systems throughout Africa.

The FC used in this type of application will be of the proton exchange membrane (PEM) construction, and the main area of application will be replacing diesel generators and batteries at sites with low loads where the diesel generator would be running inefficiently at a low load factor [1].

The application and size of the unit depend on type of site and load profile. Most remote sites, especially those operating as repeaters will exhibit a constant load profile without sudden step changes in load, which make the use of fuel cells on their own possible. Smaller telecommunications repeater sites require loads of a few hundred W at most, so compact self contained units can be installed. Larger mobile phone cell base stations can run to several kW average load and higher peak loads depending on traffic, and units with separate fuel storage facilities are common.

Back-up power application

In this application the fuel cell is provided as a backup power source which is activated and connected if the primary supply fails. Fuel is stored on site, and may require regular top-up. Early models used bottled hydrogen gas, but later versions use a variety of liquid fuels. A recent development is the self-recharging fuel-free hydrogen FC incorporating an electrolyser which generates hydrogen from water when surplus energy is available and uses the stored compressed hydrogen as a fuel when the power supply is absent [3]. Commercial models are available from several suppliers in ranges from 1,5 to 12 kW in size. Compressed hydrogen is stored separately in bottles and storage capacity is determined by the number of hydrogen gas bottles used. Self contained units delivering between 2 and 4 kW with a storage capacity of 42 kWh of electricity are available and have been successfully deployed in networks. A possible variation for sites using variable renewable energy (RE) as a primary source has a series connected electrolyser fuel cell configuration where the RE source drives the electrolyser which feeds the storage which feeds the fuel cell. Several thousand sites world-wide have been equipped with FC back-up systems [1].

Primary power application

In the primary power application the fuel cell is provided with a source of fuel which needs to be replenished at regular intervals. For remote sites the main application  would be sites with low power consumption which could run for an extended period between refuelling.

Several options are available:

  • Bottled hydrogen- early systems used this option but the problem is the supply of bottled hydrogen and transport to site. A hydrogen bottle weighs much more than the hydrogen contained in it, and there are safety issues around transport of hydrogen.
  • Liquid fuels combined with a fuel reformer have proved to be more practical as a variety of liquid fuels can be used and stored on site. Methanol is a popular fuel, but diesel and LPG can also be used. Other fuels with a greater energy density than hydrogen are becoming popular.

Hybrid primary source application

In this system the fuel cell is combined with a conventional solar PV/ battery storage system. The PV system supplies power under normal conditions, but under conditions of low solar radiation the FC is brought into operation to assist the PV source. The FC is provided with an external source of fuel. This could be compared to  a back-up power system, but it also operates under conditions of low radiation and not only total failure. Combined with an energy management system, the FC can be used to charge the battery directly at a high rate, rather than feed the load [4].

Hybrid storage source seasonal application

In this configuration an electrolyser is added and uses “surplus” energy from the PV system during the season of high solar radiation to generate hydrogen which is stored and used to supplement the output of the PV system during seasons of lower solar radiation. The long term storage capability of the FC hydrogen battery allows the optimal sizing of the PV solar array which may otherwise have to be oversized to deliver the required energy during times of least radiation. A system has been on trial in Spain and has been shown to operate satisfactorily [4].

The main application for fuel cells seems to be as a replacement for diesel generators in hybrid systems. The advantage of modularity and a wide range of sizing options allow for close matching of the FC to the load requirements. A common configuration used is a diesel/battery system where the diesel is run for short periods to charge the batteries at a high rate, which then supply the load at a much lower level. The FC could be substituted directly for this combination or in combination with batteries, depending on the load. Fuel cells are increasingly used as a replacement for conventional batteries in backup power systems.

Large ITC centres

Large high capacity FC are finding an application in data centres. Providing clean reliable power to ITC centres presents problems. Traditionally, back up power has been provided by diesel generator sets followed by downstream lead/acid battery based UPS systems closer to the equipment. Rack mount fuel cell systems for indoor applications have been available for several years in the range 5 to 35 kW and have been installed at as number of sites. A new development, an extension perhaps of success achieved in using FC for remote telecommunication sites has seen the application of large fuel cells as both back-up and primary power sources for large data centres and server blocks. The availability of MW sized FC units has made this possible. These high capacity units are of the solid oxide fuel cell (SOFC) or molten carbonate fuel cell (MCFC) types. Commercial units range in size from tens of kW to MW.

Rack mount fuel cell application

A new proposal from Microsoft [2] goes further into the design of the data centre and proposes using fuel cells at rack level and ultimately at module level to generate electric energy. Instead of distributing electricity is replaced with a gas distribution network providing distributed generation within the data centre. On site gas storage provides LPG security against failure of the main supply. Gas storage requirements would be the same as those required for storage of diesel fuel. System replaces the electrical distribution network with all its switches, circuit breakers and protection gear with low level gas distribution, reduces risk of electrical accidents and danger to personnel and equipment.

Rack-mount methanol or hydrogen gas powered FCs have been available for a number of years in sizes ranging from 5 to 35 kW. The unit fits into the rack and provides both a DC and an AC output. Power is confined to the rack which can operate independently of other units in the server. The units operate quiet and pollution free as well as bringing  reliable power close to the point of consumption

One of the problems with using rack mount FC systems is the response to step loads. Server rack loads are not constant, but subject to rough step changes as units are switched in and out of service. Early versions proposed the use of a short term UPS solution to bridge the start-up and step response time of the FC, which could be several seconds, enough to crash any server. More recent developments are considering the use of ultra-capacitors. Incorporating an ultra-capacitor into the rack unit provides a smoothly controlled output.

Replacement of the utility supply.

This approach replaces the utility supply, usually backed up by diesel generators and UPS systems. with fuel cells, and relies on a mains gas supply to run the fuel cells instead of grid electricity. A reserve supply of gas is stored on site to cater for possible disruption of the main supply. This approach has been used by a number of large data centre operators in the United States , such as Apple, Google, AT&T , Microsoft and many others [5].

CHP applications

Larger fuel cells such as the solid oxide ceramic type run at high temperatures and produce  heat in the process. If this heat is allowed to escape the FC may have an efficiency of about 40%. If the heat is captured and re-used efficiencies of the order of 80% are possible. Some CHP systems use the heat to generate cooling for the data centre via absorption chillers.

The South African market

Fuel cells use platinum group metals as catalysts and use of fuel cells in ITC industry is being actively promoted with the aim of developing the PMG metals industry  in this country.

References

[1] M Crouch: “Fuel cell systems for base stations-deep dive study”. GSM Association, www.gsma.com/mobilefordevelopment/wp-content/uploads/2012/04/Fuel_Cell_Report_for_fomatting1.pdf

[2] A Rieckstin: “No more electrical infrastructure-towards fuel cell powered data centres” HotPower13, 2013, http://research.microsoft.com/pubs/203898/fcdc.pdf

[3] Acta power: “Hydrogen battery” www.actaspa.com/wp-content/uploads/2013/08/ActaPowerLT.pdf

[4] TH Schucan: “Fuel cell innovative remote energy system for telecoms” http://ieahia.org/pdfs/FIRST.pdf

[5] Bloom Energy: “Reliable power for mission critical systems” www.bloomenergy.com/fuel-cell/mission-critical-data-center

Send your comments to: energize@ee.co.za

 

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