Application of a Solide Oxide Fuel Cell for ICT Sector

The energy sector is currently facing a multitude of challenges, from rising demand to environmental concerns. ICT (information and communications technology) is accountable for consumption of about 3% of the world's total electrical energy. By the end of 2030, it is expected that this figure will grow to 1,700 TWh/year. The ICT operators are investigating more efficient, environmental friendly and reliable power supply systems; these include PV panels, micro wind generators, Fuel Cells and novel batteries.

SOFC technology is currently considered an environment friendly solution to produce energy and to well fit CHP requirements. Exhaust gas high temperature well support the CHP applications thanks to the energy content of the co-generated heat.

Moreover, despite having lower power density with respect to Polymer Electrolyte Fuel Cells (PEFC) fed with hydrogen, SOFC based generation systems are able to use different fuels and turn them into electricity with minor system requirements than PEFC. They, in fact, can process various hydrocarbons for which, unlike hydrogen, a well-connected distribution network is still available.

Telecommunication network that needs to supply equipment distributed in various lands even where there is no power grid but not limited to, have requirements that can be properly matched by SOFC generators characteristics (direct current power production, high energy density, continuous service operations, high fuel-to-electricity conversion efficiency, cooling production by transforming heating energy), but sudden load variations, even in case of emergency, cannot be still supported. Moreover, compared with ICEs, their investment cost is a strong limitation to come up to the market. These drawbacks are even more evident if SOFCs undergo thermal and redox cycles, as those limit the cellsÕ lifetime.

For these reasons, SOFCs appear proper devices for onsite power generation. This strategy is commonly envisaged as a solution concurring to reduce transmission lines loss and bring new service where public electric grid is still absent or weak.

In contrast, SOFC based systems have some weakness points. In fact, due to their limited resistance to thermal shocks, they suffer from the impossibility to follow sudden load variations. For this reason, a system completely based on SOFC technology, especially planar SOFC, should be operated at slowly changing loads.

Several works have demonstrated possible and interesting synergies between two electrochemical devices allowing high efficiencies and flexibility thanks to electrical and thermal integration: high temperature batteries and high temperature fuel cells. SOFCs are expected to be about 50-60% efficient in converting fuel to electricity, and in cogeneration applications overall efficiency can be as high as 85%. They are good energy sources to supply reliable power at steady state, especially for telecommunication applications; however, due to their slow internal electrochemical and thermodynamic characteristics, they cannot respond to electrical load transients as quickly as desired. The realization of a hybrid system, capable of connecting production and storage devices on the one hand, and of managing and controlling the energy and its exchange with the grid on the other hand, represents the synergy of some innovative technologies, but already commercially available.

At present, the state-of-the-art of SOFC technology is not yet at commercial level, only laboratory and niche market devices are ready. This delay with respect to other solutions is due to several still unsolved problems, but likewise numerous are the achievable advantages.

The main problems linked to the SOFC technology are:

-       necessity of long start-up time (because high working temperature must be slowly reached to avoid cell's damage);

-       necessity of high temperature resistant materials (for cell hardware, interconnections and sealing);

-       necessity of constant load (despite fast electrochemical dynamics, temperature effects of abrupt load variations can damage the cell structure);

-       lower resistance to thermal cycling (so that the start-up/shut down cycle number limits the lifetime).

Against the above mentioned problems, a series of good features must be considered, the most evident are:

-       high fuel conversion performance (that allows for compact size devices);

-       fast electrochemical kinetics (low cost electro catalysts, like nickel, can be used);

-       capability of internal fuel processing (unlike other FC technologies, solid oxide does not need extremely pure hydrogen as a fuel);

-       valuable vocation for Co-generation of Heat and Power (CHP) by exploiting high temperature exhaust gases (this leads to high overall efficiency systems through the reuse of heat waste).

Moreover, as other fuel cell technologies, SOFC benefits from direct electrochemical conversion of the supplied fuel into electrical energy without combustion and moving parts. As consequences, they have high electrical efficiency (compared with traditional internal combustion engines), low noise level (only the auxiliary devices, like fans or blowers, have moving parts) and negligible (or low) emissions of environment pollutants.

In order to become more attractive for the end user in a distributed energy production market, SOFC technology applications need cost reduction.

The integration of a SOFC system with one or more storage devices allows, in fact, to use the inherent advantages of each system. From this point of view, SNC batteries may support and enhance SOFC based systems without increasing investment costs.

Another advantage from the system hybridization is higher reliability and availability of the power source, even in case of a failure in one of the two integrated devices. During peak demand the battery provides power in addition to the fuel cell, whereas the fuel cell recharges the battery during low demand periods. The key advantage of this system architecture is that the fuel cell is operated without major load variations close to constant load resulting in longer lifetime and thus reducing total costs of operation.

In the framework of the European collaborative project ÒONSITEÓ a proof-of-concept of an intelligent power supply system for telecommunication equipment and infrastructures (e.g. base stations, data centers) is under development. It features a novel hybrid concept that integrates a SOFC (Solid Oxide Fuel Cell) and high temperature Sodium-Nickel-Chloride (SNC) batteries taking advantage of the SOFC's waste heat to support the batteries thermally. The ONSITE system - in contrast to ordinary back-up systems - shall operate continuously and may feed power to the grid.

A proof of concept of a hybrid power system comprising a 2.5 kW Solid Oxide Fuel Cell, a 5 kW Sodium Nickel Chloride battery pack has been developed. The ONSITE power system is a flexible high efficiency generator providing quality power, heat and cold from natural gas to different kind of ICT loads, from small Base Transceiver Stations to small-medium datacentres. It operates on natural gas and can operate on LNG or LPG also when no natural gas grid is available. This hybrid system shall achieve better utilization of primary energy, higher power generation efficiency, use of the waste heat from the fuel cell for heating or cooling purposes and this way a significantly reduced impact on the environment. A first SOFC/SNC hybrid system with 2.5 kW net DC power was built and tested. It approached the 40% electrical efficiency. The SOFC generator comprises a HoTbox lies two SOFC stacks of 1.25 kWe net each, a reformer, a burner, a heat exchanger and a condenser to recover the water for the reforming process. The SOFC system has been installed and connected to the coolant water loop, the gas grid, the electrical shelf and the tap water grid.