Dr Heather Johnstone, Senior Editor
Major advances are being made in identifying and developing low-carbon alternatives to the world’s traditional fossil fuel based energy systems. The global installed wind capacity has reached an all-time high of close to 121 000 MW, there are plans to bring solar power from the North Africa and the Middle East to Europe and being able to produce clean energy from combusting coal is no longer a wild fantasy.
Another research area which continues to gather momentum is fuel cell technology a technology tipped to be the largest, ‘new’ industry in the 21st century. A growing number of companies are involved in the development and commercialization of technology, which generates electricity in a more environmentally benign way. One such company is Cummins Power Generation (Cummins PG).
Synonymous with big diesel engines, this US company has actually been involved in research into fuel cells since the 1960s. Although Cummins PG does not foresee fuel cells replacing diesel generator sets, it acknowledges that such systems offer several unique characteristics including their quiet operation, their high efficiency and a low vibration level.
Functioning similar to a battery, which uses electrochemical conversion, fuel cells produce electricity from fuel (on the anode side) and an oxidant (on the cathode side), which reacts in the presence of an electrolyte. Fuel cells can be used in a variety of applications including baseload power plants, electric and hybrid vehicles, auxiliary power, off-grid power supply and portable charging docks for small electronics.
Involvement in the SECA Programme
In the early 2000s, Cummins PG became involved in the US Department of Energy’s (DOE) Solid State Energy Conversion Alliance, also as SECA, programme. This programme brings together government, industry and the scientific community to promote the development of solid oxide fuel cells (SOFC). The ultimate aim is to bring the commercialization of SOFC technology for a variety of energy needs within ten years.
According to Cummins PG, it does not believe that the necessary hydrogen infrastructure will not be in place within the next 5-10 years. Thus, a major benefit of SOFC technology compared to other fuel cell technologies such as PEM is that its can run on all commercially available fuels, including LPG, natural gas or diesel, as well as hydrogen. It is able to do this because the system contains a device called a reformer, which converts all hydrocarbons into a hydrogen-rich fuel, which does not require treatment prior to entering the SOFC. The only by-products are water vapour and a small amount of carbon dioxide.
Xin Li, technical specialist at Cummins PG, predicts that on the basis of current progress SOFC-based mobile power products could be commercially demonstrated within the next 2-3 years time, with higher powered (>100kW) stationary power units becoming commercially demonstrated in 7-10 years.
PHASE 1 successfully demonstrated
In 2007, Cummins PG was one of six industry teams involved in the SECA programme to successfully complete Phase 1 tests of the first SOFC prototypes. The other industry teams were led by GE, Siemens, FuelCell Energy Delphi Automotive Systems and Acumentrics. Cummins PG’s SECA Phase 1 unit (Figure 1) was a natural gas powered unit, rated at approximately 3.5 kW, with a maximum power output of between 4.5-4.6 kW.
Figure 1: The self-contained SECA Phase 1 SOFC test unit exhibited an efficiency of 37 per cent and an availability of 99 per cent
Its test operation began in October 2006 and ended in January 2007, and was conducted at Cummins PG’s test facility in Minneapolis, MN, USA. The test system operated for more than 2200 hours, with 99 per cent availability. It demonstrated an efficiency of over 37 per cent, which compares favourably with comparably sized small IC engine based generator sets, where efficiency is generally below 30 per cent.
Figure 2 shows the voltage and current output from fuel cell stack over the total running period, which includes 1800 hour stationary state operation and nine hot thermal cycle operation. In a hot thermal cycle, the fuel cell goes from no power output to full power output. This is used to test the stability and durability of the SOFC stack over time. The test system achieved less than two per cent degradation per 1000 hours. Figure 2 also shows one cold thermal cycle, where the fuel cell went from full load to completely shutdown to room temperature and heated up again to reach full power.
Figure 2: The voltage and current output from the test unit, which ran for over 2200 hours, including both hot and cold thermal cycles.
Following the completion of the Phase 1 testing the whole unit was sent to the DOE’s own facility for final verification.
The Phase 1 SOFC power system was developed in partnership with Versa Power Systems (VPS), a fuel cell technology developer headquartered in Littleton, CO, USA, with development facilities in Calgary Canada.
The prototype system is a self-contained unit. VPS was responsible for the SOFC stack, while Cummins PG provided the ‘cold side’ components, which include the air supply system and the power electronics.
The air supply is a critical part of a SOFC. According to Xin, to maintain normal operation five channels of air are required at different locations in the fuel cell system and with different flow rates. How to control and monitor all this was one of the biggest challenges facing the Cummins PG team.
A second challenge of the SECA project was the SOFC test system could not exceed the DOE’s cost requirement, which was a modest $800/kW.
“These units offered the potential to be manufactured at costs approaching that of conventional stationary power-generation technology”, said Xin, who contributed to the design and implementation of the low cost air supply system that helped to achieve overall system costs and performance meeting aggressive DOE targets.
Commenting on the advantages of the SOFC system Xin said: “the benefits of SOFC based energy are numerous. The technology represents a highly efficient, clean emission no exhaust treatment required source of high quality power, which is compatible with other energy resources such as diesel generator sets, solar and wind.
SOFC technology can provide a reliable power generator solution for a range of applications and industries including telecommunications, recreational vehicles, marine, truck, and home combined heat and power (CHP).
In the case of CHP, the possible financial savings to the consumer are considerable. For example, for home CHP applications the natural gas powered SOFC system could deliver over 70 per cent efficiency, which when converted to current home pipeline natural gas prices in the US represents half the cost of regular supply electricity.
Cummins PG’ CHP market is currently dominated by natural gas fired engines 1000 kW to several thousand kW. According to Xin, right now the SOFC will not replace this engine technology in the market. This is because the SOFC technology for 1000 kW market is not mature enough yet.
Small-scale CHP applications
Cummins PG has also been working with the DOE’s Energy Efficiency and Renewable Energy office since September 2004 to develop and demonstrate a 2 kW prototype SOFC mobile auxiliary power unit (APU) configured to provide electrical power and heat for sleeper cab auxiliary loads of on-highway trucks.
This new application of fuel cell technology could sharply reduce engine idling time for the US’ 458 000 long-haul vehicles, cutting the trucking industry’s fuel consumption while creating virtually no pollutants.
Trucking industry sources estimate that heavy trucks (Class 7 and Class 8) spend an average of six hours per day idling, primarily to keep engines warm and the truck cabins warm or cool for driver comfort. It is believed that idling engines consume 840m gallons of diesel fuel annually, creating an enormous opportunity for fuel savings.
The results of this initiative are due to be published by the end of this year, although Cummins PG has already confirmed it is on track to meet programme objectives in the demonstration of a SOFC-based truck APU system.
Cummins PG is also keeping a close eye on future potential of the off-grid market in the US, this would include remote farms or telecommunication sites for their CHP fuel cell technology. The company sees it as a viable future commercial market.
Although diesel engines will continue to be Cummins PG’s ‘bread and butter’ the company remains committed to be one of the leading firms in SOFC technology research for both mobile and stationary applications, including high efficiency CHP.