The aim of the project is to design, build and perform a breadboard demonstration of a closed loop regenerative H2/O2 fuel cell system corresponding to 15 years of a telecom satellite in orbit. Prototech as prime contractor shall use PEM / HTPEM technology, while subcontractor Astrium GmbH – high temperature alkaline technology.
The objective of the project is to design, manufacture and set up a closed loop regenerative fuel cell system for the demonstration of water management and collection of measured performance data. The ultimate goal is to perform a Breadboard Demonstration of a closed loop hydrogen / oxygen regenerative fuel cell system corresponding to 15 years of a telecom satellite in orbit. Two tasks complement the main work: Task 2 – Conceptual design of thermal control system and Task 3 – Preliminary outline of high pressure reactant storage system.
The key issues addressed in the project were integration of a phosphoric acid doped PBI-based HTPEM fuel cell stack with a PEM electrolyzer in a closed loop, closed loop design, creation of software to automatically execute breadboard cycle testing, construction and testing of a liquid-cooled HTPEM fuel cell stack.
Next generation telecommunication satellites will put increasingly higher requirements on the power supply system. Power levels of 30 kW or more are foreseen for the next 15 years. Today, rechargeable batteries serve as secondary power, but battery systems that can sustain 30 kW for eclipse lengths of up to 72 minutes will have a major impact on the total satellite mass and its launch costs. A first order comparison with fuel cell systems shows a significant mass advantage of fuel cells for large platforms.
The closed loop system uses hydrogen and oxygen gases stored in two gas tanks to run a HTPEM FC stack during the active period. It uses external power to run the electrolyzer and store energy in form of hydrogen and oxygen to run the stack during the next active period. Water formed during the FC operation is condensed and returned to feed the electrolyzer. The closed loop RFCS breadboard demonstrator includes the following sub-systems:
- FC stack with H2 and O2 loops and water condensers
- Condensate return system
- Thermal control system
- Gas supply and storage system
- Safety and control system
FC stack is placed inside the H2 and O2 loops. Gas pumps continuously circulate gases through the stack to ensure sufficient gas flow. Fresh gas is supplied into the loops from the gas tanks by forward pressure controllers.
Water condensers are heat exchangers that are placed on the O2 and H2 loops. Condensate is returned to the oxygen tank by the condensate pump P-RE. Before mixing with the electrolyzer feed water the FC condensate passes ion-exchange filters to remove possible contaminants such as phosphoric acid and metal ions.
The temperature of the FC stack is maintained by means of thermal liquid circulation.
Electrolyzer in the system generates gases to maintain pressure in the gas tanks and runs in parallel to the fuel cell.
For data acquisition and system control a real time modular embedded control system (Compact RIO) is used, programmed with NI LabVIEW to control and monitor the system.
Safety system includes gas recombination units on H2 and O2 loops to prevent high concentrations in case of mixing of gases, and H2 and O2 gas concentration sensors. It also includes gas pressure sensors, temperature sensors and current and voltage measurements in order to automatically initiate safety measures.
The work was broken down in two phases.
Phase 1 – Proof of concept - aimed to prove that the proposed PEM electrolyzer / HTPEM FC stack system was capable to fulfil the requirements (250 cycles with degradation < 0,01% U per cycle).
Phase 2 – Closed loop RFCS demonstration – aimed to design and build a complete closed loop FC – ELY system with water management and thermal control and resulted in demonstration of 1350 complete cycles corresponding to 90 eclipses per year for 15 years in orbit.
The main goal of the project has been achieved. The concept of a closed loop FC – ELY system has been proven in Phase 1. Liquid-cooled HTPEM FC stack of 1 kW-class was developed and manufactured by Prototech and used in breadboard testing. Closed loop breadboard demonstrator has been designed, built and successfully operated from 28.09.2012 to 27.11.2012. The system operated autonomously for 1350 FC cycles and a double amount of ELY cycles. Valuable data on the system performance was obtained. In addition, a conceptual design of thermal control system and preliminary design of reactant storage system have been developed.