燃料電池（Fuel Cell, FC）是名符其實的能量轉換機器，而並非能量儲存容器。它接近於汽油或柴油發電機，而非僅是電池。以固態氧化物燃料電池（SOFC）發電量最高，約500KW至50MW，此種燃料電池最能運用在捷運供電系統上。
2.備援電力系統（Fuel Cell Back-up Power System）：燃料電池啟動只需1~2秒，適用此系統的燃料電池為PEMFC、熔融碳酸鹽燃料電池（MCFC）、SOFC三種較常用。若以成本考量，以SOFC較適合。
Fuel cells are energy transformers like gasoline/diesel fuel generators rather than energy storage vessels such as batteries, among which SOFC has the highest generating capacity. SOFC's generating capacity is about 500KW to 50MW and is most suitable for applying on MRT's power supply system.
Due to confinement of electricity capacity on fuel cells, it is only applied on the UPS System and Back-up Power System of MRT power supply, details are as follow:
1.UPS System: fuel cells are used on signal system, PRC system and low pressure water works system in the overall MRT system. The three UPS systems are made up of cell rooms. Applicable models include hydrogen-FC, PEMFC and PAFC among which hydrogen-FC possess the best efficiency and lowest cost.
2.Fuel Cell Back-up Power System: it only takes 1-2 seconds for fuel cells to be activated. Applicable models for this system include PEMFC, MCFC and SOFC. When cost is the main consideration, SOFC is the best option.
Future developments of fuel cell application on MRT power supply system are as follow:
1.Train propulsion by external power system: Using renewable energy source combined with fuel cells as isolated/ grid-connected electricity generating system is greatly supported and developed internationally. If the generating capacity of SOFC could be developed to over 800MW, the cost would greatly decrease.
2.Auto-motivation of trains from self-generated electric power with the help of DC motors: Many countries have already developed fuel cells as car engines, but compared to the 1.35MW~1.71MW power consumption of MRT EMUs, there is still a long way to go.