Think of a fuel cell system as an engine. The more power you want, the bigger fuel cell you need. A fuel cell system includes an internal battery.
The diagram below shows an example fuel cell system with an internal DC/DC converter and adjustable current limiter. This system is connected in parallel with a battery. The fuel cell system recharges the battery during light load conditions, and supplements battery power during high load conditions. As long as the average application load is less than the power capability of the fuel cell system, this system will run until the fuel cell runs out of fuel. Using a similar setup, the 25 Watt fuel cell system has been demonstrated to work with laptops that have 70 Watt peak power requirements.
Fuell Cell System electrical output
What does the future hold?
First generation fuel cell systems use a tethered approach to powering devices – the fuel cell system is stand alone and provides power through standard DC power plugs. This works for people who are desperate for remote power. Individuals in the military and industry are already starting to switch to fuel cells when they need to compute and communicate away from the grid. However, widespread commercial adoption won't occur until fuel cells are smaller and integrated into commercial portable electronics.
A standard for communications between fuel cells and laptops has been developed by Intel's Extended Battery Life working group. The standard is currently being reviewed as an addendum to the Smart Battery Data Specification (SBDS), which uses System Management Bus (SMBus) for communication. SMBus is used by laptops today to communicate with batteries, and is therefore seen as an ideal interface for integrated fuel cell systems. The addendum to SBDS for fuel cells adds additional functions that allow greater control of integrated fuel cell systems than the existing standard would allow – this can result in greater system efficiency and more feedback about fuel cell performance. Additionally, the addendum specifically defines how fuel cell systems can respond to SBDS functions and remain compatible with current SBDS devices.
UltraCell LLC's vision is simply this: integrating communication devices with compact, efficient fuel cell systems, enabling users to function for days at a time with a single, portable power supply.