UC Irvine

Current high temperature fuel cell (HTFC) systems used for stationary power applications (in the 200-300 kW size range) have very limited dynamic load following capability or are simply base load devices. Considering the economics of existing electric utility rate structures, there is little incentive to increase HTFC ramping capability beyond 1 kWs-1 (0.4% s-1). However, in order to ease concerns about grid instabilities from utility companies and increase market adoption, HTFC systems will have to increase their ramping abilities, and will likely have to incorporate electrical energy storage (EES). Because batteries have low power densities and limited lifetimes in highly cyclic applications, ultra capacitors may be the EES medium of choice. The current analyses show that, because ultra capacitors have a very low energy storage density, their integration with HTFC systems may not be feasible unless the fuel cell has a ramp rate approaching 10 kWs-1 (4% s-1) when using a worst-case design analysis. This requirement for fast dynamic load response characteristics can be reduced to 1 kWs-1 by utilizing high resolution demand data to properly size ultra capacitor systems and through demand management techniques that reduce load volatility. © 2005 Elsevier B.V. All rights reserved.