2. Fuel cell engine below that fits in the place normally taken by the diesel engine in a bus was made by Ballard Power Systems. The power of the fuel cell is about 260 kW. The unit is about 2.5m wide, 1.6m deep, and 1.33m high. Calculate the approximate power density of the fuel cell unit. Why is this less than the stacks shown in Figure 4.1, which are made by the same company. (A 260 kW fuel cell stack made by Ballard Power Systems)