The circuit’s voltage is around 1.2 volts - about as much as in a small torch battery. Just as torch batteries can be connected in series to generate higher voltages, so it is possible with fuel cells. They need to be stacked on top of each other, which is called a “fuel cell stack”. Some 4,000 single cells are needed for a fuel cell drive of 80 KW; for 1 KW of energy for a house, around 10 to 50 single cells are required.
There are no waste products such as CO2, nitrogen oxide or fine particles. The only by-product is water.