*4.2. Power*

The four thin lines in brown, red-orange, yellow-orange, and yellow, at the bottom of Figure 8 represent the power generation of the four stacks, respectively. The power fell to zero periodically as the power generation was suspended for the stack refreshing in the activation state. The theoretical optimal power generation of a single stack was approximately 1 W, and the actual power generation decreased when the reaction temperature deviated to either side from the optimal.

The thin line in red depicts the total power generated, while its 24-h daily moving average is shown by the dark red dotted line. The total power generated reached 4 W at the beginning then decreased gradually down to less than 3 W after hour 1600 when the weather warmed up. In order to compensate for the evaporation of water at high summer temperature, the methanol concentration was reduced to 80 *v*/*v*% after hour 2006 from the pure methanol for the winter. The power generation recovered to 3.3 W throughout the rest of the experiment.
