Next to the saving of fuel, the greatest advantage of water-power is due to the relatively small requirements for labor at generating stations where it is used. This is well illustrated by an example from actual practice. In a modern water-power station that contributes to electrical supply in a large city the generator capacity is 1,200 kilowatts. All of the labor connected with the operation of this station during nearly twenty-four hours per day is done by two attendants working alternate shifts.
These attendants live close to the station in a house owned by the electric company, and receive $60 each per month in addition to house rent. Considering the location, $12 per month is probably ample allowance for the rent. This brings the total expense of operation at this station for labor up to $132 per month, or $1,584 per year, a sum corresponding to $1.32 yearly per kilowatt of generator capacity.
At steam-power stations of about the above capacity, operating twenty-four hours daily, $6 is an approximate yearly cost of labor per kilowatt of generators in use. It thus appears that water-power plants may be operated at less than one-fourth of the labor expense necessary at steam stations per unit of capacity. On an average, the combined cost of fuel and labor at electric stations driven by steam-power is a little more than 76 per cent of their total cost of operation. Of this total, labor represents about 28, and fuel about 48 per cent. Water-power, by dispensing with fuel and with three-fourths of the labor charge, reduces the expense of operation at electric stations by fully 69 per cent.
But this great saving in the operating expenses of electric stations can be made only where water entirely displaces coal. If part water-power and part coal are used, the result depends on the proportion of each, and is obviously much affected by the variations of water-power capacity. In such a mixed system the saving effected by water-power must also depend on the extent to which its energy can be absorbed at all hours the day. By far the greater number of electric stations using water-power are obliged also to employ steam during either some months in the year or some hours in the day, or both.