An American electrical engineer graphically sums up this question
in the following manner:—“There are two ways of starting a
central-station for electric lighting—the investment or the
speculative plan, or the fair means or the foul. The first has
its legitimate end, but the latter is the border ruffian or
money-or-your-life policy, which enters a territory already
sufficiently covered, not for fair competition, but to make money by
being bought out.” Happily, here, we have at present only to deal
with the first plan, and the question naturally arises, “Is electric
lighting a paying investment?” It certainly will not be if the object in
view is only to compete with gas in a limited district where perhaps
it is being sold at 2_s._ 6_d._ per 1000 feet, for, as long as there
is a ready market for the coke and other by-products, gas will remain
in possession of the field. The heat from gas, which is found so
undesirable by the wealthier classes, is advantageous to those who
perhaps cannot afford a fire; in fact, gas has been truly called
the “poor man’s friend,” and, until electricity can be supplied at
a nominal price, it will be useless to expect any revenue from the
poorer districts of large cities. Quite an opposite result may be
looked for when the electric mains are laid at the doors of the wealthy
householder, or through the business neighbourhoods. Shop-owners
especially are found to immediately take up electric light, from the
fact that no fumes are given off to destroy goods or tarnish silver
or gilding, and because it can be so easily applied in a shop window
so as to efficiently light the contents without producing shadows.
The great object to be aimed at in selecting a district to be served
from a central-station is a “constant demand,” and for this reason
it is advantageous to include a business neighbourhood with shops,
public-houses, and restaurants, which require the light for a definite
period every day, and probably will each take more than double the
amount of an ordinary dwelling-house; in fashionable neighbourhoods
especially, it is not unusual to find a large number of houses vacated
at the close of the season, the interest on that portion of the
electric system which is unemployed will have to be set against the
profits of other periods of the year.
The number of gas lights which are actually used at one time in a house
is found to average only two-thirds of the total number fixed, and
with electric light this number is reduced to one-half; economy is at
once the rule with electric light, partly because of the novelty of
the illuminant, and also on account of the facility of lighting and
extinguishing by simply turning a tap or switch. The number of hours
artificial light is wanted in a residential district may be taken at
about 1000 hours per annum, that is to say, the light is required for
about four hours a day in winter and two hours in summer; this amount
is very much exceeded in clubs, shops, and even in large houses, but
1000 hours is a safe figure, and, if the supply is taken by meter,
an annual payment equivalent to 1000 hours’ supply should be a fixed
amount to be paid for, whether used or not. Mr. Crompton estimates
that a Londoner, who is a tenant or owner of a house having three
reception rooms, ten bedrooms, and usual offices, spends about £25 a
year for his lighting, which is made up as follows:—gas bill, £15;
lamp, oil, candles, matches, about £10. There would be about fifty
burners fixed; and, supposing fifty electric lights to be substituted,
he could be supplied with electricity for £25 a year, at a fair profit
to the supply company if they charged 8_d._ per Board of Trade Unit,
as practice has shown that the total number of lamp-hours with fifty
electric lamps is not more than sixty-two, so that two Units,[1] or
1_s._ 4_d._ per day, would be sufficient for the lights he would
require.
[1] Unit; see page 7.
The diagram, Fig. 1, taken from a London residential district, shows
how the number of lamps on at one time vary; the district is supposed
to be wired for 10,000 lamps, and the plant as equal to the supply of
600 kilowatts, or 600,000 watts; the number of lamps is small until
about 3 o’clock, when it gets dusk on a winter afternoon; it then
increases steadily until about 6.30 o’clock, when the curve goes up
with a rush; about this time a great number of people are preparing for
dinner, and probably the lights are on both in the dining-room and
bedrooms. The curve falls, and at about 8 it begins to sink gradually
until 10 o’clock; a great many people appear to go to bed about this
time, but a few sit up to 1 o’clock; until 6 the next morning hardly
any supply is taken, when the servants get up and prepare the rooms
for the day. The diagram, Fig. 2, is taken from the Edison Company’s
central-station at Cincinnati, and agrees fairly with the London
demand for light. Another interesting fact has been ascertained from
the observations taken at the Mauer Strasse station in Berlin, namely,
that the output varies with the temperature, it goes up or down with
the thermometer. The reason is easily explained; gas is laid on side
by side with the incandescent lamps, and the burners are first lighted
when it is cold to warm the apartments; in warm weather the electric
light alone is used. From these and other diagrams the very important
fact has been obtained, that the average daily output of a station
throughout the year is less than one-third of the total capacity of
the generating machinery, so that, although the station from which
the diagram in Fig. 1 was taken could maintain 10,000 16 candle-power
lamps simultaneously alight, the average daily output of electricity
would only equal 3500 constantly lighted; and, as the first cost of the
station is dependent on the size of the plant, the saleable output is
the important factor which governs the profits.
[Illustration: FIG. 1.]
[Illustration: FIG. 2.]