268 
The iN.Z. Journal of Science and Technology. 
[Jan. 
VIII. Efficiency of Power-production. 
Before discussing the general significance of the foregoing figures it is 
of interest to compare the efficiencies of the various fuels for power purposes. 
The production of power from coal or gas is both theoretically and prac¬ 
tically a very inefficient transformation, since so much of the heat is rendered 
“ unavailable ” for this purpose, as it is necessarily wasted by being given 
to the condenser-water. The most efficient super-power stations in the 
world consume 1 lb. of good coal per horse-power hour. The average for 
the largest and most efficient stations in New Zealand is over 3 lb. per horse¬ 
power hour, while the smaller and less efficient plants consume from 10 lb. 
to 20 lb. per horse-power hour. If we consider a small workshop, requiring 
about 50 to 100 horse-power, we may take 10 lb. per horse-power hour as 
a fair figure, seldom attained. This corresponds to an efficiency of 
33000 X 60 
10 X 13680 X 774 
X 100 = 1 *87 per cent. 
Using gas in a plant of such an output, probably an efficiency of 6 per cent, 
could be obtained. 
Comparing the various fuels for power-production under the conditions 
stated, we obtain— 
Price. 
Efficiency. 
Power for Id. 
Heao units. 
Horse-power 
Hours. 
Coal .. 
£4 per ton 
Per Cent. 
1-87 
600 
0-235 
Gas . . 
8s. 4d. per 1,000 feet 
6 
270 
0-105 
Electricity* 
IJd. per unit 
85 
1,850 
0-72 
The exact efficiencies of coal and gas for power-production may be a 
matter of discussion according to circumstances, but there can be no doubt, 
at the rates quoted, of the considerably greater economy of electricity. 
Moreover, when convience, labour, and initial cost of plant are taken into 
account, the evidence is overwhelmingly in favour of electricity. 
It may be argued that coal is initially used in the city or town generating* 
station for the production of power, which in turn is transformed into 
electricity and distributed. Each of the transformations involves loss, 
and it would thus appear that the direct generation of power should be 
more economical. Yet, on the whole, because of the higher efficiency 
possible with a larger centralized plant, and the relatively smaller running- 
expenses per horse-power, it will in most towns be more economical to 
apply the power through the medium of electricity. 
IX. Summary and General Considerations. 
It will be seen from Sections I and YI that coal, whether used in a Shack- 
lock range or open grate, gives off as useful heat in an average family-house 
about 25 per cent, of its calorific value. Averaging the figures for gas and 
* Although the price quoted for electricity is the power rate in Wellington, and 
may increase unless a more efficient plant is installed, it appears a reasonable price to 
expect when hydro-electricity becomes available. 
