1918.] The N.Z. Journal of Science and Technology. 
51 
Economy in Fuel. 
A saving in fuel results from the fact that the centralized plant is 
working under more economical conditions, the load is steadier and more 
uniform, the units of power plant are larger and therefore more economical, 
and the location is selected with a view to economical working. For the 
same energy expended in the production of wealth in a given area, the 
full consumption of a centralized plant is probably less than one-half that 
consumed in the absence of a power-supply system. This is capable of 
precise determination up to a certain point. For example, the Lake Cole¬ 
ridge plant is at the present time supplying a weekly maximum of 6,000 
horse-power at a weekly load-factor of 60 per cent. A steam plant of the 
same size and number of units would, under the same conditions of supply, 
consume 5 tons of coal per horse-power per annum, having a calorific 
value of 12,500 B.T.U. per pound, on the assumption that all the conditions 
are favourable to economical working, making a total consumption of 
30,000 tons of coal per annum. This represents an efficiency of approxi¬ 
mately 10 per cent., which is the appropriate figure for a plant of the size 
mentioned, which becomes reduced to 7J per cent, after allowing for losse i 
in transmission, distribution, and conversion. So far there is no room 
for ambiguity. Such is not the case, however, when we come to estimate 
the coal-consumption on the assumption that each power-user. is also a 
power-producer. The ambiguity arises from the fact that some power- 
users employ steam-engines; others, gas-engines driven by producer-gas or 
else by illuminating-gas ; some employ a belt drive from a common shaft, 
whilst others employ an electric drive. The prevailing mode, however, 
and the more general method of factory driving, is by belting from steam- 
power plant, and as a rule gas-power will be found only in the smaller 
power plants. Having regard to all the circumstances it will be found that 
they are, as a rule, not conducive towards economy. The small size of the 
individual power-unit, unskilled attention, the necessity of banking fires 
over a period three and a half times as long as that over which the power 
is in use, fluctuations in load, and lack of proper condensing-facilities all 
make for waste. We should not be far wrong in estimating the efficiency 
at one-half the net efficiency of a supply from a centralized power plant. 
Applying this ratio to the present Lake Coleridge area of supply, the total 
consumption for the same production would require the expenditure of 
60,000 tons of coal per annum, showing a saving of one-half, or 30,000 tons 
of coal per annum, due to centralizing the power plant and to burning the 
fuel under more economical conditions. In the present instance, inasmuch 
as the power is derived from head of water, and not from fuel, the whole 
of the 60,000 tons per annum is economized. 
The saving in fuel due to centralizing the power plant, and generating 
electricity therefrom and distributing it through a given area, is often 
estimated at a higher figure than that put forward above. Mr. B. P. Sloan 
states* that, in the case of collieries supplied from the north-east coast of 
England power system, 75 per cent, of the coal previously used for power 
purposes has been saved, representing no less than 1,000,000 tons of coal 
per annum. Mr. C. H. Merz, the greatest British authority on the subject, 
* R. P. Sloan, Fuel Economy on the North-east Coast as a Result of Electric- 
power Supply. Paper read before the Newcastle meeting of the British Association, 
1916. 
