154 SECTIONAL ADDRESSES 
per kw., depending only on the size. Even the actual station plant 
varies in cost according to the head of water, while the pipe lines, lades, 
and reservoirs may have a wide range, so that each proposed scheme 
must be considered individually for capital expenditure. Station wages 
are small, as the machinery is simple, but the upkeep of the hydraulic 
works is usually a substantial item, and one which depends largely on the 
results of natural phenomena, which cannot be foretold. The load 
factor introduces complications, differing with different types of layout. 
For comparison with steam stations, all wages, salaries, and main- 
tenance, i.e. all running costs, are taken at 14s. 6d. per kw. per annum, 
the load factor having very little effect. The corresponding figure for 
the steam stations described above is 18s. at a load factor of 0-7, and 
15s. 8d. at load factor 0-4. Or the cost per unit for the hydro-electric 
station at load factor 0-4 is 0-05 pence. Capital charges are 6 per cent. 
as before, and depreciation and reserve are put at 2-5 per cent., instead 
of 3-5. All rates, taxes, etc., are omitted as before. The curves for 
varying load factor, worked out for a range of capital costs per kw. 
from {60 to £20, are shown in Fig. 1. The power is taken as that which 
the station has normally sufficient water to supply continuously, and the 
actual annual output falls below this if the load factor is less than unity, 
due to variable demand or to shortage of water. 
At the usual load factor of 0-4, the scheme is limited to £32 per kw., 
if it is to equal the normal steam station, and to £25, if it is to compete 
with the pit-head station, disregarding all question of transmission. 
A cheap design is one in which the river is diverted into a channel or 
tunnel, and after some distance sufficient head is obtained above the 
river bed. No storage is attempted, and during periods of low water 
the output falls off and must be supplemented from a neighbouring 
steam station. Its use corresponds to what has been suggested for small 
pit-head ‘stations. The Clyde Valley stations are of this character, and 
at their cost of £27 per kw. they compare favourably with the normal 
steam station if the load factor exceeds 0-3, but they require a load factor 
of nearly 0:6 to reach the pit-head station cost. The load factor in this 
case is really the river factor, which varies between a wet and a dry year, 
but they are certainly more economical than the normal steam station. 
For stations with reservoirs the cost usually rises considerably, 
although that at Kinlochleven has exceptionally low cost and large 
storage. But such stations may be used in a different way. The daily 
fluctuations in load make no appreciable difference to a reservoir, and 
if the pipe line to the turbines is short, the extra cost of increasing the 
power of the station is small, for it only means larger pipes and larger 
turbine sets, which are cheap machines, so the cost per kw. of station 
power may be much reduced. The annual output is not increased, as 
that is limited by the water supply, but the station can operate more 
economically at low load factors, and it becomes a good peak load station. 
The cost curve is much altered in character, and an arbitrary example 
is given for comparison. The cost is divided into two parts, £36 being 
constant for all load factors as representing the reservoirs and collecting 
lades, and being calculated on the power at unity load factor, as determined 
by the annual quantity of water. Station and pipe cost at this power is 
