47 MISCELLANEOUS SUBJECTS 



materials which are practically indestructable in the 

 tropics. If the steel framework is painted about every 

 eighth year or so it will last for centuries. The founda- 

 tions would last indefinitely, and the boilers should last 

 a very long time. Experience has shown that the mirrors 

 and glass do not break, owing to the method in which 

 they are set. The only parts of the heat absorbers which 

 wear out are the rollers and racks and bearings, and even 

 these will last about ten years, and can then be easily 

 renewed at little expense. 



To convey an idea of the present possibilities of sun 

 power I might mention that the sun heat absorbers at 

 Cairo can generate steam for 50 h.p. for ten hours per 

 day every day the sun shines. The steam-producing part 

 of this plant will cost erected in the tropics, according 

 to a careful estimate when constructed under proper 

 manufacturing conditions by special machinery, the sum 

 of 1,560, being at the rate of 31 per b.h.p. 



The boiler, stack and buildings of a coal-burning plant 

 to generate the same amount of power for ten hours per 

 day throughout the year would cost 770. We now have 

 the following comparisons : 



SUN-POWER STEAM GENERATING PLANT, WORKING 365 DAYS FOR 

 IO HOURS PER DAY. 



s. d. 



Interest on capital expenditure of ,1,560 at 5 per cent. ... 78 o o 



Wear and tear depreciation at 5 per cent. ... ... ... 78 o o 



156 o o 



COAL-BURNING STEAM GENERATING PLANT, WORKING 365 DAYS FOR 

 10 HOURS PER DAY. 



s. d. 



Interest on capital expenditure of 770 at 5 per cent ... 38 10 o 



Wear and tear depreciation at 5 per cent. ... ... ... 38 10 o 



Coal consumption at 2 Ib. of coal per B.H.P., 163 tons at 



95. 8d. per ton 79 o o 



156 o o 



This shows that the sun-power plant can compete on 

 even terms with a coal-burning plant which can obtain 

 its coal at 93. 8^d. per ton delivered to the furnace doors. 

 Any excess in the cost of coal burned above this figure 

 is clear profit in favour of the sun-power plant, and as 

 the cost of coal in the more favourable places in the 



