SOLAR ENERGY FOR WATER HEATING — BROOKS 181 



The heat output of a solar water heater cannot be specified exactly 

 in comparison with auxiliary heaters because the auxiliary heater is 

 operated only when needed, whereas the solar heater, operating 

 whenever there is sunshine, is of value only when used. 



In many places, such as isolated cabins or houses where the fire 

 hazard of auxiliary water heaters is objectionable, the relative cost 

 of solar heaters is not important. In other cases where full auto- 

 matic water heaters are needed anyway, the carrying charges of a 

 solar absorber must be compared with the bare cost of fuel or 

 electricity it saves. 



Cost of commercial solar water heaters. — The nonfreeze commer- 

 cial solar water heater with special tank is sold at the factory for 

 about $3 per gallon capacity. The installed prices, including insula- 

 tion, extra pipe and fittings, labor, and the like are about $5 per 

 gallon. The small systems have a slightly higher cost than these 

 figures. 



By assuming a useful life of 18 years and servicing costs for 

 renewal of alcohol and repairs at 4 cents per gallon capacity a year 

 the total annual cost will average about 47 cents per gallon capacity 

 a year. Each gallon capacity represents a free heat absorption of 

 about 1,000 B. t. u. per day, and the nonfreeze type can be assumed 

 to be fully operative for about 270 days a year. These assumptions 

 indicate a solar heat cost per 1,000 B. t. u. of about one-sixth cent, 

 which is equivalent to an electricity rate of 6 mills per kilowatt-hour 

 when fully utilized. 



Cost of common pipe-coil solar water heater. — A standard pipe- 

 coil solar heater system (fig. 7) can be installed for about $3 per 

 gallon capacity. By assuming for this type a useful life of about 15 

 years and 210 days per year of full operation, the solar heat costs 

 about one-ninth cent per 1,000 B. t. u., which is about equal to the 

 fuel cost when using natural gas in the Sacramento Valley. 



If the solar-heater system is installed by the owner and the cost 

 considered is that for materials only, these annual carrying charges 

 might be halved, in which case the solar heater would compete 

 economically with the manual fuel-oil heater, which is bothersome 

 and a fire hazard. 



Cost of solar ahsor'ber tank heaters. — The 30-gallon range boilers, 

 hotbed sash, and insulation can be obtained for about 60 cents per 

 gallon for the enclosed tank heater shown in plate 2, fig. 2. If fully 

 utilized, this installation furnishes hot water at a cost of about one- 

 twenty-fifth cent per gallon. The least expensive system, the exposed 

 second-hand tank (pi. 2, fig. 1) for afternoon showers, heats water on 

 sunshiny days for no appreciable cost. 



