Page 366 - Handbook of Energy Engineering Calculations

2. Select, and size, the solar collector to use
The usual solar collector chosen for systems such as this is a parabolic
tracking-type unit. The preliminary required area for the collector is found by
using the rule of thumb which states: For parabolic tracking-type solar
2
collectors the required sun-exposure area is 0.55 ft per gal/min pumped
2
3
(0.093 m per 0.00379 m /min) at peak output of the pump and collector.
Another way of stating this rule of thumb is: Required tracking parabolic
2
2
solar collector area = 110 ft per hp delivered (13.7 m /kW delivered).
Thus, for a solar collector designed to deliver 10,000 gal/min (37.9
3
m /min) at peak output, the preliminary area chosen for this parabolic
2
tracking solar collector will be, A = (10,000 gal/min) (0.55 ft /gal/min) =
p
2
2
550 ft (511 m ). Or, using the second rule of thumb, A = (110)(50) = 5500
p
2
2
ft (511 m ).
Final choice of the collector area will be based on data supplied by the
collector manufacturer, refrigerant choice, refrigerant properties, and the
actual operating efficiency of the boiler chosen.

In this solar-powered pumping system, water is drawn from a sump basin
and pumped to an irrigation canal where it is channeled to the fields. The 50-
hp (37.3-kW) motor was chosen because it is large enough to provide a
meaningful demonstration of commercial size and it can be scaled up to 200
to 250 hp (149.2 to 186.5 kW) quickly and easily.

Sensors associated with the solar collector aim it at the sun in the morning,
and, as the sun moves across the sky, track it throughout the day. These same
sensing devices also rotate the collectors to a storage position at night and

during storms. This is done to lessen the chance of damage to the reflective
surfaces of the collectors. A backup control system is available for
emergencies.

3. Predict the probable operating mode of this system
In June, during the longest day of the year, the system will deliver up to 5.6
3
million gal (21,196 m ) over a 9.5-hour period. Future provisions for energy
storage can be made, if needed.

Related Calculations. Solar-powered pumps can have numerous applications

beyond irrigation. Such applications could include domestic water pumping