The Solar Design Book

Example 4, Water System

This is an example of a water system. The site is Albuquerque, New Mexico. The array will be mounted on the ground, oriented to 180° and tilted to 42°. The water use is 200 gallons per day. The storage tank supplies 15 days of water and the pump is sized to fill the tank in 5 days. There is a fire reserve of 6,000 gallons. Water use is assumed to be constant throughout the year. The pump is directly connected to the solar array without batteries. The total dynamic head is 120 feet.

The SolarSizer program is used to calculate the tank size, pump size, and solar array size. Losses are estimated to be 10% for wiring, 10% for soiling, and 10% for aging. The pump efficiency is estimated to be 42%. The array gets full sun. The pump control uses 10 Watts.

The SolarSizer program calculates the required tank size as 9,000 gallons, the required pump size as 0.195 horsepower and 2.52 gpm, and the required array size as 199 Watts. A prudent system designer would add some margin to these numbers.

Details:

The following inputs are used in the SolarSizer program.

1. Task chosen: Size a grid-connected system without batteries
2. State: New Mexico
3. City: Albuquerque
4. Fixed or tracking: Fixed
5. Tilt of Panel: 42°
6. Orientation of Panel: 180°
7. Temperature Coefficient: -0.50 %/°C (default in program)
8. Junction Temp above Amb @ 1,000 W/m2: 34.00°C (default in program)
9. Fraction of Diffuse Used: 100.00% (never changes except for concentrators)
10. Is the water use constant and known?: Yes
11. Water use per day: 200 gallons
12. Soiling loss: 10%
13. Aging loss: 10%
14. Wiring loss: 10%

In the Water tab:

1. Total dynamic head: 120 feet
2. Pump efficiency: 42%
3. Fire reserve: 6,000 gallons
4. Pump control loss: 10 Watts
5. Storage days: 15 days
6. Days to fill tank: 5 days

The SolarSizer program shows the required water tank size to be 9,000 gallons. The required pump size is shown to be 145 Watts or 0.204 horsepower with a required flow of 2.52 gpm. The required array size is 199 Watts. The worst month is December. A prudent system designer would add some margin to these numbers.

The WireSizer program can be used to size the conductors.