The Solar Design Book

Example 1, Grid-Connected Residence

This is an example of a grid-connected residence in Albuquerque, New Mexico. The array will be mounted on a roof surface that is oriented at 160° (20 degrees east of south) and tilted to 33.7° (8 in 12 pitch). The energy use is known to be 8,000 KWh per year. With some energy efficiency improvements, the energy use is expected to be 7,300 KWh per year. 50% of the utility bill will be offset by the solar system.

The SolarSizer program is used to calculate the solar array size. Losses are estimated to be 3% for wiring, 10% for soiling, and 10% for aging. The inverter efficiency is estimated to be 92%. The roof gets full sun.

The SolarSizer program calculates a required array size of 2.208 KW.

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: 33.69°
6. Orientation of Panel: 160.00°
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 AC use known?: Yes
11. Yearly AC use: 7,300 KWh/year
12. Portion of utility bill to be offset: 50%
13. Inverter Efficiency: 92%
14. Soiling loss: 10%
15. Aging loss: 10%
16. Wiring loss: 3%

The SolarSizer program indicates that the average panel size needed is 2.208 KW. Average is used rather than maximum because the utility will average out the billing over the year. The SolarSizer program also displays other information.

The WireSizer program can be used to size the conductors and breakers.