The Solar Design Book

Example 3, Grid-Connected Residence 3

This example is the same as Example 1 and 2 except the array will be mounted on a two-axis tracker. The energy is expected to be 7,300 KWh per year after energy efficiency improvements. 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 the same as Example 1, estimated to be 3% for wiring, 10% for soiling, and 10% for aging. The inverter efficiency is estimated to be 92%. The array gets full sun.

The SolarSizer program calculates a required array size of 1.738 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: Tracking
5. Type of Tracking: 2-axis
6. Temperature Coefficient: -0.50 %/°C (default in program)
7. Junction Temp above Amb @ 1,000 W/m2: 34.00°C (default in program)
8. Fraction of Diffuse Used: 100.00% (never changes except for concentrators)
9. Is the AC use known?: Yes
10. Yearly AC use: 7,300 KWh/year
11. Portion of utility bill to be offset: 50%
12. Inverter Efficiency: 92%
13. Soiling loss: 10%
14. Aging loss: 10%
15. Wiring loss: 3%

The SolarSizer program indicates that the average panel size needed is 1,738 KW. This is a 19% reduction in the size of the required array over a fixed installation, or another way to look at this: a 23% increase in power from the same size array. A life-cycle cost analysis will reveal if the tracker is justified.

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