Here's an illustration of a grid-tie (GT) only solar PV system installation for a residence in an urban area (Plano, TX (Dallas suburb), 1/4 mil pop.), designed to take advantage of all available rebates and incentives (Oncor is my utility Transmission Delivery & Service Provider). Construction started this month, Nov.
Day 0 - Design
- Electric service panel (circuit breaker) box is 200 A. Max circuit breaker size for inverter-to-panel circuit is 200 A * 20% = 40 A (AC).
- Properly derate 40 A at 65% = 26 A max, which, at 240 VAC, is 6.2 KW (AC).
- Assuming a 0.77 default PVWatts DC-to-AC Derate Factor, multiplying the inverse of 0.77 times 6.2 kW, you get max 8.1 KW (DC) for total solar PV panels output.
- Panels - Astronergy CHSM 6610M mono-crystalline, 225 Wp, 37 Voc, 8.5 A Ioc, UL Listed.
- Inverter - SMA Solar Technology Sunny Boy 7000US, 8750 W max PV power, 30 A (DC) max input current.
- DC Disconnect Switch - SMA Solar Technology - integrated with above inverter, accommodates up to 4 x 20 A (DC) strings.
Resulting System Size:
- 8.1 KW / 225 W/panel = 36 panels.
- Each panel is 5.4' x 3.3,' or 17.7 sf in area; 36 panels * 17.7 sf/panel = 636 sf min. roof area (not counting area needed for fire department 'walk around')
- 3 strings, 12 panels each string (later changed).
- 2 strings (24 panels) on the house roof (later changed).
- 1 string (12 panels) on the garage roof (later changed).
Using PVWatts Ver 2 and my specific cell location (0218386), and assuming all defaults (77% DC-to-AC derate, panel tilt at Lat. (33.156°), all panels at 180° azimuth, and no shade ever), system should produce 11.1 kWh annually.
During some periods of solar kWh production I'll be able to totally consume it. The rest of the time I'll have to 'bank' into the grid as best as possible. Best available plan appears to be to sell at 7.5 cents to TXU, my utility Retail Electric Provider.
My last-12-month's average rate at the moment is 10.3 cents. My last-12-month's electricity consumption is 29,039 kWh, which is 2420 kWh/mo, or 80 kWh/day.
Here are 2 images showing roof and electric service entrance areas, before installation begins (8:45 AM CST).
Here are 3 images showing the solar PV system equipment as it arrived.
Next: Day 1 - Installation starts.