We met Gianluca Ferrario with SPI Go Green LLC at our Texas house today. He's an engineer from Italy who's worked on solar power arrays for years. He toured our property to assess our options for solar power answered a lot of our questions:
1. We can't put it on the roof, how about a pergola? That would be fine. We knew the homeowners association would likely allow the panels on a pergola structure. It would not allow for a ground mount.
2. Where in the yard does it go? The back of the house faces west, not due south. Turns out that's still fine. He suggested a patio running along the west side of the house which would also provide shade to reduce heat gain in the summer.
3. What size system do we need? We started discussing at a 4kw system and then increased to a 5.5kw system because it was a better fit for our patio space.
4. How much power will it generate? The size of the system doesn't equate directly to the kWh on the bill - it depends on the location of the panels, tilt, and the latitude of the house/local weather conditions. For example, the same 4kw system installed in various ways produces different annual kwh of electricity:
5. What is the tilt angle? In south Texas, the optimal angle is 5 degrees because it is so close to the equator and the sun is directly overhead much of the year. However, in Minnesota, the panels should be at 45 degrees (basically a 12/12 roof pitch). You can tilt the panels for different times of the year, but you really don't gain that much so it's easier to just mount them in a static position and add an extra panel to cover the loss.
6. Can we expand the system later? Yes, but you choose an inverter size now. If you put in a larger inverter to allow for more panels, the system is less efficient.
Based on an hour meeting at the house, some e-mails between us, and trading diagrams, we had an initial design for the patio and pergola. Joe put a video together from the google sketchup drawings http://youtu.be/ve2bGj970Z8.
1. We can't put it on the roof, how about a pergola? That would be fine. We knew the homeowners association would likely allow the panels on a pergola structure. It would not allow for a ground mount.
2. Where in the yard does it go? The back of the house faces west, not due south. Turns out that's still fine. He suggested a patio running along the west side of the house which would also provide shade to reduce heat gain in the summer.
3. What size system do we need? We started discussing at a 4kw system and then increased to a 5.5kw system because it was a better fit for our patio space.
4. How much power will it generate? The size of the system doesn't equate directly to the kWh on the bill - it depends on the location of the panels, tilt, and the latitude of the house/local weather conditions. For example, the same 4kw system installed in various ways produces different annual kwh of electricity:
| NREL PVWatts calculator | |||
| Loc | kwh/yr | tilt | asimuth |
| ossie 4k | 5,158 | 22 | 180 |
| ossie 4k | 5,260 | 27 | 180 |
| ossie 4k | 5,364 | 45 | 180 |
| bethpage 4k 180 deg | 5,666 | 5 | 180 |
| bethpage 4k 225 deg | 5,641 | 5 | 225 |
5. What is the tilt angle? In south Texas, the optimal angle is 5 degrees because it is so close to the equator and the sun is directly overhead much of the year. However, in Minnesota, the panels should be at 45 degrees (basically a 12/12 roof pitch). You can tilt the panels for different times of the year, but you really don't gain that much so it's easier to just mount them in a static position and add an extra panel to cover the loss.
6. Can we expand the system later? Yes, but you choose an inverter size now. If you put in a larger inverter to allow for more panels, the system is less efficient.
Based on an hour meeting at the house, some e-mails between us, and trading diagrams, we had an initial design for the patio and pergola. Joe put a video together from the google sketchup drawings http://youtu.be/ve2bGj970Z8.
