difference in energy and roof pitch

blue

I am purchasing a house with a perfect south facing roof. No trees. It has a 6/12 pitch. I am in central Florida. What percentage of energy gain would I get if I built a 3/12 pitch ground base system instead of putting them on the roof?

Aguarancher

You can try this

https://pvwatts.nrel.gov/

blue

Thanks, I'm puzzled though. It seems a 7/12 pitch is best for central florida. Seems like 3/12 would be best. 

Estragon

Ground based may run a bit cooler (more airflow vs roof), giving a bit more potential (assuming mppt type controller).  You could also use adjustable tilt racking for seasonal tilt change, which can add to production vs a comprimise year-round tilt, or even a tracker which follows the east-west path of the sun daily.

Ground based is generally easier to install, clean, and maintain, but may also be easier to steal if that's a concern.

3/12 sounds about right to me for fixed tilt in central Florida.

BB.

Just to be clear we are talking about the same thing (showing our work):

3/12 = 0.25
arcTan 0.25 = 14 degrees
7/12 = 0.5833333
arcTan 0.583333 = 30 degrees

Using a simple solar calculator. Fixed array
The calculator shows 28 degrees from horizontal (62 degrees from horizontal) is optimum for year round harvest:

Orlando
Average Solar Insolation figures

Measured in kWh/m2/day onto a solar panel set at a 62° angle from vertical:
(For best year-round performance)

Jan	Feb	Mar	Apr	May	Jun
4.29	4.76	5.36	5.79	5.75	4.99
Jul	Aug	Sep	Oct	Nov	Dec
4.96	4.87	4.74	4.89	4.55	4.16

And for summer, 13 degrees from horizontal (77 degrees from vertical):

Orlando
Average Solar Insolation figures

Measured in kWh/m2/day onto a solar panel set at a 77° angle from vertical:
(Optimal summer settings)

Jan	Feb	Mar	Apr	May	Jun
3.80	4.40	5.21	5.91	6.14	5.39
Jul	Aug	Sep	Oct	Nov	Dec
5.32	5.07	4.72	4.60	4.06	3.63

So, if you want optimum power year round, then 28 degrees is not bad... If you want more power during summer (air conditioning), you do get a bit more energy at this time.

The data is based on actual measured harvest... And if you have summer thunderstorms or a morning/evening marine layer, that will affect the optimum angles for harvest.

-Bill

blue

Thanks, the link above was great help too. It shows a few degrees off doesn't make much difference. I'm a 50 miles north of Orlando so 30 degrees might be optimum. I was surprised. Glad I don't need to build a ground based system, much better on the roof. Lots cheaper and nice big backyard with lots of flowers and bushes to help absorb co2. Gotta help our poor planet. Thanks