Calculator or tables that estimates percentages lost for fixed mounts?

[SilverbackMP]

TLDR; Does anyone know of an easy way to calculate how much is lost by not having panels seasonally adjusted? Or at the completely wrong pitch for the average for your latitude?

Rather than installing a ground mount, I am considering building a garage/barn since I have 15 24' wide pole barn trusses in storage along with some treated 6-inch posts. I would hang 12' shed extension off of the south side to give me 24' of south-facing roof space. I would need to build a few more trusses since I want 40' in length and I'd go 2' centers instead of 4' centers on the trusses (their design specification) due to the extra load. Not as concerned about the trusses as I am about the effects of panels on a metal roof.

I figure I can build a small barn (not including a concrete floor which is completely optional) cheaper than I can buy a good ground mount....particularly since I already have some of the material.

Zero permits, zero code inspections in my area (though you still need to build to it, but not the most recent codes as they haven't been adopted...just the common sense ones).

These trusses are 4/12 pitch which is 18.4 degrees with my year-round solar average being 33 degrees. Since this is an off-grid system, I am more concerned with seasonal peaks than a grid-tied system would be.

If we're talking a few percentage points of difference....even up to 10%, I am not worried about it too much. But if we're are in the higher percentages of inefficiencies, I'll switch up my plans. However, I've read that a lower slope is actually more efficient for collection during overcast days...and my area has lots of overcast and gloom in the winter.

I've Googled until I'm blue in the face trying to find the answer to this...and the only thing that I've turned up were some sites that I don't fully trust. (I own a company that publishes high-quality informational websites, I can easily smell when someone is err bullcraping and really has no clue as to what they are writing about).

Does anyone have an idea of the percentages lost for not having panels at the correct angles?

 

[SilverbackMP]

Kind of a follow-up question. Would you install rapid disconnect on this even though my state doesn't require it? If yes, then that will push me closer to the ground mount than the roof mount.

 

[RCinFLA]

A lot depends on your location and specific location obstructions.

The WBAN charts have pretty good statistical info for various U.S. cities.

https://www.nrel.gov/docs/legosti/old/5607.pdf

https://gaftp.epa.gov/ap42/ch07/s01/reference/ref14_c07s01.pdf

 

[RCinFLA]

Local fire regulations often require a quick disconnect on outside wall with a specific label on box so fire department can get quick access to shut system down.

Most all UL approved inverters have this capability.

Beware of non-UL listed Chinese all-in-one grid tied inverters as they often do not have PV inputs isolated from AC output. The PV input lines are riding on top of AC output. If neutral grounded on inverter, and you check PV + and - inputs with AC voltmeter you may find 120vac or 240vac from each PV line to neutral/ground.

 

[DThames]

From memory....100% is full 2 axis tracking.
70% for fixed at ideal average angle, less than 74% if adjusted 4 times a year, something like 71.5-72% if adjusted 2 times a year. I made mine fixed and a little larger.

 

[SilverbackMP]

A lot depends on your location and specific location obstructions.

The WBAN charts have pretty good statistical info for various U.S. cities.

https://www.nrel.gov/docs/legosti/old/5607.pdf

https://gaftp.epa.gov/ap42/ch07/s01/reference/ref14_c07s01.pdf

Thanks a bunch, that top one shows me exactly what I needed. At -15 degrees latitude, there is a very significant decrease in the winter. I can't average these like a grid-tied system if I want to minimize the use of a generator. So the first phase of this at least should be a ground mount - whether that is fixed or adjustable.

 

[SilverbackMP]

Local fire regulations often require a quick disconnect on outside wall with a specific label on box so fire department can get quick access to shut system down.

Most all UL approved inverters have this capability.

Beware of non-UL listed Chinese all-in-one grid tied inverters as they often do not have PV inputs isolated from AC output. The PV input lines are riding on top of AC output. If neutral grounded on inverter, and you check PV + and - inputs with AC voltmeter you may find 120vac or 240vac from each PV line to neutral/ground.

Yeah, I was going to place quick disconnects at the array area and the "power shed" (separate 10x10 ish building) but the rapid shutdown stuff just seems like an added complication on an already complicated system.

I am fairly certain that we don't have any local fire regulations. This is in the middle of no where Missouri. That being said, I don't want the system to be unsafe for both liability and not to be a crappy human.

Will be using Sunny Boys and Sunny Islands. But the whole point is moot (thanks to those charts) as I will likely be using ground mounts unless I run out of power. I have the space for at least three (probably four) 40-foot mounts with zero obstructions/shading. And I could go longer if I were to add more fill. I'll probably initially do two 40-foot mounts with some like 40 (total) of bifacials since the area that I will install them as flyash fill and either needs topsoil or gravel placed back on top. Just as easier (and cheaper) to go with (limestone) gravel....should be good for bifacials IMHO.

 

[DThames]

Where in MO are you?

 

[SilverbackMP]

Where in MO are you?

Northwest of Columbia.

 

[DThames]

Northwest of Columbia.

Just wondering. We travel from AR up to Joplin and then over to St Louis, two or three times a year. You are off of that path a bit.

 

[carefulmistake]

Just as an addition, I've found this calculator to be very helpful. I was originally going to mount my panels fixed to my 3:12 lean-to metal roof but the winter loss, which is when I need it most, would be a huge loss. I experimented with the azimuth and angle to find what would work for me and it convinced me to make manually adjustable mounts for the angle with ground mounts.

PVWatts

Estimates the energy production and cost of energy of grid-connected photovoltaic (PV) energy systems throughout the world. It allows homeowners, small building owners, installers and manufacturers to easily develop estimates of the performance of potential PV installations

pvwatts.nrel.gov

Just put in your address then your system info.

 

[tomy2]

TLDR; Does anyone know of an easy way to calculate how much is lost by not having panels seasonally adjusted? Or at the completely wrong pitch for the average for your latitude?

Rather than installing a ground mount, I am considering building a garage/barn since I have 15 24' wide pole barn trusses in storage along with some treated 6-inch posts. I would hang 12' shed extension off of the south side to give me 24' of south-facing roof space. I would need to build a few more trusses since I want 40' in length and I'd go 2' centers instead of 4' centers on the trusses (their design specification) due to the extra load. Not as concerned about the trusses as I am about the effects of panels on a metal roof.

I figure I can build a small barn (not including a concrete floor which is completely optional) cheaper than I can buy a good ground mount....particularly since I already have some of the material.

Zero permits, zero code inspections in my area (though you still need to build to it, but not the most recent codes as they haven't been adopted...just the common sense ones).

These trusses are 4/12 pitch which is 18.4 degrees with my year-round solar average being 33 degrees. Since this is an off-grid system, I am more concerned with seasonal peaks than a grid-tied system would be.

If we're talking a few percentage points of difference....even up to 10%, I am not worried about it too much. But if we're are in the higher percentages of inefficiencies, I'll switch up my plans. However, I've read that a lower slope is actually more efficient for collection during overcast days...and my area has lots of overcast and gloom in the winter.

I've Googled until I'm blue in the face trying to find the answer to this...and the only thing that I've turned up were some sites that I don't fully trust. (I own a company that publishes high-quality informational websites, I can easily smell when someone is err bullcraping and really has no clue as to what they are writing about).

Does anyone have an idea of the percentages lost for not having panels at the correct angles?

Will has a video up on youtube where he tests panels at different angles in his Las Vegas driveway. As I recall the difference in output was only 5% different between 15 and 30 degrees, north to south.