How many solar panels can I fit on my rooftop?

[Propalen]

Hi all,
I have a flat rooftop with the following size and orientation:


I am planning to use JA solar 545W (2279 x 1134 x 35 mm) solar panel with 30 degrees inclination.
Also I am planning to use this type of structures with ballasts.


Any guess on max solar panels?

Thanks

 

[Propalen]

Chat GPT help

Question:
Please indicate the maximum number of solar panels for my rooftop. The rooftop is 10 by 6 meters. The 10-meter size is 134 SE orientation. Solar panels should be oriented to the south. Solar panel size is 2279 x 1134 x 35 mm.

Answer:
To determine the maximum number of solar panels that can fit on your rooftop, we need to consider a few factors, including the orientation of the rooftop and the space available.

1. Roof Orientation:You mentioned that the rooftop has a size of 10 by 6 meters, with the 10-meter side oriented at 134 degrees in the southeast (SE) direction. However, for optimal solar energy production, solar panels are typically installed facing true south (180 degrees).

To calculate the available space for solar panels, we need to determine the length along the true south direction (180 degrees) on the rooftop.

Since the rooftop is 10 meters long and oriented at 134 degrees in the southeast, we can use trigonometry to find the length along the true south direction:

Length along true south = 10 meters * cos(134 degrees - 180 degrees)Length along true south = 10 meters * cos(46 degrees)

Using a calculator:

Length along true south ≈ 7.2 meters

1. Space Available for Solar Panels: With the length along the true south direction calculated, we can now calculate the available rooftop area for solar panels:

Available rooftop area = Length along true south * Width of rooftopAvailable rooftop area = 7.2 meters * 6 metersAvailable rooftop area ≈ 43.2 square meters

1. Solar Panel Size: You provided the size of a single solar panel as 2279 x 1134 x 35 mm. To calculate its area in square meters, we need to convert the dimensions to meters:

Solar panel area = (2279 mm / 1000) * (1134 mm / 1000)Solar panel area ≈ 2.58 square meters

1. Maximum Number of Solar Panels: Now, we can determine the maximum number of solar panels that can fit on your rooftop:

Maximum number of solar panels = Available rooftop area / Solar panel areaMaximum number of solar panels ≈ 43.2 square meters / 2.58 square metersMaximum number of solar panels ≈ 16.74

Given the available rooftop space and the size of the solar panels, you can install approximately 16 solar panels on your rooftop when oriented to the south for optimal solar energy production. However, please note that other factors such as shading, obstructions, and local regulations may also affect the final number of solar panels you can install. It's recommended to consult with a solar installation professional for a more accurate assessment tailored to your specific situation.

 

[DIYrich]

Setback requirements?

 

[Propalen]

Setback requirements?

None. As long as panels, ballast and supports are within the drawn area.

 

[DIYrich]

I'm guessing 20. While the 30 degree incline shortens the horizontal space of the long length, you will want some spacing to reduce panels shading each other. If you don't mind shading, you might get 25.

4 rows of 5 bi-facial panels, with something white underneath, may be optimal.

 

[Propalen]

Thanks @DIYrich

Some calculations lead me to think that it may be required at least 3.3m between rows. I am not sure if I can fit 5 rows... Please check calculations below

https://www.todofotovoltaica.com/fo...ancia mínima entre filas de paneles es 1,07 m

Latitude: 41.992314
K = 1/tan(61-lat) = 1/tan(61-41.99)= 2.902

Distance> h*k = 1.1395 * 2.902 = 3.30m


https://www.monsolar.com/separacion-paneles-solares

 

[Propalen]

Is 3m distance too much between 2.270m and 30º solar panels?

 

[brum]

Do the drawing and math to calculate at what sun altitude there will be no shading. Then open the sun calculator and check in different seasons when shading will be gone. The calculate the estimated energy output and see if it suits you. The process is not simple, but there is likely calculator that can automate that for you.

Check also what would be the production with roof covered with flat panels and with tilted panels spaced to avoid shading. You may be surprised by the numbers.

And this is how you should start. Not with what you'll be using, but cost/production estimate on the different options and then deciding if you should go with specific structure with ballasts.

And by the way - math doesn't always tell the truth. My north roof that is not facing the sun produces more than the south one. Both with almost identical panels (minor efficiency difference, same number and size). So if you see similar numbers just go with the easier solution.

 

[Propalen]

This is the recommended setup from a solar panel dealer. It fits only 10 panes. It is obviously very safe to avoid any shadows, but I feel more panels could be fitted. How can I improve this setup? Thanks

 

[Danke]

I too have a flat roof. I ran the numbers many times. To get the most production you’re going to want about 10° tilt so you can fit the most panels on your roof. The orientation should be to one of your edges. In your case. It looks like the “SO” one. But maybe with that chimney, the SE one may get more panels. Another consideration with tilting at 30° is wind. Besides lowering the amount of panels on your roof due to that higher angle, you’re gonna need a lot more ballast.

Here is what one racking company drew up for me:

 

[Mike 134]

You said your using ballast. How much weight can your roof hold between ballast and snow loads?

 

[brum]

How can I improve this setup? Thanks

To get more the only option is to put second small rows of 3 panels behind each of the long rows. But this will almost double the cost (additional MPPT trackers, panels) and will provide about 30-40% more production conditionally. Additionally, the access to maintaining the system will get pretty limited.

I know you are not asking if this makes sense, but you just want more panels. But still - have you calculated the investment cost and the return time? If not I don't think you can get a justified decision about how many panels you need.

 

[Danke]

Is 3m distance too much between 2.270m and 30º solar panels?

No

 

[SeaGal]

How can I improve this setup? Thanks

My thoughts are based on my Renusol-tub installation, albeit ground-mount, they are designed for flat roofs...

My thoughts are:-
a) better to go for less inclination than 30 degrees, especially being in Spain. Renusol tubs are 15 degrees.
b) orientate in landscape, rather than portrait, to minimise shading.
c) flat could be an option, though the 15 degree angle will displace rain better.
d) as mentioned above, consider roof load with the ballast. I guess snow is not a big factor in Spain?
e) could consider an East-West configuration. That will be less productive overall than South facing, but will spread the generation through more of the day. But the big factor is that you can mount panels closer together on a flat surface - like this pic...

The process is not simple, but there is likely calculator that can automate that for you.

IIRC correctly, Renusol has an online calculator.

Check also what would be the production with roof covered with flat panels and with tilted panels spaced to avoid shading. You may be surprised by the numbers.

this ^^^^

I too have a flat roof. I ran the numbers many times. To get the most production you’re going to want about 10° tilt so you can fit the most panels on your roof. The orientation should be to one of your edges.

this too ^^^^

To get more the only option is to put second small rows of 3 panels behind each of the long rows.

Or consider E-W as mentioned above.

 

[shadowmaker]

If I'd want to maximize production, I'd put 6 bifacial panels vertically on the very top of the "SE" wall (not roof), three on each side of the window. Rest of the panels on the roof in "SO" orientation with ~10-20 degree tilt, but every row installed a little bit higher than the previous one to avoid shadows. Last row installed vertically (maybe aligning panels horizontally to reduce max height) and two vertical panels on the very top of the "SO" wall. Of course using bifacial panels with the whole roof painted white (~20% more production over single sided panel). This way something like 17-22 panels on the roof and 8 on the walls. Actually vertical panels could have ~80-70 degree tilt and they would still look ok on the wall.

This is just how I would do it if regulations allow and there are no other shadows than that chimney. I'm quite sure there are wall mount structures to buy, but I'd make those myself easily out of aluminium.

 

[Danke]

If I'd want to maximize production, I'd put 6 bifacial panels vertically on the very top of the "SE" wall (not roof), three on each side of the window. Rest of the panels on the roof in "SO" orientation with ~10-20 degree tilt, but every row installed a little bit higher than the previous one to avoid shadows. Last row installed vertically (maybe aligning panels horizontally to reduce max height) and two vertical panels on the very top of the "SO" wall. Of course using bifacial panels with the whole roof painted white (~20% more production over single sided panel). This way something like 17-22 panels on the roof and 8 on the walls. Actually vertical panels could have ~80-70 degree tilt and they would still look ok on the wall.

This is just how I would do it if regulations allow and there are no other shadows than that chimney. I'm quite sure there are wall mount structures to buy, but I'd make those myself easily out of aluminium.

That would be a large wind load. Depends on the roof structure, certainly structural engineers involved for that.

 

[shadowmaker]

That would be a large wind load. Depends on the roof structure, certainly structural engineers involved for that.

Very true.

 

[frasere2]

To maximize power generation, fit your panels to your roof, don't optimize for tilt. That's a common mistake that is borne from days when solar panels were expensive. If you had no obstructions you can get 20 of those panels on your roof . 16 on 10deg EW tilt, 4 on the northern edge at 30degrees. Since your roof edges are 134deg and 224deg Azimuth, either direction on the roof is about the same (since 180deg azimuth is usually best), so go for maximizing panels on the roof. You lose very little from not being at the optimum angle and azimuth. Run the numbers at PVwatts, it will be less than 20% difference in loss of power from these angles, but you are putting 100% more panels on the roof, (20 vs 10 in your picture). Use optimizers and a string inverter and it will be cheaper than microinverters, which also clip at like 380w, so your 545w panels are more like 430watt panels (you'd only produce 380w max but you'd do it for longer with a 545w panel vs a 380w panel). There are single inverters at 11.4kw, which is more than enough, even a 10kw inverter would work. You should be paying no more than $0.40-.50/watt for the panels.

 

[frasere2]

I ran the numbers at PVwatts using Spain as location, the difference in annual solar at 30° tilt, with 180° azimuth, and 10° tilt, with 224° azimuth is 6.6% (134° is the same by the way). So you lose 6.6% in power generation per panel, but you gain 100% more panels by optimizing roof space. It's not even close.

 

[Propalen]

Many thanks for all the contributions. Very interesting discussion. Replying some queries and adding some a new option to the discussion:

You said your using ballast. How much weight can your roof hold between ballast and snow loads?

The structure is reinforced concrete and can hold easily ballast and panels. Small loads are negible in my area

My thoughts are based on my Renusol-tub installation, albeit ground-mount, they are designed for flat roofs...

My thoughts are:-
a) better to go for less inclination than 30 degrees, especially being in Spain. Renusol tubs are 15 degrees.
b) orientate in landscape, rather than portrait, to minimise shading.
c) flat could be an option, though the 15 degree angle will displace rain better.
d) as mentioned above, consider roof load with the ballast. I guess snow is not a big factor in Spain?
e) could consider an East-West configuration. That will be less productive overall than South facing, but will spread the generation through more of the day. But the big factor is that you can mount panels closer together on a flat surface - like this pic...

And East-West solution is a fantastic option for a clean surface. Considering I have the chimeney. I will be limited in the space. Please check Spanish provider East-West solution Solar bloc. Their implementation looks neat.

For me at this point the best proposal is this option

If I'd want to maximize production, I'd put 6 bifacial panels vertically on the very top of the "SE" wall (not roof), three on each side of the window. Rest of the panels on the roof in "SO" orientation with ~10-20 degree tilt, but every row installed a little bit higher than the previous one to avoid shadows. Last row installed vertically (maybe aligning panels horizontally to reduce max height) and two vertical panels on the very top of the "SO" wall. Of course using bifacial panels with the whole roof painted white (~20% more production over single sided panel). This way something like 17-22 panels on the roof and 8 on the walls. Actually vertical panels could have ~80-70 degree tilt and they would still look ok on the wall.

This is just how I would do it if regulations allow and there are no other shadows than that chimney. I'm quite sure there are wall mount structures to buy, but I'd make those myself easily out of aluminium.

This will allow me to fit panels without any shadow. This is a solution from Ennovabloc named 'Vela 10º':


I dont know if I could fit the chimeney under the panels height. Would that be a bad idea?

Lets estimate I could fit 19 panels saving the chimeney at 10º inclination oriented to 136º SE. The power output will be (from globalsolaratlas.info):



With previous solution


MWh per year will be 7.795 MWh per year.

Obviously the last solution is more efficient per panel, but for my requirements the power production is quite low.

I think option 1 is best for me. Need to fit exact measurements on how many panels and how to avoid the chimney and also check regulations.

There is also an option for 15º but it will allow only to fit 3 rows. Any comments?