How much Solar energy with only vertically or horizontally mounted solar panels?

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I need some help to estimate a possible Solar energy with only vertically or horizontally mounted solar panels.

I have a flat roof and because of heavy wind situation, I cannot have my panels tilted, unless I design a very strong frame support.
So practically my solar panels can only be installed vertically against a wall or flat on top of the roof.

I plan to have may be 12 to 16 panels, but I don't have enough space to put all the panels in one location,
such as only horizontally or vertically toward the south.

The walls are oriented exactly toward the East, South, and West,
and about the latitude, I am located near San Francisco, California.

1) How can I calculate the expected solar energy for each hour of the day, for every month of the year,
and for each of the four possible panel locations, such as horizontal or vertical toward east, south, and west?

2) If hypothetically I have a total of 16 panels, and 4 panels for each of the 4 possible locations,
what would be the optimum connection combination, such as:

- Connect in series all the panels of a given location, for example only the 4 west panels together,
and use then 4 independent inverters for each of the locations to charge the batteries?

- Connect in series one of each type of location, such as one horizontal, one east, one south, and one east,
so in average I would have almost a constant level of solar energy, and use 4 independent inverters for each of the panel sets?

- Would it be preferable to use only one or two inverters and have the panels connected together in series and parallel?
 

sunshine_eggo

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Lists solar irradiance for panels in vertical, horizontal and other seasonal tilts:


You can simulate an actual array here:


Both tools will require that you run the numbers for each different array and sum manually.
 

sunshine_eggo

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2) If hypothetically I have a total of 16 panels, and 4 panels for each of the 4 possible locations,
what would be the optimum connection combination, such as:

- Connect in series all the panels of a given location, for example only the 4 west panels together,
and use then 4 independent inverters for each of the locations to charge the batteries?

Kinda this except you don't necessarily need independent inverters.

Each location could be a 4S or 2S2P array and then each array could be in parallel with the other arrays forming either:

4S4P or (2S2P)4P

The need for additional charge controllers is dictated by the battery voltage, charger limits and panels selected.

- Connect in series one of each type of location, such as one horizontal, one east, one south, and one east,
so in average I would have almost a constant level of solar energy, and use 4 independent inverters for each of the panel sets?

on average, each string of panels would always perform according to the WEAKEST panel at any given time, so your performance would pretty much be the worst of all imaginable scenarios.

In a series circuit, all components must experience the same current. If you have 4 panels in series each producing different levels of current due to different solar intensity, the lowest power panel producing the lowest current will cause all other panels in series to operate at that current.

- Would it be preferable to use only one or two inverters and have the panels connected together in series and parallel?

Depends on above.
 
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Kinda this except you don't necessarily need independent inverters.

Each location could be a 4S or 2S2P array and then each array could be in parallel with the other arrays forming either:

4S4P or (2S2P)4P

The need for additional charge controllers is dictated by the battery voltage, charger limits and panels selected.
I plan to use a 48 V battery system, as I need to store about 10 to 20 kWh of solar energy.

I noticed that some solar inverters are limited to 150 V, but I believe that some chargers would accept about 250 V,
which would allow then to put all of the 4 panels in series to lower losses, since I will have at least 300 ft of wiring?

Does having solar panels not producing any solar energy has any effect on the others panels, or is it better to use separate inverters?
 

sunshine_eggo

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I plan to use a 48 V battery system, as I need to store about 10 to 20 kWh of solar energy.

48V never a bad idea, but it's less about the kWh you need to store and more about the kW of power you need to provide. 4800W from 48V is only 100A.

I noticed that some solar inverters are limited to 150 V, but I believe that some chargers would accept about 250 V,
which would allow then to put all of the 4 panels in series to lower losses, since I will have at least 300 ft of wiring?

Maybe. It depends on voltage, wire gauge, distance and current.

You can compare scenarios with a voltage drop calculator:


Ran assuming 330W panels with 40Vmp, 8.25A Isc, 10awg and 300', 2S2P array.

12.4% is definitely on the high side.

4S of those panels would be 3.09%, which is pretty good.

You can always go with thicker wire, but it's all a trade off. How much would one configuration on 150V controllers cost vs. the other configuration on 250V+ controllers.

The higher the PV voltage, the more you have to pay attention to the PV input current limit. Some of the high voltage ones basically prevent you from putting more than one string on it.

Does having solar panels not producing any solar energy has any effect on the others panels, or is it better to use separate inverters?

You could have array 1 facing south with full sun on it, and array 2 facing east with no sun on it, but exposed to ambient light. Array 1 and 2 are wired in parallel. Array 2 would not impede array 1.
 
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You can simulate an actual array here:

On the step 3, you can provide some roof map information.

I know that I could put 4 flat panels, and may be 6 panels, depending on the exact size of the panels.
The system shows about 1.5 kWdc (10 m2) when drawing the map.
Should I include the map, or should I skip this step (?) but in this case how to put the size of the panels?

In the case of the vertically mounted panels, would including the map diagram could be of any use?
 

sunshine_eggo

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I never use that feature, so I can't say. I would expect you have to specify direction and tilt in addition to the mapped area, i.e., it can't tell what angle your roof is., and I expect it has no value for vertical panels.

While probably okay for starters and broad planning purposes, computations based on available area usually result in disappointment. You need to find panels that fit your area for best results. At that point you model each array in terms of power, tilt and orientation.

Let's say that you can get 2S2P 300W panels on your flat roof. You'd just specify a 1200W array at 0° tilt and 180° Azimuth. If you can hang the same array on your East wall, 1200W, 90° tilt and 90° Azimuth, etc.

Note that PVWatts includes weather impacts as well as solar irradiance. For any given date, it calculates the average day based on something like 30 years of data, then it picks actual day that most closely represents the calculated average. Specifics don't matter that much, but it's just good to know the output reflects weather influence as well. :)
 
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48V never a bad idea, but it's less about the kWh you need to store and more about the kW of power you need to provide. 4800W from 48V is only 100A.
To give you a little bit more or insight, if you don't mind, I estimate that I need about 20 kWh of solar energy a day,
after including various wires and efficiency convertions loses.

If there is about 6 hours of daily sun energy and only 8 of the panels really produce energy,
this mean that each panel should provide about 20 kwh / 6 h / 8 panels = about 400 W.
Is that doable?
 
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Note: This system will be used to power the lighting of some common areas of a building.
So there is a trade off between providing enough power in winter and having too much unused surplus during the summer.

If there is not enough solar energy produced, because of bad weather, or winter time, using the grid as complement,
would be more cost effective than having too much buffer solar storage bearely used may be for 6 months of the year.
Also in California where I live, electricity is a little bit cheaper in winter than in summer (I really don't know why btw).

Just to provide a little bit more details, the lighting power consumption during the day hours (like 8 am to 6pm)
is around 300 W (or a total of 3 kWh), and during the night hours (6 pm until 8 am) is around 1 kWh (or a total of 14 kWh).
So the daily consumption is about 17 kWh, but estimating an 80 % efficiency, there is a need of about 20 kWh of solar energy.

Considering also not discharging totally the batteries more than 80 %. this would also required having 20 kWh of battery capacity.
In the case of a 48 V system, this would require 420 Ah per cell, which is not common as typically cells are 280 Ah.
 

sunshine_eggo

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To give you a little bit more or insight, if you don't mind, I estimate that I need about 20 kWh of solar energy a day,
after including various wires and efficiency convertions loses.

20kWh is about 2/3 that of the average American household.


If there is about 6 hours of daily sun energy and only 8 of the panels really produce energy,
this mean that each panel should provide about 20 kwh / 6 h / 8 panels = about 400 W.
Is that doable?

Unfortunately, no. You don't get 6 hours of sun. You get far less. Panels only produce maximum power at high noon when the panels are perfectly perpendicular to the sun, and the solar radiation is exactly 1000W/m^2.

From the first link I provided:

Here's your flat roof performance:

1637358816612.png


Dec 2.17 means 2.17 equivalent solar hours from ALL DAY exposure, i.e., a 400W panel flat on your roof in Dec wil only produce 400W * 2.17h = 868Wh. If you need 20kWh/day, you need 20,000/868 = 23 400W panels to produce that energy.

In Jun, you do get something like "6 hours" per day. In June, you'll average 6.89 * 400W = 2756Wh, so you only need 20000/2756 = 7.25 panels.

Vertical panels facing West:

1637359025739.png

They'll perform a little better in the winter than the flat arrays, but you'd still need 20000/(2.92*400) = 17 panels.

East performs same as West:

1637359323366.png

Vertical panels facing South:

1637359159861.png
They'll perform substantially better in the winter than flat.

You could manually enter that data in a spreadsheet and calculate the total performance of your arrays to see what you'll need to power 20kWh.

If there is not enough solar energy produced, because of bad weather, or winter time, using the grid as complement,
would be more cost effective than having too much buffer solar storage bearely used may be for 6 months of the year.
Also in California where I live, electricity is a little bit cheaper in winter than in summer (I really don't know why btw).

Sounds like a plan

Just to provide a little bit more details, the lighting power consumption during the day hours (like 8 am to 6pm)
is around 300 W (or a total of 3 kWh), and during the night hours (6 pm until 8 am) is around 1 kWh (or a total of 14 kWh).
So the daily consumption is about 17 kWh, but estimating an 80 % efficiency, there is a need of about 20 kWh of solar energy.

80% is a good number.

Considering also not discharging totally the batteries more than 80 %. this would also required having 20 kWh of battery capacity.
In the case of a 48 V system, this would require 420 Ah per cell, which is not common as typically cells are 280 Ah.

Correct, but you could simply build 2X separate 16S 280Ah batteries each with their own BMS and wire them in parallel. Probably run you about $4500 DIY.
 
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Thank you so much for all your dedicated time to produce such nice overview.
I will compile all the numbers to have a more precise estimate of this solar project.

The 6 hours of sun was only to have rough idea of the system that I envision.
I could mention that the west panels will be facing the sun until sunset,
so from 4 pm until 7 pm there would be a little bit of additional sun light,
but maybe not sufficient enough to trigger the inverter. Also, around noon time,
the vertical panels might get a little bit of reflection from the flat roof,
but I don't know this would be really noticeable.


Something that I considering first to do is to replace the fluorescent neon tubes using ballast,
with LED based tubes in the garage area, and upgrade the stairways and hallways with LED lighting.
I assume I could drop at least by 40 % the energy consumption, thus reducing the battery capacity cost
to use only (hopefully) one set of 16 cells. May be I could consider getting some 310 Ah instead of 280 Ah cells.

For the solar panels, I have some location constraint limitations, mostly
because of the wind situation, so a total of 16 panels seems to be a maximum.
Also I will be able to only install 2 panels vertically facing south, so I might skip this option.
So maybe I should use solar panels with double side exposure,
but for a higher cost, if this was really worthwhile.

About electricity cost, we have a billing based on quota of 8 kWh per day.
So the first quota is about $.20 to $.25 per kWh.
The next three quotas are in the $.30 to $.40 per kWh.
Above four quotas, or 24 kWh per day, the cost is around $.50 per kWh.
The building is always over the four quotas, thus the idea to install some solar panels.
There is about $200 a month cost for the monthly lighting.
I plan to build a full solar system for about $4k (?)

From your experience, would there be any advantage to install the solar inverters near the solar panels,
instead of in the basement where the batteries and inverter will be located?
 
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If I may, another topic I am interested in, is to build a simple monitoring system
to measure and display the solar energy produced during the day
and the battery charging level and consumption.

I could of course use some sophisticated devices connected together
with Bluetooth, and sending information to a computer or the cloud.
But I am more interested building everything from scratch, than just connecting appliances together.

I already build a prototype system using a 12 V ion battery and a 300 W sine inverter.
I use some timers to recharge the battery to simulate the solar charging and load changes over the day.
Using a voltage controller, my system automatically switch to the grid when the battery get too low,
for example 12.5 V, and uses again the battery when the voltage is high enough, like 13 V.

I can manually make all sorts of measurements to determine the status of my system,
but I wonder how I could capture such information to be able to generate a consumption graph?
 

sunshine_eggo

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Thank you so much for all your dedicated time to produce such nice overview.
I will compile all the numbers to have a more precise estimate of this solar project.

The 6 hours of sun was only to have rough idea of the system that I envision.
I could mention that the west panels will be facing the sun until sunset,
so from 4 pm until 7 pm there would be a little bit of additional sun light,
but maybe not sufficient enough to trigger the inverter. Also, around noon time,
the vertical panels might get a little bit of reflection from the flat roof,
but I don't know this would be really noticeable.

It's the "quality" of the sunlight in those 6 hours. At morning and evening, the sun is at an extreme angle, and its rays are passing through a lot more atmosphere. Same towards sunset.

I took the liberty of building a quick planning sheet (zip attached):

1637377839881.png

2000W of south-vert panels coupled with 1600W at the other three locations, and it looks pretty good.



Something that I considering first to do is to replace the fluorescent neon tubes using ballast,
with LED based tubes in the garage area, and upgrade the stairways and hallways with LED lighting.

Yes you do.

I assume I could drop at least by 40 % the energy consumption, thus reducing the battery capacity cost
to use only (hopefully) one set of 16 cells. May be I could consider getting some 310 Ah instead of 280 Ah cells.

40% is a pretty big jump. CFL to LED is only a small improvement, but incandescent/halogen to LED is a leap. Only you know, but you should take all conservation steps first.

For the solar panels, I have some location constraint limitations, mostly
because of the wind situation, so a total of 16 panels seems to be a maximum.

This limitation may make the project impossible.

Also I will be able to only install 2 panels vertically facing south, so I might skip this option.

The south vertical panels are critical to winter production. As you can see, that's where you need the MOST solar.

So maybe I should use solar panels with double side exposure,
but for a higher cost, if this was really worthwhile.

You will be disappointed in the performance, but there will be a small benefit. Bifacial panels show the most improvement in conditions where reflection is possible, snow, water, etc.

About electricity cost, we have a billing based on quota of 8 kWh per day.
So the first quota is about $.20 to $.25 per kWh.
The next three quotas are in the $.30 to $.40 per kWh.
Above four quotas, or 24 kWh per day, the cost is around $.50 per kWh.
The building is always over the four quotas, thus the idea to install some solar panels.
There is about $200 a month cost for the monthly lighting.

I would go broke paying your rates.


I plan to build a full solar system for about $4k (?)

5000W solar = $2500
16S 280Ah battery = $2300
Mounting, wires, fuses, bits, etc. = $1000?
Inverter = $2000
MPPT = $500

$8300, and I'm probably on the low side.

From your experience, would there be any advantage to install the solar inverters near the solar panels,
instead of in the basement where the batteries and inverter will be located?

An inverter converts DC to AC, i.e., battery to house power.
A solar charge controller (SCC) is what charges battery with solar and/or feeds DC power (via battery) to inverter to power loads. SCC are also referred to as MPPT when they offer this feature, and you want an MPPT.
There are some units that provide both an inverter and MPPT in the same box. Those are All-in-Ones (AiO).
Most installations have the inverter and MPPT(s) in a central location. I would expect that's optimal for you.

If I may, another topic I am interested in, is to build a simple monitoring system
to measure and display the solar energy produced during the day

Victron offers this feature on their MPPT. Other's likely do. This is a snapshot from their app in demo mode:

1637378646494.png

and the battery charging level and consumption.

This can be provided by the BMS to some degree.

A Battery Monitor can do this as well. Snapshot from app for BMV-712:

1637378711421.png



Furthermore, if this is solar-only, and you're not over-using the system, the MPPT energy produced is proportional to your consumption.


I could of course use some sophisticated devices connected together
with Bluetooth, and sending information to a computer or the cloud.
But I am more interested building everything from scratch, than just connecting appliances together.

I'm too unskilled and lazy for that. :)

I already build a prototype system using a 12 V ion battery and a 300 W sine inverter.
I use some timers to recharge the battery to simulate the solar charging and load changes over the day.
Using a voltage controller, my system automatically switch to the grid when the battery get too low,
for example 12.5 V, and uses again the battery when the voltage is high enough, like 13 V.

I can manually make all sorts of measurements to determine the status of my system,
but I wonder how I could capture such information to be able to generate a consumption graph?

It depends on the system you choose to monitor it.
 

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@sunshine_eggo thank you so much for helping me for giving so much a head start in this project.

From your previous posting, I noticed that the vertical panels would not produce so much energy,
but would be easy to install. I wonder if moving the bottom of each panel away for about one foot
from the wall, would provide already some benefice without having to build an elaborate framing
to sustain heavy windy days?

About the solar location constraint on the roof, well the situation is that there are two small cabins,
if that the correct word to use, one build on top of the elevator and the other on top of the stairway.

The elevator 'cabin' is located in the middle of the roof, so all the walls are accessible easily.
I could probably put 3 solar panels on the east and on the west side and 2 solar panels on the south side.
The roof of the cabin is flat and build a little bit below the edges of the walls, so I could put two panels
not directly exposed to the wind.

- For this evaluation, I estimate each panel to measure about 5 feet by 3 feet, is that a typical panel size?

The stairways 'cabin' is located on one side of the building, so the south side is above
the main facade of the building. There is a narrow path were you could walk, wearing an harness,
but installing solar panels would require using scaffolding, so this is too much trouble.
On the east and west side I could certainly install 5 to 6 solar panels and on the roof I guess
there is room for at least 4 panels, depending on the location of some vents blocking some areas.

So as a summary, I estimate the following:

On the 'cabins' roof: 2 + 4 = 6 flat panels,
- so may be a [3P x 2S] combination.

On the east and the west side, (3 + 5) = 8 vertical panels, or (3 + 6) = 9 panels.
- so may be a [4P x 2S]
- or a [3P x 2S] + [1P x 3S] if this is possible?

On the south side, only 2 vertical panels,
- so a [1P x 2S]

I think that you recommended to stay around 150 V, so would you recommend using a 2S combination?

How many panels could be typically installed in parallel for a given MPPT,
considering that some panels will not produce solar energy in the case of east versus west location?

- I was think to have 3 legs, such as 'East' leg and 'West' leg of [4P x 2S] and 'Flat-South] leg of [3P x 2S]
unless I could use only 2 MPPT, or only one MPPT considering that some leg could be inactive?
 

sunshine_eggo

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@sunshine_eggo thank you so much for helping me for giving so much a head start in this project.

From your previous posting, I noticed that the vertical panels would not produce so much energy,
but would be easy to install. I wonder if moving the bottom of each panel away for about one foot
from the wall, would provide already some benefice without having to build an elaborate framing
to sustain heavy windy days?

Tilting the vertical panels by kicking the bottom out will improve your production.

About the solar location constraint on the roof, well the situation is that there are two small cabins,
if that the correct word to use, one build on top of the elevator and the other on top of the stairway.

The elevator 'cabin' is located in the middle of the roof, so all the walls are accessible easily.
I could probably put 3 solar panels on the east and on the west side and 2 solar panels on the south side.
The roof of the cabin is flat and build a little bit below the edges of the walls, so I could put two panels
not directly exposed to the wind.

- For this evaluation, I estimate each panel to measure about 5 feet by 3 feet, is that a typical panel size?

Unfortunately, most of your large panels are about 1mx2m. These smaller panels are 4-5 inches larger than 5x3:


The stairways 'cabin' is located on one side of the building, so the south side is above
the main facade of the building. There is a narrow path were you could walk, wearing an harness,
but installing solar panels would require using scaffolding, so this is too much trouble.
On the east and west side I could certainly install 5 to 6 solar panels and on the roof I guess
there is room for at least 4 panels, depending on the location of some vents blocking some areas.

As it stands, you're going to be challenged finding panels that fit.

So as a summary, I estimate the following:

On the 'cabins' roof: 2 + 4 = 6 flat panels,
- so may be a [3P x 2S] combination.

Given your 48V system, you'll need at least 2 large 24V panels in series, and I don't see how you're going to fit them.

On the east and the west side, (3 + 5) = 8 vertical panels, or (3 + 6) = 9 panels.
- so may be a [4P x 2S]
- or a [3P x 2S] + [1P x 3S] if this is possible?

If panels are going to be on the same controller, you'll need all parallel strings to have the same voltage, so 2S3P would work with 2S but not 3S2P.

On the south side, only 2 vertical panels,
- so a [1P x 2S]

I think that you recommended to stay around 150 V, so would you recommend using a 2S combination?

Yep, but again, the south side vertical is critical for meeting winter production, and you're far short of 2000W.

How many panels could be typically installed in parallel for a given MPPT,
considering that some panels will not produce solar energy in the case of east versus west location?

It depends on the panels and Vmp. Assuming one model of panel, you could have a 2S2P array on the east side in parallel with a 2S array on the West side, and you'd have no issues.
- I was think to have 3 legs, such as 'East' leg and 'West' leg of [4P x 2S] and 'Flat-South] leg of [3P x 2S]
unless I could use only 2 MPPT, or only one MPPT considering that some leg could be inactive?

Might work. However, due to the fact that you don't have the space for 5000W of solar in the correct locations, I don't see how you're going to get to 20kWh/day.
 
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About the overall cost, as you can imagine I would like to keep everything low.
This is an off-grid project, so I don't expect getting any tax credit
and I don't want to have to deal with my electrical company either.

If I can have a 6 to 8 months solar system sufficient to avoid any electricity billing this would be fine.
In winter, if I can get only 50 % of the electricity bill, I think this would still be cost effective compare
to having a beef up system providing extra un-used surplus in the summer.

I have seen many videos of systems based on Victron devices, but this is a costly solution.
Many Youtubers recommend such solution, but they might have not paid for it.
I only need to see how much solar electricity is generated every month and how much I save, or not.

Honestly, I put some $20 Watt-meters to measure the consumption in various areas of the building.
This is enough to understand the underneath of the monthly electricity bill that I receive!!!!

I have a 12 V battery monitor that I use for my car, and I can access it using a phone App.
I could use such type of device to monitor the battery voltage, and using some resistor bridge
I could also monitor the solar panels voltage.

I found also a small device that I can use to detect various events, such an overvoltage of the battery
if the BMS failed, so I can send an alert by WiFi, and disconnect the battery.
 
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@sunshine_eggo thank so much again for your feedback.

Most of the numbers I used, were on top of my head. During the Thanksgiving break,
I will spend some time on the roof to make more measurements.

If there is not enough panels for the winter case, this could still be fine if the electricity bill is still
reduced enough to be cost effective compared to a beef up system having too much unused energy.
As I can see, from your numbers, the flat panels have a solar production ration of 3 between winter and summer.

If really the number of panels is an issue, I could find another area on the roof to add more flat panels,
but this will be a very complex installation to build, mostly because of the wind situation
and the difficulty to find some sturdy anchor to attach the panels without altering too much the roof.
I think the flat roof is covered using type of felt material.

Another alternative would be to use some wind turbine, but most of the wind occurs only around sunset.
This is also a more complex system requiring more maintenance too.
 
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@sunshine_eggo I found my notes regarding the solar panel calculation.

I was using solar panels size of 65" x 39" similar to your Santa Solar reference.

- The small cabin size is 10' length (facing east and west) x 7' width (facing south and north) x 6' high.

- The larger cabin size is 24' length (facing east and west) x 9' width (facing south and north) x 9' high.

One optimization that I am considering now, in the case of the vertical walls, is to put
the solar panels horizontally instead of vertically, so it would be more easier to incline
them, like 10" away from the wall, looking a little bit like the shutter of a window.

The inclination for a 10" base and 39" high triangle would be about 15 degrees.

I could then have 8 panels on each of the east and west side of the stairways cabin,
and may be 8 flat panels on top of the stairways cabin, or a total of 24 panels.

For the elevator cabin, I could have then install 2 panels on the east, south, and west
with the same inclination of 15 degree and 2 panels on the roof. or a total of 8 panels.

So the total would be 32 panels, with
- 10 panels flat,
- 10 panels east and west with an inclination of 15 degrees,
- 2 panels on the south with an inclination of 15 degrees.
 
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