Solar panels at 90 degree angles

[iwasforcedtopickausername]

Up here, the ideal winter panel angle is about 70 degrees. 90 is not that far from it. I could have fairly consistent solar output year round with 90 degree (wall-mounted) panels. It seems like it'd keep the snow off them for sure. It's supposed to be about 70% of what an ideal angle would be for yearly production, but mounting would be so, so much cheaper and easier.

Is it worth it? Have any of you done it? I figure I can always remove from the exterior walls and do a ground mount if I need to.

(Roof mount is not a good option here. My pitch is not nearly appropriate and there's too much snow to get off the panels.)

 

[SparkyJJO]

Could make up for it by having a few more panels if you have the wall space.

 

[daviddakers]

I have mine on my most southerly facing wall… but at about 30 degrees from vertical mainly to prioritize the winter sun. I did make it so they're adjustable if I want but never have… Mostly the snow falls off but not always. Usually just have to tap them with a long pole to avalanche them though. Seen a lot of houses with roof panels covered in snow for days and I wouldn’t like to be up there clearing that so works well for me.

 

[peakbagger]

Keep in mind, PV Watts does not factor in snow reflectance. If there is snow on ground, a vertical panel is going to put out more power than the PV software will underestimate it. The one big caveat is overhangs on the building. A wall mounted panel is going to potential get shaded from a overhang in summer when the sun angle is high and the sun rises in the Northeast and sets in the NW.

With the right type of snow even a vertical panel can have snow stick to it. I have several large All Earth trackers near me that go vertical during snow storms, on rare occasions I will see them tracking east to west with a layer of snow stuck to them for a few days until the sun finally melts them off.

My 30 degree pole mount definitely can build up snow. Sometimes its just requires a tap but most of the time I need to rake them clean. BTW, make sure you factor in the height about the ground of the bottom edge of the panels and any potential areas where the snow will pile up higher than the normal snow depth. I rebuilt my pole mount at one point to hold large panels, the trade off was that the lower edge was closer to the ground. When snow slides down it builds up a lump of snow in front of the panel. I run my snowblower in front of the panel (being very careful to aim the snow away from the panels) to keep the "lump" from forming. The big commercial arrays in Mass seem to just live with lost production when they get heavy snow, even the ones up north near me seem to live with it in order to save money on the install.

 

[Northernchateau]

Up here, the ideal winter panel angle is about 70 degrees. 90 is not that far from it. I could have fairly consistent solar output year round with 90 degree (wall-mounted) panels. It seems like it'd keep the snow off them for sure. It's supposed to be about 70% of what an ideal angle would be for yearly production, but mounting would be so, so much cheaper and easier.

Is it worth it? Have any of you done it? I figure I can always remove from the exterior walls and do a ground mount if I need to.

(Roof mount is not a good option here. My pitch is not nearly appropriate and there's too much snow to get off the panels.)

You have to pick and choose your battles.
I live in a high snow area so I have them at 70 deg off horizontal right now for ease of cleaning.
Mine are adjustable and I found that I loose approx 8-10% output of I am off 35 degs from perfect. But I will tell you the colder air temps help with output.
That being said a partly snow cover panel produces next to nothing so if you are not going to be able to get the snow off, mount in a way as to reduce the snow sticking to them.

 

[Ptom]

Peakbagger nailed it, reflectance off the snow of a vertical or nearly so array will put out more power, and the lower to the ground the array the better. Which of course means one must keep up with snow removal. My main arrays, all pole mounted, are all a good 4 to 6' high at the lowest point, but my newest 1000 watt array (that will only be used in the winter months, come spring, it will be moved back to its summer location a 1/4 mile away to power a spring water pump) and I purposely set it up about 12" of the ground, about 80 degrees, but it's location is where I hike or ski everyday anyway with the dog, so I'll be able to keep up with the snow removal, I 'll leave a shovel onsite. It may be more trouble then it's worth, I don't need the extra power (grid tied, with a huge surplus year round) but I'm an efficiency nut.

 

[peakbagger]

My pole mount array is only 2 KW so on a winters day it is not putting out that much power anyhow so if I miss cleaing it off its not a major issue but I am grid tied with great net Metering deal, so no need to run generator if I screw up I have a modified DC Solar Trailer in the front yard with a couple of wood piles in front of it that mess with snow reflection and the combination of the shallow angle and the lack of snow reflection means a lower output in winter. That one also needs to be raked every storm. The 4 wall mounted panels in the background are adjustable angle, in the winter they are set at 30 degrees. They tend to melt off pretty quickly after a storm as the front of the house heats up in the sun and probably a bit of heat leakage from the building helps.

I have a 2 KW array on the second floor roof with an even shallower angle than the trailer. Raking it is a problem. I can get to the lower edge so what I do is rake off a strip exposed roof at the lower edge and maybe the first 18" inches. If the sun is out and it warms up it may shed the snow on the rest of the array but on occasion it refreezes and the seam between the upper and lower rows of panels and the panel fasteners will grab hold and the snow can be there for weeks until a really warm day. Its on stering inverter so its all or nothing.

 

[Northernchateau]

This a pair of Axitec 290 watt panel on mounted on the face of my garage.
Right now at the perfect angle. (as checked with a soda can)
If snow is in the forecast I can put them vertical in seconds.

 

[iwasforcedtopickausername]

I appreciate all the replies. Some really good info here. Thank you! Very interesting about snow reflections and vertical panels. Also a good point that if it takes me 2 hours to get outside and wipe the panels down, that's 2 hours that I'm not producing any power. A little less power in a vertical configuration may not be a big issue given that alone, at least during the winter.

This a pair of Axitec 290 watt panel on mounted on the face of my garage.
Right now at the perfect angle. (as checked with a soda can)
If snow is in the forecast I can put them vertical in seconds.

That is really neat! Could you give me some more information on that type of mount? Does going from that steep of an angle to vertical help that much with the snow?

 

[Northernchateau]

I appreciate all the replies. Some really good info here. Thank you! Very interesting about snow reflections and vertical panels. Also a good point that if it takes me 2 hours to get outside and wipe the panels down, that's 2 hours that I'm not producing any power. A little less power in a vertical configuration may not be a big issue given that alone, at least during the winter.



That is really neat! Could you give me some more information on that type of mount? Does going from that steep of an angle to vertical help that much with the snow?

I put these up a few weeks ago as a test so I don't know about the snow thing but when we do get snow coverage I will monitor the output and post results.
Now I tried to keep it simple so both panels are fasted to two pieces of Kindorf/Unistrut. I made a wall mount out of 2x6 pressure treated I has and as you can see in the picture below hung the panels off them. They do swing and the bottom right now has one leg in the middle that I can take out of change the length of to change the angle.
Later today when the sun is off them I do need to go disconnect them and zip tie the wires up.

 

[Ketchgould]

This a pair of Axitec 290 watt panel on mounted on the face of my garage.
Right now at the perfect angle. (as checked with a soda can)
If snow is in the forecast I can put them vertical in seconds.
View attachment 119438

How much does the efficiency change if you alter the angle of the panel to the sun or just leave them at one angle?

 

[Llaves]

I'm a little late to this thread but ...

Peakbagger wrote :
Keep in mind, PV Watts does not factor in snow reflectance.

This is not true. Just look at the technical manual linked on the PVWatts website and it explains the calculation and clearly explains that it includes ground reflectance and gives a reference to the formula for the ground component. Even with pristine new snow (albedo = .87), the ground reflection contribution will be dwarfed by the direct solar component on a clear day.

 

[12VoltInstalls]

How much does the efficiency change if you alter the angle of the panel to the sun or just leave them at one angle

I don’t recall the math
At my latitude it’s only ~15degrees difference and maybe 10% some of the time.
Nevertheless last winter I saw over 42A charging from two parallel 400W arrays on hood sun days, both arrays vertically mounted.
This past summer I noted the E-facing array in the middle of the afternoon was contributing almost 150W in spite of sun exposure long having ceased on that side for the day. Still all vertical.

So at higher latitudes the loss is real but not a factor I worry about verses frequently sometimes every day being snow covered which is intolerable to me.

 

[peakbagger]

Our PV watts expert can run it out to the 10th decimal point but years ago I think it was about a 20 to 30% increase for seasonal adjustment. I don't have any production metering other than a total net meterr but usually look at my instantaneous output before and after I swing the panel angle and I can see the difference. As I noted previously it is the snow sticking to all or part of the panel that is the killer for production. I have three approximately 2 KW arrays and it is quite noticeable how the instantaneous production varies with sun angle. Two are effectively ground mount while the last is fixed roof mount so its impacted by higher temps but the two ground mounts should be roughly exposed to the same temps. The adjustable pole mount output is consistently high during winter and fall while the two arrays are roughly equal during the longer days of summer when the angles are similar.

If part of the panel is exposed, the sun will usually melt off the rest but if the entire panel is covered the only hope is a warm enough day that the warm air on the backside breaks the bond between the panel face and the snow.

The big reason for the adjustable pole mount is that it was a lot easier to mount the panels solo. I would flop it facing north and nearly vertical then bolt on a couple of panels then flip it south nearly vertical and install two more, then flip it back. If I had installed the entire row one side it would have been real difficult to flip. Once they were all installed the array is mostly balanced like see saw so moving the angle is something can do solo, just unbolt the support struts, rotate the array to the new angle with one hand and rebolt the support strut to new predrilled hole. Dont underestimate the difference in snow loading between a 30 degree and 60 degree tilt. A 60 degree tilt off vertical is going to build up about as much snow as a flat array while a 30 degree tilt will hold a lot less. The biggest issue is that when the snow slides off to the base of the array is there is large mound of snow that could shade the bottom. I just run my snowblower in front of the array so it does not build up.

Modeling is great stuff but at some point you build the darn thing and get some practical experience and in my experience, seasonal adjustment is worth the effort mostly for snow cover issues. I also rake my arrays I can get to if there is snow build up. My first array is over 20 years old with the adjustable pole mount getting close. Some years I may have 4 plus feet of snow pack on the ground and others, particularly of late, far less.

BTW most large utility arrays are fixed and optimized for production as many utility tariffs treat sales at any point of the year at the same value, thus they optimize for maximum summer production and take the hit on occasion during and after a snow event. One year after a big snow dump in mass I saw a crew desperately trying to clear off a couple of acre array, the snow was piled up over the bottom of the panel to begin with so they had to remove than then rake the snown down. On the first day it was wheelbarrows and lots of shoveling then a day later bobcats and then finally they stopped as they ran out of room to dump the snow. About a week after the storm it warmed up enough to melt but they had issues a couple of other times later in the winter due to the snow build up at the bottom of the panels.

 

[12VoltInstalls]

about a 20 to 30% increase for seasonal adjustment

I believe he was asking about the winter differential between 90* versus 75* which isn’t nothing but is inconsequential if you can’t be there all day to chase snowflakes off the property so they don’t land in the panels.

If one is running solar in winter and has planned for winter solar they are likely to be 200%+ overpaneled so even at 30% gains possible in summer (unless one is selling to grid) vertical panels still meet the need

 

[Northernchateau]

How much does the efficiency change if you alter the angle of the panel to the sun or just leave them at one angle?

I am waiting to run that test. I got an inline meter a few weeks ago and we have not has a clear day since Nov 12th.
Next clear day I will take some data and post results. I will say I do notice way better output when the temp drops.

 

[12VoltInstalls]

How much does the efficiency change if you alter the angle of the panel to the sun or just leave them at one angle?

The USA government offers this which I hate https://pvwatts.nrel.gov/pvwatts.php
While this one shows optimal angles for your panels, there is an Australian calculator (that I can’t find right now to give a link for) that provides both pieces of information.
The USA calculator above dropped me from a theoretical 188kW in January for my location at 20* to 115kW at 0* angle. Or roughly a 1/3 drop in potential harvest.

But I am not convinced that is quite accurate because I’ve achieved the calculated equivalent of that 188kW in bright, full sun on a 0*F January day with vertical panels.
Since most days are not as good as that optimal day AND I’m vertical panels which are supposed to have the 1/3 hit on production the nrel calculator doesn’t compute for me. On one hand I feel I get better results than they list for vertical/0*, on the other their numbers are optimistic for a ‘proper’ panel angle.

 

[AARB]

This calculator is very accuracity: https://re.jrc.ec.europa.eu/pvg_tools/en/

 

[Hardergamer1]

There is a YT channel from Scotland highlands where they have hung panels from the south and westerly facing wall's vertical on their house to stop snow settling, basically they fixed them in place by using hinges on the top edge of each panel, which means they can flare them out from the bottom of the panels a foot or two to help when the sun is higher, also they claimed their output went up when they moved from their ideal winter 75* angle to vertical, with their thinking it was the close by water reflection, as the house is next to a lock. I try and find and link it.

Can you buy heated panels in the US/Canada? Or are they only sold commercially, As meany of the solar farms near me have them, which they run just before the sun rises to remove frost, as we don't really get snow here any more.

 

[12VoltInstalls]

also they claimed their output went up when they moved from their ideal winter 75* angle to vertical

That’s an interesting claim. I’m on the idea of reflection but what makes a panel work is the square area of exposure to the sun (or other reflection light).
While there is a ‘minor’ gain of square area exposure at the “wings” of the sun-hours early and late where there is low-angle direct sun one can’t really account for that as an increase with 180* compass point orientation imho. There’s a lot more atmosphere to pass through at low sun angles and winter sun angles in northern latitudes are already.
In mid-June I get usable wattage within 45 minutes of sunup whereas in winter - while seeing ‘some’ charge- it’s quite a long time (like an hour and a half or more depending on ice crystals high in the atmosphere) before the watts exceed my furnace demand, for example.

they have hung panels from the south and westerly facing

That also defies the math but I’m SE and SW with two strings and I experienced better performance with that arrangement myself. In my estimation/wildhat guess: it’s due to keeping the batteries at full charge closer to sunset while probably sacrificing a likely not insignificant amount of watts in the overlap between the 90* separation.
Having more panel wattage than needed makes that “loss” somewhat irrelevant in my mind since it tailored charging to my situation which is more beneficial than maximizing midday harvest when the batteries are already full at that point- especially with lead acid battery banks.

Just some thoughts to consider.