Finally, the start of my 25kw Ground Mount grid-tie system

Hedges

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Doubt it's worth a grand. What do the insolation calculator and your math say?

Also, I've read that closer to flat is better on overcast days, when clouds are the source of light.
 

live4soccer7

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@Hedges

The frontside calculation is about a wash between the two angles (35* and 45*). I honestly have no idea how to calculate the backside production.

I do know that 45* would produce more on the backside, how much I have no idea. I don't even know how much they will contribute now. There are so many variables I think that it is hard to say. If you know of a way to roughly calculate this then please do let me know.

I was basically going off of 45* would maybe be better for snow to fall off the panels and produce more on the backside and provide a more even monthly average throughout the year. Overall production on the front side over 12 months is nearly identical between the two angles.

It would probably end up costing more than $1k because they may have to put the augurs closer together and thus generating more parts. You're probably right, it's probably not worth it and I should just stick with the 35*.

Anyone here have snow? If so, what's your angle and how well does it slide off?

edit: The entire system will be south facing. I decided to just go with the single orientation.
 

live4soccer7

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I'm in the middle of building up a ground mount system similar to MarkSolar's. It's a Sunmodo rack with Adani bifacial panels, all purchased from my local CED Greentech in Burlington Vermont. Originally I was going to go the cement route, but I am very happy with the ground screws. A crew came in with a big Bobcat and put in the 16 screws in a couple of hours. Using the calculator on the Sunmobo website suggested a bunch of concrete would be needed. I would still be digging.

The screws were put in accurately enough that only minimal screwing around was needed to get everything lined up. Here is a picture of our work in progress. This represents 2 and 1/2 days of work by myself and my very understanding wife.
View attachment 60948

We had to leave on a trip but will be back new week and we hope to finish it up. Still working on the design for the connection to the house. - Mark
@SteinVT Did you have someone come in and test the vertical and lateral reactions of your ground screws?

I found this in sundmodo's / vector engineering's documents

The ground screws and helical piers must be tested to 1.5 times uplift and 2.0 times lateral reactions found in the table below. A minimum of one ground screw or helical pier must be tested.

Load (ASD) Value (lbs) Factor of Safety Test Value (lbs)
UPLIFT 2430 1.5 3650
LATERAL 1710 2 3420
 

Hedges

I See Electromagnetic Fields!
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DIY!
Consult Archimedes, or set up a tripod and use block & tackle.
 

live4soccer7

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The county/city also wants the design stamped by a WA licensed engineer. Ridiculous. If vector can do this for me then I'll just go with them and have them design the 45* and stamp it with a qualified/licensed WA engr.
 

Hedges

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A block and tackle and a known weight would be pretty accurate. Maybe inspector would accept it. If he even demands test results.
That word problem was on the test I took for a county job.

The design itself, yes, stamped engineering calculations likely required, for a structure that requires permitting.
My arrays were each small enough to avoid that.
Standard house designs do not require engineering (in my location), but creative structures e.g. cantilevers do.
 

live4soccer7

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I suppose I'll cross the testing bridge when I get there. I think the WA licensed engineered stamped drawing will be unavoidable though. The sunmodo drawings are engineer stamped, but from NH.
 

Hedges

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I forget which are how good. Somebody mentioned sites that include average weather.
Here are a couple I saved links to. Could be more in forum resources.




 

live4soccer7

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Thanks all! Vector Engr. said they would do a site specific plan (WA Stamped) for $300. I asked if that came with the $1k design plan for 45*. If so, then I'll probably consider doing the 45*.

Any additional opinions on going with 45* over 35* at my LAT (47) and using bifacial panels?
 

Hedges

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I've read that exposure of a white background to light helps bifacial production.
I think angle would only be part of that story. Height and space between panels could be another.
When sun is off-angle, the backdrop could serve as a reflector.
 

live4soccer7

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Yeah, money permitting, I will put down a gravel base where the panels are installed in the field to help keep it clean and it would help with light reflection as well
 

Brightside

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Oct 23, 2021
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Yeah, money permitting, I will put down a gravel base where the panels are installed in the field to help keep it clean and it would help with light reflection as well
I'm in a similar situation as you are. I'm at around 46 degrees latitude and have 72- Bifacial panels that I'm going to install. I currently have a 7.8kW monofacial array at 30 degrees tilt facing south that has been working great for 8 years. The panels are on a Sunmodo rack 4 up landscape orientation, the posts are in the ground with cement not the screws. I want to do the bifacial array at 45 degree tilt with a SE and SW facing orientation. I want to do the panels in portrait vs landscape because the snow hangs up on the transitions between panels, so with a 45 degree and portrait and backside bifacial power input to warm the panel, the snow should shed much easier, as there is only one frame transition for the snow to slide over.
I'm also trying to figure out racking to go with, as bifacial specific is much more expensive as it has to be custom engineered for your specific location. I like the Sunmodo that I have, it is strong and sturdy, but they don't support 45 degrees and 95PSF snow load in their calculator.
I also want 45 degrees because with the SE/SW orientation, snow sheding, and bifacial gain to consider, it really makes 45 degrees seem like the logical thing to do. But wind loading of 110MPH also requires more support at 45 degrees.
I have found that the pvwatts for my location gives me very close #'s(+/- a few percent) to my actual production from my system for the last 8 years, so that what I'm using for playing around with orientation and tilt.
I like the idea of using ground screws, as digging holes and bringing in concrete would be nice to skip this time around.
I was thinking about using a white vinyl tarp, ground stapled, for ground cover to increase bifacial gain if needed, as billboard tarps has bulk material that holds up well to the elements.
 

live4soccer7

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@Brightside

How are you calculating your gains from the back side of the bifacial panels?

Check the pricing/materials difference between portrait and landscape. It is quite a bit of a difference because you need more rails. I'm going to use the Hyundai panels and they have a frame just as a normal panel would, so mounting them won't be any different or difficult from what I see.

What's your annual average snowfall? I'm around 40", but it rarely stays long. I'm thinking between the wind and warming of the panels that the panels will very rare need cleaned or be covered in snow for any kind of duration (more than a day). It's kind of like the driveway. Once a small part of it is exposed to the sun it almost always melts. Granted, I do clear the driveway. It is also flat too.

Edit: looking at the ground screw count on unirac's site between a 35 and 45* angle increases the amount by just less than 10%. I'd think you could figure a 10% cost increase in materials overall as a rough estimate for the framework aspect.

I think the tarp idea sounds good, but if you have animals (deer, moose, coyotes, marmots) then it'll probably end up getting ripped up within a few years.

Is PVwatts accurate for you on a month to month basis or are you just looking at yearly production? I would be curious since we are on a similar latitude.

I'm almost inclined to go with 35* as a better option after thinking about it more because I get a little tree shading in the late afternoon in the winter that I do not see in the spring and summer season. I would lose some of the benefit of the 45* tilt there anyways since it would get less possible sun. It is more cloudy in the winter, traditionally, so perhaps I would benefit slightly from the 35* tilt combined with the small shade issue. There is no engineering cost. There is no additional material cost from what I've already calculated. From reading, to have snow actually "self shed" the tilt would have to be quite a bit more than 45*. I'm more banking on it simply melting. If it is looking like the weather pattern would keep the snow on it for an extended time then I might consider cleaning it off if I had the time. By rough estimates, I think it would cost about $2k to move from the 35* to the 45* for my system (engr and materials). Would I generate $2000 more in electricity from that change over 30+ years. I don't know, maybe and maybe not.
 
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Brightside

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I'm not calculating backiside gains, as I figure I'll get something, just don't know what until I do it. I have the Znshine 450W panels and they rate them up to 25% additional from the back. So, I'm just comparing to what I have now which is standard mono panels at 30 degree tilt.

We have a similar situation to you being in south central WA, in that we get snow and then it may melt before the next snow. But we normally freeze overnight, and if you don't clean the panels off and the weather stays cold, you can't clean the panels because they ice up.
We normally get a 2-6' of snow over the winter. Sometimes it melts other times it just keeps piling up, or freeze thaw with freezing rain, so I like to keep the panels clean, because like you say, one they are cleaned off they can stay clean easier than if they have snow on them from overnight.

I haven't compared the pricing to much between the landscape and portrait, as I'm still trying to figure out what racking to use. I'm more interested in the the 6 months around winter gains than summer, as I'm going to have too much power in the summer no matter what angle or orientation the panels are at. That's why I want to do 45 degrees, as also with SE and SW facing arrays the sun is lower on the horizon, so it makes sense to me to angle them up more to take advantage of the lower angle of the sun in those directions. But maybe it doesn't matter and is just splitting hairs, because it tends to be overcast more then anyway. I also am planning on SE/SW as Hedges suggests, for multiple reasons- I can't parallel 2 strings in the same orientation or I'll go over Isc rating of the inverter, wan't to minimize clipping, want power production spread out over the whole day as I don't have any loads for the peak production and to reduce power that needs to be stored.

I'm not sure about increasing albedo, as I figure I can play with that once the arrays are in, but I want to start off with them installed right to maximize potential gains. I'm planning 3-3.5' off the ground for the front edge, for both light and snow shedding, as my current panels are in the same range and I've had to dig out snow from in front of them when we've had lots of snow.

Pvwatts is accurate on a month by month production basis. I was amazed how close the #'s were to my actual production #'s. I'm most concerned with the winter months, as that's what I'm designing for.

The snow on my 30 degree panels will self shed if above freezing and sunny, but it takes awhile and cuts production substantially with the snow bunching up at the bottom of each panel, just depends on the conditions. And if you happen to go into a cold snap with it bunched up like that, you won't be able to remove the frozen snow/block until it warms up again.

Is it worth it for 45 vs 35 degrees, I don't know either. That's one of the things I'm stuck on at this point. I guess if I'm not getting bifacial specific racking then I'm already making comprimises. Iron Ridge has 45 degrees and the windloads required but not the snowloads required, but I figure the snowload is not as important as I keep the panels clean anyway.
 

live4soccer7

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I'm not calculating backiside gains, as I figure I'll get something, just don't know what until I do it. I have the Znshine 450W panels and they rate them up to 25% additional from the back. So, I'm just comparing to what I have now which is standard mono panels at 30 degree tilt.

We have a similar situation to you being in south central WA, in that we get snow and then it may melt before the next snow. But we normally freeze overnight, and if you don't clean the panels off and the weather stays cold, you can't clean the panels because they ice up.
We normally get a 2-6' of snow over the winter. Sometimes it melts other times it just keeps piling up, or freeze thaw with freezing rain, so I like to keep the panels clean, because like you say, one they are cleaned off they can stay clean easier than if they have snow on them from overnight.

I haven't compared the pricing to much between the landscape and portrait, as I'm still trying to figure out what racking to use. I'm more interested in the the 6 months around winter gains than summer, as I'm going to have too much power in the summer no matter what angle or orientation the panels are at. That's why I want to do 45 degrees, as also with SE and SW facing arrays the sun is lower on the horizon, so it makes sense to me to angle them up more to take advantage of the lower angle of the sun in those directions. But maybe it doesn't matter and is just splitting hairs, because it tends to be overcast more then anyway. I also am planning on SE/SW as Hedges suggests, for multiple reasons- I can't parallel 2 strings in the same orientation or I'll go over Isc rating of the inverter, wan't to minimize clipping, want power production spread out over the whole day as I don't have any loads for the peak production and to reduce power that needs to be stored.

I'm not sure about increasing albedo, as I figure I can play with that once the arrays are in, but I want to start off with them installed right to maximize potential gains. I'm planning 3-3.5' off the ground for the front edge, for both light and snow shedding, as my current panels are in the same range and I've had to dig out snow from in front of them when we've had lots of snow.

Pvwatts is accurate on a month by month production basis. I was amazed how close the #'s were to my actual production #'s. I'm most concerned with the winter months, as that's what I'm designing for.

The snow on my 30 degree panels will self shed if above freezing and sunny, but it takes awhile and cuts production substantially with the snow bunching up at the bottom of each panel, just depends on the conditions. And if you happen to go into a cold snap with it bunched up like that, you won't be able to remove the frozen snow/block until it warms up again.

Is it worth it for 45 vs 35 degrees, I don't know either. That's one of the things I'm stuck on at this point. I guess if I'm not getting bifacial specific racking then I'm already making comprimises. Iron Ridge has 45 degrees and the windloads required but not the snowloads required, but I figure the snowload is not as important as I keep the panels clean anyway.

One of the things I read was that the power generated from the backside will help warm the panels as well. This can help with the snow/ice situation. How much, I have not a clue. I wanted to go with the portrait setup, but the cost was a lot more on both the sunmodo and the unirac. The unirac system is way more expensive because you have to source your own pipe and pipe is VERY expensive right now. Sunmodo was an easy decision once seeing this.

I'm planning for 3' front edge as well. I think that is the highest configurable in the plan generators.

Obviously, take this with a grain of salt. Albedo numbers. It at least gives you an idea of different materials.
Item Values
Grass 0.15 – 0.26
Black earth 0.08 – 0.13
White sand, New Mexico 0.60
Snow 0.55 – 0.98
Asphalt pavement 0.09 – 0.18
Concrete pavement 0.20 – 0.40

If I could find this decently prices around here then I think this would maybe be some of the better rock or gravel you could use. If not, then I'll probably just go with 5/8" minus which is a grayish, probably providing albedo .1-.15 (similar to asphalt, but maybe a little better)
1635026312597.png
 
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