Ground-mount 9Kw solar install beginning today

[Scotty2]

You mentioned ... * 2X SMA SunnyBoy (SB 5.0-US) 5000W Inverters.
We have 5 of these in our 30kW system.
Ran 3 Inverters to one AC combiner panel, 2 to another. The reasoning was we'd never be able to afford the battery storage for 30kW production.
Our plan is for 2 Inverters to charge the (future) batteries... and the remaining 3 Inverters doing a redirect to something like a Talapia pond (warm water)...and powering the water pump to fill some large water tanks at the highest spot on the property.
An interesting note on the Sunny Boy Inverters. They have a 2kW internal Storage capacity (I think I have that right)...I've been told you can set them up to run the small pumps on your boiler/radiant system when the power is out and the so is the Sun.

 

[peakbagger]

Are you able to post the link to that thread? Id love to read through it.

https://www.hearth.com/talk/threads/any-mature-solution-for-solar-air-conditioning.155877/

 

[peakbagger]

You mentioned ... * 2X SMA SunnyBoy (SB 5.0-US) 5000W Inverters.
We have 5 of these in our 30kW system.
An interesting note on the Sunny Boy Inverters. They have a 2kW internal Storage capacity (I think I have that right)...I've been told you can set them up to run the small pumps on your boiler/radiant system when the power is out and the so is the Sun.

Technically the SPS doesn't store power, what it does is puts out a limited amount of 120 VAC to a separately switched circuit as long as sun is shining. Its not backup power as its dependent on sunlight but could be used along with UPS and some switching circuitry for some backup power.

Its more of a marketing ploy than a substitute for good generator but a neat feature nevertheless. Each circuit is rated at 1500 watts irrespective of the rating of the inverter.

 

[woodgeek]

The output math is more complicated than the number of hours of daylight per day due to the output going like cos(theta) where theta is the angle the sun makes with the panel perpendicular (and which defines the bell curve of Jim's output plot). It only makes rated output when theta = 0. If the panel were rotating in empty space once per 24 hours it would yield just 6 hours times the nominal output per day, or a capacity factor of 0.25. On a cloudless point on the earth, adjusting the tilt periodically, such a 0.25 CF would be 2200 hours * nominal power per year, 1 Watt of panel would make 2.2 kWh per year. In practice, different locations in NA with a fixed panel have between 1000-2000 hours of solar resource per year, you can google solar resource maps for your location.

 

[mol1jb]

Does anyone know the price difference in stall cost for ground vs roof mount in general? Im sure it depends on length of wire being run. I could do either at my house however the best ground mount spot on my lot is about 100ft from the house. In terms of adjustment, cleaning, snow removal, and maintenance the ground mount seems much easier to access

 

[jebatty]

It only makes rated output when theta = 0.

How I wish. Throw into the mix ambient temperature, humidity, dust, haze, clouds and other atmospheric disturbances, panel soiling, electrical resistance between the panels and the panels to the measuring device, etc., and achieving rated output is a day to celebrate. Not perfect memory, but I think my 12.3kw system achieved rated output for a fairly short period (around solar noon) once, and the original 6.9kw system achieved, and even briefly exceeded rated output, only a small handful of times.

A few interesting websites:
insert your own address: http://suncalc.net/#/41.8781,-87.6298,10/2013.12.29/20:12
insert nearest location: http://solarelectricityhandbook.com/solar-irradiance.html
insert your own address: http://www.solartopo.com/solar-orbit.htm
insert location: http://pvwatts.nrel.gov/pvwatts.php

 

[jebatty]

the best ground mount spot on my lot is about 100ft from the house. In terms of adjustment, cleaning, snow removal, and maintenance the ground mount seems much easier to access

My ground mount is 220 ft from the house. I have about a 1% loss of energy between the panels recorded total watts output and the watts measured at the house on a separate production meter.

If you go underground, install the cable which can carry the maximum amperage you can backfeed to your panel, in the event the system you install is not the largest the code permits. That will allow future added panels, if you desire, without the need to add to or re-do the underground. Also consider adding an ethernet cable. Some systems can use that to provide lots of data to your computer. My system communicates either by wi-fi or ethernet, but at 220 ft the system is beyond reliable wi-fi range.

 

[peakbagger]

Does anyone know the price difference installed cost for ground vs roof mount in general? Im sure it depends on length of wire being run. I could do either at my house however the best ground mount spot on my lot is about 100ft from the house. In terms of adjustment, cleaning, snow removal, and maintenance the ground mount seems much easier to access

Hard to do a rule of thumb as soil conditions can really screw up the cost. The solutions will vary with the soil type and owners preference. Some folks build frames out of pressure treated and then use commercial roof racking to tie the panels in. Others go with fully pre-engineered rack systems. Usually the actual foundations are designed and built for the local site. Most large solar installs I have seen in Mass are auger type feet.

One thing to consider with ground mount is access. Even though the code allows the use of mesh type screening system to be installed on the back of the panels to prevent untrained people from accessing the wiring, many inspectors seem to require a fencing to be installed around the panels to prevent access. Shading has to be taken in effect with a fence to ensure that the fence does not cast a shadow on the panels in the winter.

The other thing to consider is ground mounts can be exposed to more abuse and potential theft. I believe the OP is using theft resistant hardware. Law mowers can throw rocks as ground mounts a lot easier than a roof mount and kids with baseballs also are more likely able to tag a ground mount. Both

The general rule of thumb I have seen to be taken with grain of salt is 25 to 30% added for ground mount plus trenching. Of course the fed will pay 30% of the costs to install, so the actual increase is tempered a bit. I have heard of a few folks that used the solar install to deal with other long term issues like running power to a remote location by using the trenching I expect that's between them and their accountant on what they take for the solar credit.

Most solar contractors can give tighter bid for a roof mount as that's their bread and butter. Ground mounts will have more contingency due to the unknowns like the OP just ran into.

 

[mol1jb]

Hard to do a rule of thumb as soil conditions can really screw up the cost. The solutions will vary with the soil type and owners preference. Some folks build frames out of pressure treated and then use commercial roof racking to tie the panels in. Others go with fully pre-engineered rack systems. Usually the actual foundations are designed and built for the local site. Most large solar installs I have seen in Mass are auger type feet.

One thing to consider with ground mount is access. Even though the code allows the use of mesh type screening system to be installed on the back of the panels to prevent untrained people from accessing the wiring, many inspectors seem to require a fencing to be installed around the panels to prevent access. Shading has to be taken in effect with a fence to ensure that the fence does not cast a shadow on the panels in the winter.

The other thing to consider is ground mounts can be exposed to more abuse and potential theft. I believe the OP is using theft resistant hardware. Law mowers can throw rocks as ground mounts a lot easier than a roof mount and kids with baseballs also are more likely able to tag a ground mount. Both

The general rule of thumb I have seen to be taken with grain of salt is 25 to 30% added for ground mount plus trenching. Of course the fed will pay 30% of the costs to install, so the actual increase is tempered a bit. I have heard of a few folks that used the solar install to deal with other long term issues like running power to a remote location by using the trenching I expect that's between them and their accountant on what they take for the solar credit.

Most solar contractors can give tighter bid for a roof mount as that's their bread and butter. Ground mounts will have more contingency due to the unknowns like the OP just ran into.

Thanks for all the info. I read for a roof install that one needs to check on weight limits of the roof. How common is it that a roof is unable to support a an average sized PV system?

 

[peakbagger]

Depends on the local inspector, its pretty rare that its an issue other then having to write a check to PE to stamp a report.

 

[jebatty]

OK, need to admit again, I am a solar PV addict. I have ground mount, and I can't stand snow or ice on my panels. I need to get snow off the panels as soon as possible. If I had roof mount, I might have avoided the addiction because I would have gotten used to seeing many days of no or little winter production due to snow covered panels. But with ground mount, I need to get it off, and a soft floor broom pulls of the snow and clears the panels easily. Takes about 15 minutes.

The difference between sunny day production with snow vs no snow in the heart of December is about 30kWh, valued at $3.50. For 15 minutes of effort, that's $14/hr of tax free electricity plus the value of fresh air and some exercise. Can't resist.

 

[peakbagger]

My roof array is currently covered with 6" of frozen snow. Its going to take several days of sunny above freezing weather before I get any production from that array. To clean that one off requires a 30 foot extension ladder and snow rake. Luckily the OP is in South Carolina so I expect he doesn't have to worry about it.

 

[7acres]

Correct! I don't have to worry much about snow.

But we hit a bit of a glitch yesterday. We hit solid granite bedrock about 2' down. Apparently the Schletter system's structural needs require each pylon to be set in concrete 6' underground. The auger hit bedrock on all 6 holes. I know I have a lot of granite out here. But I put in an orchard with an auger 6 years ago and found the granite to be soft. Didn't have any issue with the Bobcat and 22" auger we used for that in the same surrounding area as the panels are slated to be installed in. But I can't argue. Here's one of the holes...



I saw the guys trying. They were manhandling that auger to get it to grab and break the granite. It only polished it up nice and flat!

 

[7acres]

The installer is looking into switching the racking system to a FlexRack product. From the short phone call I was just on it uses a ballast system that doesn't require 6' holes. I don't know much else at the moment. What do you guys think about FlexRack?

 

[peakbagger]

Bummer! I am not familiar with the particular product but ballasted systems are used extensively on large roof top arrays. If the system is designed to your location conditions which are probably high winds it should be fine.

As a DIYer I would probably just make up some struts with plates on the bottom and then drill anchors into the rock if it was not fractured. Bolted into rock is about the best anchor system bar none.

 

[Scotty2]

My ground mount is 220 ft from the house. I have about a 1% loss of energy between the panels recorded total watts output and the watts measured at the house on a separate production meter.

If you go underground, install the cable which can carry the maximum amperage you can backfeed to your panel, in the event the system you install is not the largest the code permits. That will allow future added panels, if you desire, without the need to add to or re-do the underground. Also consider adding an ethernet cable. Some systems can use that to provide lots of data to your computer. My system communicates either by wi-fi or ethernet, but at 220 ft the system is beyond reliable wi-fi range.

Our ground mount is 450' from the Inverters and Panels. We did oversize the pipe...it was still a tough pull. We used a Simpson Capstan Rope Winch from Log Home Store (broken link removed to https://www.loghomestore.com/c142-portable-winches.php)
With all the effort to trench and bury we should have dropped a spare pipe (or 2) in the trench...e.g. future 110 power, phone, array add-on, you never know.

 

[Scotty2]

Correct! I don't have to worry much about snow.

But we hit a bit of a glitch yesterday. We hit solid granite bedrock about 2' down. Apparently the Schletter system's structural needs require each pylon to be set in concrete 6' underground. The auger hit bedrock on all 6 holes. I know I have a lot of granite out here. But I put in an orchard with an auger 6 years ago and found the granite to be soft. Didn't have any issue with the Bobcat and 22" auger we used for that in the same surrounding area as the panels are slated to be installed in. But I can't argue. Here's one of the holes...

View attachment 190887

I saw the guys trying. They were manhandling that auger to get it to grab and break the granite. It only polished it up nice and flat!

Was this a hand held auger? or a Tractor/Bobcat mount?

 

[7acres]

Was this a hand held auger? or a Tractor/Bobcat mount?

Mounted to a Bobcat T190.

 

[NateB]

Bummer! I am not familiar with the particular product but ballasted systems are used extensively on large roof top arrays. If the system is designed to your location conditions which are probably high winds it should be fine.

As a DIYer I would probably just make up some struts with plates on the bottom and then drill anchors into the rock if it was not fractured. Bolted into rock is about the best anchor system bar none.

I vote for anchors in the rock, and pour the concrete.

 

[7acres]

They called back to say FlexRack has no inventory till Jan 20th. So they're going to try to make something work with the Schletter rack. They are in discussions with their structural engineer on the best way to mitigate this to make it work and up to code.

In looking at FlexRack's website I got the impression that Schletter makes a slightly higher quality product. That may not be true at all. But I'm happy to be sticking with Schletter.

 

[semipro]

I vote for anchors in the rock, and poor the concrete.

A serious consideration.
At more than 150 lb/cubic foot it won't take much granite to create the required ballast. The rock could be drilled to determine its thickness, or at least that you have the minimum to provide the required weight. Then anchors could be installed in the holes with epoxy. You'd may end up with a better foundation than was originally planned.

 

[Karl Hungus]

We are putting a 9,900 watt system on a new home build. The panels are roof mount on a workshop that's about 80 ft from the rest of the stuff is in the basement of the house.

The original plan was to run behind the grid. But at the last minute our power co. made a edict, no more behind the grid. So now I have to sell back to the power co. Because we have batteries we are in control of our power we generate. Otherwise without the batteries we'd be selling all our power back to the grid. If the power went out we'd be without power even tho we have the ability to generate power. We didn't like this. Our goal will be to be able to live without the power co. If its close we might just buy a few more batteries and pull the plug.

Our system has 30 panels, 2 inverters, 8 6v batteries that store 38kwhs, automated hydration, 2 charge controllers all tired together with a communications hub for remote viewing and parameter adjustment. Total price installed is approx 40K.
After rebates/tax credits we are paying approx 26K.

House is all electric, very energy efficient. Approx 2800 sq ft living space. Energy audit est 20Kbtu/hr to heat the place. For heat we have a air source heat pump with a 5kw backup electric res. heat coil. But we also have a 2 story masonry heater that we plan on using to heat the place, the heat pump is for backup. Hot water is also a air source heat pump.

Solar system is partially installed, the panels will be going on in the beginning of the new year.
Hopefully will be up and running in Jan.

 

[peakbagger]

A serious consideration.
At more than 150 lb/cubic foot it won't take much granite to create the required ballast. The rock could be drilled to determine its thickness, or at least that you have the minimum to provide the required weight. Then anchors could be installed in the holes with epoxy. You'd may end up with a better foundation than was originally planned.

My assumption was similar, given that apparently sound granite was found at similar depth at all holes I assume it is a solid piece of ledge. In my mechanical construction career in NH we encountered granite frequently and on occasion it was far shallower than expected. We generally did preliminary boring before excavation that would give us an opinion on the quality of rock we would probably hit. If it was solid we would end up drilling into the granite and inserting rebar with epoxy adhesive into the hole then forming up our footings and tying the anchor bolts into the rebar with appropriate overlap. I did this with multistory pipe racks that were subject to lateral (side to side) loading.

Given that the solar panel racking is most likely subject to wind uplift as the primary loading I think the easiest approach would be to cut the supplied struts and weld on baseplates or install bolted on angles to the struts and then bolt them to the granite by drilling in a reasonable embedment length and using a suitable epoxy anchor. The limitation with this approach is that the lateral support on bolted on struts is not great as it potentially acts as a pin connection. If a base plate can be added to the strut and several bolts can be installed, the lateral support is definitely increased to closer to a moment connection with far stiffer lateral support.

The devil is in the details, if its thin wall strut (similar to unistrut) it would need to be an engineered baseplate as I would not trust just a weld at the base. I don't have a structural stamp or a license in SC so it comes down to what is acceptable to the manufacturer of the racking system so that they retain liability for the overall racking design. This is a common occurrence and I expect they offer some off the shelf solution but there will most likely be a cost purchase different legs. On the auger style systems I have driven by, the contractors appear to put in the posts and rough them to a set height using a rotating laser as a reference. If one gets too high they can cut them off but the racking system has adjustments for some vertical misalignment.

 

[7acres]

Update: The work resumes tomorrow (Tuesday). The footers are all prepped with a rectangular hole for each post with, rebar and some welding. The next step is pouring the concrete. They were hoping the concrete company could fit them in Friday but I guess everyone else in the area was hoping the same thing. After the concrete goes in it will set up for 48 hours. So I guess we will only have two working days this week. Progress seems slower than I expected. But I've never been around a solar project to know. Plus we hit a brick wall (err... granite wall) and that is nobody's fault. Anyway after this concrete is in I'm hoping the rest is all downhill from there.

 

[peakbagger]

I would expect that this foundation phase is the slow spot in the project as its every foundation can be different. I expect once you get into standardized PV construction the contractor will speed up considerably