Newbie in MI

[RadiantNewbie]

Hi all, looking for information for a ground mount.
I can't see any pics until I post.

[Jason]

Hi all, looking for information for a ground mount.
I can't see any pics until I post.

Hi Radiant Newbie,

Welcome to solar panel talk, perhaps try giving a bit more info on what your looking to do, who, what , why, when, where, all that type of stuff, cheers.

[RadiantNewbie]

Hi Radiant Newbie,

Welcome to solar panel talk, perhaps try giving a bit more info on what your looking to do, who, what , why, when, where, all that type of stuff, cheers.

Thanks Jason, I'm thinking about installing a ~6.8kW ground mount system. I'll be doing the work myself, I pretty much have all of the equipment I need. We're located in Southeast Michigan, we have a nice southern slope with a shade factor of 0.97. My inspector and neighbors are all on board, I won't bug the POCO until the wife approves the funds. According to the data from a PVWatts sweep, the best angle for maximum yearly output is around 31 degrees. I'd love to start this Spring

So far my target system is 22 of either Canadian Solar or Renesola 310W panels. The odd number pretty much forces me into portrait. We'll break the array into two strings to feed the dual MPPT of an SB6000TL-22. Unfortunately, the array would be located about 450 feet from the inverter, so my 4 DC runs are going to have to be fat. I'm trying to beat down the cost, but not do it cheap, if you know what I mean.

I'd like to do a steel pipe mount, but so far I couldn't find anything that would support portrait orientation, so I've circled back to the familiar wood structure. I see most wood ground mounts use large beams supporting several foot mounted PV rails and top clamps, much like timber framing. Due to our snow load, the PV rails I've seen really can't span more than ~6 feet, and this spacing dictates the number of posts over my +36 foot span.

My thoughts are to use more of a conventionally framed structure. We'd still use 4x6 posts, notch the posts to accept spanwise 2x beams, with rafters on top, and install 2x purlins on top of the rafters to accept the panel mount. This allows the structure to carry the span and not the rails. This should certainly pass structural inspection, and I've built a few steel roof barns this way. The charts show 2x6 @ 18" OC will support my loads. I've been thinking about spacing the rafters at each of the panel breaks. This would probably upsize the rafters, and make the purlins span quite a long distance. I haven't worked through the math yet, but it could reduce the cost & complexity slightly.

Using wood purlins means that I don't need the rails for span. My thought was to screw short sections (6" or so) of rail to the purlins at each panel break, and still use top clamps. This takes my rail needs from 148 feet down to about 16', and eliminates the L-feet too. The only rail section I found that could be modified for a flat bottom mount is Mounting Systems Alpha Rail. But I can't find a local supplier, and shipping one rail is cost prohibitive. I started looking for a better solution when I realized that top mounts are a must for roof, but optional for ground mounts. Maybe bottom bolting using the factory mounting holes is the way to go?

I'm okay with fabricating mounts, but I wanted to steer clear of bending as it's not very repeatable with the equipment I have access to. I looked for Hat channel, but couldn't find anything local in a usable size. I found 'Z' channel that might work, but it means making 88 brackets. My latest thought was to use short (~6") sections of aluminum 'C' channel, 2" tall x 1" wide, with 0.130 wall. I'd drill a pair of holes all the way through the top and bottom flanges, the bottom holes to screw the channel to the purlins, the top holes to mount the panels and to allow driver access to the bottom screws.

So far the channel idea is the easiest to fabricate, length isn't critical, and all holes can be drilled in one setup on the mill Of course we'd have to use stainless fasteners, and Vycor under the channel for isolation from the PT chemicals. The individual channel alignment along the purlins might be a pain, but a spacing jig could be easily fabricated. I'd probably use lay-in lugs for bonding, unless I can find 1/4" cup washers like the panel datasheet shows?

I'm still early in the process, so I'm pretty open to change as needed.

Thanks,
Paul

[Jason]

Howdy Paul,

Thanks for that info. My solar experience has been in Australia and our rules and regs are a bit different to yours. We have done several ground mount systems but never using wood, we spent a bit of time researching off the shelf ground mount systems and found that grace solar in china do several ground mount kits and they are quite cheap and they work great. So I wont be much help to you on customized home made system.

One thing I do know re where is the inverter in relation to the panels, you are far better off pushing ac rather than dc power regarding voltage drop, so I think you need to look at mounting the inverters closer to the panels, we have built little shelters for them next to the panels in the past and that seems to work well.

There are some very knowledgeable people on this forum and there is a fair chance someone will be able to give you some good pointers, cheers and good luck

P.S Whoops sorry its solar pete here I accidently logged in as jason again, sorry.

[russ]

Wood and especially wood exposed to the weather is not a stable platform to place the panels on - it will distort and warp over time. A panel fixed to that is a problem.

[DanS26]

Howdy Paul,

Thanks for that info. My solar experience has been in Australia and our rules and regs are a bit different to yours. We have done several ground mount systems but never using wood, we spent a bit of time researching off the shelf ground mount systems and found that grace solar in china do several ground mount kits and they are quite cheap and they work great. So I wont be much help to you on customized home made system.

One thing I do know re where is the inverter in relation to the panels, you are far better off pushing ac rather than dc power regarding voltage drop, so I think you need to look at mounting the inverters closer to the panels, we have built little shelters for them next to the panels in the past and that seems to work well.

There are some very knowledgeable people on this forum and there is a fair chance someone will be able to give you some good pointers, cheers and good luck

P.S Whoops sorry its solar pete here I accidently logged in as jason again, sorry.

There is a lot less voltage drop pushing 500 volts DC than 240 volts AC. Micro inverters have a much harder time when the array is a long distance from the main service. One less wire also to run that long distance.

[Troyleere]

ground mount

Hi all, looking for information for a ground mount.
I can't see any pics until I post.

I know it weird. I keep trying to get into this. myself