house roof not pointed due south

[roblin]

We recently purchased a summer home with a steel roof. The slope is 4 in 12.

The house is oriented so that it is impossible to place PV at right angles to the roof slope or in line with the roof edge and still be pointed 180 degrees true south.

I have split the array in two sets of 4 Sharp Nt 175Uc1 in series/parallel. One is already up and pointing about 140 degrees Az/49 Elev) parallel with one roof edge. I was thinking of putting the next set of 4 panels parallel with the other edge (thus facing 230 Az/49Elev. Both these orientation are very inefficient but are better than nothing. Both sets feed into an Outback FM60 (theoretical 70V@20A, then into a 24v battery bank)

I have never seen PV panels oriented diagonally on a roof. Aside from the mounting challenges, and possibly a visually disturbing sight, is there any reason not to locate both arrays so they actually face true south? They will not be level with the horizon, being diagonal on a sloped roof and all, so I'm not sure if there will significant gain, given the monumental task of moving one and installing the other without having the roof joists laid in a simple straight line.

The racks use the Pro-Solar channel system.

Regards

Rob Linschoten

[DamonHD]

In the UK, and possibly elsewhere, you need to work harder (eg need to get planning permission) to mount panels other than parallel to your roof and/or in some other 'unconventional' layout.

The cost of not pointing due south may be less than you imagine, eg see here:

http://www.south-facing.co.uk/ImageBank/Performance-Chart.gif

Rgds

Damon

[roblin]

Damon,

Thank you for the quick reply. This place is waayy off the grid. No codes, no power, no sewers, no municipal water.... nearest town is across 15 km of rough water...

The chart is interesting. I assume it would read the same way for the Canadian

pacific-northwest. Does the elevation reading mean "off from the recommended angle" or is that the absolute elevation reading along the top?

Thanks again

Rob

[RedJoker]

If it's really that far out there, you might consider ground mounting them.  You have complete control then.

[DamonHD]

That's for a typical UK latitude, so could be true for you.

The basic rule of thumb is that the further from due south the lower the pitch/slope should be to maximise year-round collection.

Rgds

Damon

[roblin]

Redjoker,

Good point. Unfortunately, one of the down-sides of such a remote place is that people occasionally come by and steal the panels. I was thinking <hoping> that being bolted to the roof might make that effort less enjoyable.

Regards

Rob

 

[roblin]

Damon

Thanks for the clarification. Makes excellent sense.

Thx

Rob

[DamonHD]

I've had ours glued on to hopefully reduce the fun of someone trying to tamper/lift, though if they've already made it on to my roof I don't want them smashing everything up too trying to rip them off...

Rgds

Damon

[imsmooth]

I have 12kw of panels pointing a little south of east.  I have had no electric bill since.  THe only point is that you need less panels the closer you are to south.  IF I were to go true south I would generate about 1.4x my current production.  It will just cost more money, but doesn't everything?

[roblin]

Wow! Given our setup is only rated to top out at 1.4KW (set up per spec, pointed at 180 degrees true south) I was trying to squeeze out every watt. However, it is very much starting to sound like I should find some other more productive projects to focus on...

Cheers

Rob

[Ungrounded Lightning Rod]

Remember that "codes" are also about insurance company requirements to insure your site against hazards caused by the equipment (especially fire).

Even if there is no local code or (more likely) no local code ENFORCEMENT (licenses, license fees, and inspections), check your insurance requirements.  You'll probably have to build to the "model code" using UL-approved equipment to keep your insurance company happy.

If they're unhappy and your house happens to burn down, even if it wasn't caused by the RE stuff, you might find they'll refuse to pay off (and still keep all those premiums).

And even if you're running uninsured you'll want to build to code just to reduce the likelihood of a fire for your own peace of mind and resale value.  B-)  The rules might be a bit tight occasionally.  But all of them are about avoiding significant hazards and it's not always easy to see what hazard they're avoiding and come up with some non-conforming setup that also avoids them all.  Meanwhile the rules aren't all THAT expensive to follow.

[GaryGary]

Hi,

You can run PVWatts for a true south orientation, and then compare that to your actual orientation -- it will give exactly what you are losing for not being right at the ideal azimuth and elevation.

PVWatts is here:

http://rredc.nrel.gov/solar/calculators/PVWATTS/version1/

For our location an azimuth 180 at 45 degrees tilt gives 1339 KWH output for a 1 KW array for 1 year.  Going to 140 azimuth at 45 degree tilt drops it to 1266 KW per year -- only a 5% drop in output.

Does not seem like its worth going to a lot of work with odd mounts for 5%?

Gary

[roblin]

Ungrounded,

Yep, we're insured. And we're trying to do everything to code for exactly that reason. It's a good thing to mention though, because many of those codes are also just good precautionary measures.

The only thing I've drawn the line at so far are GFCI breakers. They trip way too much when the generator is running, plus I undertstand they are are also small, but steady, phantom loads.

Speaking of codes, the previous owner had a impressive waste plumbing system going, all looking very spiffy and code-like under the sinks, etc. During the pre-purchase inspection I rolled underneath the house and discovered all that waste piping stopped very nicely right under the back porch...

Regards

Rob

[roblin]

Very cool, Gary. I will try some other angles also. Following the data in Damon's post, I might try 30 degrees and see what the score would be.

Thanks

Rob

[DamonHD]

This deal stinks...  Or this sink stinks... Or this sink stink sinks the deal...

Anyway, I hope you yanked the price right down for that.

Rgds

Damon

[scottsAI]

roblin,

Consider, if ground mounted is easier to steal, how does putting them on the roof make it any more difficult? A ladder is not that hard to bring with you. Mounted panel will take time to remove regardless of where its mounted, roof offers no particular challenge to a thief.

Raised Ground mounting offers several benefits.

Better air circulation (cooled during summer)

Ability to tilt to max production over the year.

Easier for you to work on.

No risk to home from installing roof mounted panels

Ground mounted panes can become the roof for a car port, garage, barn, work shop etc.

Basically if I had a choice, my homes roof is the last place I would put PV.

Have fun,

Scott.

[roblin]

Scott

I can't say I'm not tempted. The house is in a bit of a low meadow with a ring of trees on the surrounding hill-side. I should have mentioned that in my OP. Dec through Jan the sun just barely makes over the trees mid day so the extra height was deemed useful as well. I do need firewood so perhaps I will throw that option into the mix in the future.

By the bye, this place is remote/small enough that trucks with ladders noodling down the road would be remembered by other traffic. Our ladders are relatively secure under lock and key. I am also counting on the fact that they would have about 280 pounds of panels to contend with on a slippery steel roof.

Regards

Rob

[roblin]

Gary

Did the PV-Watt_1 run and the losses at 140 Az/30 Elev is 3.3% over 12 months compared to a traditional due south setup. The relative losses are significant during the winter months but there is more power in the summer to compensate. I will probably leave the original array set for 49 and set the other for 30 - rather than changing both every August and April. I know the MPPT controller will be unhappy seeing two seperate bumps, but I believe these days the code is robust enough to deal it with it.

Thanks again

Rob

[richhagen]

One organization spent a lot of time and money to prove something that everyone should probably already know.  The harder you make it for something to occur, the less frequently it will occur.  Specifically related to crime.  If you make it require more time or energy to remove your panels, they will less likely be stolen.  Same thing for damaging them.  Although there are almost certainly limitations to the extent to which such a strategy can be practically implemented, in areas where theft is more common some effort in that regard would likely be justified. On the flip side though, the more effort required to get them mounted and in place, the less likely that is to occur as well.  Rich

[electrak]

How about a pole mount? it would take some doing to climb/cut a steel pole, you can add a tracker later, it would be a bit harder for you to install, at least without a bucket truck or like.

[roblin]

Elektrak

Sorry, I thought this thread had shuffled off its mortal coil...

This is a very remote place, no bucket truck, no concrete truck, the pipe would have to winched in and out barges...you get the picture.

If not for those impediments, the pole mount (with manual time of year adjustments)would definitely be my first choice.

Regards

Rob