DIY ground mount solar PV install

[ProDave]

This thread is to document the (probably slow) DIY installation of my ground mount solar PV

 

I have just bought the panels  I will be using 16 250W panels for the main 4KW array facing south which will leave me 2 spares that I will probably set up independantly on a small inverter facing east.

 

I shall be mounting the 16 panels as 2 rows of 8, portrait mounted, occupying about 8 metres wide by a touch over 3 metres high.

 

The first decision is how to mount them.  First off I looked for ready made mounting kits https://www.ebay.co.uk/itm/Aluminium-Ground-Mount-Kit-for-16-Solar-PV-Panels-for-Garden-Field-Farm/282218731955?hash=item41b58c19b3:m:mAhKzS4fvoS4IL4PF6CSuyg:rk:34:pf:0

 

Lovely stuff but I am not paying more for the mounting frame than I paid for the panels.

 

So seeking other ideas on this first.

 

Just to compound things, where I want to mount them is in the corner of the garden, and at that point, the ground rises a few feet up a bank.  So it will end up with the bottom, south, edge of the panels at the top of the bank, quite close to the ground, and the top, north end some distance from the ground (as the ground is lower)

 

At the moment I am thinking along the lines of make the mounting structure of fence posts concreted into the ground, and joists spanning between them.  Motivated partly by the fact is is almost certain I will close in the sides to make this into another shed / covered storage area.

 

Open to better ideas for the mounting structure.

 

One decision is what angle to mount them?  I am not wanting to maximise overall yield, rather wanting maximum period of usable power.  With that in mind I am thinking to set them to a more shallow angle which will improve early and late generation, particularly in summer. It will also help with the sloping ground issue.

 

Another off the shelf idea might be tom slope them the other way, and make a shallow pitched roof with half of them on the East side and half on the west side, but only a very shallow pitch to this.  Again with the intention of maximum as near constant usable power for as much of the day as possible.

 

Where can I model power output  throughout the day for different roof pitches and orientations?

[PeterW]

4 minutes ago, ProDave said:

Where can I model power output  throughout the day for different roof pitches and orientations?

 

PVGIS used to be the best but @Ed Davies may know of a better one. 

[ProDave]

Tried PVGIS but it just wants to tell me the total annual yield.  As this is a non FIT system that does not interest me.  I want something that can show me a graph of output vs time of day (and be able to show me that at different times of year) and then play with orientation and angles to find the maximum (in terms of hours per day) usable generation.  I have the gut feeling a very low angle E/W split will provide that but I want to model it.

[Onoff]

Unistrut? Or one of the cheaper clones. Galvanised, lasts pretty well down here as long as you galv spray the ends.

[PeterW]

PVGIS - 5 gives you the option to optimize the azimuth and orientation - just check the box and let it do the calculation. You can set one or the other so split the load and put 8 each side, do a -90/90 for east / west and combine the results. 

 

Unless you are going to go with tracking then it’s law of diminishing returns as you will gain 0.5-1% at most. 

[Onoff]

Lots of solar pv apps on the Play Store.

[ProDave]

needs to be on  line, or widoze or ubuntu

[Onoff]

Just now, ProDave said:

needs to be on  line, or widoze or ubuntu

 

No Android device?

[ProDave]

13 minutes ago, Onoff said:

 

No Android device?

I have no desire to try and use a phone as a computer.

[MikeSharp01]

8 minutes ago, ProDave said:

I have no desire to try and use a phone as a computer.

Sadly Dave it already is a computer although I agree the form factor makes using them pretty miserable for this sort of thing. Can I ask where you sourced the panels?

[newhome]

Android tablet. I use my phone 24 x 7 as a computer mind. 

[Onoff]

14 minutes ago, ProDave said:

I have no desire to try and use a phone as a computer.

 

You could load Remix OS on a Windows laptop and get the full Android experience...

[ProDave]

47 minutes ago, MikeSharp01 said:

Sadly Dave it already is a computer although I agree the form factor makes using them pretty miserable for this sort of thing. Can I ask where you sourced the panels?

The ones Bimble Solar are selling, used panels described as having damage to the backing sheet, though of the 25 only 3 show any signs of damage and it is very minor indeed.

 

If I must use android if that is the only platform the "right" software is on then I will, but I am too much of a dinosaur and prefer my computers to have a decent size screen, a proper keyboard (not a touch screen thing that takes up half the already minute screen) and a proper mouse. 

[Nickfromwales]

Aluminium box section is what I'd use. Whack that on top of the fence posts and that'll last the duration.

[billt]

PVGIS will give you average daily amounts by month, as well as total annual yield. You can play with slope and orientation to give you a good idea of the best angles to use.

 

In fact it looks as if the new PVGIS 5 will give hourly outputs, but I haven't tried it. http://re.jrc.ec.europa.eu/pvg_static/en/intro_tools.html#PVP

 

I'm not convinced by east/west splits because in the winter there just isn't any sun from those directions and in the summer you'll probably be generating too much anyway.

 

I choose about 45 degrees slope and SSW orientation ('cause that's the way the bank faces).

 

I made a frame of scaffold poles, as the commercial systems were too expensive, and I wasn't convinced of the longevity of wooden posts.

 

Used U-bolts to attach the panels to the scaffold poles, drilled holes in the frame for them.

[ProDave]

Okay I have played with PVGIS a bit more and it will give output throughout the day, but only for ONE string at a time.  So I can see if I go for an E/W split the E half peaks before mid day and the W half peaks after mid day.

 

But I want to see the SUM of the output from the 2 strings on the same graph.  I guess I could download the PVGIS output as CVS and impot it into a spreadsheet and sum the 2 outputs but that is all getting a bit clumsy.

 

I cannot believe I am the first to want to optimise an E/W split for maximum length of usable generation so I can't be the first looking for a better bit of software to do it can  I?

 

The E/W split idea is an attempt to get a more broad and more level output, rather than a relatively narrow massive peak in the middle of the day. And the low angle idea is to get more in the winter when the sun is low and also I believe it gathers more from a bright but cloudy day.  But this is why I want to model it so I have some idea what it will give.

[Jeremy Harris]

Whenever I've used PVGIS I've just copied the data from the tables into a spreadsheet and then done comparisons using that.  That way you can do things like combine the predicted output for several arrays and see what the overall shape looks like.

 

It's a bit tedious getting the data out of PVGIS and into a spreadsheet, as you need to do several PVGIS runs and then a bit of cutting and pasting of data from each, but once done you can play around with it far more easily.

 

Right now I wish we had some East facing PV, as we have clear skies and sun from the East but are generating sod all, as our 45 deg pitch array faces slightly West of South.  It's a nuisance, as I want to charge my car...

[Miek]

I would use these rails attached to a timber frame. Very good system and you can just get the rails and clamps you need, far easier than using unistrut or drilling pv frames. 

 

http://www.windandsun.co.uk/products/PV-Mounting-Structures/Schletter-Roof-Mounting#8435

 

 

I get stuff from wind and sun, very knowledgeable firm. I've no affiliation. 

[ProDave]

I have done some modeling with PVGIS.  It is a tedious struggle as the CVS file is produces won't just import into excell properly requiring some manual editing, so I have just modeled a few scenarios

 

Firstly panel elevation 35 degrees for January and June.  January shows a nice flat top for the combined data but June still shows quite a large mid day peak (though the usable duration is much longer than all south)

 

So I then tried June at 45 degree elevation.  This widens the peak somewhat.

 

These are all for E/W split.

 

 

So the steeper angle looks better with a lower but wider profile.

 

I doubt I will achieve 45 degrees without the structure becoming very tall and a bit of an eyesore, so I will probably compromise on the steepest angle I can get while keeping the overall height acceptable.

 

[Ed Davies]

22 hours ago, PeterW said:

PVGIS used to be the best but @Ed Davies may know of a better one. 

 

Sorry, I don't know of anything better.

 

22 hours ago, ProDave said:

I have the gut feeling a very low angle E/W split will provide that but I want to model it.

 

Generally speaking the elevation angle doesn't make much difference to the annual production but, as you say, annual production is not your main interest. Low angles do tend to hammer winter production. Ideally for mid winter the panels should be quite steep, somewhere between 70 and 80 ° and it begins to drop off noticeably once you get much below 60 °. I've gone for 60 ° for my design on the basis that that'll give a bit more of a trickle on the duller days as it sees a bit more cloud that the absolute optimum angle.

 

Also E/W splits have a lot going for them in terms of production at times when it's useful but again really slaughter production in winter.

 

For an arbitrary point up the river valley N of Alness with no major horizon problems, December and January monthly production in kWh for a 1 kW panel (i.e., effective hours) for various elevations facing due south and, for two elevations, facing quite a way round towards east.

 

Elv  Dec   Jan    Az -60°

90°  18    21.1

85°  18.3  21.5

80°  18.4  21.7

75°  18.4  21.8   9.77  12.2

70°  18.3  21.8

60°  17.6  21.2

50°  16.4  20.1

35°  13.8  17.4   8.42  11.4

[ProDave]

You have now got me thinking of a compound angle.  Keep them E/W split, but then cant both halves over so the S side of the roof is lower, so some slope to the S as well.

 

I can see the cardboard and sticky tape coming out now.........

[ProDave]

A quick CAD model (cardboard aided design). An E/W split, with both halves tilted south a bit as well, viewed from the south.

 

 

Might still achieve the objective of longer usable generation with the tilt hoping to improve winter performance.

 

Anyone care to suggest how to model that on PVGIS?

[Miek]

Effectively you now have a plane inclined facing SSW & SSE (approximately), so that can go into Pvgis. 

 

Depending on how handy you are and how much time you have you could make an adjustable frame. Full tracking would be the ideal solution but this is hard to achieve cost affectively, but having a frame you could tilt to increase the winter angle would be doable DIY. 

[joe90]

1 hour ago, Miek said:

but having a frame you could tilt to increase the winter angle would be doable DIY. 

 

Very early on when I considered a ground array I planned to use scaffold then the clamps could be loosened, panels jacked up for winter then tightened in place. You could even move it more than twice a year if you wanted to.

Edited December 18, 2018 by joe90

[Ed Davies]

Wouldn't a DIY system to jack a significant number of panels up and down likely twist them at least a bit? Panel lifetimes are set by the sealing of the enclosures so this seems like a good way to kill your panels quickly.