DIY ground mount solar PV install

[PeterW]

9 minutes ago, Stones said:

Also, any issues using galvanised steel Unistrut with the panels (I assume aluminium frame)?

 

I’d just put a short piece of nitrile foam tape on the unistrut where they touch and that should stop any issues. 

[Jeremy Harris]

22 minutes ago, PeterW said:

 

I’d just put a short piece of nitrile foam tape on the unistrut where they touch and that should stop any issues. 

Or just use a smear of chromate paste.  Works fine for preventing electrolytic corrosion on aeroplanes and boats.  A small tube of the stuff will do hundreds of fasteners.

[Nickfromwales]

4 minutes ago, JSHarris said:

 

Or just use a smear of chromate paste.  Works fine for preventing electrolytic corrosion on aeroplanes and boats.  A small tube of the stuff will do hundreds of fasteners.

We always used dedicated nylon washers for isolation when working on the ships. How reliable / weather resistant is the paste? 

[Stones]

So easy enough to mitigate then.  The main issue for me is going to be movement as a result of high wind speed, although I can't see there would be any practical difference using this proposed DIY method vs dedicated solar pv clamps.

[PeterW]

1 minute ago, Stones said:

So easy enough to mitigate then.  The main issue for me is going to be movement as a result of high wind speed, although I can't see there would be any practical difference using this proposed DIY method vs dedicated solar pv clamps.

 

Thats why I would leave the gaps between the panels - otherwise you have a very large kite ..!

[Ed Davies]

What centres are the Unistrut slots on? Sub-multiple of the panel width + 6mm?

[Jeremy Harris]

2 hours ago, Nickfromwales said:

We always used dedicated nylon washers for isolation when working on the ships. How reliable / weather resistant is the paste? 

 

I've used it for years, it's pretty much the standard way of assembling aircraft fasteners, which are very often cad plated steel securing aluminium alloy components.  I've also used it when fixing things to alloy masts and never seen a corrosion problem.  The nice thing about chromate paste is that it coats every bit of the fastener, plus it tends to seal against moisture ingress, both of which make it more effective, IMHO, than just using an insulating washer.

[ProDave]

2 hours ago, Ed Davies said:

What centres are the Unistrut slots on? Sub-multiple of the panel width + 6mm?

Irelevant. Look at the video a few posts up that shows the arrangement. It does not need to be accurate.

[ProDave]

3 minutes ago, JSHarris said:

 

I've used it for years, it's pretty much the standard way of assembling aircraft fasteners, which are very often cad plated steel securing aluminium alloy components.  I've also used it when fixing things to alloy masts and never seen a corrosion problem.  The nice thing about chromate paste is that it coats every bit of the fastener, plus it tends to seal against moisture ingress, both of which make it more effective, IMHO, than just using an insulating washer.

I recall using Cad plated steel screws for aluminium.  I used to have a table that showed what materials react with others and what doesn't.  I wonder where galvanised steel comes in  that table compared to cad plated?

[Jeremy Harris]

3 minutes ago, ProDave said:

I recall using Cad plated steel screws for aluminium.  I used to have a table that showed what materials react with others and what doesn't.  I wonder where galvanised steel comes in  that table compared to cad plated?

 

The table is the electrochemical series, that gives the potential difference between different metals.  A large PD means a high risk of corrosion, so ideally the metals in contact with each other shouldn't be too far apart, but using something like chromate paste will mitigate the corrosion risk to a fair degree.

 

Cadmium -0.403 V

Zinc -0.7618 V

Aluminium -1.662 V

Iron -0.447 V

 

Galvanised steel will be closer to the potential of aluminium, so slightly better than cad plated steel.

[Miek]

I've used unistrut (hot galv) to mount Ali frames pv panels for years and not noticed any corrosion, even in marine environments 10 years later. If any at all is seen its usually on any bzp fixings, so for a long life use SS or dipped galv fixings. 

[Ed Davies]

57 minutes ago, ProDave said:

Irelevant. Look at the video a few posts up that shows the arrangement. It does not need to be accurate.

 

I was watching the video when I thought of it but have just looked again. First time I didn't appreciate that the bolts are short enough that they don't go right though so you only have to avoid the places where the strut is bolted to its supports.

[Onoff]

Don't forget you can get different duties/weights of Unistrut for a given overall size. 

[Onoff]

PTFE strip here between galv steel and aluminium. Nylon washers. Sometimes with PTFE tape around the bolt or nylon top hat washers. 

[ProDave]

Stage 1 of mount done. Tanalised fence posts and decking joists.

 

 

The Unistrut will span front to back over the decking joist to mount the panels on. Then I will asses how rigid the structure is and what diagonal bracing needs to be added.

 

The eaves are over long at the moment and will be cut when the panels are on and I know where they really come to.

 

The space underneath will eventually be boarded in to become a shed with the top part up the bank just having a rough platform for limited storage, and the lower part looks an ideal candidate to become the bike shed.

 

We were planning to start mounting the panels this week as SWMBO has some time off work so could help manhandle them, but that plan looks thwarted as the Unistrut has not arrived yet.

[ProDave]

I have hit a snag.  When I chased the ebay supplier about the non arrival of my Unistrut, they replied saying it would cost £200 to deliver it here so have cancelled the order.

 

I have been phoning around and the cheapest I can find it locally is £24 per 6 metre length (compared to just a shade over £20 from ebay)  I guess I will have to stump up for that.

[ProDave]

Well I now have the Unistrut. Could not better £24 per 6M length locally.  Transporting that on the roof of the car was interesting.  Good job the cheapest supplier was also the closest, and has a handy back road route so I could drive slowly without being a nuisance.

[ProDave]

Significant progress in spite of the weather.

 

All panels now mounted, view from the East

 

View from the south

 

 

The unistrut is still to be cut to length.

 

Fixings worked reasonably well.  Between panels a simple penny washer and matching rubber washer

 

 

 

 

The end fixing was not so good. Plenty of people on ebay selling the same solar pv brackets but nobody gives any dimensions of them. As it happens they are too small for these panels, so the self tapping screw has been added to stop any inclination for the bracket to slide off.

 

 

I connected one string today, just the east facing string. It was just gone mid day when I connected it, so well past it's peak and it was generating 300W in the low winter sunshine, and gradually reduced as the sun went further.  Although all the cables are in place, I can't connect the other string until the rest of the MC4 connectors that I have ordered arrive here.

[Miek]

What's the pitch to the south? Looks like your trying to minimise your winter production! 

[ProDave]

13 minutes ago, Miek said:

What's the pitch to the south? Looks like your trying to minimise your winter production! 

Not as much as I would have liked.

 

It obviously does not help building it on a bank, sloping the wrong way.  To get the pitch to the south any more would have needed a longer post in the middle at the northern end, that was already the longest fence post I could get locally. Plus it might have made it a rather bulky dominant structure.

 

[joe90]

@ProDave that would make a good chicken shed ?just needs some sides and a door. ?

[ProDave]

15 minutes ago, joe90 said:

@ProDave that would make a good chicken shed ?just needs some sides and a door. ?

We have actually decided the lower half at the bottom of the bank is going to be the bike shed, and I will put a platform (pallets?) on the top of the bank for firewood storsge.

[ProDave]

The sun came out yesterday and at mid day with the low winter sun  we were generating 1KW So everything seems to be working and both strings performing equally at mid day.

 

A summary of costings:

PV panels £813

Generation and export meters £25

Inverter   £255

DC cable  £44

Unistrut  £192

Nuts and bolts   £50

Timber    £163

 

Total  £1542

 

As a bonus, I get a shed, just for the cost of the timber to board in the sides.

[Nickfromwales]

7 minutes ago, ProDave said:

The sun came out yesterday and at mid day with the low winter sun  we were generating 1KW So everything seems to be working and both strings performing equally at mid day.

 

A summary of costings:

PV panels £813

Generation and export meters £25

Inverter   £255

DC cable  £44

Unistrut  £192

Nuts and bolts   £50

Timber    £163

 

Total  £1542

 

As a bonus, I get a shed, just for the cost of the timber to board in the sides.

Pretty good numbers to be fair   

Let’s see what the wee beastie produces on a bright clear day. 

Good result. 

[ProDave]

0.2KWh today under a grey cloudy dull sky.  Waiting for that nice sunny day to find out, only a few minutes of sun at a time lately.

 

I still have 2 spare panels.  Those will probably end up as E facing on the end of my shed (the pallet shed) with a very cheap Chinese inverter to try and grab some early morning generation. It is surprising how often we get clear sunshine at sunrise but by about 10AM it has clouded over.