Might get the other boxes up tomorrow, any advice on distance from the ones you see here, I’m trying to stay away from that hedge although I might chop it down a bit if it’s an issue 

One other point.  Can the panels sit on the tubs without the cables attached or will they get toasted. 

There are just too many unknowns for me to comment on panel positioning.

You refer to the roof having a low point, which suggests it's sloping.
We also don't know the angle at which the panel is held by each box.

Those measurements need taking into account when you decide where the remaining two panels are placed.

If you're wanting to have sunlight on the panels during bright winter days, then the sun's azimuth above the horizon at midday will be about 15°.
It depends on your latitude of course.

I'd be drawing this out on paper in order to decide where the panels sit in order to avoid the front ones casting shadows on the others.

1.9m width is huge for a solar panel.
Is that within the advertised specification for your mounting boxes?

Most solar panels are 1.0 x 1.6m and weigh just over 20kg.
That's to ensure they come within Health and Safety guidelines for a one-man lift.

Yes, it's ok to position the panels without any of the electrical connections being made.

Just remember that they are 'live' when you eventually come to connect them!

Got myself in a pickle. I have two types of plugs, but enough to change the two last ones, negative and positive on the panels.  Can anyone explain what’s going on here and if they are compatible or should I go off and get new plugs.

Well those are "MC4" plugs and sockets.

Yes the ones on the left do indeed look different to those on the right. But one's the male half and the other is female.
Incompatibility is unlikely.

You should never attempt to change the MC4 connectors which are already on the flying leads of the solar panel. They tell you which is the negative and which is the positive!

The left-most photo doesn't look right to me. When properly assembled there is no bare conductor visible on an MC4. The second photo looks correct.

What is the "pickle" you think you're in?

@transparent I went and got new connectors the same as the ones on the panels, I was just adding problems for myself.  I had to go and get glands for my isolator box today and some bootlace crimps for the terminals, a friend is loaning me the tool to crimp those. I had to buy the mc4 tool though.  Got all the ballast in and bolted the tubs with 4 big 6mm screws and those huge square washers. Doesn’t seem to be any deflection in my joists but bolted some straps from them to the walls to prevent lift.  

The tubs, have mini rails screwed into them with two bolts each and from an engineering slant I thought a bit flimsy, but they say they don’t tear off.  There is an earth sign on the panels and an earth connection in the isolator. Are these used?

The plugs male and female had be a bit confused to start of, the male using a female insert.  The inverter  has a female socket to take a male plug and do on.

one thing I’m not sure on. If I start off and orientate a panel with the negative cable connecting to the negative return to the house then finalise with a positive tail heading back to the house.  Am I correct in saying that the inverter won’t know which end is negative and what’s positive and that there is no polarity to worry about although I have marked my positive cables.  The power simply runs in a circuit or is there some complex law I’m missing.  More curious than attempt to wire any old way. 

should have been done if I’m honest but old now and need to enjoy it more than hash on.  I got the wife to pass me the bricks up to the roof and 20 minutes of hell, never stopped moaning the whole time.  

@transparent the panels are 1.9 landscape. I fitted the boxes 1.5 metres from first row.  That should be fine I think

Posted by: @david999

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There is an earth sign on the panels and an earth connection in the isolator. Are these used?

An earth bond to the aluminium frame is required if the solar panels can be touched.

So that would apply if they were on a main house roof, for example.

You'll have decide if you think a safety earth is required on your garage roof.
It only matters if there is a fault.
The earth plays no part in the everyday functionality of the panels.

Posted by: @david999

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Am I correct in saying that the inverter won’t know which end is negative and what’s positive and that there is no polarity to worry about although I have marked my positive cables.

The inverter would certainly mind if you connected solar panels of the wrong polarity.
It would let you know quite forcefully.
You won't need an App to tell you!

You must run the entire cable loop with MC4 connections going male-to-female on each extension you make up.

@transparent so just in case I am stupid. If the string of panels begins with a positive plug that would go to the positive on the inverter. And likewise with the last one being a negative plug. It’s probably a real stupid question

It's exactly the right sort of question to ask here @david999 

Yes, the positive output from the first PV panel on the array should connect to the positive input on the inverter.

Place a panel next to the inverter and look at the MC4 connector on the end of its positive lead.
It should be of the correct polarisation to mate only with the positive input on the inverter.

Your home-made extension-leads maintain that system polarity.

@transparent thank you.  Be Thursday before my mate gives me the crimping tool so a couple of days off