Straight in at the deep end with a ground mount system

[MikeXl426]

Hi

Newly MCS accredited and looking at a 4kW ground mount system to quote for....yikes!

I'm thinking of the Schuco system which seems pretty robust, along with concrete pads. However, I'm wondering what sort of 'design' is required for the concrete. Is it 'make it big and heavy' so it won't blow over, or is there some kind of technique for calculating the size and weight of the foundation.

Thanks for your help as I really don't want to under or over spec!

p.s. The ground is rocky and rubbly about 12 inches down, so anchors are out of the question.

Mike

 

[Worcester]

Schletter.de do a whole host of ground mount options and the now have a UK office, they will even design the concrete footings for you

 

[Markc]

Hi

Newly MCS accredited and looking at a 4kW ground mount system to quote for....yikes!

I'm thinking of the Schuco system which seems pretty robust, along with concrete pads. However, I'm wondering what sort of 'design' is required for the concrete. Is it 'make it big and heavy' so it won't blow over, or is there some kind of technique for calculating the size and weight of the foundation.

Thanks for your help as I really don't want to under or over spec!

p.s. The ground is rocky and rubbly about 12 inches down, so anchors are out of the question.

Mike

This is what we done.

4 Ton sand and stone and lots of swearing!

 

[MikeXl426]

Thanks Mark

I take it no calcs then, just make it big?

Also, about what height is that systems at the back?

Mike

 

[Worcester]

You really need calcs. it not just about ground pressure, think what would happen if (from Mark C's photo) the hedge behind it was removed and a 50 mph wind came form that direction. you've potentially got an awefully big kite. So you need to take overturning moments from wind pressure into account also.

 

[Ramjam]

Mark, Is it just me or are those shadows on your brand new array?

 

[Markc]

Thanks Mark

I take it no calcs then, just make it big?

Also, about what height is that systems at the back?

Mike

We had a height restriction of no more than 2mts to the back edge. We came in at 1.9mts after cutting the front legs down to achieve it.

We did calculate the ground works for ballast weight but after all that the bases came in way over that requirement so I wouldn't bother again. Waste of time. Each base is 3mts x .06mts x 400mm depth. If that's going to move then there's nothing more we could do to stop it.

I have also seen posted pictures of this same system bolted to nothing more than paving slabs! Now there's trouble waiting to happen. After all the ground works we did I know this isn't going anywhere.

 

[Markc]

Mark, Is it just me or are those shadows on your brand new array?

No just you!

Reflection from a nearby tree which is now not there! The tree was to be gone when we installed but the Tree Surgeon hadn't come when he said he would. Now they have been cut down as it had some sort of tree disease? (Don't ask I have not a clue!)

This system has been in a year now and is performing over what we estimated.

 

[Worcester]

These photo's taken from Schletter's guide on flat roof mounting (general_hints_on_flat_roof_mounting_I400112GB.pdf) the same principles apply to ground mount, get the calcs wrong and wind loading can destroy the array:

 

[Markc]

These photo's taken from Schletter's guide on flat roof mounting (general_hints_on_flat_roof_mounting_I400112GB.pdf) the same principles apply to ground mount, get the calcs wrong and wind loading can destroy the array:

View attachment 4890

Scary stuff but just one look at the ballast weights and you can see that they are willfully inadequate.

Obviously we all know wind sheer is a concern and any design must incorporate measures to ensure the array stays put. Wind sheer is a lesser concern with ground mount over roof systems due to the likely hood of air disruption at ground level due to buildings, trees etc and the lower altitude.


There are some ground mounts that use spikes driven into the ground and then open out to grab into the soil. The array is then bolted to that. The ground mount pictured on the three concrete bases was calculated but we still ended up going over and above these calculations due to the circumstances on site. Norfolk is a horrendously flinty area (We still build with the stuff here you know!) but flint also gives excellent adhesion to the ground mount base also. So again all these things need to be taken into consideration on design.

I would never consider just blundering in and doing what I think but now after having calculated this system and still building bigger I see little need for me to calculate another one of the same size.

 

[DH Electrical]

Hi , I have looked into options for Flat Roof & Floor Mounting and i have found the easiest and best way is by using a "suntub" its a plastic moulded unit with the ali profiles moulded into the unit, if mounted on flat roofs then you simply fill the cavitys on ground level withlarge 40-50mm stones, and if on ground level you can build up a flower bed etc around it or use stones again,
should you want more info pm me and i will give you supplier details

 

[SRE]

Mark that array looks great - how did you get round planning permission? We've got a guy wanting ground mount but the planning portal says you can't have more than 3m2 without planning, I'm not sure if I'm reading the wrong bit but you can't get much on if you're limited to 3m2.

 

[MikeXl426]

I think it's 9m2 and no, you won't get much with that either. I don't think you can 'get round' planning permission. The best way is to go through the proper channels and apply properly.

 

[Markc]

Mark that array looks great - how did you get round planning permission? We've got a guy wanting ground mount but the planning portal says you can't have more than 3m2 without planning, I'm not sure if I'm reading the wrong bit but you can't get much on if you're limited to 3m2.

We didn't get around planning. The system went through planning, but the client achieved this when the planning went in for the Eco House he built. The other systems we have done we arrange simple plan drawings and calculations for planning. It's not that much to worry about from my experiance.

 

[dansk]

Hi Markc,

Great pic - can you tell us a little more about it, were did you house the inverter? and did you have to dig a long trench for the A/C back to the house?

 

[Markc]

Hi Markc,

Great pic - can you tell us a little more about it, were did you house the inverter? and did you have to dig a long trench for the A/C back to the house?

The inverter is positioned on the center rear leg. The AC side is 3core 10mm SWA trenched back to the ducting as fitted on the build which goes into the basement plant room. The panels are Schuco 185wt Mono's (3.330kWp) Inverter is a Aero-Sharp (will not use one again).

Gen meter in basement next to the consumer unit.

The tree was removed just over three months after the system was fitted and it did have a impact on the generation. Now the tree is gone is has certainly made a big increase and currently has generated just over 2000kWh.

The property (not the one in the picture, that's the neighbor) won a local "Keep Norfolk Rural" green award. PV is just one aspect. The property has Thermal, Biomass wood chip boiler, heat recovery units, heat stores, grey water and rain water harvest.

 

[Kram]

That looks great! we have also been asked to quote for a 4kW ground mounted, how much cost did you have to build into the job for the pads?

Mark

 

[Kram]

Thanks for the Schletter info, we have got our 1st flat roof system to start in the near future, i hadn't realised Schletter were now in the UK.