Panels on a flat roof

[Countrypaul]

All,

I am looking at putting some panels on a flat roof, but as always there are some restrictions.

The house is in a conservation area, luckily I have PP for the panels on the flat roof from when we renovated the place. The flat roof is on the south facing side and quite sheltered due to a steep hilside south and west and lots of trees West, North and East.

The flat roof is on a single story, approximately 9m long and 1.7m wide, with a further 0.7m of tiled roof at 42 degrees before the wall of the second story (Dormer bungalow). The flat roof has an EDPM covering and 200mm parapet wall around, the roof construction is 175mm PUR SIPS 2m long with two 150x40 joists every 1200mm, one end of the SIPS is on the external wall, and one end is supported by a joist within an I beam (205x205x80).

I am looking at putting 8 x 450W - 500W PV panels (e.g. JA Solar 460W) on the roof without penetrating the roof finish, so I believe that means ballastig in some way. As I already have a FITS system, I am thinking of something like a ME3000SP linked to 4 Pylontech US2000 batteries. Panels probably at about 30 degree angle. Have been looking at frames fastened to concrete blocks, but also the mounting trays/buckets.

I cannot find any advice on how to calculate the ballast needed for the panels due to wind loading - other than the standard get a structural engineer or PV expert to tell you. Anyone seen any calculators that might help me get an good idea of how much ballst might be required, or got any experience that would be helpful, or any other ideas?

[marshman]

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[Moxi]

Country Paul, been looking at the same thing myself today:

Renusol console tubs were the reason I looked and they point you at Euronorm 1 EN1991 which i have a copy of and which for our purposes I found next to useless so I guess thats Renusol ducking having any responsibility.

Now I am looking through these methods on wiki how

https://www.wikihow.com/Calculate-Wind- ... oefficient.

You may find something useful in amongst these 4 options - the basic method looks ok to my mind, if i find a helpful online calculator i will let you know.

Moxi

[Countrypaul]

Moxi,

I have found this now, but haven't worked my way through it yet: https://www.solarlimpets.co.uk/downloads/BRE-Digest.pdf

Paul

[Moxi]

BRE 489 page 5 table 4 will probably help you with the loads and there are plenty of calculators online to get you from the loads to a ballast determination.

https://www.solarlimpets.co.uk/downloads/BRE-Digest.pdf

Moxi

[Moxi]

ha ha SNAP!

table 4 on Page five

Moxi

[Moxi]

Paul,

Try this site for a simple no nonsense way to determine the pressure over the panels it needs input from the EuroNorm 1 but thats on the internet and the information buttons point you to the relevant sections - once you have the pressure over the panels you can determine ballast for both suction and, arguably, a conservative ballast figure for slippage.

http://bcsatools.steel-sci.org/WindLoading/Default

Moxi

[Petertc]

Have a look at k2 D dome system.
Ali frame and you can ballast with bricks
https://k2-systems.com/en-US/products/d ... system-old

[Countrypaul]

Instead of relying on ballast would it not be possible to anchor the frame down to the ground? You could achieve this using thin stainless wire rope from the frame - which could extend to the edge of the flat roof - down to some ground anchors - or even into some eyes screwed into the wall. Obviously it depends on the exact layout but it is an idea. It also reduces the weight loading on the roof - which I would be more concerned about with a load of ballast.

Many years ago (mid 1980's) we secured a 1.5m satellite dish to the flat roof on top of the house. It was mounted on 4 RSJs and steel cables ran down the roof and were anchored into eyes fixed into the house walls. The dish was motorised and need to have a clear view form horizon to horizon in order to catch all the broadcast satellites - this was in the days before the Astra "birds". All was well until the 1987 "hurricane", The top of the mount snapped and the dish was left hanging from the signal cables rolling around on the side of the roof smashing tiles all night! The bottom half of the mount didn't move !

Sorry, I missed this earlier.

The parapet wall will make fastening a frame much more difficult, there is an aluminium coping on the top of the wall. Fastening eyes in the wall is probably not a good idea, the wall is made of SIPs and then 50mm XPS and 8mm through colour render. If we could be certain to hit a joist in the wall (100 x 38) we might have a chance, but otherwise there is actually precious little to take any force. Since the area around is a thourough fare having wire ropes across probably not such a good idea either. The layout is definitely fighting the idea of anchoring the frame to the ground or walls which is a bit of a pity as I could see advantages as you point out.

[Stan]

There is the MecaWind programme and I’m sure there are others.
https://www.mecaenterprises.com/how-to- ... -pressure/