Mounting PV panels on flat roof

[fatbob]

Hi,

I'm looking for some advice/your experiences for mounting PV panels on flat roofs.  Reason being is that I'm looking to have a flat roof repaired soon and also planning to install PV panels on said roof in a year or two. It's a typical UK single storey flat roofed extension facing near dead on South (that's handy).

I want to increase the insulation on the roof whilst I'm having the work done, so the roofer has quoted to install 75mm of Kingspan insulation with a three layer waterproofing on top called 'Betagum' (which to my untrained eye looks like the kind of roofing felt you'd use on a shed, but more sturdy of course).  So far so good, but how to mount PV panels later on down the line?

Should I be looking to install a mounting frame whilst the roof is relaid (so any framework piercing the roof membrane can be sealed in at the time), or go with the type of mounts that rest on the roof and use ballast or paving to secure them in place (will the Kingspan be strong enough to support them without getting squashed ?)

I'd welcome any of your thoughts, (be kind, I'm a beginner to PV, also hope I've used the right board  )
Cheers, Bob.

[tony.]

depending on your panels etc, you could try something used on commercial roofs.

generally these are flat and still have to have air handling units, cabling etc, so 2x2 feet slabs regularly spaced out and your unistrut(for example) is fixed to this.

the slabs sit on the roof and do not puncture the roof.

clearly wind loading could be an issue

tony

[Justme]

On a flat roof the panels will need planning if they are higher than 200mm from the roof. So no sloping panels. I would see about putting a pitch on it now even if it is only a small one. You will get more insulation in, better water proofing, last longer as well as being the easier way to mount the panels later.

But it will cost more.

[billi]

  200 mm is a lot  depending on your panel dimension of course

Perhaps this helps

http://www.schletter.de/index.php/en/flat-roof/35-trapezblech-mit-pfetten.html

Or here just a picture search in German , for Flat roof PV

http://www.google.ie/images?um=1&hl=en&client=firefox-a&rlz=1R1GGLL_en-GB___IE369&biw=1024&bih=595&tbs=isch%3A1&sa=1&q=flachdach+Photovoltaik&aq=f&aqi=&aql=&oq=&gs_rfai=


Billi

[merkland]

If you read the regulations fully 200 mm does not apply to flat roofs.
For flat roofs panels must not be higher than than one meter from the plain of the roof and must not be closer than one meter to the edge of the roof(in Scotland anyway). Amendment to regulations came into force March 12th 2009.

merkland.

[merkland]

Our house has a flat roof , we currently have solar water heating panels mounted on an A frame clamped to a substantial chimney stack the pipes come through the roof inside the chimney(between liner and masonry) so there is no penetration of the roof membrane. I am currently pondering solar PV - we have a further two chimney stacks, one either end of the roof, so am thinking A frame across roof clamped to chimney stack at either end. The chimney stacks in question are substantial lumps of stone measuring about 2' by 4' in cross section!

merkland.

[2ndBillericay]

We have just installed 9 x 240w panels on our rear / south facing flat bitumen roof (which was renewed in March) and we initially looked at using the SunMount plastic tray with ballast in, or the ConSole plastic tray system but in the end we opted for the FlatFix mounting system.

The two plastic tray systems have units placed o the roof and then aggregate is placed in the base of the tub and the panel placed on as a lid.

The FlatFix system has aluminium triangle brackets and 2 cross members on the back and you place 30cm paving slabs in the back standing at an angle. The bottom of the metal brackets have a soft surface so it doesnt damage the bitumen. The FlatFix is designed to have rows of panels but we used them as single panels with a support at each end so they can be moved around to get the best spacing.

We favoured the metal ones as they look less imposing and all you see is the panel and a little back bracket when viewed from the side and we thought allowed better cooling.

There is therefore no need to puncture the roof or install any brackets. We have added some steel cable (anchored to 3 bits of wall) as added security as they are literally free to pick up from the roof.

Good luck with your plans.

[AidyB]

We have just installed 9 x 240w panels on our rear / south facing flat bitumen roof (which was renewed in March) and we initially looked at using the SunMount plastic tray with ballast in, or the ConSole plastic tray system but in the end we opted for the FlatFix mounting system.

The two plastic tray systems have units placed o the roof and then aggregate is placed in the base of the tub and the panel placed on as a lid.

The FlatFix system has aluminium triangle brackets and 2 cross members on the back and you place 30cm paving slabs in the back standing at an angle. The bottom of the metal brackets have a soft surface so it doesnt damage the bitumen. The FlatFix is designed to have rows of panels but we used them as single panels with a support at each end so they can be moved around to get the best spacing.

We favoured the metal ones as they look less imposing and all you see is the panel and a little back bracket when viewed from the side and we thought allowed better cooling.

There is therefore no need to puncture the roof or install any brackets. We have added some steel cable (anchored to 3 bits of wall) as added security as they are literally free to pick up from the roof.

Good luck with your plans.

I would estimate that the wind load calcs recommend around 100kg of ballast for each of those panels, how many paving slabs do you have on them?


To answer the original post:
The easiest way to have panels installed onto a flat roof would be to have some kind of upstand put in so that at a later date panel mounting frames can just be attached to these.
Alternatively you can create a very strong roof capable of taking around 100kg of ballast per panel and then have a frame simply lain on top (there are numerous systems available).

AB

[wookey]

If you are having a new flat roof I'd really look at the EPDM membranes rather than a bitumen-based one. It does cost some more but should last a lot longer due to the flexibility of the material. Looking at Betagum online we find: "satisfactory and economical", "Value for money". EPDM such as Sika Sarnafil says things like: "a Sarnafil roofing system will last in excess of 40 years". Many other flavours available (Cefil, Sika Trocal, Hertalan). Here's a site giving a good explanation of the options and tradoffs: http://www.london-flat-roofing.co.uk/Mineral-Felt/Mineral-Felt-Roofing.htm

So a 3layer-felt roof will work fine, but be aware you are buying the cheapest and cheerfullest (and not the most green) option.

[rondurrans]

I have had a 4 kW array installed with no mechanical fixings only ballast (slabs/flags) to my EPDM Flat Roof - see http://energy1.moonfruit.com for picture. I relied upon the clacs for the wind loads and dead loads to the property being confirmed by the installation company - I am in an exposed location on the North Wales coast and was very concerned that I might wake up one morning and find them in the garden next door!

Regards,
Ron

[JohnS]

I relied upon the clacs for the wind loads and dead loads to the property being confirmed from the installation company

Do you mean that you did the calcs and they confirmed them? or

they did the calcs and you confirmed them? or

they did the calcs and no one independently confirmed them?

[rondurrans]

Sorry not clear - I relied upon the company's calculations.

Ron

 

[fatbob]

Many thanks all for the kind advice, apologies for the lack of acknowledgement until now.

Wookey, yes you're right about the budget roofing material option, I had a quote for GRP as an option a while ago which technically looked great but the cost was terrifying !  I had not previously heard of EPDM but will investigate further.  Having looked at your comparison link the failure of my existing felt roof is down to thermal/UV stress, and on reflection by replacing like for like it will only bring similar problems further down the line.   Will have to bite the bullet and dig deeper for funds !

I really like the idea of the tray/Flatfix option to leave the integrity of the roof intact, but not sure about the roof loading of the ballast required and don't really want to have to reinforce with RSJ's etc due to cost/hassle.  I was wondering as per Billericay's experience whether I could install a tensioned anchoring system as a replacement or compliment to the ballast perhaps ?  If not, will have to look at the upstand/frame solution instead.

Could I be cheeky AidyB and ask where I could find wind loading stats to get more info on the weight of ballast required vs panel size/inclination?  The roof is a single storey high approx 2.5-3m high and we're in a fairly sheltered suburban environment in the S of England, but once or twice a year (as everywhere I suppose) we get quite stormy weather.  Realistically there's probably only room up there for perhaps 4 decent sized panels... am thinking at 100kg ballast each, the roof could *probably* support the weight of 4 of me's !

As a further open question (if it's permitted on the board of course) is there any advice anyone could give me on selecting a good MCS solar installer / or recommendations for companies that install in Berkshire ?

Once again many thanks to everyone for their help so far,
Cheers,  Bob.

[2ndBillericay]

Hi FB, our steel cable is slak to it will allow a little movement of the panels if the wind is stronger than the ballast, which it shouldnt be. we have 5 x 30x30cm slabs as balast on each 1.75m long frame. If i stand on the roof and compare my 19stone spread on 2 x size 11 boots the loading from the frames is much less.

the ballast calculations are really to stop panels flying off the roof and the structural calculations are normally done to ensure the roof doesnt collapse. We had our roof refelted last year and there were 5 of us chunky guys on the foof and no one went through.

while i apreciate formal calculations need to be done, i still like to do an actual test to confirm them and 5 chunky roofers or 3 solar installers and myself on the roof proves its strength to me.

[sr_reading]

Hi Bob,

We have just had a 2 flat roofs redone with EDPM - one with insulation, one without (garage). I found quotes not that much higher than a high quality felt roof replacement - but better gaurentees. We are very pleased with ours. Where are you in Berkshire - near Reading?

We have also had PV fitted on one of the flat roofs using a sunmount system - partly because it didn't need to break teh membrane & also didn't need lots of ballasting, we didn't like the idea of concrete blocks above our heads at night! As the panels are locked together using the mounts they need less ballasting - just around the edges is my understanding. The downside is that they are only at a 10 degree angle which isn't optimum.

Sandra