July 24, 20232 yr Hi all So we have a flat concrete roof where we want to mount our solar panels. This roof has rubberised waterproofing on. According to the manufacturer we should not drill through this waterproofing barrier as it can't be resealed properly and leaks/water damage will occur. Our next (and probably only) option is to weigh down the solar panels. The waterproofing installer suggested concrete blocks to which he sent me a few picture, I have attached them. My question is what will be a suitable weight, bearing in mind that I will most probably NOT overload the roof itself. So here are my calculations: The panels themselves are 4 x Canadian solar with a size of 2,278m x 1,134m and max wind resistance of 2400Pa Panel pressure is Pa/m^2 = (4 panelsx2400Pa)/(4 pannelsx2,278x1,134) = 9600/10.333 = 929N I will only be considering the back side as weighted and other side fixed, and also be using 5 blocks on one side. In reality I will use 10 blocks, 5 front and 5 rear, but for the purpose of calculation I will only consider the 5 blocks on the rear side. Thus 929N needs to be distributed over the 5 weight blocks. pressure/gravity = mass > 929N/9.8 = 95kg 95kg / 5 blocks = 19kg per block. I will add 20% as a safety factor. If I made a mistake please let me know, SIde note. I have it on good authority that Gosolr also weigh down their solar panels with 35kg blocks between 2 panels. So for 4 panels they will probably use 3 blocks for a total weight of 105kg. Edited July 24, 20232 yr by sjp100 Note added.
July 24, 20232 yr Are you in a windy location by chance? My pessimistic side says that the winds here in the Cape will lift those weighted panels surely
July 26, 20232 yr https://powerforum.co.za/topic/18166-12kw-sunsynk-with-18-x-575w-longi-solar-pv-modules-freedomwon-1512/
July 26, 20232 yr On 2023/07/24 at 1:25 PM, sjp100 said: According to the manufacturer we should not drill through this waterproofing barrier as it can't be resealed properly and leaks/water damage will occur. That is an easy answer for the rubberising manufacturer. I would drill 8mm holes and use chemical anchors. Fasten massive washers and use excessive silicone at the base of the anchors... you should be fine.
July 26, 20232 yr On 2023/07/24 at 1:25 PM, sjp100 said: The panels themselves are 4 x Canadian solar with a size of 2,278m x 1,134m and max wind resistance of 2400Pa Panel pressure is Pa/m^2 = (4 panelsx2400Pa)/(4 pannelsx2,278x1,134) = 9600/10.333 = 929N Pa is N/m² - so to go from Pa to N, you need to multiply by m^2. 2400Pa * 2.278m * 1.134m = 6200N ~= 620kg per panel. But, fortunately, you don't have to design for max wind loading - only expected max wind load in the area (BUT you are required to assume a CL of 2), which would give you about 280kg per panel with a max gust speed of 100km/h. You can probably get away with a lot less than that, but this is what will be required if a structural engineer has to sign off on it.
August 15, 20232 yr Author On 2023/07/26 at 11:51 PM, JustinSchoeman said: Pa is N/m² - so to go from Pa to N, you need to multiply by m^2. 2400Pa * 2.278m * 1.134m = 6200N ~= 620kg per panel. But, fortunately, you don't have to design for max wind loading - only expected max wind load in the area (BUT you are required to assume a CL of 2), which would give you about 280kg per panel with a max gust speed of 100km/h. You can probably get away with a lot less than that, but this is what will be required if a structural engineer has to sign off on it. Thanks. I do see the error I made. Made some cement blocks and will probably end up around 150kg per 2 panels. From other installs I have seen this should be adequate.
August 15, 20232 yr Author On 2023/07/26 at 8:57 PM, frivan said: That is an easy answer for the rubberising manufacturer. I would drill 8mm holes and use chemical anchors. Fasten massive washers and use excessive silicone at the base of the anchors... you should be fine. Unfortunately if we drill we void the warranty. Thus if any leaks or damage occur, regardless if it was from the solar panel mounting, they would just say not our problem.
August 15, 20232 yr Author On 2023/07/26 at 8:49 PM, madness_za said: https://powerforum.co.za/topic/18166-12kw-sunsynk-with-18-x-575w-longi-solar-pv-modules-freedomwon-1512/ Thanks, doing something similar. We are splitting the panels into pairs. Thus 2 and 2. Each pair will have about 150kg total weight weighing them down. From what I have seen with other installs this should be adequate.
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