Hey Nik,
Consider these points with your client: 1. Your racking system most likely has gaps between rows of modules, so most/all of the rain that hits modules higher up on the roof will fall through that gap and will run on the roof as normal. Only the lowest row of modules will collect rain that could “jump the gap”. The 100yr worst rainfall rate in Vermont (listed as in Bratteboro) is 2.7”/hr. The quick math has that as 31 gallons/hr for a standard 60cell module. Which is 0.5gpm. So if they wanted to test this, they should be able to let a garden hose lose on a single solar module (usually far, far more than 0.5gpm, a short piece of garden hose can put out more than 15GPM actually, 30 times the 100yr rainfall rate) and see if that is enough water to jump the gap (be sure to face the hose uphill so the water has a chance to spread laterally and also not be forced off the module edge at an artificially high speed from the water pressure). My bet is that it will not. And you most likely just tested at 3-5times the 100yr storm level of rainfall in your area. 2. If the client is not satisfied with the above. Depending on your racking system, some racks offer skirts. The skirts usually have a curve down to the roof from the module edge, the curve would direct the water down to the roof from the bottom row of modules via surface tension. The water layer will stick to the skirt and follow it down, even if inertia would normally force the water to arc over the gutter. You see that phenomena at water parks sometimes where the water slide has a little hump to give the tube riders a bit of air time, but the water stays stuck as a film to the water slide itself. Surface tension at work. Not to add to your worries, but in Vermont, I’d be more worried of ice sheeting on the bottom row of modules and bypassing the gutter, to fall of pedestrians or people entering the house if your gutters overhung the entrance. But you get a lot of snow in Vermont, so houses there may designed that particular hazard out of most home construction. With Regards, Daniel Young, NABCEP Certified PV Installation ProfessionalTM: Cert #031508-90 From: RE-wrenches <re-wrenches-boun...@lists.re-wrenches.org> On Behalf Of Nik Ponzio, Building Energy Sent: Monday, April 30, 2018 8:32 AM To: RE-wrenches <re-wrenches@lists.re-wrenches.org> Subject: [RE-wrenches] rain guard We have a roofmount PV array that is very close to the run gutter. The customer is concerned that the runoff during heavy rain will overshoot the gutter. So I'm looking for a product that will mount at the lower edge of the array and slow down the rain water. I looked that Alpine SnowGuards but they all have a small gap between top of solar module and bottom of the snow rail. Any suggestions? -- Nik Ponzio Building Energy 1570 South Brownell Road Williston, VT 05495 802-859-3384 ext.115 http://www.BuildingEnergyVT.com
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