Rob Beckers
20th June 2010, 06:34
We're currently installing a 5.7 kW solar installation (for my business), going on a rooftop, for MicroFIT use. That means the home owners will get 80.2 cents for every kWh produced, for the next 20 years. There is some shading part of the year due to trees for this roof, and they are looking at a simple payback time just shy of 10 years. That means in 20 years (the contract term) they double the money that is invested, making for a 5% annual return-on-investment.
I thought it might be informative to post about a rooftop PV installation in some detail. It's not rocket science, though as always, the devil is in the details.
Much of the first day went to setting out where the rails are going, and finding the roof trusses. The tool of choice to locate trusses is a mallet; you can hear/feel it when you hit a truss by banging on the shingles. To find the actual center of the trusses I'm using a Bosch DTect-150 (http://www.bosch-pt.co.uk/boptocs2-uk/Product.jsp?country=GB&lang=en&division=gw&ccat_id=101302&object_id=23307), this is basically a super-stud-finder, that uses microwave to 'see through' surfaces. If works for any non-conducting material; concrete, wood, plastic, and sees up to 15 cm deep. I put a thin plastic sheet underneath, to have a smooth surface for the scanner to work on (it is actually a foldable cutting sheet purchased at a dollar shop). The Bosch scanner works like a charm! There are quite a few false echos, due to nails and such, but with a little work it does find the trusses and allows one to mark the exact center without having to drill test holes. The rail locations are marked with a chalk line, while I use lumber crayons (bright yellow chalk) to mark truss locations.
The norm for PV installations is to bolt an L-foot directly to the shingles. I believe that is a poor practice (tell a roofer you're going to drill 100+ holes in the roof and won't flash them, he'll declare you crazy!). Instead, I'm using a product called FlatJack (http://www.ttisolar.com/products/flatjack.html) that combines a foot with flashing, sealing off every roof penetration. They are not cheap, adding $15 for each roof attachment, but it will never leak. To make absolutely sure, we also caulk each hole with a tri-polymer based sealant, called Geocel 2300 (http://www.geocelusa.com/products/all-constructionbuilding-products.html?page=shop.product_details&flypage=flypage.tpl&product_id=46&category_id=1&keyword=2300). This is the latest and greatest in roof sealants, it's clear, lasts 50-years with UV exposure, and will stick to almost anything, including wet shingles.
Here is a picture of the FlatJack feet going on.
826
Each foot is held down by two stainless steel lag screws, we're using 1/4" x 3" screws, and the feet are spaced 48" (except for corner points, where wind uplift is highest). The feet of each row of PV modules alternate, so the load is spread over all trusses. This was all approved by a structural engineer, since Ottawa City requires stamped engineering drawings. We're actually putting in a few more feet than needed, for a variety of reasons.
Here is a FlatJack foot, they are made of stainless steel.
827
After adding the flashing part of a FlatJack, it looks like this.
828
We ran into one surprise along the way: The roof trusses did not extend all the way to the outside wall of the house. We ended up a truss short on both sides (the PV rails allow a 16" overhang). From the last truss the roof was build up from 2x4 lumber nailed perpendicular to that truss, extending out to the eave. One of the guys had the unfortunate task of going under the roof, and screwing pieces of 2x4 blocking between those rafter tails, to create a surface for another row of feet. You can see in the picture that we spaced the last two rows of feet just 24" apart, for that reason (in row is in a truss, the final row is in the blocking).
829
With the feet down, the rails are next. We are using Conergy's Suntop system (http://conergy.ca/desktopdefault.aspx/tabid-3070/4341_read-7670/), which is relatively simple to put down. All the materials are aluminum and stainless steel. This is not cheap, but will look the same in 20 years as it does today. Believe it or not, but there is an outfit here in town that uses galvanized steel Unistrut (or an Ontario made version of it), yet they still charge $10 per installed Watt! While this is good for their bottom line (galvanized steel is cheap), they are definitely short-changing their customers.
The next picture shows the rails in place.
830
The last picture for this post has a close-up of an attachment point.
831
This is as far as we got last week, due to supply problems. The couplers that join two pieces of PV rail together were missing. They have since arrived, so we will finish up this install next week.
More to follow...
-RoB-
I thought it might be informative to post about a rooftop PV installation in some detail. It's not rocket science, though as always, the devil is in the details.
Much of the first day went to setting out where the rails are going, and finding the roof trusses. The tool of choice to locate trusses is a mallet; you can hear/feel it when you hit a truss by banging on the shingles. To find the actual center of the trusses I'm using a Bosch DTect-150 (http://www.bosch-pt.co.uk/boptocs2-uk/Product.jsp?country=GB&lang=en&division=gw&ccat_id=101302&object_id=23307), this is basically a super-stud-finder, that uses microwave to 'see through' surfaces. If works for any non-conducting material; concrete, wood, plastic, and sees up to 15 cm deep. I put a thin plastic sheet underneath, to have a smooth surface for the scanner to work on (it is actually a foldable cutting sheet purchased at a dollar shop). The Bosch scanner works like a charm! There are quite a few false echos, due to nails and such, but with a little work it does find the trusses and allows one to mark the exact center without having to drill test holes. The rail locations are marked with a chalk line, while I use lumber crayons (bright yellow chalk) to mark truss locations.
The norm for PV installations is to bolt an L-foot directly to the shingles. I believe that is a poor practice (tell a roofer you're going to drill 100+ holes in the roof and won't flash them, he'll declare you crazy!). Instead, I'm using a product called FlatJack (http://www.ttisolar.com/products/flatjack.html) that combines a foot with flashing, sealing off every roof penetration. They are not cheap, adding $15 for each roof attachment, but it will never leak. To make absolutely sure, we also caulk each hole with a tri-polymer based sealant, called Geocel 2300 (http://www.geocelusa.com/products/all-constructionbuilding-products.html?page=shop.product_details&flypage=flypage.tpl&product_id=46&category_id=1&keyword=2300). This is the latest and greatest in roof sealants, it's clear, lasts 50-years with UV exposure, and will stick to almost anything, including wet shingles.
Here is a picture of the FlatJack feet going on.
826
Each foot is held down by two stainless steel lag screws, we're using 1/4" x 3" screws, and the feet are spaced 48" (except for corner points, where wind uplift is highest). The feet of each row of PV modules alternate, so the load is spread over all trusses. This was all approved by a structural engineer, since Ottawa City requires stamped engineering drawings. We're actually putting in a few more feet than needed, for a variety of reasons.
Here is a FlatJack foot, they are made of stainless steel.
827
After adding the flashing part of a FlatJack, it looks like this.
828
We ran into one surprise along the way: The roof trusses did not extend all the way to the outside wall of the house. We ended up a truss short on both sides (the PV rails allow a 16" overhang). From the last truss the roof was build up from 2x4 lumber nailed perpendicular to that truss, extending out to the eave. One of the guys had the unfortunate task of going under the roof, and screwing pieces of 2x4 blocking between those rafter tails, to create a surface for another row of feet. You can see in the picture that we spaced the last two rows of feet just 24" apart, for that reason (in row is in a truss, the final row is in the blocking).
829
With the feet down, the rails are next. We are using Conergy's Suntop system (http://conergy.ca/desktopdefault.aspx/tabid-3070/4341_read-7670/), which is relatively simple to put down. All the materials are aluminum and stainless steel. This is not cheap, but will look the same in 20 years as it does today. Believe it or not, but there is an outfit here in town that uses galvanized steel Unistrut (or an Ontario made version of it), yet they still charge $10 per installed Watt! While this is good for their bottom line (galvanized steel is cheap), they are definitely short-changing their customers.
The next picture shows the rails in place.
830
The last picture for this post has a close-up of an attachment point.
831
This is as far as we got last week, due to supply problems. The couplers that join two pieces of PV rail together were missing. They have since arrived, so we will finish up this install next week.
More to follow...
-RoB-