Today, the weather was perfect, temperature around 73 degrees, no wind, no rain, just plenty of bright sunshine. What better day than today to install my Hot Water Solar system? And you, being the astute reader, will say “none,” and you will be quite correct.
If the saying “save the best for last” holds true, that means the worst must come first. Good God, I hope so. The worst in this case was crawling around in the attic installing the back bracing and drilling the mounting holes up through the roof to attach the collector mounting brackets. The main problem is in the back addition, the attic is only 3 feet high in the center. Towards the edges, it is more like 18 inches or so. Drilling and screwing a 10 foot long 2X6 with only 18 inches of space, most of which is taken up by insulation, is not a happy task. I was going to crawl back up there and take some pictures after I mounted the panels on the roof, but I just don’t have the heart. I will take some pictures tomorrow and post an update.
The roof rafters are 2X6 and the sheathing is 1/2 inch CDX. I mounted a 2X6 laterally across the rafters and screwed it to the bottom of the rafters. I then drilled the mounting holes through the 2X6 backer and the roof as close to the 2X6 rafters as I could. Next the the mounting bolt, on the opposite side of the rafter, I placed another 2X6 spacer block to help support the sheathing.
Then I used 8 by 3/8 inch bolts to attach the mounting hardware to the roof. I used plenty of roofing cement on the up hill side of the mounts to prevent leaks. Jay stayed outside on the roof and tightened down the mounting bolts, while I was still in the attic holding the nuts with a wrench.
The next part was to lift each collector up on the roof. They are 4 X 10 feet and weigh 147 pounds each, according the the manufacturer’s spec sheet. We leaned the collector against the roof, then lifted it up and slid it as far up onto the roof as we could. Then Jay, who is a good bit taller than I am, held it there while I ran up the ladder and grabbed the other side. We then slid it further up on the roof, then I held it while Jay ran up the ladder, etc. Finally we were able to get the collectors positioned over the lower mounts and I attached the lower side of the collector to the roof.
I used an old piece of lumber to prop up the back of the collector and took a measurement with my digital protractor. I was looking for a tilt angle between 50 -54 degrees. For more information on why I choose that particular angle, you can check out solar hot water system mounting and location. The first angle was too great, around 59 degrees. I trimmed 10 inches off the board, propped up collector, then measured again, 50 degrees. I figured that was as good as it gets, so I cut and drilled the aluminum back strut to fit the mounts and bolted everything down.
Collector manufactures specs:
Next I sat down and did a few calculations to see how the weight was distributed around the roof. Since the collectors are mounted at a fifty degree angle, some of the weight is on the back mounts, but most of it falls on the front two mounts. To figure this out, we can use a little bit of trigonometry. The Sine function is simply a ratio of the opposite side over the hypotenuse on any triangle. The tilt angle is 50 degrees, so the sine of 50 degrees is .776, therefore we take 159.8 lbs (collector weight 147 lbs plus 1.6 gallons of water, 12.8 lbs) x .776 and get 124 pounds. There are two mounts, so 124 lbs divided by 2 equals 62 lbs. There is 62 pounds static load on each of the front mounts. The rear mounts carry less. 159.8 lbs minus 124 lbs is 36 pounds, divided by 2 is 18 pounds on each of the rear mounts. This does not include additional loads such as heavy snow and uplift from the wind. Those calculations would be pretty complicated and I don’t feel motivated enough to sit down and do them all. Fortunately, the collectors are mounted almost sideways to the prevailing winter wind, which usually blows out of the north west, so there wind load should be relatively minor. What do you think, Todd?
Tomorrow, I start soldering pipe and all that fun stuff. Special thanks go out to Jay for driving over and helping me lift those things up on the roof, and to my Mom for taking the pictures.
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Hi there. Great project. I’m into alternative energy but alas, not a homeowner, as you know. Probably you wrote about this already, but I have two questions for you:
1. did you consider making the collectors yourself rather than purchasing them?
2. you must have a way to figure out how much energy you’re saving by giving your hot water a boost, right?
Cheers from Vienna!
Hi Sarah, I did consider making the collectors myself, but I decided not to because
1) I wanted the system to last. These collectors have a 25 year guarantee. We are in a pretty tough climate in the winter time and durability is important.
2) The manufactured collectors have higher efficiencies, which is also important in the winter months for at least getting some use out of the system.
3) They look better
I estimate I will save about 25 to 30 percent on the electric bill, which is between 3000 to 3500 kWh per year. Our last electric bill was 0.142 per kWh, which means a savings of $426 to $497 per year.
Paul, you totally rock for getting up there and doing it. I’m math impaired, not to mention I’m not comfortable climbing around on roofs, but you’re reminding me that as a kid, I had no such problem: I worked one summer in the early 1970s with my best friend’s dad building a PV system in his backyard at his place on the Chesapeake Bay. He had built a tower out back that we had to climb up, and we worked up top in the blazing sun. A retired nuclear physicist with no intention of sitting around, he’d turned his considerable brain power to solar research and was experimenting with a combined PV/hot water system. I helped him build the prototypes from scratch. Solar systems for the consumer were pretty expensive back then and he was trying to build something affordable that did double duty. He continued his research until he passed away, some years ago, now, and I honestly don’t know what became of his research, but it sure was an education and an inspiration for me. He was the guy who first turned me on to the notion and the possibility of energy independence at the individual level. I’ve heard some guys saying, recently, that rooftop collectors are the wrong way to go, that it’s hopelessly inefficient and we should invest in mass collectors. I can see the efficiency part, but then individuals are still tied to the grid. They haven’t yet convinced that individual collectors are a bad idea.
Jen, a number of things… Concentrated solar power is more efficient, no doubt about it. However, as you said, it takes control out of the individual and puts it back into big business. Secondly, as more and more people become interested in solar power, both photovoltaics and solar thermal, the incentive for corporations to develop more efficient products will become larger. Right now, photovoltaics offer between 9-16 percent efficiency, solar thermal, such as the system that I am putting in, is about 60 percent or so. Both of these can be improved upon (and to some extent have been in the laboratory).
The good thing about photovoltaics and small wind/hydro is the distributed power generation. If enough of these systems are installed, the need for more conventionally powered (e.g. fossil fuel) generating plants will decrease, as will the need to string high tension power lines all over the place. Right now, there is a fight about a high tension power line project in the Delaware river valley, about 35 miles south of here. The reason why it is needed is because the New York metro area continues to grow and need more power. The solution, according to the power line proponents is to generate the power out by Rochester and send it down these lines. First, that is terribly inefficient. Second, a beautiful and historic area will be ruined by a set of huge towers. Third, if NYC wants more power, let them generate it down there somewhere. Imagine if every building in NYC had a couple of kilowatts of solar power installed on it. That might do the trick.
The only way we can stop these mega corporations (or in this case, the US department of energy) is if we all stand together and speak very loudly.
Um, ahem, well, thanks for the comment.
Paul,
Nice job on the solar panels! I have to agree with you, working in the attic is one of my least favorite jobs. It’s also amazing to me to see how older houses are framed with 2×6 rafters. Those houses stand up to the snow and wind loads quite well yet today’s codes require roofs with 2×10 and 2×12 construction….hmmm….such a waste! Anyway, nice start on the project and I look forward to seeing how it all comes out.
Thanks, Todd. That is interesting about the larger rafters in new houses. I suppose over the years some improperly build 2X6 rafter roofs have failed, so they increased the size to compensate. Probably has something to do with a law suit. The other factor is perhaps more accurate wind data. This area used to be a 70 mile per hour basic wind speed, but now it is a 90 mile per hour basic wind speed.
More importantly, how is my ladder?