You have to look at it from another angle here as it can be more than about an extra amount of solar energy being produced. These are PVs and will take some abuse, but to have too much buildup I don't believe i'd trust it. Even if the PVs are fine there's the added weight of the snow as well as the PVs on the roof putting a great deal of strain on the roof itself.
Barring that, you have to watch as all of that weight when it comes down can be very dangerous, especially if any of it turns to ice. It may not be the same quantity of snow that normally would fall off of the roof as it could hang up and build in some spots more than others that the roof itself would've allowed to pass more evenly and possibly sooner. Crap happens.
Of course most times everything will be fine, but once in awhile it can happen unexpectedly.
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Yep. The idea in my head has been to use a long wiper like that with a rubber blade on it and dual chain drives like garage door openers on the ends of it with UHMW poly guides on the ends of the wiper.
For us, 10% more production means that much less generator hours in a year's time. I got enough stuff laying around my shop to build a wiper like that for less than a 100 bucks. The biggest problem is getting motivated to do it. And that motivation usually don't occur until mid-December when I'm chipping ice off panels again.Leave a comment:
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You mean like this?
The challenge is figuring out how to build the system in a way that's economical. The system in that video costs something like $10K for a 10kw array, and it's just not worth it for something which might increase annual production by 10% at most. It's cheaper to just get more modules to make up for the loss.
I imagine you could DIY a system for a whole lot less, since the bill of materials is pretty simple. On the other hand, it's going to have to be able to exert a fair bit of force without risking crashing against the array, and the linear bearings will have to work when covered in snow and ice (otherwise what's the point).Leave a comment:
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There are some threads over at the Midnite forum about pushing current into panels from the grid (or generator or battery) to heat up the panels and melt snow off. It does work, but whether it's cost effective... I don't know.
I guess that a heat tape along the bottom edge of the panel would be the best bang for the buck... as Chris said, once you get a bare area started the sun can take over.
--mapmakerLeave a comment:
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It might. You can sort of gauge it by how much snow you have collect on your roof and stay there. The solar panels won't shed that snow any better than the roof does unless it's just a dusting that the solar can get thru enough to warm the panels underneath it and melt it off.
I've had it in the back of my mind for years to invent some sort of device with a big windshield wiper blade on it that I can just push a button and have it wipe the snow off them solar panels. If you can even get it down to a 1/4" thick, then the solar can get thru and warm them enough to melt it off after a few days. But if it's an inch or more, it sticks to 'em like glue. People would never believe snow and ice can stick to glass like that until they come here and visit in the winter time and leave their car sitting outside in a blizzard once. If you've ever done that and had to scrape the windshield on your car - well, solar panels are the same thing except way bigger and way harder to get at. And once it's on there, she's on there to stay. Around here we call it tungsten carbide ice because it's tougher than any steel known to man.Leave a comment:
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Unfortunately, ice scraper on a long pole won't be an option for the array on top of the house. It's just too high off the ground.
I'm guessing that this is going be very dependent on the micro-climate. Here in the Twin Cities, between the urban heat island and being about 100-200 miles south, we're at least one and maybe two USDA zones warmer than you are in northern WI. The electrician at QBP told me that his panels shed snow fairly readily; on the other hand, there are solar arrays nearby which stayed dark this year from December until March.
I guess I will just have to see how it goes. Fortunately, I'm not trying to live off-grid, so it's really just a financial question of how much power loss I'm willing to live with.Leave a comment:
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That might be the theory, but our south facing array tilted at 75° refuses to "self plow" in March. What happens is that the snow collects on them, the panels warm just enough from solar insolation getting thru the snow to melt a little on the surface of the glass, and then it freezes and becomes permanent. I have found that it is imperative to get the panels cleaned off after a snow ASAP or it turns into a long and tedious process of scraping ice off with an ice scraper on a long pole.
The other thing is to make sure bottom edge of the panels hang over the roof line. If they don't, snow will build up at the base of the panels on the roof and you'll be up there with an axe chopping it off. BTDT too.Leave a comment:
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By my calculations, we should get back 85% of the installation cost from the federal tax credit and the state incentive payments alone. Reduced usage/net metering is on top of that.
Snow is an interesting question. One of the two arrays will be over the garage and easy to rake off, the other will be three stories above the ground and almost impossible to reach. My installer tells me that losing 10% of annual production because of snow cover is a conservative estimate, and based on what I see from public monitoring of other local systems that sounds reasonable. Of course a lot depends on the winter we have. This past winter (one of the coldest and snowiest in years), some systems were dark for three solid months. Our darkest months are November and December, and our snowiest months tend to be January, February, and March. But by March, the sun is high enough that the panels should "self plow" (dump the snow onto the ground) fairly readily.
My plan is that for the first year I will rake the snow off the garage array and not worry about the high-up array. We will have them on separate monitoring, so I will be able to readily see how much difference the effort of raking actually makes.
Then I can decide whether it makes more sense to (a) not bother raking the snow off the garage, or (b) try to figure out some way to remove the snow from the unreachable array.Leave a comment:
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It went well, and I got to ask a lot of questions. I toured the rooftop installation at Quality Bicycle Products, which has been in place for almost two years, and was hosted by the facility electrician who was in change of the installation.
His bottom line was that, at least for this installation, it performed as advertised and the manufacturer stood behind it. QBP has an older, more conventional, PV system, and the TenK modules (with reflectors) outperform the older system by a big margin.
I'm told that TenK just completed moving to a larger factory, which is part of what's been causing some backlog.
At the level of the complete system, the TenK system doesn't seem to be that much more expensive. The quote I got was for about 10% more per watt than the cheapest quote for any system, and there was more than 10% variance between installers.
I think we just have more expensive PV in Minnesota, because it's not as mature and competitive a market as in California or Arizona. Labor and overhead is something like half the cost of a PV system, so it really matters if you're in a place with lots of experienced installers.Leave a comment:
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Me too!
Hey! I'm also getting a TenK panel installation via the Made in MN rebate. Mine is a 10kwh installation (24 panels) and the price per watt is $4.68 so it sounds like we got similar estimates. I think TenK panels just cost a lot more than the imported ones. I don't know when the panels will actually be available, but I hope its as soon as June.
My installer said that pretty much every residential applicant got approved since 50% was directed to residential and most of the applications were commercial. That is unlikely to be true next year, so we're lucky to have gotten in early.
The parallel nature of the TenK panels is appealing, as is the safety of the low voltage DC. You'll have to let me know how your tour of the installation goes.Leave a comment:
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Moving forward on MN solar installation
We've finalized the design of the solar installation for my home in the Twin Cities. It will consist of 16 410W TenK modules for 6.56kw, divided into two arrays of 8 modules each. One array faces SW, the other SE. Estimated annual production is about 5,800 kWh.
The total system price will be about $30K, or $4.57/W. This is higher than what I've been hearing from some people in other parts of the country, but is the second-lowest bid of the four bids I got. I guess solar is just more expensive here--we don't have as many installers competing against each other here as in some parts of the country.
In addition to the usual 30% federal rebate, we qualify for a new Made In Minnesota solar credit which will pay a production incentive of $0.29/kWh for the first ten years. That's crazy generous, and I honestly think they goofed and set the rate too high. They could have set the rate lower and stretched the pot of money further, and maybe that's what they will do next year. In any event, we have been formally notified that our system is accepted into the incentive program so we're good to go.
The main frustration at this point is that the TenK modules are in short supply, so we won't be able to get them until June (by current estimate). I had been hoping to start the installation as soon as the snow was off our roof (which, BTW, was just this past Monday!) in order to catch as much of the summer sun as possible. No such luck.
Knowing that TenK is a fairly young company with a relatively new product, I've been doing a lot of research. Tomorrow afternoon I have a tour of one of their first installations, which I arranged through a friend-of-a-friend. This site has been in production about two years--if there are any questions I should ask or things I should look for, please let me know!
I'll post pictures when we actually start the installation.
P.S. I was curious about where the money to fund the "Made in Minnesota" solar incentive is coming from, so I did some research. It's being funded through excess dollars from a conservation program run by the state's electric utilities. Minnesota has required our power companies to set aside a percentage of their revenue each year to pay for conservation efforts like rebates on efficient appliances and light bulbs, home energy audits, and so forth. Apparently there has been some money left over, so this is where it's going.
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