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Bert

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Reply with quote  #11 
I have two of these and really like them.
https://www.amazon.com/dp/B009Z6CW7O/ref=twister_B00VKV940U?_encoding=UTF8&th=1
That's 100 watts for one panel.  If you need that much.




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Bert K.
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gbwillson

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Reply with quote  #12 
Don-

I'll admit Krautman's tube build got me thinking how much I like the square aluminum tubes. But he used ⅛" thick walled tubes that were welded. So if he has a design change, it's a pain to fix. But flexibility in building is just one of the reasons for trying the connectors. Ease of build and weight savings are another couple of reasons. I paid less than $100 for the tube connectors. I purchased a few extra connectors just in case I have a last minute epiphany. And should I change my mind or screw up cutting a tube piece, I don't have to drag things back to the welder. I'm not sure of the depth until I make the final choice for the fan setup. If I put 12V fans internally, the box would likely be deeper than one with an external fan like I'm currently using. I'm still searching for the best way to protect the polyiso. With seasonal moves, I don't like the idea of only polyiso for the exterior. And if I end up using an aluminum skin, I can purchase 6" wide aluminum flashing rolls for the sides and sheets of aluminum for the back. 

No, I'm still forced to have a seasonal setup and takedown for my collectors. My idea for a stand-free collector is to have a single large 10"-12" pneumatic caster attache to the bottom edge of the collector. There will likely be small helper casters at each end of the collector. This would be similar to how a lumber cart works, rocking in the middle, and highly maneuverable. I'd roll the collector into position, and lean it back to 60˚against a couple of posts, level and secure the collector to the ground. No more lifting!!!!! Even at my goal of being under 100 pounds total, It's too big to lift by myself. Easy-Peasy!
The casters are pretty cheap too:
http://www.menards.com/main/home-decor/furniture/casters-furniture-hardware/casters/shepherd-10-rigid-pneumatic-caster/p-1444442251789.htm












stmbtwle

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Reply with quote  #13 
Greg,

Never hurts to go over what the minimum requirements are.   Determine what the amp rating of your fan is, if nothing else connect it to a battery and an ammeter.  Exactly how much extra you need is a guessing game depending on conditions but maybe 50%.  The amp rating on the panel is on the back of the panel but bear in mind this is under "standard" conditions, not cloudy.  

A solar panel has 4 ratings:  Vmp (voltage max power), Imp (current max power). these are what the "watts" rating is calculated from.  The other 2 are Voc (max voltage open circuit) and Isc (max current on a short circuit).  Unlike a battery they will NOT put out more than that even when shorted.  You can find these figures in the advertised specs for that panel.

A 12v solar panel can put out as much as 21 volts on an open circuit.  As soon as you put a load on it that voltage will come down to 17 or so (max power), and your electric fan should handle that fine at least I've never had a problem, even with computer fans.  The panel in good sun will probably run your motor faster than what would be normal for a battery or a power supply.  When a cloud goes over the panel output will drop and the fan will slow down, but your collector is producing less heat too, so it's sorta self-regulating.  An oversized panel will be less responsive to clouds than an undersized one as it has more "reserve power".  If you think you're getting too much power I think a $10 dc speed control from Ebay would do the trick. You may want it anyway to find that "sweet spot".  Yes PV panels will work in cloudy weather, just not as well.  But then your collector is reduced, too, so it's self adjusting.  You can't hurt a small panel by overloading it, just your fan may not run as fast as you want. If you think you need more power you can order another panel of the same voltage and connect them in parallel.  You can connect a 60w panel in parallel with a 20w panel as long as the voltages are the same (check the specs).

A warning about solid state devices such as an Arduino.  They draw very little power but aren't rated for the higher voltage.   You'll need a 12v voltage regulator chip from Radio shack ($2).  Easy to hook up only three wires, +in, 12v out, and common negative.  They're only good for 1 amp though so don't try running your fan with one though you could connect several in parallel to get the amp rating you need, or find a higher capacity regulator.

Hope that answers your question...

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Willie, Tampa Bay
KevinH

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Reply with quote  #14 
Greg,
There are a couple rating methods for the panels, both are based on 1000 watts/sq meter solar radiation.  There is a little info here on BIS:
http://www.builditsolar.com/Projects/PV/EnphasePV/PVPanelRatings.htm

I don't know what watts/sq meter we get here in MN in the winter and you would have to take into account what the panel would produce at the morning / afternoon angles.  There are only brief times in the early morning and late afternoon where I would want the fans to run slower.  The cold winter temps are a plus for solar PV.

As Willie mentioned depending on the load the solar panels can output more than 12V.  Although the fans can probably operate at the higher voltages I would be concerned about shortening their life.  A voltage regulator or a battery in the circuit would help with that.

One other thing to consider when running the fans directly from the solar panel is snow.  If snow covered the PV panel, but the snow slid off the ZP, the PV panel may not put out enough to power the fans.

I think the hardest part of going with a row of DC fans is figuring out the ratings and number of fans needed.  I used three 120mm fans rated 113cfm with a 5.91mm static pressure on my latest collectors.  I originally thought that would be too much, but it was actually a little lower than I wanted for the final cfm output of the system as a whole (probably needed a bit more on the static pressure rating).  When fans are run in parallel the pressure of a single fan needs to be sufficient.  Multiple parallel fans are done to get more cfm.

You could probably fit up to 9 120mm (~4.75") fans in your collector, but that increases the depth at the fan end.  For the 16' length and amount of ducting I'm guessing you would need a higher static pressure fan than I used.  I don't remember what you are running your current collector at, but it was well over 3cfm/sq ft.  Higher static pressure/higher cfm equals more current.  My 3 fans total about 22-23W.  A single 200 cfm / 16mm static pressure fan is almost 24W.  It's difficult to say what combination of fans / ratings you would need.  Idaho Tom also used a row of DC fans in his Cinefoil collector, but he had large in/out openings (most of his posts are gone).

The pressure/cfm graph is the best way to compare fans.  You can get an idea of the cfm from the graph at a certain pressure drop to compare the relative performance of different fans.  BIS has some info here on collector pressure drops he measured.
http://www.builditsolar.com/Projects/SpaceHeating/FanSizing/FanSizing.htm

Kevin H
MN

Bert

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Reply with quote  #15 
Here's an article on series and parallel fans.
http://www.greenheck.com/library/articles/42

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Bert K.
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gbwillson

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Reply with quote  #16 
Interesting information Bert-

I'll have to contemplate further before I commit to DC fans. It will probably be when I'm about finished with the basic framing and installation. But I was kind of thinking of splitting my fans between the intake and the exhaust. I know fans placed tightly side by side disturb the flow pattern of each adjacent fan, So by placing some fans at the intake and some at the exhaust, I can space the fans some distance apart. This would also help alleviate some of the glazing bulge when a single powerful fan is used to push air through the ZP. 

Kevin-I have absolutely no idea how of what I would need for me to reach my CFM output goal. I do have an adjustable 12V power supply that I could use until I know my fan power needs. Small fans are cheap, so I could buy a few extra and add fans as needed until the CFM needs were met. Then I could purchase the required power supply. But I still have no clue as to the static pressure needs. I know the ZP has lower resistance than same-sized 2-screen, but that was tested using 4x8 text units, using far less velocity. 

Nice thing about using the fittings, is that it allows me to control the size and depth of the collector box, and make changes rather quickly, and inexpensively.

Greg in MN
gbwillson

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Reply with quote  #17 
Hi gang-

Every year I try to start my builds before things get too cold. And every year life gets in the way, and this year was no different. But, the next few days are supposed to be rainy, so outdoor projects will be delayed, hopefully not until spring. So now is a great time to get off to a good start on my new ZP build.

I actually had a possible opportunity to have my aluminum tubing welded up like my friend Craig did. But the logistics of a welding unit, a person to weld and a 50 amp 220v power supply never were able to come together over the last month. This was to be done pro-bono, with a few bucks and plenty of food. When the plans collapsed, I went to a local welding shop for an estimate to have my aluminum tube skeleton welded up. It turns out that TIG welding has a going rate of about $2.50 per INCH!!! So my estimate came to over $800! Needless to say, welding was far out of my budget. And thankfully I didn't end up screwing over the generous offer by the neighbor of a friend by cheaping out on fair payment for welding.

So back to the plastic connectors for assembly. Don't get me wrong, I like the connectors, but when the opportunity arose to possibly have the cage welded, I jumped at the opportunity. But the connector connections will need quite a bit of work to make them solid. Many braces, gussets, screws and glues will be needed to stiffen up my collector cages. I say cages as I will be making two 4x8 sections, and bolting them together for final assembly once they leave the basement workshop. So let the fun begin...

Greg in MN
Rick H Parker

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Reply with quote  #18 
Quote:
Originally Posted by gbwillson
Hi gang-


I actually had a possible opportunity to have my aluminum tubing welded up like my friend Craig did.
But the logistics of a welding unit, a person to weld and a 50 amp 220v power supply never were able to come together over the last month.


Greg in MN


You can braze Aluminum with a propane torch.


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Rick H Parker
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gbwillson

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Reply with quote  #19 
Rick-

I had previously thought about trying to braze my aluminum tubes but decided they are not strong enough. I think it was Kevin that suggested brazing. My tube walls are 1/16" thick which would allow very little material to bond a joint together. Mathias Wandel did some testing on some brazed aluminum tubes. The strength of the joint varied greatly depending on the type of force that was being applied. Some test joints broke with as much as 500# of pressure, while others broke with as little as 40#. If my collector was to be permanently installed I'd be willing to give brazing my tubes a try. But the thought of trying to repair a broken joint once the collector was built doesn't seem like a wise idea.

Greg in MN


Brazing strength test:
Bruce

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Reply with quote  #20 
Greg, are you done yet?  Online and blowing heat? LOL   We all know how things seem to take longer to do than we planned!  This gets even more so as we get older, it seems ;-)  When I started my Project in July, I thought I would easily have it done by October.   I am retired but seem to have so much more to do these days.  This is a neat project you have here.  Have fun and update us from time to time, but don't worry about time...we can wait! Good Luck!
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