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Solexx vs Polycarbonate  RSS feed

 
Paul Ladendorf
Posts: 38
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I'm debating on whether to use the Solexx light diffusing panels or polycarbonate.

My goal is to overwinter citrus and tomatoes, grow greens in the winter and generally just get food as early as possible in the spring.

First off, I can't find the R value for the Solexx but assume its probably comparable to polycarbonate. Every time I read an article or watch a video about Solexx, they say "its a great insulator". But that really doesn't mean anything. The R value is the bottom line.

Also, am I understanding that Solexx reduces heat in the greenhouse? Any idea by how much? That is great in the warmer months and/or if you're not storing the heat but in the winter or if you want to store heat it wouldn't be desirable. Am I thinking straight?

I'm also guessing that Solexx would be better for plants that don't need as much direct light. That issue seems a bit controversial as I've heard some people say that all plants do better in diffuse light.

Polycarbonate and Solexx are comparable in price as far as I've seen.

Thanks for any insights.


 
Dillon Nichols
pollinator
Posts: 597
Location: Victoria BC
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Hi Paul,

Funny timing, I just picked up a few 4x8 sheets of 5mm Solexx today, it was getting cleared out as the local distributor unfortunately seems to have died.


As far as the lowered heat in the summer vs winter, I was thinking about that earlier. If you are doing an above ground greenhouse, one could use glass, or something else transparent, for the walls, and Solexx for the roof. That way, in the winter when you want the heat, you'll be getting more energy through the walls than the roof compared to summer courtesy of the low angle sunlight...


Looking to see what I'd gotten my hands on, I found this table of claimed R and U-values for Solexx vs some alternatives @ http://www.led-grow-master.com/Paneling.html

Makes it sound pretty impressive...

solexx-insulation-r-value-chart.png
[Thumbnail for solexx-insulation-r-value-chart.png]
 
Paul Ladendorf
Posts: 38
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Thanks Dillon. That's interesting you say that about glass on the walls because that's exactly what I'm doing since I already have it. I love how you said "claimed" in regards to the R value because until I see an independent test, I take those claims w/a grain of salt.
 
Dillon Nichols
pollinator
Posts: 597
Location: Victoria BC
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I tracked down the same table of stats on the solexx.ca site, but don't see anything to quantify any third party testing. The pictures of snowload on a small greenhouse are impressive though. Sent them an email seeking more info, will report back if anything comes of it.

R-values listed for polycarbonate (@ polycarbonatestore.com) seem close to the numbers Solexx lists for those options, for what that's worth:
8mm 3-wall: R1.93
10mm 2-wall: R1.9
8mm 2-wall: R1.7

However, that site also sells:
16mm 3-wall, R2.5
16mm 5-wall, R2.78
25mm 3-wall, R2.941

I don't see light transmission rated on the solexx.ca site; http://www.led-grow-master.com/Paneling.html states '72-77% soft, diffused light'. Is that the light transmission value? Beats me...


I think the glass/solexx or glass/polycarb mix is pretty promising, allows for some use of scavenged glass to keep the cost down, but avoids it for the roof which would be harder, and riskier, to do that way.
 
Paul Ladendorf
Posts: 38
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Dillon,

Thanks for posting those numbers. Yea, my wall glass came from salvaged defunct sliding glass doors. I'm a little concerned with the heat loss from single pane glass though so am considering insulating it with bubble wrap as shown here: http://www.builditsolar.com/Projects/Conservation/bubblewrap.htm

 
Bernard Erinaceous
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Hi Paul,

I currently operate a greenhouse that employs Solexx as it's only glazing. As a point of comparison, it's roughly 1200sqft, roughly 6ft below grade, and utilizes a solid north wall with lots of thermal mass throughout.

I'm not the biggest fan of the Solexx. It has it's benefits, namely a purportedly higher R value and, especially where I'm at, the ability to withstand hail storms in better shape than hard walled polycarbonates. The thing that bothers me the most about it, however, is the rather drastic expansion and contraction of the material with fluctuations in temperature. Our structure is covered in a shingle-lap fashion, rolling out strips the entire length of the structure and starting from the bottom up. As a result, the overlapping portions that span the gaps between the rafters expand and contract considerably. The manufacturer suggests installing it when it's 60 or so degrees F to mitigate this expansion but we still see gaps up to around 4 inches where it laps. With added work and some creativity, it can be mitigated, but bear in mind that it has to flex some so attaching it too well can lead to it ripping out from whatever you use to fasten it (we used metal roofing screws).

Here's an photo of some of the gaps that form. These were on a 70-80degree day. They get worse when it's even hotter and sunnier.


A friend with an even larger in-ground structure attempted to run his parallel with the rafters so that the overlap landed on the rafters. They also tried to screw more frequently (4" as opposed to our 6-8"). The result is an extremely leaky greenhouse that rains almost as hard inside as it does outside.

A potential solution that we're investigating, though not my favorite, is applying gutter sealant at the lap joints before screwing it down. The stuff is extremely tenacious but still stretches enough to allow the solexx to flex and yet prevent large gaps in the structure. We haven't employed it at any real scale yet but our tests of gluing w/out screwing then leaving the pieces on the sunny dash of a truck on a 95 degree day were promising.

To directly address some of your questions:

-Solexx doesn't really mitigate heat gain in our structure. Granted, we have tons of thermal mass to exacerbate the situation, but we were achieving temps of upwards of 120 degrees in early spring (zone 4) when the outside temps were between 40-60. We still use a 30% shade cloth during peak heat. The claims that I'm seeing on their website don't so much say that it reduces the heating of the greenhouse directly but that it's "superior" insulative properties reduce the amount of additional heat needed to maintain temps during colder seasons. That much I've observed. On day's when it's 10-20 below 0, the temps in our structure tend to be 18-25 degrees above 0 with no additional heating.

-Plants that like indirect light may benefit. It does, to some extent, diffuse useable amounts of light but I don't think that it's much of a factor. We grow plenty of sun loving plants that get plenty of light, even with the additional 30% shade cloth. At the same time, plants in shadier areas of the greenhouse don't seem to benefit much from the supposedly even diffusion of light offered by solexx. They still appear leggy and stunted compared to those in more direct light environments. Still, it's workable, just gotta plan accordingly based on your site and your needs.

My apologies for the wall of text. This is one of the first times I've had something meaningful to contribute whilst the discussion was still active!


 
Rebecca Norman
gardener
Posts: 1255
Location: Ladakh, Indian Himalayas at 10,500 feet, zone 5
126
food preservation greening the desert solar trees
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Location, location, location, folks! Please add your location or at least a region and zone to your profile, so the rest of us can have a better idea whether our experience would be relevant to you.

I love having an attached greenhouse on my house here in the high desert. Very important is that we remove the greenhouse for the summer, approx May - October. It gets badly overheated already in April and early May, though we ventilate as best we can. Better ventilation would help in those shoulder seasons, but even ventilation might be not enough in midsummer with the intense sun at our location. If we left these greenhouses on, I think the plants would get cooked in them.

We use flexible film. We used to use a more transparent type but it tended to rip in our bad spring winds. The past 4 or 5 years we are using a film called something like Silpoline that is tougher but less transparent (sorry, I'm not the one who purchased it). Inside the greenhouses does go a few degrees below freezing during mid-winter nights and mornings, but it heats our houses and provides veggies, and a nice greenspace to enjoy when there's nothing green outdoors. We used a rigid polycarbonate on another building once, and the expansion and contraction were a big problem. Check the UV resistance of your material, as plastics that aren't UV resistant (or installed upside down with the UV-resistant side down) start breaking down in one or two years in our sunny climate.

We don't have hail or heavy snow loads, but we do have destructive winds, especially in spring. We have a problem with feral dogs breaking in, and also sometimes our students can't resist playing cricket near the houses. We have extreme sunniness and fairly low latitude (34N?) so loss of transparency is not crucial to us, but UV resistance is. Your situation is probably different.
 
Paul Ladendorf
Posts: 38
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Bernard,

Thanks for sharing your experience. That's really helpful. I've heard others talk about issues with polycarbonate expanding and contracting as well.

 
matt sorrells
Posts: 126
Location: Canton, NC
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I'm just getting used to a greenhouse with Solexx as well. I put the 3.5 mil stuff on, and it is almost blindingly bright in there when the sun is out. Doesnt help that I painted my block walls white, lol. I have thermostat operated shutters on one end and a thermostat operated fan on the other end and a window below that. The shutters open at 80, pulling air across the greenhouse via chimney effect, and then at 95 the fan kicks on pulling air from the window and shutters. I planted in the ground in this underground greenhouse, so the at ground temp is still 10 to 15 degrees cooler at this time than the air temp. The hottest I've seen it in there was around 100 (in the peak) during an 80 degree day.

I've noticed the expansion as well. I chalked it up to my perfect expectations failing me. I was instructed to put the material on in the middle of the highs and lows ( I guessed 40s since we get temps from the teens to 80s, with occasional higher and lower). My expectations were of a perfectly flat roof as I had made all the trusses as flat as possible, but within a few days of it being on, I was noticing that my expectations were letting me down and that was all there was to it. I have not noticed any leaks in the structure, however when it was sealed off in the winter I would get rain inside when the temp would rise as the sun hit it. Pretty neat actually - sunny outside and raining inside. I sealed it off in the winter to mitigate warm air running out of the shutters like a sieve. I feel the solexx insulates very well. With the shutters masked off, I was holding 20 degrees warmer than outside with only a few old holiday lights running. This year I will have a completed rocket mass heater to run and I hope to maintain warm temps.

If I had it to do over again, I'd still use Solexx. I'm happy with it - we just have to remember that no product is going to operate as a double pane window would (and even that wouldnt do THAT great if a greenhouse was made of all those). I've already had my youngest throw a hard dirtball at it accidentally which bounced off like a drum with no damage.

The only thing I noticed is that the rubber backed screws do let moisture in between the layers, but perhaps it is because I did not tighten enough.

Also, if you do get solexx, you should seal the ends with silicone. This is very difficult on smaller pieces, as silicone off-gasses and will push itself out of the cell. maddening.
 
Dillon Nichols
pollinator
Posts: 597
Location: Victoria BC
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*Blast* the unreliable 'new post' alerts, I have got to stop relying on them!


Bernard and Matt, that is really helpful information, thanks!

Can either of you quantify the observed expand/contract cycle further, in terms of total measured change for a given temperature swing?

Is this movement happening only width-wise(across the cavities/ribs), length-wise(with the cavities/ribs), or in both dimensions?

My sheets are nominal 4x8, and I also bought the 'H-channel' that Solexx sells to join the sheets. Now I'm wondering if the H-channel slots are deep enough to work reliably...
 
Bruce Warren
Posts: 2
Location: Brookings, OR
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Regarding SOLEXX'S panel joint mating. They provide a "H" panel that slides in-between the 4' panels. I have their Oasis, 8' X 12', live in the SW corner of Brookings, OR. In the spring weather, cool, sunny, had temperatures in the high 90 inside. I have the temperature controlled exhaust fan with the vent louvers tied together electrically. Ended up, ordering another door frame and had that screened. It helps keep the temp lower. Key word there is LOWER. Come the cooler months, I will replace the poly-siding door back on. As we all know, SOLEXX is a white-ish material. With that in mind, you will understand why there is a decal just to the right of the door frame, "SLOEXX GROWING ROOM, 11th COMMANDMENT; Thou shalt not call me GREENHOUSE." Mine has only been up since April, no leaks. Am growing green beans, snow peas, tomatoes, cucumbers, yellow squash, zucchini and bell peppers. Already harvesting snow peas, green beans, cucumbers, yellow squash, and zucchini. Needless to say, I've got lots of trellising up.

Bruce
Brookings, OR
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