Glass Glazing: I'm sure clear is best but could a smoky gray still work?

System

I've been wanting to try out something along the lines of a DIY solar can furnace and/or thermosiphon water heater. I have access to a LARGE piece of glass from a conference table, unfortunately it is not 100% clear. You can still see through it but it has a smoky charcoal tint. Would it be worthwhile to even try it out or should i kept looking for something clear.

Cariboocoot

Re: Glass Glazing: I'm sure clear is best but could a smoky gray still work?

Look for something clear.
If you could test that glass in full sun with a light meter you'd be amazed at how much light the "slight" tint blocks. Probably blocks more of the near infrared than of the visible. You want as much energy to get through the glass as possible. The more that acts on the collector the more efficient it will be.

System2

Re: Glass Glazing: I'm sure clear is best but could a smoky gray still work?

Thanks for moving it in a more appropriate place and a quick response. I wasn't sure where it fit best. That's a shame as this is a really large nice piece of glass for free.

rollandelliott

Re: Glass Glazing: I'm sure clear is best but could a smoky gray still work?

i think it depends on where you live,
in florida I would do it, cause it would work fine
in north carolina it would probably still be OK
but if you live in Michigan, maybe not..........
also you can't cut tempered glass
is it square or round?
If round it's going to be a pain to retrofit a systen under it.

2manytoyz

Re: Glass Glazing: I'm sure clear is best but could a smoky gray still work?

I'm in FL, and had thoughts of putting a Lexan cover over my solar panels to prevent damage during hail storms & hurricanes.

As a quick test, I put a piece over a panel to find out how it might affect the performance. I was surprised at the results.

http://www.youtube.com/watch?v=IEDPUQKlE-I

One person suggested it was the angle of the panel casting a shadow, ignoring the fact the panel never was moved, and the Lexan sheet layed flat on the panel.

But to show the Lexan always blocks some light (creating a shadow), I made another video:

http://www.youtube.com/watch?v=gO3_xC-4SKk

Lexan is not perfectly clear. It has a slight tint to it. Sitting next to a piece of clear glass, it's easy to see the difference. This apparently blocks enough of the light spectrum to affect the performance of solar panels. Scratch this idea off my list.

So that said, I'd recommend the same test with any material you plan on putting over your panel. Might not like the results, especially with any material with any level of tint.

ggunn

Re: Glass Glazing: I'm sure clear is best but could a smoky gray still work?

2manytoyz wrote: »

I'm in FL, and had thoughts of putting a Lexan cover over my solar panels to prevent damage during hail storms & hurricanes.

As a quick test, I put a piece over a panel to find out how it might affect the performance. I was surprised at the results.

http://www.youtube.com/watch?v=IEDPUQKlE-I

One person suggested it was the angle of the panel casting a shadow, ignoring the fact the panel never was moved, and the Lexan sheet layed flat on the panel.

But to show the Lexan always blocks some light (creating a shadow), I made another video:

http://www.youtube.com/watch?v=gO3_xC-4SKk

Lexan is not perfectly clear. It has a slight tint to it. Sitting next to a piece of clear glass, it's easy to see the difference. This apparently blocks enough of the light spectrum to affect the performance of solar panels. Scratch this idea off my list.

So that said, I'd recommend the same test with any material you plan on putting over your panel. Might not like the results, especially with any material with any level of tint.

Even if it looks perfectly clear, much of the energy production comes from the high frequencies ranging into the UV which we cannot see.

techntrek

Re: Glass Glazing: I'm sure clear is best but could a smoky gray still work?

2manytoyz wrote: »

I'm in FL, and had thoughts of putting a Lexan cover over my solar panels to prevent damage during hail storms & hurricanes.

Not an option for hail storms since they are sudden, but you could still use your idea for hurricanes and get some output. Better than putting plywood over your array and cutting all production.

rollandelliott

Re: Glass Glazing: I'm sure clear is best but could a smoky gray still work?

"Even if it looks perfectly clear, much of the energy production comes from the high frequencies ranging into the UV which we cannot see. "

regular glass blocks a huge amount of UV light. That is why photographic lenses which record UV light are often made of quartz.

Most clear materials will transmit both visible and infrared light easily. infrared light can heat things up more than UV for solar thermal.

rollandelliott

Re: Glass Glazing: I'm sure clear is best but could a smoky gray still work?

that's not comparing apples to apples. He wants to produce solar thermal energy, not PV. Many solar thermal systems have lots of excess heat. A little bit of tint might not be a big deal for a thermal system.

sure, it is comparing apples to apples as it is the same solar energy. it matters not that you intend to make electricity or heat with the sun's energy as the amount of electricity produced can be a makeshift indicator of the efficiency reduction introduced by that smokey tinted glass. most pvs respond well into the infra red range and that is the spectrum for heat production.

niel

Re: Glass Glazing: I'm sure clear is best but could a smoky gray still work?

don't know what happened when i first tried to reply.

anyway, yes, it is comparing apples to apples for it doesn't matter if one is using that same solar energy to produce heat or electricity. most pvs respond well into the infra red range and that is the range that causes heat production making the pv into a rough efficiency indicator by showing the losses of various glasses through lowered power production. a loss is a loss and somebody looking to harvest the sun's energy, no matter the purpose of it, just does not want the spectrum partially blocked.

rollandelliott

Re: Glass Glazing: I'm sure clear is best but could a smoky gray still work?

solar thermal systems can typically heat way more water than a person needs and are very effcient.

solar pv systems are rather ineffcient on the other hand, many people's systems do not even provide enough electricity to power their household needs.

Therefore solar thermal systems can use a glazing that is not as effcient.

Two real world examples.

Company at www.solarroofing.com uses clear plastic cardboard (brand name polygal) instead of glass as a glazing. Polygal's light transmission specifications are much less than glass.

People often wash/clean their solar panels to improve electricity production. However you dont' hear the same advise about solar thermal because it is so much more effcient.

bottom line you can theoretically debate things and do experiments, etc, but in the real world you can use a glazing that is slightly tinted, and does not transmit as effciently as the low iron glass used in Solar PV and still have a great solar thermal system.

ggunn

Re: Glass Glazing: I'm sure clear is best but could a smoky gray still work?

rollandelliott wrote: »

that's not comparing apples to apples. He wants to produce solar thermal energy, not PV. Many solar thermal systems have lots of excess heat. A little bit of tint might not be a big deal for a thermal system.

My bad. I thought we were talking about PV.

The Original Ralph

Re: Glass Glazing: I'm sure clear is best but could a smoky gray still work?

for the heck of it, it wouldn't take a lot to set both that tinted glass and a pc of clear glass over an enclosed area, side by side, blackened everything under the glass and simply measure the temps you're getting

when i needed to cure some fiberglass pcs that were rather large (the hotter the temp you cure epoxy at, the higher it's thermal set is or the temp at which it'll soften and lose it's shape memory)

Using totally non-optical 6 mil plastic film from Lowe's, set up like a tent over a 4' long airplane canopy, on an asphalt surface (therefore not totally black), i was able to hit 193F between 12:00 to 3:00PM

fwiw