Encapsulating with EVA

[Mike90250]

EVA is a VERY special plastic hot melt glue / sealant. It's special property is that is impervious to water vapor (and quite UV resistant). Water vapor is not stopped by paints, or most epoxies. Water vapor zooms right through silicone sealant (it's a cure agent for most silicone in a tube products)

[bcroe]

Many many semiconductor devices are not in airtight packages.
Most likely the CPU you're using to read this (and the web servers' CPUs ) are not in airtight packages.

Some devices have what is called glass passivation. This protects what appears to be a bare
die. No doubt there are other methods I have not kept up with. Protection is necessary.
Bruce Roe

[foo1bar]

Silicon semiconductor devices are always in an airtight package, because otherwise moisture would
destroy them in a fairly short time. This includes solar cells. Bruce Roe

Many many semiconductor devices are not in airtight packages.
Most likely the CPU you're using to read this (and the web servers' CPUs ) are not in airtight packages.

Most server CPUs have packages that the back side of the die is directly exposed - the heat sink for the system directly contacts the back side of the die.
Even for older CPU packaging where there is a metal slug as part of the package the package isn't air-tight. The air inside it goes significant temperature increases (ex. 20C to 70C in minutes) So I think even small amounts of trapped air could create enough force to force things apart. Those types of packages usually had a built-in air hole/channel to equalize pressure inside and outside.
If you go back even further to 386/486 timeframe, those packages were probably air-tight - they had a cavity that would be filled in with an encapsulant after the wirebonding was finished.

But the general idea that you don't want moisture on semiconductor devices (including solar cells) is true.

[littleharbor]

I would think , besides fully encapsulating the cells, the front EVA sheet would cushion the cell and prevent it from cracking while under vacuum. With the soldered tabbing and inter cell connections there is no way the cells would lay perfectly flush against the glass.

[bcroe]

do we really need EVA sheet in front of solar cells?

Silicon semiconductor devices are always in an airtight package, because otherwise moisture would
destroy them in a fairly short time. This includes solar cells. Bruce Roe

[Mike90250]

do we really need EVA sheet in front of solar cells?

I don't know for sure. You could read the post just before yours, and see if the answer is more clear.

[sdold]

do we really need EVA sheet in front of solar cells?

If only we had a forum member in the EVA business who could educate us.

[Erin]

do we really need EVA sheet in front of solar cells?

[Erin]

is function of EVA here is protection and package of solar panel?

[Mike90250]

Do we really need EVA sheet in front of solar cells ?

Only if you want a moisture proof seal to the front glass (needs vacuum lamination). EVA also provides some resilience between the thermal coefficients too.

[caliman]

Do we really need EVA sheet in front of solar cells ?

[Mike90250]

mike. can you give the name and address of the 2 places that have the broken trackers that you say are broken.I would like to go and see them
tks

They are in Northern California. One is a store right along hwy 101 , the other is a private resort 40 miles down a dirt road.
I cannot name them, and the arrays are not quite large enough to make out in google earth.

[conntaxman]

solar tracker

Ive seen the site of a large solar company, with about 8 tracker arrays in their parking lot. All have been broken and frozen for 6+ years.

I've been to a large off grid campsite, with about 4 of my size arrays (3Kw x 4) on 4 tracker poles. All broken, and unable to keep running. He had to re-align by hand and lock down.

I also know 1 person with a 800w passive tracker (uses butane inside hollow tubes as counterweights to track the sun. That is still working after 12 years.

So if you are building a smallish tracker (1kw) you are likely to know how it works and able to get replacement parts. But generally, they fail.

mike. can you give the name and address of the 2 places that have the broken trackers that you say are broken.I would like to go and see them
tks

[s.xavier]

nothing wrong with DIY modules but to say they will work anywhere near manufactured modules is a tough sell... after you take into account the production costs and time allocation how much do you really save compared to a manufactured system???

the idea of large scale production fundamentally will bring down costs... you can build a car from scratch but can you honestly really say it will work as well as a BMW or Benz?? I'm not doubting you can't and innovation/imagination should be fostered but lets take into account other variables... like while building this system, isn't there something more important to allocate your time??

just my two cents

[bruceme]

Stupid simple passive alignment

I think I found a link to that passive tracker system. Super simple and I really like it. Does this look right?

http://towardsabettertinyhouse.wordpress.com/2011/03/01/super-cheap-easy-to-build-solar-tracker/

The readers digest version(of this one)... It uses a dual-sided gas filled piston with shade slats. If the left side gets hot... it expands more than the right and angles the entire unit into the sun... BRILLIANT!

-Bruce