Thin film (amorphous) PV, overcast friendly?

[lifer]

I know there were a lot of (old) discussions around this subject but I wonder if there's any (good?) news about this technology.

Right now, the sky outside my window is the most plain and smooth GRAY surface I ever seen - and that's the third day in a row like that. My poly PVs are simply defeated (from 1800W per hour few days ago).

I read some commecial stuff (datasheets included in this category for a reason) about specific thin film panels (Sharp, Schott) but the power vs irradiance diagram looks similar to mono/poly PVs.

The only difference I noticed is the negative temperature coefficient (though overcast and high temp will never meet!) so I don't see any real advantage here.

In hot/sunny days the PV power output is at its highest level anyway so a 20% attenuation (because of positive temperature coefficient) it's not an issue (speaking of classic crystaline technology).

So, what's the catch? They also advertise the vertical mounting option (on walls, facades) and higher efficiency on diffused lighting condition. Thus I could mount them on my wall facing north?

Anyway, I have a lot of space available to mount them at any angle on a flat roof (no shading) but I need to know what's the real gain on overcast (versus actual poly I have). Does anyone have any recent experience with these amorphous panels?

[DamonHD]

Hi,

In this graph:



the green line is the ratio of generator of two otherwise reasonably-matched PV systems on a school roof, amorphous to mono.

There are complications, but that does seem to indicate that amorphous does better in overcast conditions from the amorphous being about 60% of output in winter and 40% in summer.

Rgds

Damon

[lifer]

Thanks, Damon!  I read your topic about that school roof project but I still don't really understand the graph.

So, for a specific low light condition, if a mono PV panel outputs 400Wh (by example), the amorphous PV will generate around 600Wh (60% of total generated power)?

Anyway, my poly PVs are more than enough during regular (sunny) days so I'm not concerning about amorphous efficiency on summer. I just need more power during this overcast periods and I try to find out if it's better to buy more poly PVs or give amorphous a chance.

By the way, did you use a MPPT charge controller, a simple PWM one or direct charging?

[Flux]

I don't know about the thin film amorphous units but at one time there was  a lot of amorphous stuff that looked to be good value for money if you could cope with the greater size. Nearly all the stuff I met proved to have a very short life and aged rapidly so I would want a lot of reassurance about life as well as performance to even consider the things.

I don't think the low light performance is likely to be drastically better so you are looking at lots of units and life proved short it may not pay off at all.

Flux

[lifer]

Schott Solar - Thin film

That's 30 yrs, Flux!.. dare to deny that?!

[Flux]

OK thanks for the link, it's certainly not the technology I had dealings with so perhaps we can ignore the life issue.

I still think the results will not be fantastic in poor light so I still don't know how the cost effectiveness will compare with polycrystalline . The output of solar in days without shadows falls so rapidly that it ought to become the accepted standard here in the uk if it was drastically better.

Similar situation to wind turbines in low wind areas, at what point does it cease to be cost effective.

Flux

[DamonHD]

So, for a specific low light condition, if a mono PV panel outputs 400Wh (by example), the amorphous PV will generate around 600Wh (60% of total generated power)?

That sort of thing but be clear that that is 60% of a much lower overall output.  I expect typically 1--10% of full output under heavy--light cloud.

By the way, did you use a MPPT charge controller, a simple PWM one or direct charging?

MPPT grid-tied.

Rgds

Damon

[lifer]

I've got 5 -10% from my current poly panels so that's not what I wanted to hear.

Thanks for your advices, Flux. Seems like the amorphous panels aren't that long awaited breakthrough technology. Maybe the spectrally-selective (infrared) panels would save us one (overcast) day.

Glad to hear you're living in the UK, too (besides Damon). I have some good friends that keep asking me to move there. To be honest, the UK overcast climate was the only major impediment. I prayed for amorphous panels to clear the road with no luck..

[mab]

I've got some good amorphous (unisolar) which I've had for 7ish years and are still going well - 100% rated output as far as I can tell; shadow tolerant and seem to work well in low light (still putting mA into the battery when the sun has set with a sunlit cloud overhead).

There were/are some dirt cheap amorphous which I had some ~ twenty years ago and they were poor in anything other than direct sunlight and didn't last long.

I bought the Unisolar at a time when I could get them for half the price (per watt) of the crystalline types, but whilst they may be a little better in low light, you won't be getting much power from any type in low light so I would tend buy whatever offered the best price per watt (with a decent quality & lifetime), which would give me the most watts for my budget, which would in turn give me most Wh into the battery for the money spent whatever the light level.

It does depend where you are in the UK - I'm in SW Wales so I can go a long time without seeing the sun, but if you're in the east, southeast or on the south coast it is quite a lot sunnier on average. I'd swear that I used to get more energy from 300W of PV in suffolk than I do from 900W here. Luckily I took the climate into account when I moved here and got a place with hydro-potential (currently running 400w - one thing Wales doesn't lack is rainfall).

[lifer]

That explains the lack of informations on various manufacturer websites:  SHARP Thin film. No graphs, no diagrams - just "ultimate" useless characteristics (frameless design, no cadmium).

The best solution for low light condition: more batteries.

[lifer]

Digging a little deeper, I become familiar with the whole thin film specific technologies. I must admit I made a confusion at first (thin film = amorphous).

Actually, there are three main variants of thin film category: amorphous silicon (a-Si), cadmium telluride (CdTe) and copper indium (gallium) selenide (CIS/CIGS).

From what I've read so far, the last one (CIS/CIGS) has the biggest potential. The leading manufacturer is the japanese based company Solar Frontier.

CdTe has a north-american leader (First Solar) but the technology make use of high toxicity component (cadmium) and it's future is not so bright.

Anyway, neither of these has a clear advantage over crystalline panels in low-light condition (they are "just better", as Damon has suggested with that graph).

For more detailed informations:

Best Thin-Film solar panels
Solar Frontier - Low light behaviour
First Solar - Product range)