Pliable Solar Cells on a Roll

klevin writes "New Scientist is running a story on someone else who's developed thin, flexible, photovoltaic cells: 'The thin and bendy solar panels can be stuck to fabrics, sheets or backpacks and promise a go-anywhere electricity supply.' Whatever happened to those sheets of solar cells that some university here in the US developed several years back? As I remember, the concept was that they could be draped across roof-tops and whatnot. Never heard anything after that." We had post about solar building clothing last year.

Iowa Thin Film Technologies

[Anonymous Coward]

The poster might have been thinking about Iowa Thin Film Techologies [iowathinfilm.com]...

Flat vs. Flexible Info

[sahrss]

To address some of Klevin's confusion, since I've been following solar panel advancements:

Thin, flexible cells have been around for a while. One reason they haven't caught on heavily is because they're nowhere near as 'powerful' (efficient at conversion) as hard panels. Did a quick search (don't take this data *too* seriously, but it represents what's normal); compare panels from these two pages:
Flexible [solar-electric.com]
Solid [solar-electric.com]

Specifically, compare "Unisolar 32 watt flexible solar panel" from the first link to "Shell ST40 thin film CIS 40 watt solar panel" on the second. The flexible panel is 940 sq. inches and 32 watts, while the solid panel 663 sq. inches and 40 watts. Big difference in watt per area.

I ended up choosing a big solid one to fit in the rear dash of my car; flexible would have been easier to deal with, but it won't fold, and produces less power. (I use the panel in my car to power my laptop/cell phone combo while camping and stuff, it's very cool and gets a lot of questions from random interested people!)

Here's another chart to compare the two: Product Page [selectsolar.co.uk]
Tried to find an efficiency rating chart comparing the two types, but no luck. The numbers are out there somewhere...

Re:Not really

[krymsin01]

Yes, you are correct in that, but if you made the sail out of a large, lightweight, flexible solar panel, you'd be generating electricity and momentum.

Re:Not really

[Anonymous Coward]

Oddly enough, not so much the force but the momentum. And not subatomic particals so much as light. Stars appearently make a lot of light. And that's why solar sails, as opposed to cells, are reflective. The radiation pressure equation would probably provide more insight into this should you wish to investigate further.

cell phone

[Anonymous Coward]

Cell phones, and battery powered devices in general are pretty easy to figure out.

If your phone has a 780mAh LIon battery (it does, roughly), then the battery contains 0.78*3.7 (3.7 is the nominal voltage) or 2.8Wh of power. then you figure out how long the battery lasts.

In the case of a phone, just turned on, doing nothing, it probably lasts at least 56 hours. 2.8Wh/56 = 0.05W. The phone is using 50mW of power on average. When you are talking, you probably get about 5.6 hours of talk time. So it's using 0.5W (500mW) on average.

All this is pretty easy to do with battery-powered devices. If you have a wall-powered device you need something to measure the power usage, like a Kill-A-Watt.

Is $US52 per square metre about right?

[thorpie]

They quote 7% efficiency, 1 euro per watt.
Full sun is 1000 watts/sq metre, so with 7% efficiency we get 70 watts/square metre, so it has a cost of 70 euros/sq metre or, at 1.33 euros to the dollar, about $US52.60/sq metre.
Cover a 10 * 4 metre area of roof for $2,100 and get enough energy, in the middle of summer, to boil your 2 kw electic kettle all day.
At 12c per kwH for electricity, @ 2.8 kw * 6 hours/day * 365 days/year gives a cost saving of $735 pa, or a repayment of the $2,100 capital in 3 years

Are these numbers OK?

At this price will it be practical to disconnect from the grid sometime soon?

Weight is the key...

[The Kiloman]

Usually people imagine solar sails as being made of a very VERY thin film,on the order of a few micrometers thick... the point being that there's very little additional mass created by the sails themselves since you need so much surface area to create any appreciable force. Also, the less mass that's used for the sails, the more mass that's available for payload (or just plain not there, which means greater acceleration).

Here's a few links (thanks Google and the obligatory Wikipedia):
A geocities-looking site with some usefull info [solarsails.info]
Planetary Society has some more info [planetary.org]
Wikipedia entry [wikipedia.org]

Re:Is $US52 per square metre about right?

[DustyShadow]

I think you 1.33 US dollars to 1 euro.

Re:Hmmm.

[The_Dougster]

Piezoelecticity is a force to voltage type thing and while pretty nifty, is unrelated to photovoltaic cells.

For the laymen out there, I'll explain this in technical terms. If you have a roughly cylindrical quartz crystal, and if you squeeze it, the crystal lattices "snap" into an alternative arrangement which free's up some electrons and essentially produces a static charge. When you remove the stress, the crystal lattice snaps back into its rest state and wants its electrons back.

Conversely, by applying an alternating current to a quartz crystal, you can make it physically stretch and shrink.

Because a quartz crystal is somewhat like a spring, a given shape/mass/volume of it will possess a resonant vibrational frequency. If you apply a signal to the crystal at or near the resonant frequency, the crystal's vibrational magnitude will increase, just like the famous Tacoma Narrows bridge "Galloping Girdy".

Piezoelectricity is a weird and wonderfull direct mechanical to electrical conversion phenomenon and it is typically used in electronics to convert a sloppy signal into a more precise one, or by utilizing higher harmonic modes, to multiply a lower frequency into a higher one.

Re:Is $US52 per square metre about right?

[drphil]

Although there is nothing wrong with your calculation per se, there are a lot of costs it doesn't include, so it is low by quite a bit. The 1 euro per W (peak Watt or average W - article doesn't say) is only the cost for just the solar cell at high volume manufacturing. At that point you are still quite a long ways from installing this on your roof cost-wise. You still have to put the solar cell in a module, then install it in a panel, then install the panel on your roof along with a rectifier (since your house expects AC) plus other equipment and power storage if you want to be competely off-grid - there are costs, of course, each step of the way.

The rule of thumb I came across when I was studying the econ of solar cells ~18 months ago was that for thin film cell solar to be viable (without govt subsidy) it had to be manufactured for $1/pW (or one euro, depending on exchange rate) and had to have at least 10% efficiency. If the 10% efficiency is not met then the downstream costs eat you alive because you have to install so much more area of solar cells to get the required power.

The current advances in flexible solar have been excellent and the solar market is growing at ~30% (although still >90% c-Si cells), but unless you are willing pay a price to be "green" or your govt gives you a fat subsidy for installing the solar power it will take you many years to repay your capital - on the order of 10 or more if you currently have ready access to the power grid. If you are remote from the grid, solar is actually a great deal cheaper today - but by using Si-based solar which is manufactured on relatively large scale today and has 15% efficiencies versus thin film.

Govt subsidies are still going strong in Japan - Germany is wavering. With G(lobal) W(arming) Bush in office the increase in solar in the US is going to be from the Eco-minded willing to take a bath $$-wise or off grid applications - well, there are also cats who are pretty good at utilizing passive solar power.

Re:Flat vs. Flexible Info

[RealUlli]

You mean, like this [webasto.com]?

Cheers, Ulli

www.oksolar.com/roof/

[6800]

www.oksolar.com/roof/ You can start there :-)

And you can buy them

[Migraineman]

TFA talks about the product entering mainstream production in a couple of years. You can purchase the Iowa Thin Film solar cells now. They're about 7% efficient, as they claim. They're not expensive, and you can get them at a number of distributors. [iowathinfilm.com] I've personally used Jameco and Sundance Solar.

Solar power?

[galenoftheshadows]

Several U.S. Companies now provide solar shingles, in fact, my company has two vendors that carry them, they're just not quite popular yet because they're still a tad pricey.

Re:Is $US52 per square metre about right?

[DaChesserCat]

Let's say it's 1 Euro/watt. That's about $1.33 USD/watt, or about $1,330/kW.

The next factor to consider is the solar insolation [solarseller.com] for your area. This tells you how many hours of direct sunlight you get, for your area, each day. In my case, the annual average is about 4.5 hours / day.

At that rate, 1 kW of photovoltaics will give me about 4.5 kWh of electricity, per day, on average.

Also in my area, electricity is about 7 cent/kWh. Consequently, that 1 kW PV array will save me about 31.5 cents/day, on average. Thats 4,222 days (about 11 years and 7 months) for payoff. If your area gets more direct sunlight, or your electrical rates are higher, your payoff period would be shorter.

That's the bare, basics of the whole thing. Don't forget: PV makes DC current, but most of your household stuff runs on AC, so you'll need an inverter. Count on a low four-figures for something that can handle the load for a small-medium household. Also, to go off-grid, you'd need some kind of batteries for energy storage (otherwise, the power goes out when the sun goes down), as well as a controller to regulate power to/from them, etc. That gets really expensive, really quick. Consequently, while you may not be able to go off-grid, you could probably do net metering [awea.org] and reduce (if not eliminate) your electric bill.

Re:Didn't RTFA, but...

[clonan]

We are actually unlikly to get much past about 50%

This is the best plant chlorophyl (sp?) systems can get. It is also sad but true that it is extremly rare that machines, silicon or other, significantly out do nature in efficiancy.

HOWEVER, since the average solar energy hitting earth is 1.4 kW/m^2 that means that even at 50% we are taking in 700 w/m^2. Now since the average energy use for a home is 17,130 kw/h that means we will need an average of 24-25 square meters to power a house.

Then of course there is no light at night so we will need to double the area to 50 square meters and add a battery system.

But REGARDLESS at even 50% efficiency we can power most single family american houses with simply the roof area!