Monday, May 26, 2008

Solid State Physics in the Garden

This spring, a nice little gadget is popping up in the yards and gardens of villages and suburbs in Germany: Small lanterns, with lids equipped with solar cells that collect sunlight during daytime and give it back at night.

  


Here is how such a lantern looks like:



The lid not only bears the solar cells, it contains also a rechargeable battery, a bit of electronics, and a white light-emitting diode (LED) that produces the light at night.



The LED is actually quite tiny, but it gives off a very bright and concentrated spot of light. This light is refracted and dispersed by the corrugated casing of transparent plastic.

Photons of sunlight hitting the semiconducting material of the photovoltaic solar cell can promote electric charges from the valence to the conduction band, where they can move and create a small direct electric voltage, if the material is suitably engineered. This voltage is used to charge the battery. When no light falls on the solar cells, the electronics allows the battery to discharge via the LED; where just the inverse process takes place: Electric charges recombine across the band gap, thereby emitting photons. LEDs that can give off white light are a relative recent development, and rely on quite sophisticated recipes to combine different semiconducting materials.

The solar constant, the flux of energy from the sun hitting the Earth, is 1.37 kW/m² at the top of the atmosphere, but there is of course absorption, clouds blocking the light, the constant change of day and night, the height of the Sun varying with the seasons... - as a result, the annual average of solar power arriving at ground level is about 120 W/m² for Germany (or 1 MWh/m² per year). The solar cell of the lamp has an area of roughly 50 cm² (7 × 7 cm²), so it can harvest roughly 0.6 W. Assuming an efficiency of 15% for a standard multicrystalline Si solar cell, the solar panel produces a power of about 10 mW on average over the year. During the summer months, this power may be higher by a factor of two or so, but it is still quite small - yet big enough to light steps in the garden path all night long.








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16 comments:

Phil Warnell said...

Hi Stefan,


These things are neat little gismos, yet I have to wonder with the embodied energy content considered as in their manufacture, life cycle and disposal would stack up to be as to consider their real worth. I would suspect that a more conventional approach perhaps might actually leave a smaller carbon foot print. This of course is to point out what is another of the challenges presented when we attempt to diminish the use of fossil fuels; that is many things that first appear to be solutions, in the end when looked at in more depth turn out actually to add more to the problem.

Best,
Phil

Bee said...

In Arizona the meters at the parking lots used to be solar powerd. Luckily they were out of order most of the time ;-)

Bee said...

Off-Topic,

Anybody seen this

http://arxiv.org/abs/0805.3991

"Neutrino Counter Nuclear Weapon
Authors: Alfred Tang

Abstract: Radiations produced by neutrino-antineutrino annihilation at the Z0 pole can be used to heat up the primary stage of a thermonuclear warhead and can in principle detonate the device remotely. Neutrino-antineutrino annihilation can also be used as a tactical assault weapon to target hideouts that are unreachable by conventional means."

Haven't we had this story before? It sounds strangely familiar.

Plato said...

Stefan:When no light falls on the solar cells, the electronics allows the battery to discharge via the LED; where just the inverse process takes place: Electric charges recombine across the band gap, thereby emitting photons. LEDs that can give off white light are a relative recent development, and rely on quite sophisticated recipes to combine different semiconducting materials

Same here in Canada so technologies are not far behind/ahead with an ocean in between.

Accent lighting has it's moments, we all know that right:)Romanticism measured in "candlelights" has new way in which to imagine relationships under the light of this new moon?:)

Anyway the process pointed out is an interesting one in terms of energy usage and the metering process spoken about.

If one is to consider the energy costs and how we are currently being raped to justify the depletion of a valuable resource while it exists, such strategies and pompous wealth creation, is part and parcel of the best intentioned environmentalists who currently hold pension, whose funds that are invested for them which contribute to such things as, "smoking of all things." Tis is not a mean of justification but of the contradiction we live unintentionally as we go about our lives.

Software that we use dictating the resources and futures, in some artfully constructed room fabrication, as a result of environmental scanning?:)

Ah Bee, now we are getting to the jest of the order of things, in which consternation of neutrino applications maybe becoming the forefront of new methods of communication, then why not in some government arsenal for such treatments?

Plato said...

Maybe a blog entry given to the Cern group for this question? Dorigo, where are you?

Raise your hands if your at Cern, if you are not skillfully using this information in your own countries to advance the technologies apart from the group effort?

Go ask Joe Kapusta if this is not worth considering.

Arun said...

The big convenience of this type of lighting is not having to lay copper wires; and not having to worry about snagging the wire when digging in the garden.

I have the wired type lighting and have been contemplating a switch to these for a while.

stefan said...

Hi Phil, Plato,

concerning the embodied energy content, life cycle and disposal - that's actually a very important point.

The lantern seems to be produced in China, no idea at what cost in energy and to the environment. And the life span of the solar panel is given with just two years, which is pretty short - and after that, you are left with stuff you shouldn't just throw away with your domestic waste.

As far as I know, this is still kind of a problem with photovoltaics, that the manufacture is expensive and harmful to the environment, and that the solar cell has to run for at least ten years or so until it has harvested as much solar energy as was used in its manufacture. But I think there is some progress.


Hi Arun,

The big convenience of this type of lighting is not having to lay copper wires

absolutely - it's just cute that you can plug these lanterns anywhere in the garden, and then they just sit there and work..

Best, Stefan

Phil Warnell said...

Hi Stefan,

“As far as I know, this is still kind of a problem with photovoltaics, that the manufacture is expensive and harmful to the environment, and that the solar cell has to run for at least ten years or so until it has harvested as much solar energy as was used in its manufacture. But I think there is some progress.”

I hope it’s not taken that I’m anti Photovoltaics or some such thing. As for instance, your own country is leading the way in the practical implementation and use of such technology, with many German farmers setting aside some land and installing solar collection panels that put power back on the grid in a practical fashion. With the levels that the government has set for the price paid for what they contribute, many are doing such even though it doesn’t garner them much above the break even level. I think with most being descendent from several generations of farmers, they have a closer association with the earth then many us city slickers and as such find this consistent with their personal philosophical centre.

It seems as I get older I’m becoming more and more of a tree hugger, although at the same time mindful of many that declare themselves such, as I know they are not aware of how the total thing should be considered as exemplified with this embodied energy concern. Also, it should realized such assessment methodologies are as of yet far from being an exact science; with special interest, ethics ,politics and just poor science being mixed in to further confuse and complicate things.

Best,

Phil

Javier said...

I have readed a new about the achievement of could fusion. I am not expert neither in solid state physic nor in nuclear physic, so I can´t make a too critical reading. The actual paper behind the press release is this:

http://www.journalarchive.jst.go.jp/jnlpdf.php?cdjournal=pjab1977&cdvol=74&noissue=7&startpage=155&lang=en&from=jnlabstract

If some of you (stefahn, bee) have a good enoguth expertise on the topic, or can consult someone who has it, may be you cuold give an opinion beyond the usual one in these cases of "just be cautious".

Plato said...

Stefan,

While Phil is congratulating the efforts by Germany's farm workers, Germany itself, in regards to Kyoto protocols, has shown it efforts in it's use of windmills for energy consumption, and returns on investment, as a good sign, yet, I hear that the discomfort of the noise can be unsettling while these windmills grind away?

Windmills do not work in all areas just as "sunlight can be limited."

Phil:although at the same time mindful of many that declare themselves such, as I know they are not aware of how the total thing should be considered as exemplified with this embodied energy concern.

I felt guilty working in a industry, and sought to give back by doing some research on "replanting efforts." Looking at what we could do with "reforestation by producing superior seedlings." It was that ole magnet thing by introducing fields measured in gauss with a probe might influence, of course the controls did not succeed, so to no avail. Nature's selection seemed most apt when the best trees were harvested of their cones.

I did by my own efforts see "signs of the times" that the climate did have it's affect on "beetle manifestation" that have destroyed trees, and it these trees now that are being used to fuel Co-generation plants for producing electricity and returning power back to the grids.

"Natures way is to burn," and it would not take much for such a thing to happen in dry forests. The potential is very great for such a fire to happen, and yet, lush lands are always a result.

Also, it should realized such assessment methodologies are as of yet far from being an exact science; with special interest, ethics ,politics and just poor science being mixed in to further confuse and complicate things.

Javier points about cold fusion which was an interesting one, although, such caution is of course warranted, as we look at the subjects of another, using sonoluminence.

It was in this instance, I saw correlations in "bubble collapses" geometrics, which were induced by vibration, that I saw as emulating "the collapse of a blackhole." Ya, I know, layman dreamer. :)

But central then was the idea that energy could be transmitted back into the universe in the form of dark energy?

So to see Iron man and the use of a energy source that was manufacture is a interesting idea in such a hand held device. :)

Cost of energy is always an important factor, and knowing what goes into it has to be exceeded by output, or, we get those "crazy machines" that continually work.

Can't remember the name right now.

Arun said...

Visited a vast windmill farm in India. If the machines there are typical, noise is not a problem.

stefan said...

Today I heard a discussion on Deutschlandfunk about energy supply in Germany and the future of the nuclear power phase-out that was decided about in 2000.

As a side remark, it was noted that renewable energies (mostly wind and photovoltaics) have supplied 14 per cent of all electricity in 2007 (see "Big boost for renewable energies" by the German Department of the Environment). Indeed, this growth has been possible only by large subsidies for solar and wind farms.

And at least in some rural areas, there is a growing resistance against what is often called "Verspargelung", the growing number of large windmills in regions more or less untouched by industries.

Best, Stefan

Plato said...

I think blade angles might be a contributor to noise.

Although wind power plants have relatively little impact on the environment compared to other conventional power plants, there is some concern over the noise produced by the rotor blades, aesthetic (visual) impacts, and sometimes birds have been killed by flying into the rotors. Most of these problems have been resolved or greatly reduced through technological development or by properly siting wind plants.

Phil Warnell said...

Hi Stefan,

YOU SAID: “And at least in some rural areas, there is a growing resistance against what is often called "Verspargelung", the growing number of large windmills in regions more or less untouched by industries.”

You had me curious what this "Verspargelung" meant so I followed the link you provided to find:

““Hundreds of citizens’ groups have sprung up in Germany to battle “Verspargelung der Landschaft"—a new phrase in the German lexicon—meaning “the transformation of the German landscape into an asparagus field.” “”

I suspect that those protesting must be carnivores and their true concern is with the growing number of vegetarians. I did warn that special interest served to muddy the waters when it comes to such issues :-)


Best,

Phil

Phil Warnell said...

Hi Stefan,

In regard to your "Verspargelung", another more serious thought just crossed my mind. That is I was wondering what the power potential would be if we replaced every telephone/electric pole with wind mills and placed larger ones atop all the power transmission grid towers. In as much of the urban and rural landscape is already occupied with these currently existing “asparagus stalks” it seems to be more practical that they serve multi purposes and not just accommodate supporting those few aesthetically pleasing wires.

Best,

Phil

Plato said...

Oh Phil,

Your fractalizing the situation?:)