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Author Topic: How do solar cells work?  (Read 5200 times)

Offline thedoc

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How do solar cells work?
« on: 07/06/2011 10:34:16 »
Fifty years from now, our kids are going to look incredulously at us and ask – "you burnt things to get electricity?" We’ll answer – "yes, but only until we realised how cheap and efficient renewable energy could be." In this article, Niraj Lal looks at a growing part of our electrical future: the solar cell...

Read the article then tell us what you think...
« Last Edit: 07/06/2011 10:34:16 by _system »


 

Offline thedoc

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How do solar cells work?
« Reply #1 on: 07/06/2011 10:34:16 »
« Last Edit: 07/06/2011 10:34:16 by _system »
 

Peter Miskelly

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« Reply #2 on: 27/01/2011 20:00:02 »
I just read your article on solar cells, very good but the thing I question is that 300W is enough to power a microwave.  This can’t be a domestic microwave http://microwavecooking.com/World_Smallest_Microwave_Oven.htm

The world’s smallest microwave allegedly, (it was the first hit in a search and it’s a coincidence it’s produced by GE - and anyway it may be the physical size they refer to).  One of my pet peeves is that microwave ovens are only 50% efficient, and they normally advertise the cooking power instead of the power it consumes.  This may be 500W but it will use 1kW to cook your food.

What do you think?

Regards,
 
Peter Miskelly
Reliability Engineer
GE Intelligent Platforms
Embedded Systems
 

Offline Niraj Lal

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How do solar cells work?
« Reply #3 on: 27/01/2011 23:08:49 »
Hi Peter,

I think you're definitely right.  My understanding was that the power that's advertised on the little sticker on the front of microwaves is the power that they use (and not just the cooking power!).  I agree - it's slightly misleading hey?

I'm in Australia at the moment - but back home in Cambridge I've got a little power meter that I can stick into a socket to find out how much power an appliance consumes.  I'll test it out on my housemate's microwave as soon as I get back - but I reckon you'll be definitely right in that it'll be closer to using 1kW.

Does GE advertise the cooking power or the power consumed on their microwaves?  Does the world's smallest microwave consume 500W when working?
I reckon it's awesome if it does.

Thanks heaps for the comment!


Cheers,


- Nij.
 

Niraj Lal

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« Reply #4 on: 25/02/2011 17:33:48 »
Author's note:

Since writing this article, I've found out about two additional ways of generating.  They aren't generating much electricity at the moment  - and one of them is a little esoteric, but they definitely are different ways of moving charge around - and making electricity flow.

The two are Electrokinesis from an electrical double layer in microfluidic channels, and Thermionic Emission.  Further information about both is below:


Electrokinesis from the electrical double layer in microfluidic channels

This is a way of using charge that accumulates along the edge of small glass channels that have water flowing through them.  The charge flow is known as the streaming current - and is the reverse process of what's known as electro-osmosis.  Electrokinesis with microfluidics was first discovered in 1964 by JF Oesterle, but then forgot about for a while.  It was re-discovered in 2003 by researchers at the University of Alberta - who are currently exploring ways that it might be harnessed for useful power generation.  The interested reader is referred to the paper here: DOI: 10.1088/0960-1317/13/6/320


Thermionic Effect

This is the second way of generating electricity not mentioned in the above article.  It's an effect I really should have known about before - the physicist who first understood it, Sir Owen Richardson, made his discoveries in the Cavendish Laboratory at the University of Cambridge and was awarded the Nobel Prize for figuring out the Law which now bears his name.

Richardson's Law describes how metals eject charges when they are heated.
As a metal gets hotter and hotter some of the charges within them start moving so vigorously that they escape the attraction of their surrounding atoms in the metal and ping away from the surface.  By collecting the charges that ping off, and connecting up the circuit back to the metal, we can make electricity flow.
The thermionic effect formed the basis of work done in the late 1800s on some of the earliest detection of radio waves and some of the earliest fabrication of vacuum-tube diodes.
The effect was actively investigated by US and Russian space agencies during the Cold War for remote power generation from the heat generated by nuclear fission.
It isn't under intense investigation at the moment, and isn't powering many appliances around the world - but it certainly deserves it's place in a list on the different ways of generating electricity.

A brief note on other ways of generating electricity:

It's my hunch that there are a few other ways of making electricity out there, some that have already been discovered that I'm not yet aware of, and some also that haven't been discovered by anybody yet.
I've got an inkling that scientists of the future will look back and realise that there's a way of generating electricity from almost any situation in which work is done (in the physical sense of work) or in almost any way in which nature generates a potential difference of energy.

The fundamental physics behind each, though, will come down to the central fact about our universe that there are two types of charge where like charges repel and unlike charges attract.
It's exciting stuff - who knows what will be powering our world in years to come?

- Nij.

PS. I plugged my power meter into the microwave in our office kitchen in the Kapitza building of the Cavendish Laboratories. On the front of the microwave is written "500W" - but!  the amount of power it drew was about 1100W - so Peter, you're definitely right.  Cheers for letting us know,

- N.
« Last Edit: 07/06/2011 09:55:49 by daveshorts »
 

Madeleine

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« Reply #5 on: 02/08/2012 13:54:40 »
Hi,

I was actually just wondering if you could let me know how you made up the graph of the solar spectrum and filled in the area under the graph corresponding to visible light with a rainbow gradient? Looks great!

If you could let me know how you did it I'd really appreciate it, as I would like to use a similar image for educational purposes.
 

Niraj Lal

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« Reply #6 on: 15/10/2012 06:54:04 »
Hi Madeleine, I whipped up the graph in powerpoint, but would be happy to forward it to you if you'd like?  The best way to contact me is via email at niraj.lal@cantab.net.
Cheers!  

- Nij.
 

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« Reply #6 on: 15/10/2012 06:54:04 »

 

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