[sci.electronics] SOLAR CELLS WITH HIGHPWER TO AREA RATIO

rajha@girtab.usc.edu (T.R. Rajha) (06/21/91)

I am looking for a solar cell that can charge a NiCd battery in a
device while the device is in its standby mode.

There are a few important considerations:

The device will be used mostly indoors. Therefore the solar cell 
should be able to operate in the indoor ambient lighting including
incandecent and fluorescent lights. 

The solar cell should have a high power to area ratio.

It should be able to deliver a charge of approx. 50 mA at 4 volts

It should fit in area of approx. 60 sq. cm

If you are aware of the existence of solar cells that meet or atleast
come close to meeting these specifications, please email me at

rajha@girtab.usc.ed

Thanks very much.

S. Rajha
Engg. Dept.			Ph: (213) 783-7684
PMI/Asahi Corp.			Fax: (213) 618-6821
P.O. Box 2914			Email: rajha@girtab.usc.ed
Torrance, CA 90509

wreck@fmsrl7.UUCP (Ron Carter) (06/25/91)

In article <17973@chaph.usc.edu> rajha@girtab.usc.edu (T.R. Rajha) writes:
[wants a high power/area solar cell]
>The device will be used mostly indoors. Therefore the solar cell 
>should be able to operate in the indoor ambient lighting including
>incandecent and fluorescent lights. 

Have you considered how little power is available in most
interior lighting?

>It should be able to deliver a charge of approx. 50 mA at 4 volts

So you want 200 mW output.

>It should fit in area of approx. 60 sq. cm

So, 3.3 mW/cm^2, or 33 W/m^2.

Direct sunlight is about 1 KW/m^2 under the atmosphere.
The most efficient gallium-arsenide solar cells are
something like 20% efficient; they would produce 200 W/m^2
in full sunlight.  If you used them in your system, you
would be able to produce your desired power down to about
1/6 of full-solar illumination (170 W/m^2).

Indoor lighting is nowhere near that powerful.

I'm afraid you want something which doesn't exist.  Sorry.

strong@tc.fluke.COM (Norm Strong) (06/27/91)

In article <17973@chaph.usc.edu> rajha@girtab.usc.edu (T.R. Rajha) writes:
}I am looking for a solar cell that can charge a NiCd battery in a
}device while the device is in its standby mode.
}
}There are a few important considerations:
}
}The device will be used mostly indoors. Therefore the solar cell 
}should be able to operate in the indoor ambient lighting including
}incandecent and fluorescent lights. 
}
}The solar cell should have a high power to area ratio.
}
}It should be able to deliver a charge of approx. 50 mA at 4 volts
}
}It should fit in area of approx. 60 sq. cm

Indoors it's impossible.  You're asking for 3.3mw/cm**2.  Since 
strong commercial lighting is only about 2mw/cm**2, even cells with 100%
efficiency would not give you the current you need.  The 5% typical
efficiency will fall way short of your goals.  

Outside in the noonday sun:  No problem.    

-- 

Norm Strong  (strong@tc.fluke.com)
2528 31st S.   Seattle WA 98144   USA