Don Theoretical solar-cell efficiency calculation excludes photons of insufficient energy for electron-hole-pair production. Also photon energy beyond pair-production requiement is converted to heat (and cannot produce electricity). Electron-hole pairs produced in doped regions above or below the depletion zone quickly recombine, producing no electricity. Also silicon band gap decreases with temperature so the voltage decreases as the solar cell heats up. For silicon, a 20% efficiency is fairly good.
Solar intensity above the atmosphere is 1400W/m^^2. Typical (IEC60068-2-5, Bellcore, MIL-STD-810) solar intensity test level is 1120W/m^^2. David Sterner -----Original Message----- From: [email protected] [mailto:[email protected]] Sent: Friday, June 07, 2002 12:44 PM To: Andrew Carson Cc: [email protected] Subject: RE: IEC 60950 & Solar Cells If I remember correctly, solar intensity in space is about 1.5 kW per square meter. At sea level at the equator it something like 1.1 kW per square meter on a clear day. So there is significant significant loss coming through the atmosphere, but certainly not 90%. Perhaps there is 90% reduction of some wavelengths (UV light through a good thick stratospheric ozone layer?). "Andrew Carson" <[email protected]> on 06/07/2002 09:33:05 AM To: Don Borowski/SEL@SEL, [email protected] cc: Subject: RE: IEC 60950 & Solar Cells I thought the Suns Solar Intensity was 1kW per square meter above the Earths atmosphere and what hit the ground was reduced by 90%. But it has been a few years since my college days :-) Andrew Carson - Senior Compliance Engineer, Xyratex, UK Phone: +44 (0)23 9249 6855 Fax: +44 (0)23 9249 6014 -----Original Message----- From: [email protected] [mailto:[email protected]] Sent: 07 June 2002 15:09 To: [email protected] Subject: RE: IEC 60950 & Solar Cells For the power limit part of the problem, a good rule of thumb to use for solar intensity is 1 kW per square meter. A garden variety solar cell (single crystal) is easily 10% efficiency these days, and the best ones are past 20%, so this yields 100 watts to beyond 200 watts per square meter for the expected power. Don Borowski Schweitzer Engineering Labs Pullman, WA "Andrew Carson" <[email protected]> on 06/07/2002 02:19:03 AM Please respond to "Andrew Carson" <[email protected]> To: "Ron Pickard" <[email protected]>, [email protected] cc: (bcc: Don Borowski/SEL) Subject: RE: IEC 60950 & Solar Cells Ron Some help, I hope, to your questions. "Would this small LCD display device even be required to be evaluated to IEC 60950 3rd Edition or to IEC 60950-1?" This depends on what you are trying to achieve, good company practices, or a countries regulatory requirements. For Europe, the product does not need safety testing under the scope of the LVD, but would do under the RTTE. For the US market, there is no legislation that says the equipment vendor must safety test. So this will be driven by your customer and market place requirement. Depending on the equipments intended function, you might find more guidance in the UL Audio and Video equipment standards. "Would a solar cell energy source be treated similarly to a battery?" No. You do not have the risk of explosion associated with a battery, but then again the Solar Cell is not a limited Energy device like a battery. Treat the Solar Cell like an external SELV power source. As long as the sun still shines, it will continue to deliver power. However, for maximum energy available form the Cell, even in the most extreme fault conditions, there is a physical upper limit to how much solar energy can be converted into electricity. Off the top of my head it is around 10W per square meter with today's technology. Should you be concerned over the safety of a Solar Cell powered LCD screen. Yes. If the LCD screen has a back light inverter, then some very high voltages could be present within the equipment. So single fault protection. You also need to address the chemical nature of the LCD screen and any risk to the operator in a fault condition. Hope this helps. Andrew Carson - Senior Compliance Engineer, Xyratex, UK Phone: +44 (0)23 9249 6855 Fax: +44 (0)23 9249 6014 -----Original Message----- From: Ron Pickard [mailto:[email protected]] Sent: 06 June 2002 23:26 To: [email protected] Subject: IEC 60950 & Solar Cells To all, First, a little background. I have been asked a question that I did not know the answer to, which relates to a potential new product. As I understand it, this device will be relatively small, consume very little power and will only display particular information depending on the application. What I have been told, this device will be powered by a solar cell with a potential 3V coin battery for back up (the battery part is iffy). I can't give anymore information about it because I don't know any more. Now, to the questions. As the scope of IEC 60950 3rd Edition or IEC 60950-1 applies to equipment that is powered "up to" 600V", it would seem that the standard would apply to this product. However, I cannot find a single reference to a solar cell energy source. Would a solar cell energy source be treated similarly to a battery? Would this small LCD display device even be required to be evaluated to IEC 60950 3rd Edition or to IEC 60950-1? As always, I look forward to your insightful replies. Best regards, Ron Pickard [email protected] This e-mail may contain SEL confidential information. The opinions expressed are not necessarily those of SEL. Any unauthorized disclosure, distribution or other use is prohibited. If you received this e-mail in error, please notify the sender, permanently delete it, and destroy any printout. Thank you. ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. 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Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: [email protected] Dave Heald: [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on "browse" and then "emc-pstc mailing list" ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: [email protected] Dave Heald: [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on "browse" and then "emc-pstc mailing list"
