Shading Of Photovoltaic Cells
Question:
>Would the item below imply that shading is not such a big issue for >polycrystalline and amorphous module strings and only relevant to >monocystalline ?
It is just as serious a problem with polycrystalline. The major technical question is the reverse voltage breakdown voltage of the cells. The higher the breakdown voltage, the more power available to cause hot spots. The older amorphous cells have low breakdown voltage, but I do not know about the newer dual and triple junction, higher efficiency products just coming on the market Bill Kaszeta
Response:
Would the item below imply that shading is not such a big issue for polycrystalline and amorphous module strings and only relevant to monocystalline ? – Hide quoted text — Show quoted text ->UK >The basic problem with shadows on PV arrays is that the shadowed >part acts like a high resistance connection. If the system voltage is >high enough (generally over a nominal 24 volts) and the shadowed >area is small (such as a whole cell), then the shadowed area must >dissipate far more energy than it usually produces. This dissipation >causes hot spots than can destroy a PV module and even start a fire. >To avoid this safety problem, bypass diodes are installed across >every 16 to 18 cells in series and these diodes provide an alternate >path for the current and limit the voltage across the shaded cells. If >there are parallel strings of PV modules with bypass diodes, then >string isolation diodes are required to protect the bypass diodes >from excess currents that could come from the parallel series >strings of modules.
– Chris Laughton Tel/Fax 0151 606 0207 The Solar Design Company 57 Wood Lane, Greasby, Wirral, England L49 2PU.
Response:
>I’m mid way through an MSc in Renewable Energy Systems Technology at >Loughborough University in the UK and am about to get to grips with my >dissertation.. >Can anyone suggest some good sources of information about effects of >shading on solar PV arrays, performance drops, temperature probs etc ??
Andy: Contact Sandia National Laboratories in Albuquerque NM. They publish a series of excellent technical books on this and other PV related subjects. Available for free. I don’t have their address here. Gene A. Townsend
Response:
I’m mid way through an MSc in Renewable Energy Systems Technology at Loughborough University in the UK and am about to get to grips with my dissertation.. Can anyone suggest some good sources of information about effects of shading on solar PV arrays, performance drops, temperature probs etc ?? Any help appreciated. Thanks. Andy Bodycombe Centre for Renewable Energy Systems Technology Loughborough University UK
Response:
>I’m mid way through an MSc in Renewable Energy Systems Technology at >Loughborough University in the UK and am about to get to grips with my >dissertation.. >Can anyone suggest some good sources of information about effects of >shading on solar PV arrays, performance drops, temperature probs etc ?? >Any help appreciated. >Thanks. >Andy Bodycombe >Centre for Renewable Energy Systems Technology >Loughborough University >UK
The basic problem with shadows on PV arrays is that the shadowed part acts like a high resistance connection. If the system voltage is high enough (generally over a nominal 24 volts) and the shadowed area is small (such as a whole cell), then the shadowed area must dissipate far more energy than it usually produces. This dissipation causes hot spots than can destroy a PV module and even start a fire. To avoid this safety problem, bypass diodes are installed across every 16 to 18 cells in series and these diodes provide an alternate path for the current and limit the voltage across the shaded cells. If there are parallel strings of PV modules with bypass diodes, then string isolation diodes are required to protect the bypass diodes from excess currents that could come from the parallel series strings of modules. Bill Kaszeta Photovoltaic Resources Int’l Mesa Arizona USA
