Solar Lighting: 5 Issues

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RSSfeed Registered Users Posts: 3,810 ✭✭
Solar lights are very practical items to get to grips with; however there are a few things that you should know to ensure that you get the most from them. High quality solar products offer plenty of light once treated correctly and set up properly. Of course, it doesn’t take a lot of time or [...]The post Solar Lighting: 5 Issues appeared first on Solar Feeds.

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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
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    Re: Solar Lighting: 5 Issues
    RSSfeed wrote: »
    Solar lights are very practical items to get to grips with; however there are a few things that you should know to ensure that you get the most from them. High quality solar products offer plenty of light once treated correctly and set up properly. Of course, it doesn’t take a lot of time or [...]The post Solar Lighting: 5 Issues appeared first on Solar Feeds.
    They got halfway through before the first whopper. And it may have been an editor who was responsible for that:
    Charging under solar light is the only way to re-charge a panel and anything else is a waste of time and also of fossil fuels.
    SMA SB 3000, old BP panels.
  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
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    Re: Solar Lighting: 5 Issues
    inetdog wrote: »
    They got halfway through before the first whopper. And it may have been an editor who was responsible for that:
    What about this one: "A lot of people tend to try and charge the lights behind glass, however this doesn’t really work and will reduce the amount of potential for charging by around 90% in most cases. Solar panels indoors will take a lot longer to charge or maybe won’t even charge at all. So, try and ensure that when charging, you do so outside in the openness of day."

    Solar "panels" are made out of glass. Glass does not transmit IR very well, but most PV energy is harvested from the other end of the spectrum.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,522 admin
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    Re: Solar Lighting: 5 Issues

    Many of today's modern energy efficient windows have double (or even triple) panes (which reflect light and absorb some wavelengths) and "low E" glass (sputtered metal film to reflect UV and IR). All my windows have bug screens on them, so that reduces light too (blocking sunlight and diffraction). There are various forms of tinting to reduce light transfer/heating/UV into the home also. Larger doors and windows use double weight glass (or thicker).

    And solar panels use "low iron" thin (single weight ~1/8" think) glass to improve light transmission too (something like another 20% if I recall correctly).

    So--For me, it is very easy to suggest that trying to charge solar devices behind a window can easily cut sun by 1/2 or more. 90% reduction would certainly be possible in some conditions.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
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    Re: Solar Lighting: 5 Issues
    BB. wrote: »
    Many of today's modern energy efficient windows have double (or even triple) panes (which reflect light and absorb some wavelengths) and "low E" glass (sputtered metal film to reflect UV and IR). All my windows have bug screens on them, so that reduces light too (blocking sunlight and diffraction). There are various forms of tinting to reduce light transfer/heating/UV into the home also. Larger doors and windows use double weight glass (or thicker).

    And solar panels use "low iron" thin (single weight ~1/8" think) glass to improve light transmission too (something like another 20% if I recall correctly).

    So--For me, it is very easy to suggest that trying to charge solar devices behind a window can easily cut sun by 1/2 or more. 90% reduction would certainly be possible in some conditions.

    -Bill

    I have seen comparisons that show low iron as making at most a 5% difference, and being small compared to reflections and other losses. Commercial panels seem to use low iron routinely, but for a DIY builder, the difference in glass cost may not be justified. (Since the panels may not last long anyway. :-))
    SMA SB 3000, old BP panels.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,522 admin
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    Re: Solar Lighting: 5 Issues

    I agree that it is probably not worth getting low iron glass--And most people probably are using recycled glass/sliding doors for Solar Thermal collectors (thicker glass and, if I remember correctly, more losses).

    And I was really talking more about recharging "solar devices" behind a home's windows as having all of that "energy loss"... Was not really discussing DIY solar panels (electric or thermal).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
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    Re: Solar Lighting: 5 Issues
    BB. wrote: »
    I agree that it is probably not worth getting low iron glass--And most people probably are using recycled glass/sliding doors for Solar Thermal collectors (thicker glass and, if I remember correctly, more losses).

    And I was really talking more about recharging "solar devices" behind a home's windows as having all of that "energy loss"... Was not really discussing DIY solar panels (electric or thermal).

    -Bill
    I'm still skeptical. Most PV energy is harvested from the visible wavelengths toward the blue end of the spectrum; if the view through a window glass does not appear darker or redder than through an open space, I wouldn't expect the losses to be that great.
  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
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    Re: Solar Lighting: 5 Issues
    ggunn wrote: »
    I'm still skeptical. Most PV energy is harvested from the visible wavelengths toward the blue end of the spectrum; if the view through a window glass does not appear darker or redder than through an open space, I wouldn't expect the losses to be that great.

    Our eyes are not very good in distinguishing small differences in light level unless there is a direct comparison available. If you can partially open the window or door, so that you see both a direct image and a through the glass image next to each other the visible comparison could be valid. Or you can make the difference more noticeable by taking two or more panes of glass (with a spacer in between so they are not touching).
    The biggest loss for plain glass will be the reflections at both the front and back faces, and those will be greater the shallower the angle between the light and the glass gets.
    If the light is coming down at a 45 degree angle to the window, you will lose quite a bit of light from reflections even if you orient the panel itself perpendicular to the light rays.
    But if you do not mount a window-sized panel parallel to and adjacent to the window, you will have shading effects that will be worse than the other losses.
    SMA SB 3000, old BP panels.
  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
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    Re: Solar Lighting: 5 Issues
    inetdog wrote: »
    Our eyes are not very good in distinguishing small differences in light level unless there is a direct comparison available. If you can partially open the window or door, so that you see both a direct image and a through the glass image next to each other the visible comparison could be valid. Or you can make the difference more noticeable by taking two or more panes of glass (with a spacer in between so they are not touching).
    The biggest loss for plain glass will be the reflections at both the front and back faces, and those will be greater the shallower the angle between the light and the glass gets.
    If the light is coming down at a 45 degree angle to the window, you will lose quite a bit of light from reflections even if you orient the panel itself perpendicular to the light rays.
    But if you do not mount a window-sized panel parallel to and adjacent to the window, you will have shading effects that will be worse than the other losses.
    Granted; I just don't see where the light going through a pane of glass reduces the charging 90-100% as the article claims.
  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
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    Re: Solar Lighting: 5 Issues
    ggunn wrote: »
    Granted; I just don't see where the light going through a pane of glass reduces the charging 90-100% as the article claims.
    The article forgot to mention the window screen and the curtains. Otherwise quite accurate.:cool:
    SMA SB 3000, old BP panels.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
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    Re: Solar Lighting: 5 Issues

    The main problem with sun through a window on to a PV is that your best angle for the PV will rarely be achieved, since windows tend to be vertical and PV prefers to be parallel to the sun. Angle makes a large difference in output.
  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
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    Re: Solar Lighting: 5 Issues
    inetdog wrote: »
    The article forgot to mention the window screen and the curtains. Otherwise quite accurate.:cool:
    So then I guess gathering energy for PV through a brick wall is right out... :D
  • Thom
    Thom Solar Expert Posts: 196 ✭✭✭
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    Re: Solar Lighting: 5 Issues
    inetdog wrote: »
    The article forgot to mention the window screen and the curtains. Otherwise quite accurate.:cool:

    You forgot the window storm shutters and bars . :0)
    Off grid since 1984. 430w of panel, 300w suresine , 4 gc batteries 12v system, Rogue mpt3024 charge controller , air breeze windmill, Mikita 2400w generator . Added 2@ 100w panel with a midnight brat 
  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
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    Re: Solar Lighting: 5 Issues
    ggunn wrote: »
    So then I guess gathering energy for PV through a brick wall is right out... :D
    Oh I wouldn't say that - - a "friend" of mine has great success recharging his batteries using the "ultra violet light" coming from the moon at night, so you should in a similar way get even better results from behind a brick wall. During the day the sun warms the wall, which then, (using these special bricks I sell) convert that warmth into moon-like ultra violet which will then continue to charge your batteries long after the sun goes down. :D
  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
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    Re: Solar Lighting: 5 Issues
    Oh I wouldn't say that - - a "friend" of mine has great success recharging his batteries using the "ultra violet light" coming from the moon at night, so you should in a similar way get even better results from behind a brick wall. During the day the sun warms the wall, which then, (using these special bricks I sell) convert that warmth into moon-like ultra violet which will then continue to charge your batteries long after the sun goes down. :D

    Oh Boy can I then use ultraviolet paint to dayglo the room for lighting?