Solar powered lighting questions

ilovethesun
ilovethesun Registered Users Posts: 2

Hi all! Just registered today and have some questions about solar lighting.

I wanted "off grid" solar powered lighting, so I purchased a few outdoor solar security lights. The panels are setting in East facing windows, and the setup is working really well. Where I have the solar lights installed, I have used the solar lights exclusively in those rooms since April of this year. With very few exceptions, I haven't needed to take the lights outside to charge; they've remained in the windows and worked great with the amount of sun they've received. 

One of the lights is 100w and 7.4v. The solar panel that came with it is 32w (can't remember the voltage...darn... I'm not home right now).

My question is: What will happen if I disconnect the panel that came with it and plug in a 100w. 18v solar panel? The panel is a Rockpals 100w foldable solar panel that has built in regulation for devices it charges. Will it fry the light? Will it cause a fire? Will this even work? I wanted to get some opinions from knowledgeable people before risking destroying my light. PS: I will do this experiment outside, not inside my home, in case of a fire hazard.

My goal with this: During gloomy stretches of weather, like when it is predicted that we will only get a couple of hours of sunlight in a day, I'd like to be able to charge the light up faster.

Is my logic messed up, or will the 100w solar panel charge the light faster than the 32w solar panel (if it doesn't destroy the light LOL)?

Thanks!

Comments

  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    The light sounds like it may be a couple of ~3.2v lithium battery cells.  The 100w 18v panel is very likely designed to charge a 12v nominal lead acid battery, and unless the light is designed to take that, it may well be a mistake to use it.  Lithiums are quite sensitive to overcharging, can be hazardous.

    That said, it's possible the 32w panel that came with the light is also 18v and the light is able to charge using that voltage.  My guess is it's likely lower voltage though.  I wouldn't recommend trying the bigger panel without knowing more about how the light charging system is designed.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    As you guessed--The output voltage of the panel does matter. Many times, these small "application specific" solar powered lights use different working voltages for the solar panels (maybe 6-9 volts) vs the Vmp~18 volts for a typical Off Grid battery charging panel (for 12 volt battery bank with a PWM controller)...

    And, the type of charge controller also matters. MPPT controllers are more expensive but can take the high voltage/low current of the solar panel and efficiently down convert to the low voltage/high current needed to charge the battery bank.

    With a PWM controller (assuming that is what an inexpensive security light uses), the "higher voltage" of an "18 volt Vmp" 100 Watt panel may not supply any more energy than a 6 volt 32 watt panel. It is is the panel current that "matters" with a PWM controller--And the higher voltage from that 18 volt Vmp (typically >22 volts Voc) of that type of panel can damage/ruin the electronics of your security light.

    An alternative--If you are mounting the lights in the room behind the window, if you can dismount the panel and move it outside the window, you probably will see 2x or more improvement in charging current/energy from the solar array, as the window glass usually blocks/reflects much of the solar energy.

    You can use a solar irradiance calculator and see what is the best angle for an external panel facing east would be for optimum harvest... Say fixed angle for St. Louis Mo facing east:
    http://www.solarelectricityhandbook.com/solar-irradiance.html

    Saint Louis
    Average Solar Insolation figures

    Measured in kWh/m2/day onto a solar panel set at a 36° angle from vertical:
    (Optimal winter settings)

    JanFebMarAprMayJun
    2.77
     
    3.02
     
    3.46
     
    3.64
     
    3.55
     
    3.64
     
    JulAugSepOctNovDec
    3.80
     
    3.86
     
    4.05
     
    3.74
     
    2.82
     
    2.58
     

    For St Louis, facing east, 36 degree from vertical will give you your best winter harvest.

    Also, you may wish to check what the lights are really drawing... Most anything these days is going to use LED. A 100 Watt filament bulb is getting rare, and a 100 Watt LED is way more than most lights use (that would light up a whole room like daylight).

    If it is a filament bulb, then replacing with an LED (of much less wattage--1-5 Watts is pretty bright) will give you much more runtime too.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • ilovethesun
    ilovethesun Registered Users Posts: 2
    Thanks so much for the replies. I'm glad I asked because I probably would have sacrificed one of my cherished lights LOL!