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    • What should I use for PV barn lighting

    Solar Expert Posts: 223 ✭✭✭
    in Off Grid Solar & Battery Systems #1
    Can you guys help me setup lighting for my barn?
    Here's what I have :motion activated 2-18 watt led solar spotlight with a 6" square solar panel from local hardware store.
    It's not enough light I want to add 2-3 more 18 watt cfl's to light up the barn.
    average use time 10 minutes 2-3 times per week.
    I have a deep cycle 12 v trolling motor battery and an old APC computer ups (600) watt. I will wire the lights to the UPS and use the power switch on the UPS to turn the lights on and off.
    I would like to keep the battery charged with a solar panel & charge controller

    Lots of trees around the barn, a panel that works with ambient light would probably be best. As the barn only gets maybe 1-2 hrs of full sunlight depending on the time of year
    What's the best solar panel and charge controller combination to use for this application.
    thanks
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    • Super Moderators, Administrators Posts: 33,680 admin
      #2
      Re: What should I use for PV barn lighting

      My 3.5 kW array will generate about 20-50 watts when mounted in shade--So probably not very useful for your application.

      Taking some guesses:
      • 3 CFL * 18 watts * 10 minutes/60 min per hour * 3 times per week / 7 days per week = 3.9 WH per day
      • 3.9 WH per day * 1/1 hour of sun per day * 1/0.30 efficiency for small system = 13 watt panel minimum
      The 0.30 (30%) end to end system efficiency is fairly conservative--but getting a 20-30 watt panel would not hurt you (allow for larger battery bank, more light at times).

      You can use a very small charge controller like this one for $29 as you don't need any thing fancy:

      wind-sun_2106_44182486SunGuard 4.5 amp solar charge controller

      Battery wise, assuming 5% minimum charge rate and a 13 watt solar panel:
      • 13 watt * 1/0.05 * 1/14 volt charging = 19 AH battery maximum recommended size
      If yo have a 100 AH 12 volt trolling motor battery (flooded cell, not sealed/agm), you should have:
      • 100 AH * 14 volts * 0.05 = 70 watts of solar panel minimum

      An AGM battery may be a better choice (for longer battery life) or a smaller flooded cell battery if you choose to stay with a smaller solar panel.

      With the flooded cell battery, you can monitor the state of charge with a hydrometer and see if your smaller panel keeps up with it... Or take it in once a month (or whatever) and charge/equalize it at home as needed.

      -Bill
      Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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    • Solar Expert Posts: 741 ✭✭
      #3
      Re: What should I use for PV barn lighting

      Look at 12V lighting. The ACP UPS is a MSW and some CFL's lights may not like it.
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    • Solar Expert Posts: 223 ✭✭✭
      #4
      Re: What should I use for PV barn lighting
      BB. wrote: »
      My 3.5 kW array will generate about 20-50 watts when mounted in shade--So probably not very useful for your application.

      Taking some guesses:
      • 3 CFL * 18 watts * 10 minutes/60 min per hour * 3 times per week / 7 days per week = 3.9 WH per day
      • 3.9 WH per day * 1/1 hour of sun per day * 1/0.30 efficiency for small system = 13 watt panel minimum
      The 0.30 (30%) end to end system efficiency is fairly conservative--but getting a 20-30 watt panel would not hurt you (allow for larger battery bank, more light at times).

      You can use a very small charge controller like this one for $29 as you don't need any thing fancy:

      wind-sun_2106_44182486SunGuard 4.5 amp solar charge controller

      Battery wise, assuming 5% minimum charge rate and a 13 watt solar panel:
      • 13 watt * 1/0.05 * 1/14 volt charging = 19 AH battery maximum recommended size
      If yo have a 100 AH 12 volt trolling motor battery (flooded cell, not sealed/agm), you should have:
      • 100 AH * 14 volts * 0.05 = 70 watts of solar panel minimum

      An AGM battery may be a better choice (for longer battery life) or a smaller flooded cell battery if you choose to stay with a smaller solar panel.

      With the flooded cell battery, you can monitor the state of charge with a hydrometer and see if your smaller panel keeps up with it... Or take it in once a month (or whatever) and charge/equalize it at home as needed.

      -Bill

      Thanks Bill,
      Just placed the order for KC40 panel & sunguard with our sponsor.
      Luc
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    • Super Moderators, Administrators Posts: 33,680 admin
      #5
      Re: What should I use for PV barn lighting

      Luc,

      You are very welcome... And by the way, I would agree with n3qik and watch how your particular CFL's run on the APC...

      Some will run OK, others may not start (especially at low temperatures) or may buzz/have short life.

      And in cold weather with little run time, it can take several minutes for a CFL to "warm up" and generate full light.

      Looking at LED lighting, or even small halogen type lighting may be a better fit.

      Lastly, a 600 watt inverter may have a lot of "tare losses" (larger inverters can take quite a bit of power just to run the electronics). A smaller TSW (or MSW) inverter may also help reduce your power needs.

      -Bill
      Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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    • Solar Expert Posts: 108 ✭✭✭✭
      #6
      Re: What should I use for PV barn lighting

      Just wondering, Is this for daytime use or night? Would skylights work if its during the day?
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    • Solar Expert Posts: 223 ✭✭✭
      #7
      Re: What should I use for PV barn lighting
      nvyseal wrote: »
      Just wondering, Is this for daytime use or night? Would skylights work if its during the day?

      This is just a temporary solution to get some light where needed, and later to keep batteries charged.
      Both day and night, already have a window on each side of the barn. Lots of shade in the summer, so sky light will only help after leaves are off the trees or if I cut the trees down.
      The long term plan is for an additional 3.5 KW grid tie PV system for the roof.
      In the next couple of years I will cut down the trees, dig a trench to the house for power and install the PV system, plus a low temp air to water heat pump system for heating and cooling the house.
      As always the only thing holding me back is time & $ !!!!
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    • Solar Expert Posts: 2,397 ✭✭✭✭
      #8
      Re: What should I use for PV barn lighting
      LucMan wrote: »
      As always the only thing holding me back is time & $ !!!!

      HAHAHA :D Me too! Bags of Dirty money donations are accepted.
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