Not sure what all these readings mean

Blindowl1234
Blindowl1234 Registered Users Posts: 54 ✭✭
edited July 2016 in Solar Beginners Corner #1
Still experimenting with my little 125 watt solar setup for the last few months....adding another 100 watt panel next week. My chinese controller lol has a reading which says output to the batteries. Question is the reading after 30 days says 8 KW. So I'm guessing it's put 8 KW (8000 watts) into the batteries? So dividing that by 30 I come up with about 266 per day. Is that 266 watts per day into the batteries...? Batteries total 200 amp 12 volt setup. Led lights are 25 watts total and we use them 8 hours each night (200 watts) . Full charge usually by 1 pm with decent sun. Batteries on a cloudy day drop to maybe 75% over night, full sun and they're still at 90% by sunrise. I just was curious what to make of the 8 KW it was showing and if my math was anywhere near correct lol. Thanks
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,642 admin
    #2
    Your math sounds approximately correct... Just to clarify units... Watts is a "rate" (like 60 miles per hour).

    Watt*Hours is an "amount" (like drove 400 miles).
    • 25 watts * 8 hours per night = 200 Watt*Hours per night
    • 8,000 WH per month * 1/30 days = 267 WH per day
    • 267 WH per day / 8 hours per night = 33 Watt average load
    Note, flooded cell lead acid batteries are about 80% efficient (typical "worst case"). So, your 200 Watt*Hour per day load would be:
    • 200 Watt*Hour / 0.80 batt eff = ~250 Watt*Hours per day from solar array to recharge your nightly usage.
    And for your system, depending on where it is installed, say you have 4 hours of sun minimum (average) for 9 months of the year (non-winter). Then a 125 Watt panel would generate:
    • 125 Watts * 0.61 DC off grid system eff * 4.0 hours typical minimum sun = 305 Watts of typical minimum DC loading
    So your system seems to be operating pretty nicely.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Blindowl1234
    Blindowl1234 Registered Users Posts: 54 ✭✭
    #3
    Thanks Bill for the info that's what I wanted to confirm. Yeah it's doing good this summer averaging 6-7 hours of sun easily. Running a few small things during the day, after the batteries are fully charged, to make use of all that extra summer sun lol
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