How Many Watts Does My Solar Panel Need To Be If I Am Running Lights Only At Night?
Oct 03, 2009 in
diy
I want to use 12vDc rope lighting that is 3 watts per foot and i am looking to use approx 64 ft of light. I am probably only going to have the lights on for 3-4 hours at night. I will be running the lights off a 12 volt car battery. What wattage will my solar panel need to be to recharge the battery all through the day. I would appreciate any help, Thank You! I am also looking at led lighting that is only 0.8 watt per foot.
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4 comments
ericnuts on October 3, 2009 at 8:47 pm
Your numbers give 172 watts which at 12 volts is 14.33 amps. In theory, you would need to have a 57 amp hour battery, but auto batteries despise being absolutely discharged so you would either need a more expensive deep discharge battery, or a much privileged amp-hour car battery or a cut off circuit to cut off the power when it dropped to about 10 volts (or both)
You didn’t say where you are, which is critical for the amount of light you get, especially if you are running this through the small dark days of winter. If you can only get 4 hours of excellent sunlight when you want 4 hours of night light, then you need at least 200 watts of solar supplied power and enough battery capacity to hold it from high to low voltage limits.
Carrie on October 3, 2009 at 9:06 pm
Here is the math.
3W/ft * 64 ft = 192W
4hr * 192W = 768Whr < --- energy needed per day
768Whr / 12v = 64Ahr
64Ahr * 200%(d-rate) = 128Ahr <--- Your battery needs to be a minimum 128 Amp - Hour to opperate without damaging itself.
At Boise, Idaho — Latitude: 43.6 we get 5 sun hours per day average
If your latitude is less than that, your sun hours will likely be greater.
768Whr / 5hr = 153.6W ~ 160W panel required.
I highly recommend that you get a charge controller in addition to this panel, as it will protect your batteries and enable charging all through low light conditions. Some even come with automatic light timers and or motion sensors:http://www.aurorapower.net/products/list…
For more information on solar electric components and layout visit: http://www.aurorapower.net/alternative-e…
Hope that helps!
mike1942 on October 3, 2009 at 9:10 pm
you should find some answers herehttp://www.google.ca/search?hl=en&source…
also herehttp://www.google.ca/search?hl=en&source…
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Diana on October 3, 2009 at 10:07 pm
You can use a 1-2 160W solar panels costing less than $200.