Solar Panel Ratings
What is the power rating on Solar panels mean?
So i’m looking into using a solar panel to charge some 12V – DC – 5AH batteries. I’m planning on using a 12V solar panel. Ive been looking online and see alot with different ratings such as (2W, 5W, 7W, etc). What does the power rating mean?
Thanks
Hey JT, J3 is correct on the math, except that 12 volts is the, “nominal,” voltage of the system. The problem here is that to charge a 12 volt battery usually requires at least a 15 volt power source. To accommodate this, panels are generally wired for 18 volts, allowing the charger controller or other wiring to use up a small amount, and still leave enough for the battery to charge on. A 7 watt panel that is wired for a 12 volt nominal system will likely have an open circuit voltage of 18 volts. To get to the amperage, take the watts and divide by the panel voltage (7 / 18 = .4 amps) When a manufacturer states rated watts, they are taking the panels open circuit voltage and multiplying it by its short circuit current. A panel that has an open circuit voltage of 18 and a short circuit current of 1 amp will be advertised as an 18 watt panel. Hence, a 9 watt panel will put out 1/2 amp.
In actual practice, you will never be able to reach the rated watts, because the panel voltage always degrades to match the battery’s charge curve voltage at the time. So even if you get an 18 watt panel, with an amp rating of 1 amp, it will put 1 amp into the battery, but if the battery voltage happens to be 14.5 while it’s charging, then the wattage from that 18 watt panel is 14.5 X 1 = 14.5 watts.
Charging a 5AH battery is no problem for a panel that only puts out 10 or 15 watts, it will take a few days. If it’s just one 5 AH battery, I would go with one of the battery maintainers at the auto parts store for $30 or so, they don’t usually put out more than 1/2 amp or so anyway. At 1/2 amp, it would take 10 solid hours of sunlight to put 5 AH into your battery. If you’re looking at panels online and don’t know what to get, just look for the specific ratings, not the wattage. Make sure the VOC, or open circuit voltage is at least a few volts higher than your battery voltage, and the short circuit current is about how many amps you want to charge your battery at. The watt rating doesn’t matter much for battery charging, only the amps. Good luck, Rudydoo
What Type of Electrical Panels Are Good For Solar?
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Sunforce 7 Amp Charge Controller $17.41 The Sunforce 60012 7 Amp Charge Controller prevents overcharging of 12-volt batteries. It is intended for use with 12-volt solar panels, and can handle up to 7 amps of array current and up to 100 watts of solar power. The controller is easy to use with a charging light that indicates that your battery is charging, and a green light that indicates a fully charged battery. The 60012 measures 4 x 1 x… |