Filed under: Solar Education. Tagged as: 12v solar panel, solar battery charger, solar panel 12v, solar panels, solar panels 12v.
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This article covers some common mistakes people make when they are looking to buy a 12v solar panel. Installing solar powered products for improving your life is rarely a strait-forward craft. There are always tricky bugs that creep up and a sharp eye needs to always be kept on voltages and power ratings. Read this article to prevent yourself from succumbing to these common pitfalls that are specific to 12v systems using 12 volt solar panels:
Panel Voltage Should Be 1.5x Higher
Many people who decide to purchase a 12v solar panel do so in order to charge a 12 volt automotive battery. They want to use a solar panel 12v to charge a 12v battery – makes sense right? Unfortunately, it’s not that simple.
Automotive, 12v batteries are only nominally 12 volts. During operation they will vary from 13.5 volts down to 10.5 volts. Additionally, a solar panels 12v output will undergo some loss before it actually reaches the battery. These losses come from the internal resistance of the panel, the voltage drop across a protection diode, the resistance of the connecting wires, and finally the internal resistance of the battery.
For this reason, solar power experts recommend that solar panels be rated for an output voltage that is 1.5 times greater than the battery to be charged. In this case, that would be 18 volts (nominal). This gives room for voltage drops between the panel and the battery so that by the time the energy reaches the battery it still has enough voltage to charge it.
Use a Protection Diode
If you are purchasing a 12v solar panel for use in a battery powered system or for charging batteries, be sure the panel either comes with a protection diode or you know how to install one. The best option is to purchase a charge controller to sit between the battery and panel in order to ensure they ‘play nice’ together.
Electrical current is often analogized to water flow. A diode acts just like a one-way valve, allowing electrical current to flow one way. In this case, we want the current to flow from the panel to the battery. At night, the voltage of your 12v solar panel will decrease far enough that the battery will be able to discharge into the cells. This will fry your panel! A simple $0.10 diode will prevent this from happening.
Ensure The Proper Power Rating
In the event you want to use a solar panels 12v output to drive a system directly (no batteries involved), then the situation changes. You do in fact want a 12v solar panel for this system and no diode is needed so long as there is no way for energy from somewhere else in the system to discharge into the panel at night. In this case be very wary of the power rating of the 12v solar panel.
If you are trying to run a 15 watt pump with a 12v solar panel, you would want the solar panel to be rated for 15 watts, right? Wrong.
A pump or other load is typically rated at the power required for operation. The power rating for a solar panel is the maximum power output in full sunlight. If it’s a cloudy day or the panel is partially shaded, you won’t get anywhere near the rated power. For this reason, solar power experts recommend that the power rating of a solar panel be two (and preferably three) times greater than the load you desire to power with it. In this example, you’d want a 45 watt, 12v solar panel in order to power a 15 watt pump reliably.