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I have to put together a small solar system for a college project.

I have solar cells with an output of 3.65A and 0.6V. Now if I paralel two groups of two cells connected in series I will double the amps and volts. And the output power will be like 8W.

The question is, do a 1.2V panel really work? Can I charge a 12V battery? I mean the panel will be 8W and high amperage low voltage.

Do I need to have a minimum 12V panel to charge battery? This means I will have to put in series 20 cells to obtain 12V.

Are there high voltage low amperage solar cells so I don't need to put together so many cells?

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If you want to charge a 12 V battery, you need a bit more than 12 V.

One way to achieve that is to put enough individual cells in series. Another way is to have the panel produce a lower voltage and use a electronic circuit called a boost converter. These convert low voltage at high current to high voltage at low current.

If you're clever, you can build in optimal use of the solar array and battery charge management into the boost converter. However, if the panel can only put out 8 W, which is 670 mA at 12 V, then you can just size the battery so that it can take 670 mA indefinitely without harm. Or, if this is a lead-acid battery, just have the boost converter produce 13.6 V when it can, but never more. A "12V" car batter, for example, can take that indefinitely.

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  • $\begingroup$ Hey Olin, great answer.. do you have any more information/links on how to size batteries and how to determine what over-charging they can cope with indefinitely, etc.? $\endgroup$ – jhabbott Jun 16 '15 at 11:12
  • $\begingroup$ @Jhabbot: The only real answer is to see the datasheet for whatever specific battery you are using. This is particularly important if it's a lithium type. Lead-acid batteries are generally more forgiving. You can safely keep it topped off by using the "float charge" method, which is to apply about 13.6 V to a "12V" battery. This is what cars have been doing for the better part of a century. Really only the method to regulate this voltage has changed, but the voltage and the principle behind it has stayed the same. Note that this is independent of the battery size. $\endgroup$ – Olin Lathrop Jun 16 '15 at 11:52
  • $\begingroup$ Thanks for the answer Olin, I have another question regarding your answer: "these convert low voltage at high current to high voltage at low current" - isn't the mppt charge controller doing something similar to this? converts high voltage at low voltage and increase the current and matches the panel's power $\endgroup$ – Robert Ramsey Jun 28 '15 at 16:19
  • $\begingroup$ @Robert: "high voltage at low voltage" makes no sense. MPPT controlers try to run the solar panel at the voltage/current operating point for highest total power. $\endgroup$ – Olin Lathrop Jun 28 '15 at 17:54

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