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solar charging regulators

Discussion in 'Renewable Energy' started by Thunderchild, Mar 15, 2009.

  1. RCinFLA

    RCinFLA Well-Known Member

    Jul 23, 2009
    FLA, USA
    A solar cell is an illumination dependent current source with a parallel inherent shunt diode. see Solar cells

    Unloaded, all the generated current goes down the inherent diode. If the panels are 20 watts it means that at 25 deg C they will produce about 1.2 amps at about 16.5 vdc when exposed to one sun (1000 watts/meter^2)

    Your panel has 36 cells in series. The parallel diode conduction point is dependent on temperature with lower voltage when hot (0.4v) and higher voltage when cold (0.7 vdc). Since there are 36 cells in series this diode voltage is times 36. To get maximum power out of the panel you run it so the illumination based current source dumps about 0.3% of its current down the diode. This gives the maximum power yield out of the panel.

    A Maximum Power Point controller is a switching power supply with a switch pumped coil for power conversion that hunts for a panel loading to produce the maximum V x I yield. The cost does not justify their use unless you are talking about >1000 watt panels.

    As a current source you can put the panel directly across the 12v battery and it will pump in 1.2 amps at full sun. Problem is once the battery is charged it will still keep pumping in the 1.2 amps.

    A PWM controller is just a series switch that as the battery voltage reaches its charge state the controller starts opening and closing a series connected MOSFET switch to the panel to keep the voltage on the battery in proper range. There is also a disconnect when panel drops below useable level of output.
    Last edited: Oct 1, 2009

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