24 volt solar panels

Discussion in 'General Electronics Chat' started by ShockBoy, Jan 15, 2010.

  1. ShockBoy

    Thread Starter Active Member

    Oct 27, 2009
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    I have taken the advice of Sgt. and downgraded my expetations for my 2 24v solar panels. My question to you all is what advice for me do you have in regards to using these panels--knowing more identical panels will come in the future--the most efficient way? Wookie has stated that the use of led light replacement is a good idea and I agree. I am thinking of running led emergency lights throughout the house for the occasional outage. Any suggestions would be appreciated. Thanks all.
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    I did suggest that LED lighting would be a good idea for a beginning project.

    However, you really need to get your requirements nailed down. Starting off in the high-use areas (like perhaps the living room and kitchen) might be a good idea.

    You've mentioned a 24v solar panel. 12v lead-acid batteries generally are bulk-charged at a constant current to about 14.5v, and then charged at a constant voltage until current is reduced to a certain level. You will need to consult manufacturer's documentation to determine optimal charge parameters.

    An array that puts out 24v would not be able to charge two 12v or four 6v batteries in series; at least 28v would be required.

    [eta]
    You'll need to figure out what will work out to be the best for your needs.

    Low voltage means higher currents. High current means more loss of power in the wiring. For your LED lighting, you might consider using 24v wiring, but you will need to increase your solar array to output at least 28v to charge a pair of 12v batteries in series. You will also need a charge controller. Undercharging or overcharging your batteries will shorten their lives significantly, which will cost you money.

    You also need to be aware of what might be available commercially for inverters. Your long-term goal is to get off the grid, but that's quite a ways away.

    There are buck-type LED power controllers available that don't cost a lot of money - but you'll have to build the circuit yourself. They can be very efficient.
     
    Last edited: Jan 15, 2010
  3. ShockBoy

    Thread Starter Active Member

    Oct 27, 2009
    186
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    I take your advice to heart Sgt. It has not been wrong yet. Thank You for helping me, and future help.
    I am at the very beginning of this venture, I have built two 24v solar panels, that can be series'd to 48v if need be. I have heard of at-panel-micro inverters that reduce the power loss and I am curious about that. For me I am planning on increasing my panels yearly. Whether that means series'ing them into higher voltage, or going for the current increase; I am not at that decision yet. What are buck-type led power controllers? I work with tape-length(25ft. each roll) led strings using 12v wall wort.
     
  4. ShockBoy

    Thread Starter Active Member

    Oct 27, 2009
    186
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    here is what I plan to use for my charge controller. It is all over the internet. I know I need a heat sink for the vr, since my voltage is higher than the 18v average this controller is based on.
     
  5. HeliEye

    New Member

    Feb 6, 2010
    9
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    I designed a 'wierd' solar charger many years ago, I say wierd, as I didn't go down the conventional 'shunt' regulator path, to me seems inefficient?
    My design used a form of constant and DC pulse charge, depending on the battery level. yup, I can hear you say "that definately sounds wierd"
    Explanation: I used a MAX917 nano power comparator for battery voltage monitoring, the output of which switched a VN10LF N-ch mosfet which gated the P-Ch mosfet controlling the solar panel (10W BP-Solar type) output charge to the 18AHr Gel battery, if the battery was below 13.8V (or whatever is decided max volts) then full charge current (800mA) was applied to the battery (assuming bright sunlight), when 13.8V was reached the charging is stopped, the battery Volts sag and the process is repeated, but this time in pulse-mode, the sharp rise time, it was thought, would help with de-sulphation?
    Cost for this version charger? almost pennies, all SMD, no stupid heatsinks, shunts etc, it seems to be efficient, as this charger is in dozens of remote solar powered weather stations, and been running 5 years to date, with no failures.
    Trying to find schema.. buried in archive somewhere.

    Steve
    I just love lateral thought ;-)
     
  6. spinnaker

    AAC Fanatic!

    Oct 29, 2009
    4,866
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    So you did nothing to control the voltage level coming from the solar panel?
     
  7. HeliEye

    New Member

    Feb 6, 2010
    9
    0
    Hi Spinnaker, good question, but in testing I found the comparatively weak current from the panel (750mA ish) going into the 18AHr battery, the battery internal impedance clamped this down, as the comparator kills the charge at 13.8V it only delivered short maintenances pulses there after. There is also the constant draw on the battery from the weather station gear and GSM Modem.
    I tested a fully charged battery in full sunlight with the charger operating, no matter how long I left it there the battery never got over 13.8V. I was deliberately trying to over-charge the battery, it just never happened. I was more interested in giving the battery the fast short pulses when it was charged. I've had no negative feedback from the company I designed this for, apparently all still working fine, longer than the 5 year life the batteries are good for.

    Cheers

    Steve
     
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