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Directly using PV panel (without batteries/inverter)

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  • Directly using PV panel (without batteries/inverter)

    Hey guys,
    i want to know if can can directly hook up some load (like LED) to PV panels directly, (Of course voltage/power ratings are almost equal).
    ie- no intermediate device connected .. wires from PV panels connected across LED strip (12V).
    Will it work ? if so what about stability?


    honestly speaking i'm quite new to practical solar applications. but detailed electronic explanations are welcome.
    Also please do suggest some books/sources to deeply understand PV panels output,

  • #2
    panel wattage varies quite a bit as sunlight conditions change (clouds and such) and so the load has to be insensitive to this fluctuation. Water heater elements come to mind as about the only simple loads that are not damaged.

    What are you thinking of ?
    Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister

    Comment


    • #3
      Originally posted by TyrionLannister View Post
      Hey guys,
      i want to know if can can directly hook up some load (like LED) to PV panels directly, (Of course voltage/power ratings are almost equal).
      ie- no intermediate device connected .. wires from PV panels connected across LED strip (12V).
      Will it work ? if so what about stability?
      If you do a very good job of matching load to source (i.e. choose a panel that can never exceed the maximum current of the LED, and a voltage range that will support it) then that can work. Most people use additional protection (regulators etc) so they can use a larger panel, which will give them more uniform performance throughout the day.

      Comment


      • #4
        Originally posted by TyrionLannister View Post
        Hey guys,
        i want to know if can can directly hook up some load (like LED) to PV panels directly, (Of course voltage/power ratings are almost equal).
        ie- no intermediate device connected .. wires from PV panels connected across LED strip (12V).
        Will it work ? if so what about stability?


        honestly speaking i'm quite new to practical solar applications. but detailed electronic explanations are welcome.
        Also please do suggest some books/sources to deeply understand PV panels output,
        PV panels produce DC voltage at an amount of amps based upon the amount of direct illumination, 1000wts/M2 across the P/N junction the amount of theorized "holes" that shift domains increases with more light, from the photo-electron emission materials exposed to light. So if you want to know how your theorized LED light would work, it would turn on when it reached a functional voltage and then it would get as bright as it could when considering load vs supply. I.e. 42vdc divided by 3 LED units ran in series to equal the voltage from a 72 cell panel, then considering the watts would be a direct output based on the consumption of the device or in the case of a JINKO 300wt panel would be 7.14A divided among the 3 LED units, or 2.38A each @ 14VDC.
        Most LED lights of higher output can use up to 15VDC I believe and if not you can put a resistor or two in line to step the voltage down.
        Practically, you could have a parallel panel setup to fill in the gaps for Amps. If a LED failed it would stop the other two in the string from working. LED's are like the opposite of solar panels, they are a band-gap P/N junction that emits light when charged, and both act like a DC battery when configuring series and parallel circuits.
        Sunlight, on my solar.. makes me happy.

        Comment


        • #5
          Originally posted by solarddy View Post
          Most LED lights of higher output can use up to 15VDC I believe
          Forward voltages of visible LED's range from ~1.6 volts (red) to ~3.6 volts (blue or white.)
          and if not you can put a resistor or two in line to step the voltage down.
          LED's care about current, not voltage. Ballast resistors reduce the current, given a specific input voltage and device voltage. They are not as effective as actual current regulation, as well as being very inefficient - to adequately regulate current with a resistor you have to drop a significant fraction of the device's nominal forward voltage.

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          • #6
            Circuit protection - a good idea

            Fused connection from panel to the device you're powering, rated @ 150% of load/wiring is a good idea and required by NEC.

            In answer to your question, yes it will work just fine if voltages match, just don't forget circuit protection.
            Sunlight, on my solar.. makes me happy.

            Comment


            • #7
              Originally posted by TyrionLannister View Post
              Hey guys,
              i want to know if can can directly hook up some load (like LED) to PV panels directly, (Of course voltage/power ratings are almost equal).
              ie- no intermediate device connected .. wires from PV panels connected across LED strip (12V).
              Will it work ? if so what about stability?


              honestly speaking i'm quite new to practical solar applications. but detailed electronic explanations are welcome.
              Also please do suggest some books/sources to deeply understand PV panels output,
              I wonder if you can use an MPPT charge controller without a battery to help get the most power out of the panels?

              Comment


              • #8
                Originally posted by createthis View Post
                I wonder if you can use an MPPT charge controller without a battery to help get the most power out of the panels?
                You could except for the fact that most if not all MPPT CCs require a connection to the battery to boot up before you make the connection to the panels.
                The equivalent to what you suggest would be to use a very small battery.
                SunnyBoy 3000 US, 18 BP Solar 175B panels.

                Comment


                • #9
                  Originally posted by inetdog View Post
                  You could except for the fact that most if not all MPPT CCs require a connection to the battery to boot up before you make the connection to the panels.
                  The equivalent to what you suggest would be to use a very small battery.
                  Would a super capacitor work?

                  Comment


                  • #10
                    Originally posted by createthis View Post
                    Would a super capacitor work?
                    Nope. The voltage on a super cap varies more with state of charge than a battery does. (Linearly in fact).
                    Good for riding through a passing cloud maybe, but not much more than that.
                    SunnyBoy 3000 US, 18 BP Solar 175B panels.

                    Comment


                    • #11
                      Originally posted by createthis View Post
                      Would a super capacitor work?
                      If it's large enough, and you precharge it with a separate supply to wake up the MPPT controller, yes. But then you have to ask - why spend all that money/effort when you could just use a battery? Would be far cheaper.

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