Electronic Basics #29: Solar Panel & Charge Controller

Electronic Basics #29: Solar Panel & Charge Controller

if you are looking for easy-to-use regenerative energy source nowadays then your best bet is to do those solar panels by simply shining light on them they can create an output voltage that is capable of powering small loads or even bigger ones if we increase the size of the solar panel but how can we reach their maximum power outputs and how do we have to wire them up to for example charge up a battery let’s find out if we have a closer look at this 100 watt solar panel we can see that it consists of individual solar cells those basically make up all commercially available solar panels and of course you can buy such cells online as well after soldering a tap water to the prawns SD – terminal empty bag SD plus terminal we can use a multimeter to measure voltage up around 0.5 volts when light hits the cell surface that is pretty much the maximum output voltage of one cell which is also the reason why a solar panel connects many of those cells in series in order to increase the output voltage my 100 watt panel for example connects 36 cells in series to create an open circuit voltage of around 14 point 3 volts but if you are not thinking about soldering many bare solar cells in series instead of buying a proper solar panel to save a bit of money then it is noteworthy that those cells are extremely brittle and thus can be hard to work with so having a proper housing for the cells is definitely worth the money now if we have a closer look at the smaller solar panel we can see it there consists of 12 cells in series but creating such a serious connection also has one big negative side effects just imagine that the cloud could partly prevent lights to get the complete surface of the solar cells that means that one part of the serious action now features much higher resistance and since current meets the flow to all the cells the power outputs would decrease drastically as an example we can hook up a five millimeter red LED which draws 3.8 million from the solar panel and thus creates output voltage of one point seven six volts which equals an output power of six point seven million watts but if I cover the last two cells of the panel so one sixth of the complete surface the LED only draws 2.2 million at an output voltage of 1.71 volts which equals an output power of 3.8 million what’s that means the power decreased by 43% while the surface area are only degrees by 17% that is terrible to solve this problem we could add so-called bypass diodes in parallel to each cell so that current could flow through it instead of the higher resistance solar cell obviously with panels this smaller this does not make much sense but if we take a look inside the junction box of the 100 watt panel we can actually see two diodes those are placed in between behalf of the solar cells empty plus and minus terminal of course this is not the ideal solution but through the two diodes the panel can uphold the power outputs if one half of the panel is starting by clouds or something similar another kind of diode you often see here are so called blocking diodes and are used when solar panels are connected in parallel in order to decouple them from one another and prevent reverse current flow through them and now that we know how solar panels are wired up it is time to use different loads to test out their power output potential but to lower your optimism right from the start we will probably never get 100 watts from 100 tunnel since those characteristics were determined under so-called STC’s aka standard test conditions those includes any radians of 1,000 watt per square meter a solar cell temperature of 25 degrees Celsius and an am value of 1.5 which means that the sunlight travel to an air mass of 1.5 times D value up the atmosphere with my 0.6 watt panel here for example I achieve no power of 16 point 5 millivolts with a green LED and output power of 13 point 2 millivolts move a blue LED and an output power of 9.5 milliwatts with red LED but why does the output voltage vary that much depending on what kind of load I attach we can find the reason by having a look at lease implied equivalent circuit diagram of a solar cell if no load is attached so an open circuit it acts like the constant current source that lets the current flow through diodes which therefore create the characteristic cell voltage of around half of alts parallel to that we got a resistor which represents the power losses caused by the semiconductor material defects and at the end we got a series resistor which represents the power losses two wires terminal connections and so on if we now add a load to the cell the current from the constant current source device itself and creates more complicated electrical Network but what we know for certain is that by varying the load on the outputs we should be able to find an optimum at which we can draw the most power from the cell so I got myself my DIY power logger hooked up the solar panel were five kilo ampere and Charmander loads inserted a micro SD card and started slowly decreasing the resistance of the loads while simultaneously D constantly changing voltage and current values we’re saved on the SD cards afterwards I imported the acquired data into Excel and created a suitable XY diagram after printing it out and connecting the dots to one another we can see two characteristic points first off the open circuit voltage where no current flows empty short-circuit current where there’s almost no voltage those values are pretty always mentioned on a solar panel but what is also mentioned on my solar panel is the NTP voltage and current nppes stands for maximum power points which is not visible in my diagram so forth so I multiplied the current and voltage values and added a power line in the diagram which makes our maximum power point easy to find this point equals an output voltage of around four point four volts and the current of four milliamps so load resistance of 1100 ohms now of course you don’t want to simply add a resistor book the required value to the outputs and be happy about that you can heat it up the most efficient way you usually want to charge up a battery that is where we can use charge controllers the best ones of this kind of so-called MPPT ones or maximum power point tracking ones those usually utilize some kind of switching converter to act as the ideal MPP loads and thus a charge of the battery other more inefficient kinds simply use PWM to charge of the battery but they do not try to find the MPP and thus can decrease the efficiency of up to 40% and with that being said you already know quite a bit about solar panels and how to use them properly if you learned something new don’t forget to Like share and subscribe stay creative and I will see you next time

100 thoughts on “Electronic Basics #29: Solar Panel & Charge Controller

  1. Interesting to see that you also fell for the MPPT scam. The one shown in this video is actually not an MPPT type controller. The MPPT on its case is the name of the company manufacturing these.
    How about making our own?

  2. Really nice video! I learnt something from it.

    I have a youtube channel recently created. Please support. 🙂

  3. Solar panels absolutely need to be encapsulated in a specialized resin to keep humidity from destroying them. I have no idea if the resin affects the performance but it is necessary. DIYers can do iot.

  4. I just had this exact topic last week in uni (I study renewable energies) and you explained it exactly the way our professor did, awesome (Y)

  5. Hi Great Scott,

    I bought the NRF52840 Development Kit (Bluetooth 5 module).
    I know that I can connect it to the Arduino Uno to program it with Arduino IDE but I don't know how to connect it to the arduino.

    Can you please help me?


    Joey Absi

  6. Hi Scott, really nice explanation ! I actually waiting for a little solar panel to use with pwm regulator -> battery.
    Add second source of charging, like wind turbine is really complex, if you have a good solution for that, it'll be really interesting to explain 🙂
    thanks for your work !

  7. I never heard of MPPT. Try what I learned in electronics college, Maximum Power Transfer. Basically the internal resistance loads are matched. This way of thinking has been around for decades before solar cells became mainstream and it really does work. Good work charting via real life measurements, though!

  8. Great Scott => please disassemble a MPPT controller and explain us the science behind their operation.

    I have opened few controllers (both working & dead) but unable to analyse the working, since i don't have oscilloscope & other sophisticated test equipment's.

  9. Channels like GreatScott! and Mr. Carlson's Lab make me wonder how did my school/college teachers ever got their job. Five minutes of GreatScott! is equivalent to at least one 45min school class. Thank you for making the knowledge available to everybody for free. Stay creative 🙂

  10. Hallo Scott,
    Ich kann leider kein Englisch. 🙁 Kannst du mir bitte sagen wo die diese einzelne Zellen her hast?
    Gruß Drilon

  11. Please more of these videos in which you explain a lot. I found it very clear and easy to understand! Great video!

    [I found your controller comparison video, after posting a comment so i removed it and updated it it a bit…]
    But i have a question,.. Can a MPPT handle 24/7 power consumtion? And if you have a small pannel, do you always need a expansive controller? (i'm not taking about in the same price range, but if there are different type of controllers for ammount of output? Im just looking for possibilities, like for an raspberry-ish system like O-droid or somthing like that…. or maybe i can use it for another experiment….

    If you have time to help me, I would really appreciate the effort.
    If not I'll continue watching your videos. And try to learn more, as I'm not that good with electricity.
    But you really make it seem so easy. Thank you for making such interesting videos!

  12. love your work. Great presentation , one of the most succinct I've seen. I also love the use of fully analog diagrams (with a pen) to more effectively focus the student on the equations.

  13. hey i though about building somekind of an charge controller wich is basicly an an opamp, pod and a cap wich then make the cap simply decharge at the a set voltage so that the cap alwasys keeps its voltage at the mpp voltage i think if that is working the system will automaticly output the max amps at the voltage.

  14. Some one fooled you because in my country the solar panel of size 5cm length 2cm breadth gives me 2 volts 500mah😂😂😂

  15. Which diode should i use for 6v mini panels? I have 2 group series and rest 10 entire parallel so there is ~13 Voc and 1000mah I short. I have also dc dc buck step down to charge my phone as a conclusion there is only one diode that i put on the + output is that wrong?

  16. Thanks for answering my question. I kinda wanted to see a circuit that tries to find the best power point, and the buck boost integrated into it. Basicly, a fancy joule thief in order ot use, not only low Volt/Amps of solar, but any other small power source, (IE, wind farm). Building a buck/boost to handle that kind of power would probably be impractical, but if you could show a joule theif/buck/boost that would send that information to a proper charge controller, that would be cool. Kinda like handing off the heavy load to something that can handle the heavy load.

    But, thanks again sir!

  17. Forgive me if I'm wrong, new at electronics and GreatScott!, this site is intriguing. You mention diodes to bypass entire panels. I have 2x groups of 12 panels on my roof. From what I understand each group runs in series to pump up the voltage, and dumps that into the inverter (twin feed). My installer says if one panel suffers in a group then all those in the group suffer. Pretty much what you're saying on the panel you show. If I put high enough voltage diodes at the entrance/exit to each panel, have I effectively put in 'optimisers'? Have I isolated the poor performance of individual panels so the efficiency of the group is improved?

  18. NO HATE, But I created a solar mobile charger and the output of the 4 solar panels in series was 7 volts in sunlight, and 2 of the solar panel were only 1×1 inch the other two are 2×2 inch . Your solar panel is so big and still gives less than 1 volts.
    And my solar panels were rigid and not easy to break like yours.
    Great Scott I am not opposing u but just telling u.

  19. hi my name in manuel and I love all your electronic videos I wanted to ask you where to buy those little solar panels, thank

  20. Hey scott i am planning to make a solar powered mobile charging circuit .. i dont want a bulk circuit .. please suggest me a good circuit

  21. Awesome video what kind of marker or pen do you use when you design your projects and where can you buy it

  22. A small error: The MPPT M20 is a PWM Charge controller. Ok, the name remember us a MPPT but the price and the specs will remember us that it's a 20A PWM =)

  23. In 6:33, the measured open circuit voltage (Voc) appears to be 5.4V, however, in 6:45, it appears that the rated Voc of the panel is 22.6V. What is the reason behind this drop in Voc on the measured value? I am assuming the Voc rating shown on the panel is indeed for the panel you have done the measurement…

  24. WOW! thank you for the lesson. As always you provide good information in a compressed time frame without wasting any time. Keep up the good work. 🙂

  25. very interesting and thanks for your sharing. Can I share it on my linkedin post? My linkedin account is https://www.linkedin.com/in/solarenergy-conniewang, waiting for your reply. Have a nice weekend.

  26. love it, good explanation^^ I've learn a lot about solar panels xD ,please continue of doing great things

  27. So I'm trying to size a 30 amp service at 110v. How many ah do I need when it comes to batteries before my 8kw inverter? IDK if it's 8kw in 110 or 12v but I'll never draw the 65amps this thing can put out. 30 amp Max. I can size my panels etc later.

  28. Hi! Dont know why this video was not recommended to me a few weeks before! It is a very interesting video on solar panel. And i am making a MPPT charge controller for my 12 V 10 W panel to charge a 12 V 1.3 Ah battery.

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