Saturday, October 13, 2012

Homemade Solar MPPT Circuit - Poor Mans Maximum Power Point Tracker Circuit

MPPT stands for maximum power point tracker, which is an electronic system designed for optimizing the varying power output from a solar panel module such that the connected battery exploits the maximum available power from the solar panel.


We know that the output from a solar panel is directly proportional to the degree of the incident sunlight, and also the ambient temperature. When the sun  rays are perpendicular to the solar panel, it generates the maximum amount of voltage, and deteriorates as the angle shifts away from 90 degrees  The atmospheric temperature around the panel also affects the efficiency of the panel, which falls with increase in the temperature.

Therefore we may conclude that when the sun rays are near to 90 degrees over the panel and when the temperature is around 30 degrees, the efficiency of the panel is toward maximum, the rate decreases as the above two parameters drift away from their rated values.

The above voltage is generally used for charging a battery, a lead acid battery, which in turn is used for operating an inverter. However just as the solar panel has its own operating criteria, the battery too is no less and offers some strict conditions for getting optimally charged.

The conditions are, the battery must be charged at relatively higher current initially which must be gradually decreased to almost zero when the battery attains a voltage 15% higher than its normal rating.

Assuming a fully discharged 12V battery, with a voltage anywhere around 11.5V, may be charged at around C/2 rate initially (C=AH of the battery), this will stat filling the battery relatively quickly and will pull its voltage to may be around 13V within a couple of hours.

At this point the current should be automatically reduced to say C/5 rate, this will again help to keep the fast charging pace without damaging the battery and raise its voltage to around 13.5V within the next 1 hour.

Following the above steps, now the current may be further reduced to C/10 rate which makes sure the charging rate and the pace does not slow down.

Finally when the battery voltage reaches around 14.3V, the process may be reduced to a C/50 rate which almost stops the charging process yet restricts the charge from falling to lower levels.

The entire process charges a deep discharged battery within a span of 6 hours without affecting the life of the battery.

An MPPT is employed exactly for ensuring that the above procedure is extracted optimally from a particular solar panel.

A solar panel may be unable to provide high current outputs but it definitely is able to provide with higher voltages.

The trick would be to convert the higher voltage levels to higher current levels through appropriate optimization of the solar panel output.

A very simple yet effective MPPT type device can be made by employing a LM338 IC and a few opamps.

Let's understand the proposed MPPT circuit (solar optimizer) with the help of the following points:

The figure shows an LM338 voltage regulator circuit which has a current control feature also in the form of the transistor BC547 connected across adjustment and ground pin of the IC.

The two opamps are configured as comparators. In fact many such stages may be incorporated for enhancing the effects.

In the present design A1's pin#3 preset is adjusted such that the output of A1 goes high when the sun shine intensity over the panel is about 20% less than the peak value.

Similarly, A2 stage is adjusted such that its output goes high when the sunshine is about 50% less than the peak value.

When A1 output goes high, RL#1 triggers connecting R2 in line with the circuit, disconnecting R1.

Initially at peak sun shine, R1 whose value is selected a lot lower, allows maximum current to reach the battery.

When sunshine drops, voltage of the panel also drops and now we cannot afford to draw heavy current from the panel because that would bring down the voltage below 12V which might entirely stop the charging process.

Therefore as explained above A1 comes into action and disconnects R1 and connects R2. R2 is selected at a higher value and allows only limited amount current to the battery such that the solar voltage does not crash below 15 vots, a level that's imperatively required at the input of LM338.

When the sunshine falls below the second set threshold, A2 activates RL#2 which in turn switches R3 to make the current to the battery even lower making sure that the voltage at the input of the LM338 never drops below 15V, yet the charging rate to the battery is always maintained to the nearest optimum levels.

If the opamp stages are increased with more number of relays and subsequent current control actions, the unit can be optimized with even better efficiency.


The above procedure charge the battery rapidly at high current during peak sunshines and lowers the current as the sun intensity over the panel drops, and correspondingly supplies the battery with the correct rated current such that the it gets fully charged at the end of the day.

What Happens with a Battery Which may not be Discharged?

Suppose in case the battery is not optimally discharged in order to go through the above process the next morning, the situation may be fatal to the battery, because the initial high current might have negative affects over the battery because it's yet to discharged to the specified ratings.

To check the above issue, a couple of more opamps are introduced, A3, A4, which monitor the voltage level of the battery and initiate the same actions as done by A1, A2, so that the current to the battery is optimized with respect to the voltage or the charge level present with the battery during that period of time.



84 comments:

  1. will you please provide a printed circuit this for me. if please contact through rameshrenj@yahoo.com

    ReplyDelete
    Replies
    1. PCB is not available for this design.

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  2. some components in schematic are not labeled like R1,R2,R3 & some diodes. can you supply the value of the said parts? it will be useless if the label is incomplete. and is this project is tested?. tnx.

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    Replies
    1. The relay diodes are 1N4007.

      R1,R2 and R3 will need to be dimensioned as per the charging specs and in turn will depend on the solar and the battery ratings.

      R1,R2,R3 in series or individually basically decide the current output of the charger, and may be calculated from the formula:

      R = o.7/charging rate

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    2. the circuit is not tested but should work as everything is pretty straightforward in the design....

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  3. Brilliant !!!
    but sir can i ask about the max rates this circuit can work with ?

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    Replies
    1. Thanks!

      The maximum rate is 5 amp (30V), because that's the maximum current LM338 can handle

      Delete
  4. This circuit does not appear to actually perform the MPPT function, only a controlled charge. My understanding of MPPT has been that all solar panels produce a current proportional to sunlight, and a max voltage that varies as a function of temperature, thus power is a product of the panels V-I characteristic and the max power occurs at a peak. There is an impedance that can be applied to the panel such that this maximum power is extracted from the panel. In order to always hit this point, an algorithm is needed to search for it and a DC-DC converter whose duty cycle can be varied is needed to match the maximum panel voltage the the voltage that the battery is at, thus effectively making the battery always appear to the panel as the perfect impedance necessary to extract the maximum power. This circuit has a linear regulator, which steps voltage down by dissipating it as heat instead of exchanging voltage for current. While you can certainly do a much better job of regulating the battery charging process, I don't think this circuit gives you any additional power. I hope I am not coming across as rude, and I may have misunderstood some aspect of what is going on in this circuit, I just wanted to let you know that this may not be accomplishing what it is supposed to do.

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    Replies
    1. You perfectly got it. This is not MPPT.
      Shan

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    2. I have tried to provide an alternative, easier solution to the new hobbyists, because the actual concept would be beyond their reach to understand and build.....

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    3. Then it may be fairest to be honest about that.

      NONE of the circuits that you label as such, are actually MPPTs, as none of them will transfer maximum power to their load (the battery). If you want a cheap and easy way to non-MPPT charge a battery, you could suffice with a diode between solar panel and battery, perhaps with a relay or MOSFET to turn of charging once the battery is full. This will work better than any of the designs you've posted.

      Misinformation is worse than no information at all. Two project teams at my school have attempted to use your designs as a basis for their MPPT, only to lose valuable time and resources before finding they don't work as advertised.They now risk failing their course, as we don't give them a passing grade if they can't demonstrate MPPT functionality. (They have learned a valuable lesson -- don't just trust any information you find on the Internet...)

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    4. I don't blame you for this comment because may be you yourself are much ill informed about electronics and might have failed to understand the above circuit details.

      The above mppt cannot be considered a real mppt only because it doesn't employ I/V curve tracking but that doesn't take away its credit of being extremely efficient than the ordinary solar chargers that you are referring to.

      How much do school students know about electronics and how much experience do they have this such field? I have seen experienced hobbyists consulting me for days and multiple failures until finally I make them succeed in making a particular project.

      If your students couldn't make this simple looking solar optimizer then imagine what they would do with an actual mppt.

      People appreciate me for providing alternate innovations, concepts, inventions that are easier and much effective.

      It's unfortunate that there are folks who like to break their frustrations on creative helping engineers like me who are very rare online.

      If you are unable to understand a concept you better quit instead of criticizing it due to your own inefficiency.

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    5. ...if anybody points out faults in my designed circuits I would welcome that, but just criticizing blindly could be foolish..

      Delete
  5. Hi Swagatam,

    do you have or can you a design circuit for DC-DC converter with high current?

    input: 10~50vdc
    output: 12 or 13.8 vdc
    current: min=10 amps
    max=100 amps

    Regards,
    Mike

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    Replies
    1. Hi Mike,

      I think the circuit shown in the following link might work for your application also:

      http://homemadecircuitsandschematics.blogspot.in/2012/10/motorcycle-full-wave-shunt-regulator.html

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    2. hi swagatam,

      i saw the circuit.
      what i want is a regulator using one or two 12v battery and the out put would be 13.8 is it possible?
      i think this circuit will save the lifespan of the battery.

      by the way thanks for your quick response.

      Regards,
      Mike

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    3. Hi Mike,

      Do you mean a boost converter, which would lift 12V to 13.8 volt...??

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    4. yes sir...

      Thanks and Regards,

      Delete
    5. You may refer the following article for understanding a boost converter circuit:

      http://homemadecircuitsandschematics.blogspot.in/2012/09/led-emergency-light-circuit-using-boost.html

      Make T1 = TIP36

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    6. Hi Swagatam,

      the circuit you referring, can i used it to a grid tie inverter? i would like to use a battery instead of a solar panel.

      Regards,

      Delete
    7. No you cannot use it as a grid tie because the circuit won't be isolated from grid mains and may get damaged.

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    8. do you have or can make a circuit for voltage regulator to use a battery to power the grid tie inverter?

      Specs of Voltage Regulation:
      Input voltage= 10V~32V
      Output voltage= adjustable (12~35V )
      Output Current= 10A~30A

      Thanks in advance

      Regards,

      Delete
    9. Presently I do not have this circuit, but will try to figure it out...

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    10. Thanks a lot Swagatam...

      i hope you can do it and post it here in your site.

      Regards,
      Mike

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    11. Sure Mike,

      will try my best....

      Delete
    12. Hi Swagatam,

      any news about my request?

      Regards,
      Mike

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    13. Hi Mike,

      you may try the circuit shown at the end of this article, just replace the 7812 IC with a LM338.

      http://homemadecircuitsandschematics.blogspot.in/2012/11/high-current-transistor-tip36-datasheet.html

      Delete
    14. Hi Swagatam,

      you said on the blog TIP36 that LM338 will be use in separate power supply. can you tell me if this is possible now just to replace 7812 by LM338??

      Regards,

      Delete
    15. Hi Mike,

      Just replacing will not do, you will have to replace with a standard LM338 configuration, using preset, 240 Ohms resistor etc.

      Delete
    16. Thanks Swagatam...

      i'll try to do it.

      Regards,
      Mike

      Delete
  6. Hi Swagatam,

    what is the difference between 7812 to LM338?

    Regards,
    Mike

    ReplyDelete
    Replies
    1. Hi Mike,

      7812 will produce fixed 12V, LM338 can be made to produce any voltage between 1.25 to 30V

      Delete
  7. Hii swagatam i want to make this circuit for 48v and 70amp so what changes will i have to make in this circuit.???

    ReplyDelete
    Replies
    1. Hi KKaranjia,

      This circuit cannot be modified for oer 32V, because the IClm338 cannot tolerate more than 32V....I think the following circuit will work if integrated with the above opamp stage:

      http://homemadecircuitsandschematics.blogspot.in/2012/10/high-voltage-high-current-dc-regulator.html

      Delete
  8. can you please help and integrate them as i am not able to understand where to connect and in that other circuit also cant be operated beyond 20v or 30v and in the charge controller i require the input will be around 60v and the output required is 48v

    ReplyDelete
    Replies
    1. I'll try to do it, i will inform you when it's done.

      Delete
    2. Hello kkranjia,

      I am finding it difficult to design a high voltage MPPT with the above concept, because the IC324 won't accept more than 32 volts, I'll try to come up with a PWM based design which would be more suitable, but it might take some time.

      Delete
  9. Hello sir here is piku
    can u help me in the ratings of some components and infomation of MPPT-

    1)diode connected in parallel to relay coil
    2) information about 10 Amp diode
    3) 4K7
    4) rating of green and red coloured diode
    5)240

    ReplyDelete
    Replies
    1. Hello Piku,

      1) = 1N4007

      2) 10 amp diode = two 6A4 diodes connected in parallel

      3) 4k7 = 1/4 watt, 4.7K resistor

      4) green and red color LEDs

      5) = 240 ohms, 1/4 watt resistor

      Delete
  10. I really appreciate that you tried to bring out some circuits for micro inverter solar projects. Every thing related to this topic is secret and no good circuits are available still. Thx.

    ReplyDelete
  11. in this circuit where the output need to take please note .guru_ram86@yahoo.com

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  12. hi sir...
    will this solar panel move automatically in the direction of sun.
    i hv a project "automatic solar tracking system" and for that i want a circuit diagram.
    so can u help me sir. ?
    thanking you

    ReplyDelete
    Replies
    1. Hi Ramsahay,

      The above circuit will not move the panel, refer to the following circuit design:

      http://homemadecircuitsandschematics.blogspot.in/2011/12/how-to-build-dual-solar-tracker-system.html

      Delete
    2. hi sir,
      i want to design 12v 30A mppt controller help me

      Delete
    3. i'll try to design it and post it.

      Delete
  13. hi sir,
    Thanks for your reply sir. mppt controler using microcontroller(arduino) sir.please reply me

    ReplyDelete
    Replies
    1. hi seetha,

      microcontroller mppt design is not available with me presently...

      Delete
  14. hi sir,how are you?actually i want to know i am already using a pwm based solar charger with my inverter.but want to use MPPT.can you publish a cicuit which can handle 24v 30 amp. thanks

    ReplyDelete
    Replies
    1. Hi Ravi,

      I'll try to design it for you, however making the SMPS part in the MPPT can be little difficult, if I succeed I'll post it here for you.

      Delete
    2. thanks sir,can i divide the circuit in 2 part in first part the battery will be directly connected to the solar and in the evening and before noon a voltage amplifier will increase the volt to a desired level.is it possible?

      Delete
    3. Yes you can do it, the following two circuits can be combined to produce the intended effects:

      http://homemadecircuitsandschematics.blogspot.in/2013/04/simple-solar-mppt-circuit-using-ic555.html

      http://homemadecircuitsandschematics.blogspot.in/2013/06/universal-ic-555-buck-boost-circuit.html

      Delete
  15. Hi. Great site.
    I agree with the mppt concept. We live completely of grid. We have 8 x 240w 24v solar panels connected with 4 x 40a 24v pwm controllers to batteries and a 3kw wind turbine. Power to the house is done via 3kw pure sine wave inverter. My idea is to connect a simple mppt circuit infront of my pwm controllers. Do you think this will enhance the solar panels charge rate, more important in early mornings and late afternoons.
    If so can you please help with a simple design for 24v 40a mppt circuit than can installed in front of my pwm controllers.
    Thanks
    If so

    ReplyDelete
    Replies
    1. Hi, Thanks!

      It will depend on how the PWM controllers are configured.
      I am assuming the connected batteries to be rated at 12V and the PWM controllers generating the required 14V for charging these batteries.
      If this is so, then I think the PWM controllers would itself be quite efficient in optimizing the solar panel current, and external MPpTs wouldn't be required.

      Delete
    2. Hi
      No sorry we have 24V battery bank. The PWM's are charging at 28.8V. My solar panels open V are +- 40V, I think it would be better to install a dc - dc converter in front of the PWM controller to change the higher volts low amp to lower volt higher amp. Can a converter be made with high current +-40A.
      Thanks

      Delete
    3. Yes, you can try a buck converter using a IC555 circuit, connect it in between the pwm converter and the solar panel, one suitable design can be understood here:

      http://homemadecircuitsandschematics.blogspot.in/2013/06/universal-ic-555-buck-boost-circuit.html

      Delete
  16. hi i am planning to connect this mppt circuit io dual axis solar tracker.
    1) if my solar pannel rating is 50w what must be the R1,R2,R3 values
    2) Are the relays in this circuit are 12v 8 pin relay
    3)In the circuit an arrow pointing 10k resistor, is this resistor variable 10k resistor
    4) in the circuit the connecting wires are disconnected in some places how the wires connected there

    ReplyDelete
    Replies
    1. 1) resistor values will depend on the battery AH rating.
      2)relays are 12v 5 pin, spdt
      3)those are presets or trimpots
      4) the gap indicates that the overlapping wires are not connected in anyway.

      Delete
  17. hi!
    thanks a lot in helping me in completing the dual axis solar tracker it's working perfectly
    my next step is to connect the solar panel of dual axis solar tracker to this simple mppt circuit
    is this idea good
    Here in the circuit A3 and A4 are the other 1/2 of IC 324 then in circuit A3 is +v and ground connection are these connections pin 4 and 11 in IC 324?

    ReplyDelete
    Replies
    1. You are welcome!

      The IC 324 has four quad opamps in one package, the supply for the entire IC is at the pins 4 and 11.

      Delete
    2. I would recommend the simpler zero drop charger design which is shown below, it's basically a voltage regulator circuit that optimizes the solar parameters and avoids unnecessary loading of the panel.

      http://homemadecircuitsandschematics.blogspot.in/2013/08/simple-zero-drop-solar-charger-circuit.html

      Delete
  18. In the circuit one transistor base is connected to 100 ohms and after that an a connection with big dot is left freely what to connect there?

    ReplyDelete
    Replies
    1. ignore the dot, remove it from the circuit, it's a drawing mistake.

      Delete
  19. 1) R1 R2 and R3 = 0.7/ charging rate in kilo ohms or ohms?
    2) Is 4K7 is preset resistor?

    ReplyDelete
    Replies
    1. 1) it's in Ohms.
      2)4k7 can be a preset or a pot. It should be a 10k preset/pot actually

      Delete
  20. when will the red and green led's glow?

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  21. How to set the 10k preset values explain briefly?

    ReplyDelete
    Replies
    1. pls make the circuit first, then I'll explain it further.

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  22. Where the ground in the circuit conneted?

    ReplyDelete
    Replies
    1. transistor emitter lines need to be connected together

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  23. i made the circuit,but my solar panel is giving 10 volts without mppt but when the mppt is connected only 6 volts is measured. I measured this 6v by taking away the battery and connected a multimeter in place of battery it showed 6 volts. how can maximum power can be obtained with reduced voltage.
    i connected 3 w 9v solar pannel and 12v 1.3AH battery
    and the red led is always glowing even when the battery is dischearging

    ReplyDelete
    Replies
    1. how can you charge a 12V batt with a 9v input?????

      you will need a 18v panel for a 12v batt and the above circuit.

      also replace the 4k7 pot under LM38 with a 10k pot for getting a 15V adjustable range

      Delete
  24. Does it mean both the transistor emitter points should be connected

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  25. The ground points must be connected to battery -ve or solar panel - ve

    ReplyDelete
  26. Why that much high rating 10 amp diode is used?

    ReplyDelete
    Replies
    1. So that bigger batteries upto 100ah can be charged, you can use smaller diodes suiting your requirements.

      Delete
  27. sir gud day,
    thank you for your informative and helpful blog.
    my some question is:
    1.in R1,2,3 0.7ohms, how many watts i apply if my battery is 12v 40AH and my solar panel is 50w, 12v-20v. pls.. give me exact value of the resistor 1,2,3.
    2.IC324 is it also LM324 if i buy in elect. store.
    3.all 4 presets 10k parts under ic324 is it automatically set already or i manually configuring the value to set the right output, if manually do, will you mind how to set this in correct value.
    Hope you appreciated me. Thanks very much!

    ReplyDelete
    Replies
    1. The above circuit procedures could be quite complicated for anyone who may new in the field, it's for the experts....I'll try to update the article soon with an identical design but using lesser number of components and hassle free setting procedures....so please keep in touch until then

      Delete

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Readers are advised to proceed with the construction of the presented circuits only after understanding the concepts from the core. Not adhering to this can lead to failures and frustrations.