Build MPPT based solar charger

Discussion in 'General Electronics Chat' started by shiva007nand, Jan 9, 2016.

  1. shiva007nand

    Thread Starter Member

    Sep 25, 2015
    38
    1
    I am looking forward to build mppt based solar charger.
    I have google lot of stuff but I did not find specific solution for it.
    I am little bit confused because some mppt solar charger
    have build in MPPT logic, manufacturers like TI ans LT.
    some people are building mppt using PIC micro controller.
    which one is the easiest way to build 20 A mppt solar charger ??
     
  2. MrAl

    Well-Known Member

    Jun 17, 2014
    2,439
    492
    Hi,

    There are different ways to do max power point tracking.

    The main idea for the panel measurement types is you calculate the power I*V where I is the array current and V is the array voltage. When the product I*V is highest, you've got the max power point, but only for that level of sunlight brightness. To find this point sometimes the load power is varied so that several load values can be checked to see which one gives the highest I*V product.
    Another way however is to use a separate small solar cell to measure and then assume some factor that equates to the right setting for the controller.

    There is also the possibility of adjusting the angle of the panel mechanically because the panel output is also dependent on the angle relative to the position of the sun at that time of day. The relative output is dependent on cos(Angle) where when cos(Angle)=1 the sun is directly overhead (perpendicular to the front surface of the panel). If you intend to adjust that too then that is a different algorithm, and adjusting that so that the angle is right means you get the max power relative to the angle. Unfortunately, for year round tracking the angle is two dimensional too. so there are two angles to consider, but one angle is more important and that is the angle that tracks the longest apparent sun travel.

    There's quite a bit to this so if you are new to control theory you might find it a little difficult to handle.
     
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  3. wayneh

    Expert

    Sep 9, 2010
    12,145
    3,056
    There is a rule of thumb for the size of an installation, below which it does not make sense to implement MPPT, because the small improvement in output could not possibly recover the overhead.

    I suspect your panel may be to small to justify the trouble, but perhaps an expert can advise.
     
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  4. crutschow

    Expert

    Mar 14, 2008
    13,028
    3,238
    A dedicated MPPT control chip would likely be the easier way to build an MPPT controller as compared to using a microcontroller.
     
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  5. shiva007nand

    Thread Starter Member

    Sep 25, 2015
    38
    1
    Yeah I think in similar way, because there in micro controller there are lot of other factors included.
    Like external memory, bug in code or system hang.

    what will be the difference in cost if I selected dedicated MPPT solar charge converter ??
    do you have any knowledge of dedicated mppt solar charge IC ?? or have you used it before ??
     
  6. shiva007nand

    Thread Starter Member

    Sep 25, 2015
    38
    1
    For governments technical specification, they have strictly included that they need MPPT based solar
    charger for each system. so, I am stick on MPPT based solar charger.

    due to lack of knowledge, please tell me what is rule of thumb for size of installation ??
     
  7. shiva007nand

    Thread Starter Member

    Sep 25, 2015
    38
    1
    there are certain companies who do solar tracking using rotary method like NextTracker.
    but the problem is that you have to put some external mechanism to rotate panel according to sunlight,
    so there is possibility of wastage of power to rotate the panel.
     
  8. MrAl

    Well-Known Member

    Jun 17, 2014
    2,439
    492
    Hello again,

    The decision to MPP track would be base on a lot of mostly electrical factors, and the decision to rotate would be based on electrical and mechanical factors. Of course environmental factors kick in too.

    One of the main things in MPP tracking is converter efficiency. If the converter being used is not efficient enough, then MPP tracking may actually use more power. Also, the decision whether to use an algorithm or just another separate solar cell to measure the sun's intensity and thereby make a decent decision on the MPP.

    The thing about rotating something though is mostly about the rotational friction and balance. If the object to be rotated has good bearings and is balanced at it's center of gravity, it takes almost no power to rotate it. If there is a significant wind however that can add to the resistance to a rotation, so it also depends on how much wind and how often and even if another decision is made as to when to rotate and when not too based on the wind power.
    For example, in theory in a no wind condition and zero friction you can rotate a Mack truck with your pinky finger. It might take some time to get rotating up to a certain speed, but i would not think a solar application would need much speed. In fact, we can estimate about 36 degrees/hour over a 10 hour period. So maybe rotate once per hour or something like that.
    But yes there will be some power, and that's where the electrical aspect comes in. Does the gain in power beat the loss in power due to the rotation energy. We have to keep in mind that the energy wasted due to improper angle can be significant too, because of the cos(angle) rule. This would have to be weighted in with the power obtained using a standing still array mounted at optimal constant angle.

    The point of using a converter or not is sort of a separate issue anyway, because if the voltage of the panel does not match the load well enough there will be significant loss.

    All this means this is probably one of the most interesting control theory optimization problems for ground based projects.
     
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  9. shiva007nand

    Thread Starter Member

    Sep 25, 2015
    38
    1
    Thanks for such a deep details, sorted most of the problems.
    Now I have to learn more about control theory.
     
  10. MrAl

    Well-Known Member

    Jun 17, 2014
    2,439
    492
    Hi again,

    Probably one of the most interesting areas in electronics.

    Control theory is what allows airplanes to fly, rockets to escape gravity, the (ex) Space Shuttle to maneuver and make reentry into the atmosphere, to name just a few.
     
  11. Lestraveled

    Well-Known Member

    May 19, 2014
    1,957
    1,215
    There two functions that share the description, "Maximum power point tracking". One function is to physically re-position your solar collectors to maximize the amount of energy being collected by your panels. The other function is to maximize the usage of the energy that is produced by your panels by adjusting the battery charger charge profile. This second function is the most commonly used way to increase efficiency. It just requires a smarter charger.

    The cutoff point for benefiting from a MPPT charger is pretty low. First, when a solar panel has the capacity to over charge its storage battery, you will need a charge controller. Small switching power converters are very cost effective for this purpose. Next, adding an MPPT function to the switching power converter is a small upgrade. In other words, if you have to build smart battery charger it is not that much more to make it a little smarter and have a MPPT function.
     
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  12. Bernard

    AAC Fanatic!

    Aug 7, 2008
    4,173
    397
    Also to be useful the load needs to be able to absorb all of the SP output like the grid or a discharged battery. For a battery, once charged MPPT serves no useful purpose.
     
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