Connecting output of solar and wind generators together

telljftelljf Registered Users Posts: 26 ✭✭
Hi, posting again after a long time.

Can I connect the output of wind turbine and solar panels, both 24V systems, to the same distributer box which then takes it to the charge controller? The combined amps are OK, the wires can handle it. Any known issues with this configuration, like the solar panels reverse charging from the wind output during night.

Thanks.
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  • PhotowhitPhotowhit Solar Expert Posts: 5,878 ✭✭✭✭✭
    edited July 7 #2
    telljf said:
    Can I connect the output of wind turbine and solar panels, both 24V systems, to the same distributer box which then takes it to the charge controller? The combined amps are OK, the wires can handle it. Any known issues with this configuration, like the solar panels reverse charging from the wind output during night.
    Usually, you will want wind and solar on different charge controllers.
    Solar can just be turned off, while wind cannot, wind must make power while spinning and you will want a diversion charge controller that uses a 'dump load' once the batteries are fully charged.

    Perhaps more of an explanation here;

    Diversion Load Controllers (thesolarstore.com)

    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • telljftelljf Registered Users Posts: 26 ✭✭
    Shouldn't the charge controller take care of the battery charging once it reaches float, even if turbines are turning? The wind turbines are anyway not expected to provide more than a float charge on average in my case. 

    During day the solar and wind may generate slightly different voltage and connected together in parallel, may adopt the lower voltage of the two like connecting two panels of different rating. The charge controller shouldn't know if the solar or wind is supplying power.

    But what I am concerned about is if the wind charge will go into solar panels and solar charge will go into turbine when either of them is idle without voltage potential to block the reverse flow. Anyone has experience using this configuration? Connecting the two source in the same distribution box, reduces the trouble of taking additional wiring as the panels and wind turbine are close together..
  • BB.BB. Super Moderators, Administrators Posts: 32,741 admin
    Assuming you have HAWT (horizontal axis wind turbines)--These types of turbines can over-speed and even self destruct if they are not properly loaded (charging a battery bank/load bank) or shutdown (brake, load bank, shorted output, feathered, furled, etc.)....

    With wind turbines, the basic setup is to wire the turbine "directly" to the battery bank. And when the bank is "full", using a dump/diversion controller, the controller starts "dumping" current to a load bank (typically a bunch of resistors) to keep the turbine loaded and prevent the battery bank from over charging.

    Solar panels (in general), on the other hand, are perfectly happy supplying current (zero to full current) to the charge controller/battery bank. So when the battery bank is full, the "series connected" solar charge controller simply turns off the charging current to the battery bank.

    If you have a series solar charge controller and a diversion wind controller--you might set it up like this:

    Solar Controller: 14.7 volts charging set point
    Wind Controller: 14.9 volts diversion set point

    The solar charge controller operated "normally" and the diversion controller only "dumps" energy from the wind turbine on windy days/times to keep the battery bank from over charging.

    The above is a very simplified explanation--But correct for basic understanding and how a "simple system" is configured/operates.

    We have an issue here that there are many different turbines/controllers/systems out there. With lots of variations in how they are connected and how they run.

    Can you give us the name/model/links to your system components (wind turbine, charge controller, etc.)?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • telljftelljf Registered Users Posts: 26 ✭✭
    Thanks Bill for the detailed explanation as usual. 
    I have ordered a Vertical wind turbine from Alibaba. I know you all will not be pleased with it, but I have my reasons. I plan to install it on my terrace and VAWT is more suited there due to its lower sound, speed and wind survival abilities and maintainability. I am giving their link below:

    https://www.alibaba.com/product-detail/MAX-600W-12V-24V-400W-Wind_1600227882843.html

    It is 400W rated, 600W Max VAWT, I expect a few amps from it at best given the wind here, but even if it gives 600W at 24V, it is about 25amps. I have a 400AH battery bank, with 4 parallel strings with 100AH each. Total 8 batteries, more than 10 years old, connected to a 800W panel. So this battery bank should be able to handle the max current that the wind turbine can churn out.

    They are providing a standard wind controller with the item, which I guess converts the 3 phase AC to DC. This could be directly connected to the battery if a new wire can be pulled to the battery bank I think. I am investigating if that could be avoided and the out from their controller can be connected to the solar distribution box.

    Once I install and operate the turbine, I will update you on how well the VAWT perform.

    Jacob
  • BB.BB. Super Moderators, Administrators Posts: 32,741 admin
    edited July 11 #6
    VAWT (as I understand) typically do not need direct connection to the battery bank for RPM limiting (battery loading of alternator)--So that is one possible answer (no need for dump controller)(???).

    Usually the issues are not with "gusts" or a quick wind storm (or any controller charging event). For example, a typical lead acid battery bank will overheat with even 2.5% rate of charge it is goes on for many hours. One battery vendor suggested batteries have "failed" if they draw more than 2% rate of charge in float (continuous current flow for hours/days/weeks/etc.) as anything more runs the risk of catastrophic battery failure (even to the point of fire). Or, in your case:
    • 400 Amps * 0.02 "uncontrolled" charging current = 8 amps
    • 8 amps * 30 VDC charging = 24 Watts of "gassing and heating" to bank
    Granted, I am not expecting 25 amps from your VAWT (you are correct--I don't think there is a successful VAWT installation that has reliably generated power ever--Let alone reliably for a 1+ year period).

    Anyway--I would, at the very least monitor charging current and perhaps even put a remote reading thermometer in/on the battery bank and monitor temperatures. If you see an unexpected rise (60C or 140F is absolute max temperature for Rolls lead acid).

    If this was a lithium bank, they do not take "uncontrolled" or "over charging" very well at all (can easily "kill" the cell/battery).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • telljftelljf Registered Users Posts: 26 ✭✭
    It is a lead acid battery. I am planning to put a docwattson in line to the turbine to monitor its current and AH in the beginning. Like what you said, the turbine has to consistently deliver >240W to maintain float by itself. That is not going to happen here.

    Though my original question of connecting the wind output to solar distribution box is open. 

    Jacob
  • BB.BB. Super Moderators, Administrators Posts: 32,741 admin
    I am not quite sure I understand your solar distribution box question... If the question is can you parallel the output of a wind turbine with a solar array at the solar combiner box--The answer ranges from it depends to probably not a good idea.

    For me, the big issue is that most alternators when not connected to a voltage source (i.e., a battery bank) directly (and/or dump controller/resistor bank) can output unregulated voltage. I have never measured wind turbine alternators, but old 12 volt car alternators can easily over 100 volts--Their regulators are not designed to output a "stable" 14.4 volts (or whatever) unless there is a battery bank to keep the voltage stable.

    So, if you parallel your wind turbine with the solar array--You run the risk of over voltaging your solar array (feeding a 50-100 VDC typical array output max) and ruining your array. If you know your wind alternator will not exceed ~Voc-array, then less of an issue.

    Another question--If you are using an MPPT charge controller--The controller is looking to solve the equation Pmp=Vmp*Imp ... The MPPT controller will vary the current drawn from the array and measure the voltage and figure out what Vmp-array is at any particular instant in time. When you add a Wind Turbine into the array--The whole issue becomes much more cloudy.

    The I*V curve may no longer have a specific peak--But may have several--The peak Vmp-array, the peak of Vmp-alternator, and the peak of Vmp-array+Vmp-alternator added together. It becomes an issue with many (few, some, all?) MPPT controller which peak they will lock on too (a local peak, or the overall optimum peak).

    Using MPPT controllers with wind (and water) turbines can increase the total turbine harvest a bunch... One vendor (as I recall) suggested that a typical HAWT can increase harvest by 2.5x or so (over time). MPPT is sort of the electrical equivalent of placing an automatic transmission between the turbine blades and the alternator--To best match that RPM and Torque from the wind to the I*V curve of the alternator.

    My suggestion (again, I am not a MPPT/PWM system designer)--I would connect the solar array => charge controller => battery bank as normal.

    And connect the wind turbine system, as designed to the battery bank:

    Turbine => battery bank => dump controller

    OR

    Trubine => MPPT controller => Battery Bank
                          +=> MPPT dump/shunt function (when battery bank is full

    Turbine => MPPT controller => Battery Bank (no over voltage/charge control as you suggest)

    OR

    Turbine => Battery Bank (no charge controller--Your basic suggestion that the turbine will not over charge bank)

    OR

    Turbine => MPPT controller => Battery Bank => Dump Controller

    Your Thoughts?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • telljftelljf Registered Users Posts: 26 ✭✭
    Here the difference I believe Bill is that they are using a 3 phase AC generator for the wind turbine and using a rectifier circuit to convert it to the right voltage. AC generators have better efficiency and lower losses and that could be the reason they use AC generators. Then the rectifier output is fed to a controller circuit like found in a typical charge controller. Check their controller image below:

    You can see 3 green wires that come from the generator and then a red and green for the battery. I think it is always regulated voltage that will reach the battery.

    I connect the wind turbine to the solar distribution box in parallel to the panels, just as if it is another panel.. I think the wind controller should bring the voltage to about 30V when it starts to turn with very small current and raises the current as it gains speed. Then it should work, and will appear as just another solar panel. It will be indistinguishable to the solar charge controller down the line.

    But if I have a MPPT controller, I might have some issues as you mentioned, especially if the turbine Vopen varies widely.

    But I don't, in fact my solar charge controller stopped working (I think) some years back and it is just bypassing the current through it, and voltage is held by batteries. I found that I actually do not need a charge controller as I consume what is produced each day. I have a low DOD, not too many panels and the battery bank is large that it can handle ups and downs in charge current. Only when I leave for some trip, I disconnect some of the panels to maintain float. It has survived and the batteries are more than 10 years old.

    My concern about connecting the turbine to the panels was if it will charge the panels at night, but they have some diodes I believe to prevent reverse flow. Also if the panel voltage will affect the turbine when turbine is not turning. But that also should not be an issue because the turbine is loaded by the batteries anyway. Both panels and turbine are held to battery voltage irrespective of whether one or both are working.

    So I think, technically it should be OK to connect the wind turbine to the solar distribution box, unless somebody has done it and faced some problem.

    Jacob
  • BB.BB. Super Moderators, Administrators Posts: 32,741 admin
    Solar cells are just "giant diodes"... So putting 30 volts against a Vmp~36 volt array with a wind turbine is not going to damage anything.

    There is a little leakage current back through the array when they are "dark". And in times past, they would install blocking diode to prevent night time leakage current back into the array.

    Series diodes were dropped when modern solar charge controllers were designed. The solar charge controller is supposed to "disconnect" the array when it is dark.

    The reasons they use AC generators--Which are really "alternators"--From what I know is that they use slip rings to power the rotating field (the 3 phase "stator" or stationary" coils harvest the energy). The rotor is supplied with variable current to adjust output current (and voltage). Slip rings and brushes typically last longer than commutators (used in DC Generators).

    Most wind turbine alternators differ in that they use powerful permanent magnets for the rotating field (rotor). This saves current for field coils (more efficient) and no slip rings, no brushes/rings to wear out.

    However, this means that that Wind Turbine Alternator's output cannot be varied (fixed magnetic field). So you are back with needing some method to regulate power output... Dump loads, furling out of wind, feathering prop, shorting output of alternator (stall blades), brakes, etc. are all used singly or in multiples.

    The output voltage of the alternator still varies with RPM. Higher RPM, higher output voltage. When you connect the alternator => rectifier => Battery bank does fix the output to battery voltage.

    An MPPT controller is sort of like having a transmission between a motor and the wheels. The MPPT lets the power source (solar panels, wind turbine, etc.) run at its optimum voltage and current, and efficiently "down convert" to the voltage and current the battery needs.

    For example, say you have an array that can output 72 Vmp @ 8 Amps in full sun. And a 24 volt battery bank. The math looks like this:

    For MPPT controller
    • Power = Voltage * Current
    • 36 Vmp * 8 amps = 288 Watt panels, two in series for Vmp-array = 72 volts @ 8 amps
    • 72 Volts * 8 Amps * 0.77 panel+controller deratings = 443.5 Watts available solar power
    • Battery Charging Current = I = P/V = 443.5 Watts available / 29.0 volts battery charging (>80% full) = 15.3 Amps into battery
    • Battery Charging Current = 443.5 / 23 volt battery bus (battery <80% SoC, loads on DC bus) = 19.3 Amps into battery
    This is the advantage of the MPPT controller. It "matches" the I*V curve of the input power source to the output curve of the load.

    The 77% derating is typical deratings for warm to hot climates. Vmp falls with increasing cell temperatures.

    In Winter (sub freezing conditions), you can get upwards of 10-20% more voltage, and more harvest because of cold weather. (Vmp rises as cells get cold).

    A PWM controller works differently from a Math point of view--But a properly designed system is just about as efficient (roughly 77% for solar) under "Typical" conditions.

    For example, say you have 2x 36 Vmp panels rated for 8 Amps each (240 Watts per panel, 480 Watts total)--Same as above. And your battery bank is around 29.5 volts charging.
    • 2x panels with Vmp (spec) of 36 volts and 8 amps Imp; Paralleling panels give Imp=16 amps
    • PWM Controller: 29.0 Volts battery charging * 16 amps * 0.95% eff PWM controller = 401 Watts into battery @ 16 amps
    • PWM Controller: 23.0 Volts battery bus charge/loads * 16 amps * 0.95 eff = 349.6 Watts into battery @ 16 Amps
    So a properly designed PWM system with solar panels output nearly the same charging power and current to the battery bank in "typical' conditions.

    MPPT has other advantages such as supporting >100 VDC to > 400+ VDC from the solar array (high voltage, low current, allows smaller AWG copper wire and to send power longer distances).

    And with Turbine/alternator--One MPPT Mfg. had increased average harvest upwards of 2.5x more energy by allowing higher RPM/Higher Voltage output during windy conditions.

    There are lots of "variables" here... The above is just a rough example of how and why... As with anything electrical/power related, the details matter.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • telljftelljf Registered Users Posts: 26 ✭✭
    Yes, MPPT especially suited when the panel rated voltage and battery bank voltage varies much and becomes more useful when the battery is deep discharged and charging.

    In that respect, wind controllers are MPPT as the magnetic field is constant, higher speed means higher change in flux => higher AC voltage, which then the controller converts to current at a fixed output DC voltage. But I am not sure how it will respond to the load voltage.
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