Charge Controller for Wind vs. Solar

Iguana GregIguana Greg Registered Users Posts: 8
I have approximately 250 wats of solar panels and a small wind generator. Being new to the wind side of the eco energy I have to ask if it is ok to have the solar and wind generator share the same charge controller? I have used SunSei cc25000 in the past to regulate my solar power. Can I simply tie the wind power into that as well or not?

It seems that the erratic voltage coming from the wind generator might "confuse" the controller being shared with the solar voltage.

Was looking at the Steca PRS2020 or Xantrex c-35 charge controllers to perhaps share the two energy sources.

Your thoughts and ideas are appreciated.

Comments

  • n3qikn3qik Solar Expert Posts: 741 ✭✭
    Re: Charge Controller for Wind vs. Solar

    You need a charge controller that is for wind. This has a dump load built in. This keeps the wind for over speeding after the batteries are charged.
  • BB.BB. Super Moderators, Administrators Posts: 31,612 admin
    Re: Charge Controller for Wind vs. Solar

    In general, the answer is no and yes... Sorry :blush:

    Normally, a solar charge controller is some version of a on/off switch between the solar panels and the battery bank. When the battery is low, the "switch" is on and current flows from the solar panels to the batteries.

    When the batteries are full, the switch is opened, and the current stops flowing.

    For a wind turbine, it is generally wired directly to the battery bank. When the battery is low, the "shunt controller" (diversion, by-pass, etc.) controller switch is open.

    When the battery is full (and the turbine putting energy into the battery bank), the charge controller turns on and sends the energy (typically) to an electric heater (air or water). When the battery is discharged a bit, the charge controller turns off and the turbine recharges the battery bank again.

    The reason for this is that HAWT (Horizontal Wind Turbines) will over speed and can self-destruct if they do not have an electrical load always attached--like a battery bank or electric heater (some turbines do have other methods to control over-speed to).

    There are some solar charge controllers that can function in either mode... And there is one new one (from BlueSky?) that can do both at the same time.

    So, the above is the "no" reason you cannot share one charge controller. For an installation with both wind (or water) turbine and solar PV panels--you would normally install 1x Solar Charge controller and 1 or 2 shunt controllers (2 is recommended so that you have a backup and don't overcharge the batteries and cause other problems).

    The "yes" reason would be to hard wire the solar panels directly to the battery bank just like the wind turbine and only run a shunt controller. That will work OK--but it is not as desirable for keeping the battery charged (you are actually charging/discharging the battery all the time while under "float" charging.

    Of course, there is more complexity... PWM vs MPPT charge controllers for Solar PV panels--And coming out now/soon MPPT charge controllers for Wind/Water Turbines (I don't know the details).

    -Bill

    PS: One Thread should be enough... It gets confusing when two people answer the same question in two different threads.
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Iguana GregIguana Greg Registered Users Posts: 8
    Re: Charge Controller for Wind vs. Solar

    Thank you B.B / Moderator

    I am an engineer at a new job in Nicaragua. So I walked into this very unorganized "eco system" as they call it. The wind generator was hooked straight into the battery bank with no regulator of any kind. At times it is producing 19 Vdc. I know this is way to high of voltage to charge a battery, even the AGM batteries we use. So I disconnected it from the bank. It has not beenattached to anything and still producing 12-19 Vdc when ever I test it with my multimeter.

    Shouldn't there be some charge controller in line to regulate the voltage at a constant rate?

    I have 4 - Deka Solar 8D 257Ah batteries in my bank, so I never really worry about over charging them so I would probably not put a shunt in place. Agree?

    Thanks again.
  • BB.BB. Super Moderators, Administrators Posts: 31,612 admin
    Re: Charge Controller for Wind vs. Solar
    Thank you B.B / Moderator
    Just call me Bill (and don't call me late to dinner ;)). Moderator just means that I can delete spam...
    The wind generator was hooked straight into the battery bank with no regulator of any kind. At times it is producing 19 Vdc. I know this is way to high of voltage to charge a battery, even the AGM batteries we use. So I disconnected it from the bank. It has not been attached to anything and still producing 12-19 Vdc when ever I test it with my multimeter.
    Actually, think of the system differently... The batteries are really the voltage regulator. The hold the voltage between ~12-14.4 volts.

    Solar panels are pure current sources--they do not regulate voltage at all... And Alternators are not stable voltage sources either (either more like a current limited source). They become another current source to the battery bank too.

    If an alternator outputs 10 amps between 15-150 volts (we had a little box that would disconnect the alternator and you could power 120 VDC compatible tools/lights with it) and you connect it to a large battery bank, The battery bank will hold the voltage at ~14 volts and the alternator will be current limited to ~10 amps (by RPM and design of magnets, coils, iron).

    And, if you ever work on your car--you never disconnect the battery from a running car... The alternator can over-voltage and take out all of your electronics/engine controllers/lights in the car.

    So, the roll of the charge controller is to source (or sink) current to assist the battery to maintain its constant output voltage.
    Shouldn't there be some charge controller in line to regulate the voltage at a constant rate?
    The only time you need to "regulate the output voltage" of an alternator/generator is when they operate without an attached energy storage device (battery, grid, etc.) to supply stable DC (or AC) voltage.
    I have 4 - Deka Solar 8D 257Ah batteries in my bank, so I never really worry about over charging them so I would probably not put a shunt in place. Agree?

    We use the 20 Hour rate when talking about battery capacity--pretty close to how off-grid systems use their batteries. So, the Deka would be around 245 AH at 12 volts.

    I guess this is a 12 volt battery bank--So the bank capacity is:
    • 4x 245 AH = 980 AH @ 12 VDC
    Normally, we use 1% of bank rating for "trickle charging", and 5-13% rule of thumb for system design. AGM's can certainly support below 5% and above 13%--But there is usually not very good reasons to do so. The rough range of charging current would be (rounding up/down is no big deal--just showing the math):
    • 5% * 980 AH = 49 amps minimum
    • 13% * 980 AH =127.4 amps maximum
    Assuming a 0.77 derating for solar panels and charge controller losses, the above would like:
    • 49 amps * 14.4 volts * 1/0.77 derating = 916 watts
    • 127.4 amps * 14.4 volts * 1/0.77 derating = 2,383 watts
    So, a nicely sized charging system would be somewhere around the above range for proper and cost effective charging of the battery bank.

    Now, running the wind turbine (or any charging source) into an AGM battery bank without any charge control is probably a bad idea unless you keep a close watch on the system.

    AGM batteries do very poorly when overcharged. They are very efficient at charging and any excess energy is turned into H2 and 02 gasses.

    A flooded cell battery would simply vent off the gasses and you would add some distilled water at the end of the month.

    With AGM, there is a small piece of metal catalyst in the cell cap. If you gas the batteries too much--that catalyst can over heat and the cell will vent gas/electrolyte. And because AGM's are not designed to be refilled--you shorten the service life of the battery tremendously.

    Read the battery manual (PDF) and monitor the charging voltage/battery temperature and make sure you fall within their recommend limits.

    If you can do this without a shunt controller with the wind turbine--More power to you (;)). If this is an unattended setup or you don't have people who you can trust to monitor the system (and flip on loads when needed to dissipate excess charging current)--then you should really consider placing a simple shunt controller and load on the battery bank for safety/long life.

    There is no way from my keyboard I can tell if you need the shunt controller or not. It all depends on how much power your turbine produces. And you need to design for worst case conditions (a few days of a wind storm when nobody is there as an example).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Iguana GregIguana Greg Registered Users Posts: 8
    Re: Charge Controller for Wind vs. Solar

    Bill...Can you be a little more specific? Just Kidding, great explanation, I just got a nice little free lesson, much appreciated.

    The system I walked into has a "Black and Decker" 25 Amp Automatic charger to charge the 4-8A8Ds. Luckly the inverter shuts down at 12.2volts so the batteries still have a lot of juice in them when recharging is started. Still takes about 10-12 hours to charge the bank as full as it can.

    I am looking at the Xantrex TrueCharge2 60Amp charger to replace it. It has an AGM selector on it. But, being on an island 50 miles off the Nicaraguan cost I am pretty limited. I have only found a TrueCharge 40amp model in the capital of Managua.

    Would it be ok to use 2 of the 40 amp chargers at the same time on the same bank? I have done it in the past by putting the positive on the first terminal of the first battery and the negative on the last negative in the bank.
  • BB.BB. Super Moderators, Administrators Posts: 31,612 admin
    Re: Charge Controller for Wind vs. Solar

    Yea--If you are within 20% of any calculations for solar--You are pretty much "dead on"... I keep the excess precision numbers because people can do the math and confirm they did it right (or I did it wrong :blush:).

    And when using example calculations in the next steps--it is easier to follow 127.4 between equations than if I round everything to 100 even (where did that 100 amps/volts/watts/va/ohms etc. come from suff :p).

    Of course we can do everything with Algebra and Greek variables... Want to try and follow those steps? :cool::roll:

    Yes, you can parallel chargers (AC/Solar/etc.). When making up your battery bank, there should be one place where all of the cable lengths balance between all of the series/parallel connections. That is where both the loads and the chargers should all connect.

    Smart Gauge website

    Again, AGM's are very easily damage by over charging. So--keep track of the voltage at the battery bank and, if there is an option, get the remote battery temperature sensor (hot batteries need lower charging voltages).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Iguana GregIguana Greg Registered Users Posts: 8
    Re: Charge Controller for Wind vs. Solar

    One problem I have experienced in hard wiring the solar / wind power to the bank without any kind of charge controller is that the automatic battery charger is reading the overall voltage of the bank and then feels that the bank is charged. Is this simply because a cheap $60 battery charger is being used?

    I usually use the solar / wind power supply along with the battery charger and then when the charger says "battery fully charged" I disconnect the solar and wind connects and turn the charger back on and about 5 hours later it turns back off, saying "battery fully charged."

    Knowing the characteristics of the AGM battery I know they are not fully charged as the charger only puts out 13.5 Vdc. The bank usually last about 10 hours using a 3000 watt inverter only put out 600-800 watts. (the bank is just running 10 - 14 watt fluorescent bulbs and 3-4 small room fans through out the night.)

    Again, should I just have the solar / wind power hooked up to an On/Off switch and us it when the charger is not in use?

    Thank you Wise One for your insight to my ignorance............
  • BB.BB. Super Moderators, Administrators Posts: 31,612 admin
    Re: Charge Controller for Wind vs. Solar

    Well, that ain't me.

    Generally you leave the solar charger connected all the time. While charging, it will output 14.4 volts or so. Once the battery is charged, it will fall back to 13.6 volts for float charging.

    Regular car type chargers are all over the map and generally do not charge as high voltage as a deep cycle charger would. And many will not fall back to float voltage for standby charging.

    More or less, throw an accurate volt meter on the battery and see what it does. Then go from there (if you are not able to get a true AGM/deep cycle charger at this time).

    Disconnecting your wind turbine can be a problem as it may over speed in hi winds without the battery load.

    -Bill

    By the way--check the losses on that large inverter. That large of inverter can use 30 to 60 watts with no loads on it.

    A smaller inverter may be more efficient for your small loads.
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Iguana GregIguana Greg Registered Users Posts: 8
    Re: Charge Controller for Wind vs. Solar

    Thanks again Bill...But what I am not understanding is that the wind / solar power produces 16 - 19 Vdc at any given time, that is not unsafe to directly hardwire to the battery?

    Obviously at almost no amperage but still 19 Vdc just does not sound right for charging.

    Or is this where your wonderful math algorithms come into play?

    Your thoughts......
  • BB.BB. Super Moderators, Administrators Posts: 31,612 admin
    Re: Charge Controller for Wind vs. Solar

    Basically, the "small" wind turbine cannot overcome the battery's natural state to hold 12 volts (or whatever) on its terminal regardless of charging or discharging.

    Now, if you want to get more complex... Remember:
    • Power = Voltage * Current
    Say the wind turbine can output 19 volts at 10 amps or 14.4 volts at 10 amps:
    • Power available = 19 volts * 10 amps = 190 watts
    • Power into battery = 14.4 volts * 10 amps = 144 watts
    So--There is a "loss" in output when connecting the alternator directly to the battery bank.

    And there is this same "Problem" with solar panels too... Pmp=Vmp*Imp... But Vmp changes with temperature... A Vmp=17.5 volt panel may have Vmp= 14 volts on a really hot day and Vmp near 20 volts on a very cold day.

    So, on a very cold day, the Vmp of the panel is ~20 volts and the battery is charging at 14.4 volt. Say the panel has Imp=10 amps
    • 20v * 10 amps = 200 watts (ideal Vmp*Imp)
    • 14.4 volts * 10 amps = 144 watts (voltage miss-match between panel and battery)
    A MPPT (Maximum Power Point Tracking) solar charge controller can figure out the optimum input voltage/current from a solar panel (and a few for wind turbines to) and "down convert" at 95% or greater efficiency to the lower battery voltage:
    • 200 watts * 0.95 eff = 190 watts available power from panel+charger
    • 190 watts / 14.4 volts = 13.2 amps into battery bank
    A MPPT is a digital switching power supply which using inductors can efficiently step down high voltage / low current from the solar panels into low voltage / high current used by the battery bank for charging. Sort of like the DC version of a variable AC transformer.

    Now, back to your original question... The battery is a voltage source/sink (within limits) and will set the voltage for the system. Any current drawn from or added to the battery will change its chemical state rather than its output voltage (which is different than a capacitor where its store energy content changes with the square of its voltage.

    So, unless you pump large amounts of current into the battery bank or boil it dry--It is really not going to move very far from 12-14 volts regardless of the current supplied.

    Another way of looking at the battery, a "typical" mid sized storage battery may have 5 milli-ohms of resistance (0.005 ohms). It would take 100 amps to raise the voltage 0.5 volts just based on battery resistance alone.

    So, the voltage will change with added current from your wind turbine--but just not very much.

    And the ultimate output voltage of the alternator, whether it is 19 volts or even 150 VDC is irrelevant for a properly operating off-grid battery system. All the alternator needs to produce is a voltage that is higher than:
    • Valt >Vbatt-charging + wiring voltage drop + rectifier voltage drop
    Of course, if you are trying to generate as much power from your small alternator as possible, you would want to spin it very fast and connect it to some sort of high voltage load--Which these "new" series of Wind Turbine Charge Controllers do these days--MPPT for alternators. They let the turbine spin faster and again find the optimum Pmp=Vmp*Imp operating point for the turbine.

    I believe one of the people here testing an about to be released charge controller got 2.5x (or more?) wattage from their wind turbine when attached to an MPPT type charge controller than if the turbine was simply attached to the battery bank as normal...

    Of course, that probably requires pretty extraordinary winds to do that too... But even in normal winds, they are stilling for a significant increase in average power from wind turbines connected to an MPPT turbine charge controller.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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