Solar System Performance

SolarSiteNGSolarSiteNG Registered Users Posts: 3
Hello,

I am very new to solar technology.
I recently had "2200W" of solar panels and charge controller added to my existing inverter/backup generator setup.

What I have is:

10 panels in series, 220 W, 30V each
Xantrex C60 charge controller, with the remote display panel.
Xantrex XW4024 inverter with 740Ah (24V) battery bank

I live in Port Harcourt, Nigeria and we have typically a 7am sunrise and 6pm sunset all year round.
However, from the display panel of my charge controller, I have never seen more than 400W generated from the panels.
That was at 13:00 with the sun directly overhead. Most times I see about 180-270W.

This seems low compared to what I was told my panels could generate, and the level of sunlight.
Is this realistic, or should I be getting more power from my system?

Comments

  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Re: Solar System Performance
    10 panels in series, 220 W, 30V each
    Xantrex C60 charge controller, with the remote display panel.
    Xantrex XW4024 inverter with 740Ah (24V) battery bank

    Welcome to the forum,
    I think your ten panels are in parallel, not series.

    There are a few reasons why you may not be getting full power... The first reason is that your batteries are not discharged very far. When the batteries are nearly full, you can't push much power into them. When your controller is putting out only 400 watts, are you running any loads (other than charging the batteries).

    Another reason (and the one to worry about) is that your panels do not produce a high enough voltage to push any current into your batteries.
    You may need to get an MPPT controller and reconfigure your panels into a series/parallel configuration.

    Tell us more about your system, batteries, combiner box, cable sizes and lengths, etc.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • BB.BB. Super Moderators, Administrators Posts: 29,804 admin
    Re: Solar System Performance

    Can you tell us more about the solar panels? Vmp and Imp ratings?

    Also, you say you have the panels in series--More than likely, you intended to type that you have the panels in parallel (adding current, not adding voltage).

    Next, assuming the Vmp is ~30 volts (pretty common), and you have the panels in parallel (Imp should be around 7.33 amps), the problem is the C60 charge controller and the Vmp=30 volt panels on a 24 volt battery bank.

    The Vmp voltage of a solar panel is a "marketing" specification. A panel under full sun in a hot climate can have Vmp at operating temperature in the range of 24 VDC--Which is not high enough voltage to charge a 24 volt battery bank. For a C60 charge controller (PWM type), you ideally would have a Vmp-array-stc in the 35-40 volt range--Which you cannot do with these panels.

    So, you have two options, one is to get another PWM charge controller rated for higher voltages (like a C40) and put two panels in series and 5 strings in parallel from Vmp-array-stc ~60 volts which would give you an Imp-array rating of ~36.7 amps. It will work, but your array will only operate at ~58% efficiency compared to a "properly" configured system. The C60 would not work here because the array voltage is too high.

    Your other choice is to get an MPPT (maximum power point tracking) charge controller and configure the array to 2 panels in series, then 5 strings in parallel. The correct MPPT charge controller will take the high voltage/low current of the array and efficiently "down convert" to lower voltage/higher current need by the battery bank. This is the "correct" design for you situation (and the array will operate at 100% of its capability). You will have to decide if the extra money for the "proper" MPPT charge controller is worth it for your installation (and your available cash).

    This is a very common mistake in the "solar industry". People call these "24 volt" panels--And they technically are--However, a "24 volt" panel for charging a 24 volt battery bank as a Vmp-stc (standard test conditions) rated for ~35-40 volts when all the "deratings" are taken into account. These panels were designed for use with Grid Tied solar power systems. The panels work fine for their intended application because GT systems can take a wide range of input voltage (Vmp-array) is typically in the 200-400 volt range--So they put a whole bunch of panels in series to make everything work.

    PWM (Pulse Width Moduation) charge controllers are an "older" and "less expensive" type of charge controller that need the "exact" solar panel input voltage to work properly and efficiently when connected to the appropriate voltage battery bank. Too low of Vmp-array, and the batteries will simply not get very much charging current (your present problem). And too high of Vmp-array can damage some "24 volt" charge controller and/or is simply not very efficient.

    An MPPT (Maximum Power Point Tracking) charge controller has a "buck mode switching power supply" internally which sort of behaves like an AC Variable Transformer and can efficiently change the high voltage of the array to low voltage of the battery bank--at ~95% conversion efficiency (power is conserved during the conversion). However, these type of charge controllers are much more expensive (around 3-5x more costly) than a "cheap" PWM charge controller. There are cheaper Asian MPPT charge controllers out there--But it is sort of hit or miss if those type of controller work well or not (and many are cheap PWM type charge controllers simply labeled "MPPT").

    Another "nice thing" with MPPT charge controllers is you can have high Vmp-array voltages (3 panels in series for your panels) and use much smaller diameter copper wire from the array to the charge controller (save can mount solar array much farther away from the battery bank). For any charge controller, you need to keep the charge controller close to the battery bank with short+heavy cables (for a 24 volt battery bank, you only want ~0.1 to 0.2 volt drop on the battery cables for best controller operation).

    Here are some MPPT type charge controllers that will work for your needs--However, you may find some European or Asian models easier to buy locally. Ideally, you need a 60 amp @ 24 volt minimum charge controller for your 2,200 watt array:

    Midnite Classic
    (you need the standard 150 VDC model)
    MorningStar (some new high Vmp-array voltage units, put 5 panels in series, two parallel strings)
    Outback
    Schneider/Xantrex standard array voltage
    Schneider/Xantrex high array voltage

    Feel free to ask more questions--Solar and MPPT charge controllers are a complex subject--And doing it 1/2 a world away in English (for you if not your native language or an engineer/electrician) is not easy either.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • westbranchwestbranch Solar Expert Posts: 5,175 ✭✭✭✭
    Re: Solar System Performance

    Simply put you need about 35V (+-) to get a full charge on a 24 volt battery, so 30 is too low . Putting 2 panels in series you get ~ 60 Volts, and with that PWM CC you are not getting any benefit out of the voltage from 35 to 60V, you are losing/wasting ~ 40% of your production.

    The max production from that 2200W x 73% derating = ~1600W, so the 400W you actually got is about 25% (or more) of what you can expect in cooler climates. What is you average daily temp? High temps also lower PV output.
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • SolInvictusSolInvictus Solar Expert Posts: 138
    Re: Solar System Performance
    BB. wrote: »
    Here are some MPPT type charge controllers that will work for your needs--However, you may find some European or Asian models easier to buy locally. Ideally, you need a 60 amp @ 24 volt minimum charge controller for your 2,200 watt array
    Shouldn't that be at least an 80 A at 24 V MPPT charge controller?

    2200 W * .9 (efficiency of MPPT charge controller) / 24 V = 82.5 A
    2200 W * .9 / 28.8 V = 68.8 A

    Maybe 2 charge controllers for this large PV array.
  • BB.BB. Super Moderators, Administrators Posts: 29,804 admin
    Re: Solar System Performance

    Realistically, in a standard to warm climate, plus a little dust on the array--I use 0.77 derating for solar panels + charge controller, and use ~28-29 volts for charging:

    2,200 watts * 0.77 derating * 1/29 volts charging = 58.4 amps typical maximum output (you may get a bit of "clipping" of output on cool/clear days.

    There is nothing wrong with 80 amp controller--Unless you can get a 60 amp controller for better pricing.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • SolarSiteNGSolarSiteNG Registered Users Posts: 3
    Re: Solar System Performance

    Hello,

    Thanks everyone for the responses, they have been very useful.

    I spoke with my installer and he confirmed that I have 5 strings with two panels in each string. The specs for my panels are as follows:

    Sharp 230wts panel.
    Volts at pmax.vmp. 30V.
    Current at pmax. Imp, 9.33A.
    Open circuit volt, 36.6V.
    Short circuit current ISC, 10.74A.
    Max series fuse rate, 10A.
    Max system voltage. 1000VDc.

    I have placed an order for the Xantrex MPPT60-150 charge controller.
    Hopefully this will help.

    I have a question concerning the operating voltage.
    With the xantrex controller, would it be better to have strings with 3 panels in series (90V) than to have strings with 2 panels in series (60V)?

    @vtmaps
    My panels are about 15m away from my charge controller (shortest possible distance). My batteries are Trojan L16RE-B, 6V, 370Ah batteries.
    I will get details about the cable thickness tomorrow.

    @BB
    If I understand the calculation correctly, from a 2200W system, should I expect a peak power of about 58.4 A (1400W) if all the typical losses are considered?



    Shaibu
  • BB.BB. Super Moderators, Administrators Posts: 29,804 admin
    Re: Solar System Performance

    Shaibu,
    I have placed an order for the Xantrex MPPT60-150 charge controller.
    Hopefully this will help.

    I have a question concerning the operating voltage.
    With the xantrex controller, would it be better to have strings with 3 panels in series (90V) than to have strings with 2 panels in series (60V)?

    This should help a lot. Check the firmware (controller software) level and compare (call?) with current version. Sometimes controllers are built some time ago and take awhile to move through the supply chain. These controller (as I understand) need an additional device (hardware dongle or optional communications adapter) to upgrade firmware.
    @vtmaps
    My panels are about 15m away from my charge controller (shortest possible distance). My batteries are Trojan L16RE-B, 6V, 370Ah batteries.
    I will get details about the cable thickness tomorrow.

    You are looking at the voltage drop in the cable from the Solar array to the charge controller. Typically we aim for ~1% to 3% maximum voltage drop (and this is also the approximate power loss) in the cable. Use a voltage drop calculator and see what the present voltage drop would be based on cable diameter vs a 60 volt or 90 volt Vmp array.

    Also--Double check the short/heavy cable from the charge controller to the battery bank... Ideally for a 24 volt battery bank, you want around 0.1 to 0.2 volt drop maximum.
    @BB
    If I understand the calculation correctly, from a 2200W system, should I expect a peak power of about 58.4 A (1400W) if all the typical losses are considered?

    MPPT Controller are "constant power" type devices... So the actual current and power depends on the battery voltage at that time (and the maximum rated current of the controller). For example:

    58.4 volts * 29 volts battery charging = 1,693.6 Watts

    But, you actually have a 2,300 watt array, so the typical maximum (typical) charging current would be:

    2,300 watts * 0.77 panel+controller deratings * 1/29 volts battery charging = 61 amps typical

    And because the XW will "clip at ~60 amps", the "optimum/maximum" current will be at:

    2,300 watt array * 0.77 panel+controller deratings * 1/60 amps maximum = 29.5 volts Battery Charging Voltage when controller will "clip" output to 60 amps maximum

    When the battery is usually below 29.5 volt in full sun, at ~29.5 volts the charge controller will limit its maximum output current to its rated value of 60 amps. This does not hurt the controller, it just how MPPT controllers work. But because (usually) the system has some "deratings" (solar panels) and losses (wiring, charge controller efficiency, etc.) and average battery charging voltage, you should not hit the clipping limit that often, or lose much current when clipping (a couple amps or less?).

    The additional losses because of a (very slightly) undersized controller--Typically the efficiency would be around 60a/61a = 0.98 of array vs controller power at ~29 volts. Again does not hurt anything, but you might lose a bit of available power during the middle of the day.

    If your system hits clipping limits a lot, you can always get a second (very expensive) charge controller and split the array in 1/2 through each controller. No clipping, but is the extra money for a second controller worth the (usually) small improvement in output? Only you can make that decision.

    Of course, if you ever expand the system, you can add a second controller for more panels. Or--Next time pick a vendor with 80 amp or more output per controller (if available in your region and if your local shop/installer is familiar with the other brand of equipment).

    You are right on the edge of a reason to pick a larger capacity controller--But it is not a problem... Just a cost/benefit question to you. Panels get dusty, they may lose upwards of 3% of their output the first year (2,300 watts * 0.97 = 2,231 watt actual), you may have more humidity in the air that somebody else on a few hundred foot tall hill/mountain, etc. Solar power is not that accurate or predictable to get unhappy over this small amount of "available capacity issues". On a real system, you would be hard pressed to accurately measure the differences in power output with standard volt and current meters to with a "real accuracy" of ~5% to 10%.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • zonebluezoneblue Solar Expert Posts: 1,218 ✭✭✭✭
    Re: Solar System Performance

    5 strings of two will work fine. 3 strings will lose more in the controller than the gain from wire loss.
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
    http://zoneblue.org/cms/page.php?view=off-grid-solar


  • SolarSiteNGSolarSiteNG Registered Users Posts: 3
    Re: Solar System Performance

    Hello,

    I have installed the Xantrex MPPT 60 charge controller and the good news is that I have seen up to 580W from the panels compared with 430 Watts maximum in the past.
    The bad news is that 580 W is not enough. Typical load can hit 700-900W, plus I need to charge the batteries, not maintain them.

    Before I installed the MPPT, I measured the panel voltage (from the terminals of the charge controller) when about 17A was coming from my panels.
    The voltage was 25.2V. I assume that I need at lease 27-28 volts to charge the batteriesDoes this mean my cable is too long? or do I have substandard panels?

    If the cable length is unchangeable, what else can I do to improve the pose from the panels?

    Shaibu
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Re: Solar System Performance
    The voltage was 25.2V. I assume that I need at lease 27-28 volts to charge the batteriesDoes this mean my cable is too long? or do I have substandard panels?

    Are you sure the 25.2 was the panel voltage? Your panel voltage should be about 55 - 60 volts. What was the battery voltage when you saw 25.2 coming from the panels?

    Assuming the 25.2 was the battery voltage, it probably means that your panels do not produce enough power to raise the battery voltage. You mentioned that you have 370 ah of L-16 batteries (one string, four total, I presume). Your panels could charge those batteries, but only if you had no loads and didn't start from too low an SOC.

    If you do have 25.2 volts on the battery while you are charging it, you must be at a very very low SOC. Of course, if you were drawing 700-900 watts while you were charging it with 580 watts, then you weren't really charging the battery.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • SolInvictusSolInvictus Solar Expert Posts: 138
    Re: Solar System Performance
    Sharp 230wts panel.
    Volts at pmax.vmp. 30V.
    Current at pmax. Imp, 9.33A.
    Open circuit volt, 36.6V.
    Short circuit current ISC, 10.74A.
    Max series fuse rate, 10A.
    Max system voltage. 1000VDc.
    These specifications are inconsistent because 9.33 A * 30 V = 280 W, not 230 W. The series fuse rating should be 15 A. 10 A is less than the listed Isc which does not make sense.

    Are your PV panels Sharp ND-U230C1?
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Re: Solar System Performance
    These specifications are inconsistent because 9.33 A * 30 V = 280 W, not 230 W. The series fuse rating should be 15 A. 10 A is less than the listed Isc which does not make sense.

    Nice catch, SolInvictus. So, even more things are not adding up. --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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