Series Circuit

drraptor
drraptor Solar Expert Posts: 218 ✭✭
Is this the correct way to wire 2 solar panels in series ? :-)
EkR1GBi.png

Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Series Circuit

    In a word, yes.
    But I have to use more than one word because of the 18 character posting minimum. :D
  • drraptor
    drraptor Solar Expert Posts: 218 ✭✭
    Re: Series Circuit

    Thanks
    How do you huys connect a MC-4 end with a combiner box/ busbar which doesn't have any MC-4 end ?
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Series Circuit
    drraptor wrote: »
    Thanks
    How do you huys connect a MC-4 end with a combiner box/ busbar which doesn't have any MC-4 end ?

    Buy a short MC4 extension cable and cut it in half: you get a positive and a negative pigtail.
  • drraptor
    drraptor Solar Expert Posts: 218 ✭✭
    Re: Series Circuit

    Is it mandatory to use a MC4 disconnect tool for disconnecting ? http://www.solar-electric.com/how-to-use-mc4-connectors-cables.html/
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Series Circuit

    From a "code" point of view--Anything that can have "exposed/dangerous" electrical connections need to use a tool to access (i.e., a screw driver to pull a cover on a breaker panel).

    Can you open an MC4 without the two little "wrenches"--I will let others who know answer that question.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Series Circuit
    drraptor wrote: »

    One to hold, the other to pop the locks.
    Try taking them apart without the tools and get frustration and possibly broken connectors (as well as skinned knuckles). Thing is you usually don't have to take them apart once assembled. If you are designing a portable system (such as 'mobile' panels for an RV) switch the line to a connector that can be more easily disconnected like the Anderson type.
  • drraptor
    drraptor Solar Expert Posts: 218 ✭✭
  • drraptor
    drraptor Solar Expert Posts: 218 ✭✭
    Re: Series Circuit

    giving out 58V on the CC solar panel terminal. Around 1A from Panels, while it is converted to ~3.5 to ~5.6A on the battery terminals. @ 8:30Am with cloud cover.
  • drraptor
    drraptor Solar Expert Posts: 218 ✭✭
    Re: Series Circuit

    These are prepared MC-4 pigtails I used. Got these for $2.5/pair

    AHfZGHl.jpg
  • drraptor
    drraptor Solar Expert Posts: 218 ✭✭
    Re: Series Circuit

    Are these values fine ?

    Time 3:00pm
    PV voltage : 18.0V
    PV current : 4.61A
    Battery Voltage : 12.3V
    CC current : 6.43A

    According to Google weather is clear. Temperature 41 degree Celsius Wind : 11km/h, humidity 23%

    this much voltage drop ?? normal value should be ~57-58V.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Series Circuit

    Good question.

    First of all 3:00 PM is probably not 'prime sun time' so the panels won't be putting out their maximum. Insolation makes a big difference on power production.

    Second, how are you measuring "PV Volts"? If that is the input Voltage to an MPPT controller from your two panels is series something is wrong. That's around Vmp for the one 150 Watt panel I should think. It may be that there is not enough sun on the panels or it may be a wiring problem. If your controller is a PWM type you're wasting a whole panel as the battery will simply pull the Voltage down to its level and the power is lost.

    Battery Voltage indicates the battery is definitely not charged. By that hour of the day you should have been through Bulk and Absorb and be at Float somewhere above 13 Volts.

    Current depends on the panel output (again subject to the sun) and the amount of power the system requires. Since the Battery Voltage indicates a lock of charge I would expect much higher current if the sun is good.

    150 Watt panel is 6 Amps and thus should be 25 Vmp (odd numbers).
    205 Watt panel is 5.8 Amps and thus should be 35 Vmp (closer to normal).
    From that the PV Voltage at noon (i.e. full sun straight on) with these two in series should be around 60 Volts. The array is 355 Watts total, and the peak current to a 12 Volt system would be approximately 23 Amps.

    It sounds as though you are not using an MPPT type charge controller, thus wasting a lot of potential power.
  • drraptor
    drraptor Solar Expert Posts: 218 ✭✭
    Re: Series Circuit
    Good question.

    First of all 3:00 PM is probably not 'prime sun time' so the panels won't be putting out their maximum. Insolation makes a big difference on power production.

    Second, how are you measuring "PV Volts"? If that is the input Voltage to an MPPT controller from your two panels is series something is wrong. That's around Vmp for the one 150 Watt panel I should think. It may be that there is not enough sun on the panels or it may be a wiring problem. If your controller is a PWM type you're wasting a whole panel as the battery will simply pull the Voltage down to its level and the power is lost.

    PV volts were measured from the PV terminal of the MPPT charge controller, while PV current was measured using a clamp meter.
    Battery Voltage indicates the battery is definitely not charged. By that hour of the day you should have been through Bulk and Absorb and be at Float somewhere above 13 Volts.

    Current depends on the panel output (again subject to the sun) and the amount of power the system requires. Since the Battery Voltage indicates a lock of charge I would expect much higher current if the sun is good.

    150 Watt panel is 6 Amps and thus should be 25 Vmp (odd numbers).
    205 Watt panel is 5.8 Amps and thus should be 35 Vmp (closer to normal).
    From that the PV Voltage at noon (i.e. full sun straight on) with these two in series should be around 60 Volts. The array is 355 Watts total, and the peak current to a 12 Volt system would be approximately 23 Amps.

    It sounds as though you are not using an MPPT type charge controller, thus wasting a lot of potential power.

    The VOC for the array measured at 8:00am (before connecting to the CC) was 58V.

    the following values are from yesterday, except I measured the voltage at the battery terminal written as Battery Voltage/V and also measured the voltage at the Battery terminal on the CC written as CC Voltage/V, and there was slight difference of 0.4V between the two.

    Weather was 37 degree Celsius max and 34 degrees Celsius low, on June 1 2014.



    Date
    Time
    PV Current/A
    CC current/A
    PV Voltage/V
    CC voltage/V
    Battery Voltage/ V
    PV Power/W
    CC Power/W


    01/06/2014
    01:10:00
    4.49
    14.09
    53.9
    14
    13.6
    242.011
    197.26




    PV voltage 36V @ sunset June 2 2014 8)

    So is this due to panels not be on the proper angle for this part of the year ?
    Secondly PV voltage of 18V was some kind of anomaly, due to a stray cloud or some bird sitting on the 205W mono-crystalline ? what I believe is that Mon-crystalline panels are prone to shading ? :-)
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Series Circuit

    All panels are subject to shading issues.
    The only way to get full power readings is with strong, direct sunlight on them.
    When the light on the panels drops off for whatever reason (including shading or indirect angle) power drops off.
    Your second set of numbers is better, but it still shows less than full power potential at the panels:
    4.49 Amps * 53.9 Volts = 242 Watts whereas the most you would see would be (Vmp + Vmp) * 5.8.
    Some of that lower power can be due to how much the batteries need. A way to check that you can get maximum output is to turn on some loads equal to the total array Watts and see what it will do under demand at maximum sun time.
  • drraptor
    drraptor Solar Expert Posts: 218 ✭✭
    Re: Series Circuit
    All panels are subject to shading issues.
    The only way to get full power readings is with strong, direct sunlight on them.
    When the light on the panels drops off for whatever reason (including shading or indirect angle) power drops off.
    Your second set of numbers is better, but it still shows less than full power potential at the panels:
    4.49 Amps * 53.9 Volts = 242 Watts whereas the most you would see would be (Vmp + Vmp) * 5.8.
    Some of that lower power can be due to how much the batteries need. A way to check that you can get maximum output is to turn on some loads equal to the total array Watts and see what it will do under demand at maximum sun time.


    Now I'm releasing my mistake, I should have searched for 150W panels specs on-line. It is a unbranded panels without any spec sheet. :blush:

    anyway it spec should be like
    Nominal peak power(Pmax): 150W
    Maximum power voltage(Vmp): 18V

    Maximum power current(Imp): 8.33A

    Open-circuit voltage(Voc): 22V

    Short-circuit current(Isc): 9.1A

    but I have never measured ISC 9.1A. :-) even in full sun.

    The closet match with these specs could have been 255W panel ISC 8.87A but it could have gone over the limit of my CC with total array size of 405W and 31A. CC only supports 390W @12V and 30A. :blush:

    Should I change it ? next charge controller supports charging current upto 45A, array upto 585W 12V will cost additional $50.
    While 255W panel will cost additional $45. :-)

    My calculations were based on if I wanted to expanded I will go with 205+205+205+150W = 765 @ 24V
    On 45A charge 255+255+255+255+150=1170W @ 24V could have been a match made in heaven.:blush: Is 1170W @24V efficient should I think about 48V beyond 700W ?
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Series Circuit

    You can measure Voc easily enough. You can also measure an approximate Isc. But if you have a Voc and a Wattage rating the other numbers can be approximated.
    Voc of 22 means the Vmp is likely 18. 150 Watts / 18 = 8.3 Imp. Isc is usually 1/2 Amp higher or 8.8. You will not see Isc into a circuit, only to a short.

    In series with a panel that has an Imp of 5.8 the panel will be limited to 18 * 5.8 or 104 Watts. At that point your maximum array is now 104 + 205 or 309 Watts, which you'll typically see 77% of or 237 Watts. At 242 Watts you've got good insolation; the biggest problem is the current bottleneck.

    So the question is: good enough?

    45 Amps @ 24 Volts would be about 1400 Watts of array. That would be five 255 Watt panels, which is not going to be good because you don't want them all in parallel. Six would be wasting half a panel. Four would be good (two parallel strings of two in series), but again: good enough? Depends on how much battery you're trying to charge.

    As a rule trying to get a certain array size by mixing dissimilar panels is frustrating because of the incompatibility of Voltage and/or current specs. It is better to build it either slightly larger or slightly smaller (providing power needs are met) using identical panels.
  • drraptor
    drraptor Solar Expert Posts: 218 ✭✭
    Re: Series Circuit
    You can measure Voc easily enough. You can also measure an approximate Isc. But if you have a Voc and a Wattage rating the other numbers can be approximated.
    Voc of 22 means the Vmp is likely 18. 150 Watts / 18 = 8.3 Imp. Isc is usually 1/2 Amp higher or 8.8. You will not see Isc into a circuit, only to a short.

    In series with a panel that has an Imp of 5.8 the panel will be limited to 18 * 5.8 or 104 Watts. At that point your maximum array is now 104 + 205 or 309 Watts, which you'll typically see 77% of or 237 Watts. At 242 Watts you've got good insolation; the biggest problem is the current bottleneck.

    So the question is: good enough?

    45 Amps @ 24 Volts would be about 1400 Watts of array. That would be five 255 Watt panels, which is not going to be good because you don't want them all in parallel. Six would be wasting half a panel. Four would be good (two parallel strings of two in series), but again: good enough? Depends on how much battery you're trying to charge.

    As a rule trying to get a certain array size by mixing dissimilar panels is frustrating because of the incompatibility of Voltage and/or current specs. It is better to build it either slightly larger or slightly smaller (providing power needs are met) using identical panels.
    that was bit difficult.
    So with my current setup, I'm 46watts down.

    I got to learn quite a few things from this setup
    • Buy as large Charge controller as you can afford, check prices for all available even if you are not going to buy it. (I did spent more than 2 hours with local installer, by looking at Morningstar Ts-45 PWM, it was available . for $250. )
    • don't try to mix and match panels.
    • search and gets you facts right (I didn't searched for 150W polycrystalline's specsheets, only relied on my own measurements e.g measuring the ISC by shorting the panel through a digital multimeter)
    • Mounting should be adjustable, so that you can change according to the time of the year.
    • Clear your mind on every silly question you have in your mind
    • We have got quite good insolation in Pakistan :cool:


    This is just my first solar project, i think I should leave it as it is, don't mess around much with it. Wait a few more years, until prices drop further.

    There has been a considerable drop already
    • Chinese Panels cost in 2006 was $4.25 (at current currency rates)
    • In 2013 Chinese Panels without warranty were ava. for $0.7. While Canadian Solar, Suntech were available for $1.00 to $1.15 while Japanese and Korean brands used to cost $1.60
    • In 2014 Chinese Panels without warranty drop to $0.3 (in winter) and $0.7(in Summer). While Canadian Solar,trina, renesola are available for $0.80 to $0.95. While Japanese brands such as Sharp costs between $1.00 to $1.10. American brands such as Solar world costs $1.33 to $1.40(Polycrystalline)
    With energy costs as high as $0.27/KWh I think we are getting to Grid parity sooner rather than later. What should be the rate of the Solar panels to achieve Grid parity ? Battery costs (in winter) are ~$0.73/Ah. Mounting costs ~$0.12/watt of Solar panels. Charge controller will be imported ( through a friend or relative ), so US prices can be considered e.g Midnite Classic 200 costs $610
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Series Circuit

    I live in Canada. Don't talk to me about prices! Everything is expensive here except grid power which is extremely cheap. At our price structure solar will never achieve parity with grid power; it's unlikely solar will come down much further which means utility rates will have to go up 5X to match and that isn't going to happen when the utility is a Crown Corporation and politicians want to get re-elected.

    The only reason I have anything to do with solar is because there are many places here that have no grid available (I own one of them) so suddenly solar is the cheap option (compared to gasoline in a generator at nearly $6 a gallon US).
  • drraptor
    drraptor Solar Expert Posts: 218 ✭✭
    Re: Series Circuit
    I live in Canada. Don't talk to me about prices! Everything is expensive here except grid power which is extremely cheap. At our price structure solar will never achieve parity with grid power; it's unlikely solar will come down much further which means utility rates will have to go up 5X to match and that isn't going to happen when the utility is a Crown Corporation and politicians want to get re-elected.


    In Canada the major source of grid electricity is Hydro (there is no better source and cheaper source of electricity. here it cost just $0.01/KWh to generate from hydro.). It was similar case in Pakistan until few years back, but now hydro's share has been reduced to mere 35% or even less.
    while your politicians don't allow any increase in electricity costs, our don't allow construction of new dams. :grr while they are busy in inaugurating coal fired power plants :cry:

    there has be a formula for calculating grid parity
    The only reason I have anything to do with solar is because there are many places here that have no grid available (I own one of them) so suddenly solar is the cheap option (compared to gasoline in a generator at nearly $6 a gallon US).

    and the Noise it generates 8)