How much do my panels really produce?

aleman83aleman83 Registered Users Posts: 24
Hello everybody,

I have my new setup running now, and I am really interested in how much they could really produce during one day. I have a Midnite Solar Classic lite 200 Charge controller which will of course regulate down the current as the battery is charged. So I was wondering: Is there a way how I can measure how many KWh my panels actually produce compared to what my usage is. Does the Midnite Solar Classic keep track on how many KWh would be produced each day even though they're not used?
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Comments

  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
    Re: How much do my panels really produce?

    the lower left reading on the mngp is the kwh sent to the batteries. what you use would need to be done with a battery monitor and that will go between your batteries and loads. keep in mind that with loads on during charging that the batteries actually receive the input watts to the batteries - the output watts to the loads.
  • aleman83aleman83 Registered Users Posts: 24
    Re: How much do my panels really produce?
    niel wrote: »
    the lower left reading on the mngp is the kwh sent to the batteries.

    But that is just what's sent to the batteries by the charge controller and not what was potentially produced by the panels right? It would be great to see how much they actually can produce every day.
  • mtdocmtdoc Solar Expert Posts: 600 ✭✭
    Re: How much do my panels really produce?

    If the Classic is in Bulk then it should represent what the panels are capable of producing. Not so once in absorb or float.

    Are you off grid? If so I think you would need to have enough load going to keep the Classic in Bulk during sun hours.

    For my set-up, when I am in "grid interactive" mode (i.e. the Grid is connected) - my Classic never gets out of bulk due to selling - so what the Classic reports is it what my panels can produce.
  • BB.BB. Super Moderators, Administrators Posts: 29,489 admin
    Re: How much do my panels really produce?

    Hmmm... Add an algorithm to an MPPT charge controller to include a "predicted" output (based on MPPT sweeps, Voc, IV curve, etc.) from array. As long as it is within 5-10%--it would probably be helpful to folks.

    Otherwise, there is no way of "knowing" the output of an MPPT controller unless you have a load (like a GT Hybrid Inverter) that can use the "excess" power.

    The other way would be to install a sunlight sensor (or a small solar panel mounted next to your array)--And just measure the sunlight energy collected per day (to get better than 10% accuracy, you would need solar panel temperature too--Perhaps measure Voc of the the sunlight sensor every 15 minutes to plug into the power equation).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • VicVic Solar Expert Posts: 2,970 ✭✭✭✭
    Re: How much do my panels really produce?

    The venerable OB MX-60 would do fairly slow sweeps every 15 minutes IIRC, The data was available inside the CC. The MN Classic does micro sweeps, or sweepettes, but probably, the data is available inside the Classic. If off grid, when the batts are fully charged, it is possible that the batts simplly will not accept nearly as much current as the PV will produce, depending on AH capacity of bank, and PV capability.

    BB's sensors are a neat idea. There is quite a lot of data collection that would be interesting. Another way to do this is to occasionally run the batts down to a point where the CC never exits Bulk for the entire day ... OH, yea, not that desireable, but in recent heat waves, we probably were able to see most of the PV's capability, due to trying to extract max A/C output, while just getting through Abs stage. It is possible for one to get buried in data, which is never reviewed. Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH [email protected], 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
  • mtdocmtdoc Solar Expert Posts: 600 ✭✭
    Re: How much do my panels really produce?

    Yeah, it would be cool if the Midnite engineers could set up the Classic to display "unused PV production" or something like that. If offgrid it might be useful to decide what opportunity loads could be added. :-)
  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
    Re: How much do my panels really produce?

    am i missing something here as the amps and volts both in and out of the classic are available to be seen on the mngp and not just kwh for the day? simple volts x amps gives current watts. as was said already, if it is in bulk it is pretty much delivering all that the pvs are capable of more or less. i say this because it is also notable that the engineers at midnite cannot predict the insolation one is receiving at any given time either.
  • VicVic Solar Expert Posts: 2,970 ✭✭✭✭
    Re: How much do my panels really produce?

    Hi niel,

    The way that I read the OP --" I am really interested in how much they could really produce during one day", not as wanting a PREDICTION, but rather In an off-grid (assumed) situation, where PV capability exceeds that required to just recharge the batts fully, and supply some day-time loads, .. What is the total daily capability of the PV array on a given day. How many Kwh could it produce if the array was fully loaded for the entire day.

    As an off-gridder, I have wondered that very thing. Many OG folks get into Float by mid-day. We often do run opportunity loads manually, but it is almost impossible to extract every last watt from the PV, while still just staying in Float.

    My intreptation. Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH [email protected], 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
    Re: How much do my panels really produce?

    no matter what that is going to be a prediction and would be valid for that day only. insolation levels vary day to day anyway making this moot, but one can certainly get a good idea based on when the absorb stage stops and goes to float. even that is guessing to a point that the rest of the day will end just as the beginning of the day started, aka same curve.
  • mtdocmtdoc Solar Expert Posts: 600 ✭✭
    Re: How much do my panels really produce?
    niel wrote: »
    no matter what that is going to be a prediction and would be valid for that day only.


    I would think that the classic could track the difference between available watts from PV versus watts delivered to the battery and report that number. In that case it would not be a prediction but an actual number based on what the PV was able to produce that day.

    Maybe that's harder to do than it sounds for an armchair engineer such as myself...:roll:
  • VicVic Solar Expert Posts: 2,970 ✭✭✭✭
    Re: How much do my panels really produce?

    niel,

    Guess that I am not making myself clear.

    It is NOT a prediction. It could be a running tabulation of consumed vs what could have been produced if only the loads on the system happened to be larger.


    But, what I was TRYING to describe (my interpretation of what the OP was), is at the very end of the day, let's say that the CC is sleeping, the sun has set -- no more PV for that day, that, there could be a screen with the total PV power delivered vs the total maximum PV power that could have been consumed if the loads were maxed out.

    The above is just my interpretation of what the OP was addressing. It is quite possible that this is off target. But, there is no prediction required, at all. It is toatlly retrospective (with the possible exception that there is one instant in which it is current). From my tired old Engineering mind.

    Looking at the PVin voltage can give one SOME idea of how heavily loaded the PV array happens to be, and so on ... Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH [email protected], 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
  • westbranchwestbranch Solar Expert Posts: 5,142 ✭✭✭✭
    Re: How much do my panels really produce?

    Can we possibly use some different words here ( I know, hair splitting), that is:

    1. How many watts [V*A] were received by the CC (not 'produced') and

    2. How many watts [V*A] were sent to the battery

    the difference would then be what is 'lost' or available for opportunity load use.

    With line loss and other system inefficiencies one can never really know what the panels 'produced'...
     
    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
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: How much do my panels really produce?
    westbranch wrote: »
    Can we possibly use some different words here ( I know, hair splitting), that is:

    1. How many watts [V*A] were received by the CC (not 'produced') and

    2. How many watts [V*A] were sent to the battery

    the difference would then be what is 'lost' or available for opportunity load use.

    With line loss and other system inefficiencies one can never really know what the panels 'produced'...

    I would like to split another hair on this one. The difference between number 1 and 2 has nothing to do with what is available for opportunity loads. It only reflects inefficiencies or what is actually sent to opportunity loads rather than the battery by the CC. FWIW, the only inefficiencies between the panel output and the CC input will be line and diode losses. And maybe the losses in an optimizer if one is present.

    The amount available for opportunity loads starts with the amount "available from" the panels at the moment, whether they are actually producing that or not and whether that is being received by the CC or not. The "amount produced by the panels" is just as bad, because regardless of what they could do under those light and temperature conditions, the panels will not produce more than what is demanded of them.
    And you cannot measure the "amount available" directly without using an MPPT controller to actually pull all that it can from the panels.
    SMA SB 3000, old BP panels.
  • BB.BB. Super Moderators, Administrators Posts: 29,489 admin
    Re: How much do my panels really produce?

    The MPPT charge controller never really "received" the VA from the panels in the first place. It reduced the average amount of current from the solar array (either in PWM mode, or some other method).

    So there is no "easy" point to measure and say that the array could have supplied 4,000 WH today, but the controller only supplied 2,000 WH to the loads/battery bank today.

    The charge controller would have to estimate the total amount of sun (current) and voltage (temperature dependent) over time for the day. The MPPT sweep done every X minutes (for the last 10 minutes, the array Vmp=17.5 and Imp=7.3 amps), then 10 minutes later another MPPT sweep. Add up all the 10 minute sweep data blocks for total available WH per day (with fudge factors).

    But does the controller even perform MPPT sweeps when in Absorb or Float mode (the controller has to "dump" the sweep energy into the battery bank/loads). Perhaps it does, because it need to account for changing light conditions????

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: How much do my panels really produce?
    Vic wrote: »
    Looking at the PVin voltage can give one SOME idea of how heavily loaded the PV array happens to be, and so on ... Vic

    Exactly. What you need to get is not a prediction of what could have been produced, but rather an estimate of what could have been produced.
    The problem with that is that you have to be able to simulate from just two numbers (power and voltage) what the MPPT controller would derive from travelling up and down on the output V versus I curve of the array.

    To some extent you can guestimate where the array is relative to maximum output by looking at the voltage relative to the full power Vmp, but that relationship will also depend on the current being drawn and its interaction with the effective internal resistance of the array. If the Vmp of the array is in fact independent of the amount of light falling on the array, then you have a chance of doing the calculation. Otherwise you would have to use experimental results for every combination of V, insolation, and P.
    SMA SB 3000, old BP panels.
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: How much do my panels really produce?
    BB. wrote: »

    The other way would be to install a sunlight sensor (or a small solar panel mounted next to your array)--And just measure the sunlight energy collected per day (to get better than 10% accuracy, you would need solar panel temperature too--Perhaps measure Voc of the the sunlight sensor every 15 minutes to plug into the power equation).

    -Bill

    Make that "measure the Isc of the sunlight sensor" (if it is a PV cell) to get the insolation, then use the Voc to get the temperature. Probably what you meant, but not totally obvious.
    SMA SB 3000, old BP panels.
  • westbranchwestbranch Solar Expert Posts: 5,142 ✭✭✭✭
    Re: How much do my panels really produce?
    inetdog wrote: »
    To some extent you can guesstimate where the array is relative to maximum output by looking at the voltage relative to the full power Vmp, but that relationship will also depend on the current being drawn and its interaction with the effective internal resistance of the array. .

    Inetdog, does this resistance include the effect of temp on 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
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: How much do my panels really produce?
    westbranch wrote: »
    Inetdog, does this resistance include the effect of temp on PV output?

    Nope. The temperature affects the Voc as well as the Vmp, so there is no way it corresponds directly to internal resistance.

    The effect of temperature on the output of the panels is a separate correction factor that I forgot to mention.
    SMA SB 3000, old BP panels.
  • aleman83aleman83 Registered Users Posts: 24
    Re: How much do my panels really produce?
    niel,

    Guess that I am not making myself clear.

    It is NOT a prediction. It could be a running tabulation of consumed vs what could have been produced if only the loads on the system happened to be larger.


    But, what I was TRYING to describe (my interpretation of what the OP was), is at the very end of the day, let's say that the CC is sleeping, the sun has set -- no more PV for that day, that, there could be a screen with the total PV power delivered vs the total maximum PV power that could have been consumed if the loads were maxed out.

    The above is just my interpretation of what the OP was addressing. It is quite possible that this is off target. But, there is no prediction required, at all. It is toatlly retrospective (with the possible exception that there is one instant in which it is current). From my tired old Engineering mind.

    Looking at the PVin voltage can give one SOME idea of how heavily loaded the PV array happens to be, and so on ... Vic

    That is actually exactly what I meant. And after reading through the thread now I'm really surprised that nobody has asked that question before. And yes, I am offgrid and exactly because of that I am really interested in how much power I could potentially produce with my setup so I can run opportunity loads such as running the freezers colder during daytime to store extra energy during the day so I won't need to use battery power at night. Of course I can still run them and find out by trying how much I can do, but I really think it would be brilliant to have a number by the end of the day to get maximum usage of the system. I can understand now that most people might not wonder about this since they're just selling their excess power, but unfortunately this is not an option for me. But yet I would really like to use what I'm producing without just having it sit and waste there.

    aleman
  • PhotowhitPhotowhit Solar Expert Posts: 4,994 ✭✭✭✭
    Re: How much do my panels really produce?

    Well I saw this thread as going where no "Off Gridder" needs to go, regardless of the "Fizzyics". Off grid has to have tremendous losses. If the sun is shining and your looking at topping off your batteries early run your freezer a bit longer or do your wash, heat water, what ever you do when you have plenty of sun your always going to need the extra storage for long cloudy periods, and the extra array to replenish that storage.

    Knowing how much your wasting might just upset you.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do more...lol
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Re: How much do my panels really produce?
    aleman83 wrote: »
    But yet I would really like to use what I'm producing without just having it sit and waste there.

    I suspect that you missed inetdog's point. If you're not using it you are not producing it. Solar panels do not produce any energy unless there is somewhere for it to go.

    Wind turbines are different. They must have a load or they will disintegrate. When the battery is full the turbine output is switched to a diversion or dump load.

    You could do the same for a solar panel. When the battery is full, switch the charge controller output to a diversion load. That diverted energy can be measured accurately.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • aleman83aleman83 Registered Users Posts: 24
    Re: How much do my panels really produce?
    vtmaps wrote: »
    I suspect that you missed inetdog's point. If you're not using it you are not producing it. Solar panels do not produce any energy unless there is somewhere for it to go.

    Wind turbines are different. They must have a load or they will disintegrate. When the battery is full the turbine output is switched to a diversion or dump load.

    You could do the same for a solar panel. When the battery is full, switch the charge controller output to a diversion load. That diverted energy can be measured accurately.

    --vtMaps

    Sorry, but I live in the bush where power is precious and how can it be so hard to understand what I mean? "What I could potentially produce"! At any given day. Sort of what pvwatts calculates. I would just love to know how many kwh I could produce max on a cloudy and on a sunny day. Just so I can plan my usage a little better!
  • westbranchwestbranch Solar Expert Posts: 5,142 ✭✭✭✭
    Re: How much do my panels really produce?

    there is a rule of thumb that is used for planning the battery size you will need: that is, plan for X days without sun, the norm for X is 3 days... insolation on a cloudy day can range from almost nil and up from there, just depends on how thick the cloud is...

    YMMV

    HTH
     
    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
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Re: How much do my panels really produce?
    aleman83 wrote: »
    I would just love to know how many kwh I could produce max on a cloudy and on a sunny day. Just so I can plan my usage a little better!

    The only way I can think to do it is with a diversion (dump load) controller. If the controller doesn't display its input, run the diverted current through a shunt and get your answer with a battery monitor.
    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • BB.BB. Super Moderators, Administrators Posts: 29,489 admin
    Re: How much do my panels really produce?

    An mppt sweep every ten minutes would give pretty accurate data to maker a daily available power estimate.

    just total it up and log once a day (if possible).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: How much do my panels really produce?
    BB. wrote: »
    An mppt sweep every ten minutes would give pretty accurate data to maker a daily available power estimate.

    just total it up and log once a day (if possible).

    -Bill

    Does the MPPT controller include an internal dump load to use during its sweeps, or is the MPPT sweep function only actually active during bulk charging? If the latter, it would not give you the available power numbers you want for more than part of the day.
    SMA SB 3000, old BP panels.
  • PhotowhitPhotowhit Solar Expert Posts: 4,994 ✭✭✭✭
    Re: How much do my panels really produce?

    OK, I understand that the energy is important, but what can you do with the information?

    You'll still only be able to handle extra loads when you have the extra energy, charting it across a year is just a number that I can't see any use for. You can't just use 1/365th of it each day, you'll run your batteries down the first couple cloudy days. I don't think you can have a healthy off grid system with out back up that doesn't waste 50% of the array's potential, with out living in a desert, even then there has to be waste.

    Indeed you'd need smarter charge controllers just to not waste the 'extra' power while charging the last 10% of battery capacity.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do more...lol
  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
    Re: How much do my panels really produce?

    careful photowhit as it's starting to look like you are agreeing with me.:-):cool:
  • westbranchwestbranch Solar Expert Posts: 5,142 ✭✭✭✭
    Re: How much do my panels really produce?
    Photowhit wrote: »
    I don't think you can have a healthy off grid system with out back up that doesn't waste 50% of the array's potential, with out living in a desert, even then there has to be waste.

    Indeed you'd need smarter charge controllers just to not waste the 'extra' power while charging the last 10% of battery capacity.

    I'm with you PW, KISS.

    A poster that has not been around for a while (Brock?) used his MX60 (?) Aux out put to throw a switch that turned on the power to his freezer when his bank was at Absorb (or Float, I forget now) and as I see it this is the only type of automated setup one could use for optimal use of opportunity power use. Otherwise you do it manually and just sit and wait, sunny days or cloudy... JMHO
     
    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
  • PhotowhitPhotowhit Solar Expert Posts: 4,994 ✭✭✭✭
    Re: How much do my panels really produce?
    niel wrote: »
    careful photowhit as it's starting to look like you are agreeing with me.:-):cool:

    Darn... Maybe it's setting up my 'next' system with too much array... I'll work on it. :D
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do more...lol
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