Capacitor Role in a PV System

SolaRAC
SolaRAC Solar Expert Posts: 52 ✭✭✭✭
So.. I've been thinking about capacitors like those used in vehicles with custom sound sytems. I noticed there isn't much mention of capacitors on this forum; maybe I'm overthinking this.

Wouldn't you say it's critical to have a capacitor buffer the current flow from the batteries to the inveter in a PV setup? (i.e. protect the battery from current spikes)

Your thoughts?


Thanks in advance guys..
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Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,433 admin
    Re: Capacitor Role in a PV System

    It may help... Turns out, usually, it is difficult to use a capacitor to store large amounts of energy (say a few seconds worth of power to start a 1 HP well pump) when you have only a 24 volt nominal voltage which can only vary by a couple volts (~21 volt cutoff, ~29 volts while charging battery bank). A switch mode power supply will use ~340 volt nominal capacitors to store energy for ~1/2 cycle of AC power (1/120th of a second for 60 Hz).

    However, be that as it may be--Turns out there is a 120 Hz current waveform drawn by a single phase inverter (squared power draw--i.e., power each 1/2 of AC output power sine wave). You can use a capacitor to filter that current, to a degree, from reaching the battery bank.

    I cannot remember exactly (to find it), but there was a recent thread here where a person wanted to use large capacitors to reduce the sized needed for his battery bank (had an alternative power energy source--perhaps a fuel cell??). Excessive ripple current on a battery bank can cause them to run hot and even have "micro" discharging every 1/2 cycle.

    For various reasons, I don't really think a "super cap" will solved any of our battery bank sizing issues at this time. Too expensive, and surprisingly, "super caps" have less power on life than the average battery bank (as little as 2 years of power on life for one super cap model I looked at).

    -Bill

    The usual answer, large battery bank (roughly, AH rating = 2.5*Surge Current), keep cables short, heavy, and run in parallel/twisted (don't make separate +/- runs, or runs with big separate loops of +/- cables). If your surge current is in the range of audio frequencies (i.e., not starting motors), then capacitors at the input to the load may help.
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Capacitor Role in a PV System

    i would say it's useless. a battery is a huge capacitor in its own way and if there are current spikes the battery can't take then the battery capacity is not big enough and/or you are using too small of wire to the inverter. a cap could work theoretically if the surge is short in duration and the cap large enough in value, but i'd rather invest in more battery capacity and/or better wires to the inverter. caps have leakage too which can waste some power.
  • calbiker
    calbiker Banned Posts: 50 ✭✭✭✭
    Re: Capacitor Role in a PV System

    There shouldn't be any current spikes. Current is well regulated by the buck regulator inductor.

    During Ton: I = (V_array - B_bat) / L
    During Toff: I = (V_bat + V_diode) / L

    Edit,
    My bad, thought topic was converter, not inverter.

    Even though the battery acts like a big capacitor, cable inductance (between battery and inverter) will, to-an-extent make the battery capacitance look invisible. You still want a capacitor and emi inductor at the input of the inverter.
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: Capacitor Role in a PV System

    Caps do have a role in an inveter's DC input. But they have to be in the inverter, or the wires inductance swamps them out somewhat.

    here's a couple threads that cover the details & pros & cons.

    http://forum.solar-electric.com/showthread.php?15053-Of-GTIs-battery-sizing-and-capacitor-banks&highlight=ripple+capacitor

    http://forum.solar-electric.com/showthread.php?13550-Inverter-input-ripple-capacitor(s)&highlight=ripple+capacitor

    http://forum.solar-electric.com/showthread.php?11709-xw-6048-battery-bank-ah-size-kWh-production&highlight=ripple+capacitor

    Good Luck
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

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  • Windsun
    Windsun Solar Expert Posts: 1,164 ✭✭
    Re: Capacitor Role in a PV System

    The impedance of nearly any battery system is so low and huge compared to any reasonable sized capacitor that a capacitor will have little, if any, effect.
  • calbiker
    calbiker Banned Posts: 50 ✭✭✭✭
    Re: Capacitor Role in a PV System
    Windsun wrote: »
    The impedance of nearly any battery system is so low and huge compared to any reasonable sized capacitor that a capacitor will have little, if any, effect.

    Impedance my be low at 10 Hz, but not at 10 kHz.
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Capacitor Role in a PV System
    calbiker wrote: »
    Impedance my be low at 10 Hz, but not at 10 kHz.

    are you feeding high frequency ac to the inverter? i hope not. dc does not have an impedance as only ac does. batteries do buffer ac to a degree anyway and like i said, surges that a battery can't handle means you have too little ah capacity in the battery bank.
  • calbiker
    calbiker Banned Posts: 50 ✭✭✭✭
    Re: Capacitor Role in a PV System

    Yes! Very high frequency (square wave).

    Attachment not found.


    niel wrote: »
    are you feeding high frequency ac to the inverter? i hope not.
  • SolaRAC
    SolaRAC Solar Expert Posts: 52 ✭✭✭✭
    Re: Capacitor Role in a PV System

    Very useful information.

    Thanks for the input guys.
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Capacitor Role in a PV System

    calbiker,
    that's nothing more than an inverter and you aren't feeding it into the battery, but rather drawing from the battery to operate the inverter. if it is very high in frequency (square wave harmonic content) and you worry about it backfeeding to the battery then put a choke in line with the b+ before the electrolytic cap input to the inverter. now if you have too little ah capacity in the battery the inverter will pump the battery up and down with the load no matter if you filter the b+ or not.

    i know what you were saying about stereos and it is due to the amplifier pumping the battery or power supply. this induces an artificial signal across the board equal to the frequency of that pumping action. peaks on stereos are very brief though unlike surges that can occur on a battery from an inverter at high draw. it boils down to insufficient power being supplied to the inverter or stereo.
  • calbiker
    calbiker Banned Posts: 50 ✭✭✭✭
    Re: Capacitor Role in a PV System
    niel wrote: »
    calbiker,
    that's nothing more than an inverter and you aren't feeding it into the battery, but rather drawing from the battery to operate the inverter. if it is very high in frequency (square wave harmonic content) and you worry about it backfeeding to the battery then put a choke in line with the b+ before the electrolytic cap input to the inverter. now if you have too little ah capacity in the battery the inverter will pump the battery up and down with the load no matter if you filter the b+ or not.

    Exactly, and that's what I said in my first post. If high frequency harmonics isn't a problem, then there wouldn't be that big cap on the front end of the inverter circuit I posted. For that cap to work, it needs a low esr. Anyways, that was the OP's question. A poorly designed inverter will generate emi. The best fix isn't adding a capacitor, but an inductor.

    Even though the battery acts as a huge capacitor at low frequencies, high frequencies (as are generated by square waves) are still a problem.

    Cal
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Capacitor Role in a PV System

    Hmm. I thought the OP was pondering whether or not a substantial capacitor on the inverter's input could help mitigate the current surges imposed on the battery bank by sudden high demands (due to the cap's faster action at delivering and taking on power as opposed to deep cycle batteries which are known to be a bit "sluggish" in this respect).

    Personally I don't think it would and agree with the others who said sizing the bank properly for such loads is the answer.
  • calbiker
    calbiker Banned Posts: 50 ✭✭✭✭
    Re: Capacitor Role in a PV System

    I suppose you can read the OP to mean current SURGE. But he did say current SPIKES. Spikes are generated by the rising edge of the switching fet. The only way to eliminate spikes is to place a low esr capacitor very close to the fet. It needs to be apart of the inverter design.

    Cal
    Hmm. I thought the OP was pondering whether or not a substantial capacitor on the inverter's input could help mitigate the current surges imposed on the battery bank by sudden high demands (due to the cap's faster action at delivering and taking on power as opposed to deep cycle batteries which are known to be a bit "sluggish" in this respect).
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Capacitor Role in a PV System

    calbiker,
    i think a ceramic disk cap would also help at the input in the same area as the electrolytic cap and the best exact value would depend on the frequency of the inverter, but i would imagine a wide variety of values will work to one degree or another.
  • john p
    john p Solar Expert Posts: 814 ✭✭✭
    Re: Capacitor Role in a PV System

    a ceramic cap would only offer minor filtering above about 10khz . and at the input be just aboiut useless ,It would need to be in the output stage of the inverter to be any use and if the inverter is good design it will be filtered already.
    Super caps at the input of the inverter will do nothing useful,just help empty your wallet.
    Super caps degrade faster than you would imagine. 2000 to 3000 full charge /discharges will degrade them as much as 20%. But if you can get enough of them you can make a great fun toy.. We have a 100,000 farad 24v pack that can do amazing things with a instant full discharge .it will melt off about 4"of a 1" dia copper bar when that is bought into contact with a v8 engine block.
    The reason they use them semi successfullly in audio installs is because most car power amps are class "D" not the linear "A""B".. A well designed AB amp will have an adequate cap bank to withstand all possible music output demands .
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Capacitor Role in a PV System

    i did mean in addition to the choke and we are not talking of filtering the square wave to make it sinusodial on its output, but to prevent the backfeeding of any harmonic content from making it to the batteries. the very nature of a modsine inverter is that it is rich in harmonic content as that is what a square wave is is the sine waveform with harmonics going way up. btw a cap will pass 10khz to ground, but it's a matter of how much resistivity would be there at that frequency for that value of a cap. this should not be very difficult to filter out going to the battery in most cases, but sometimes it can be problematic. what solarac was initially referring to and referenced the stereo example for was the inverter pumping the battery with high load surges and this you can't filter out as that is a problem with insufficient battery capacity.

    it also occured to me that the op may be thinking a cap to be used on ac voltage just like it does for dc voltages and that's not quite going to work for many reasons.
  • calbiker
    calbiker Banned Posts: 50 ✭✭✭✭
    Re: Capacitor Role in a PV System
    niel wrote: »
    what solarac was initially referring to and referenced the stereo example for was the inverter pumping the battery with high load surges and this you can't filter out as that is a problem with insufficient battery capacity.

    What may *appear* as a battery capacity deficiency, is most likely an inverter cabling deficiency. I bet the cold cranking amps of the battery is more than sufficient to cover the surge. Cable resistance is the problem. Use short, big cables.

    Cal
  • bill von novak
    bill von novak Solar Expert Posts: 891 ✭✭✭✭
    Re: Capacitor Role in a PV System
    calbiker wrote: »
    Impedance my be low at 10 Hz, but not at 10 kHz.

    Agreed. For EMI filtering capacitors can be quite useful. Small caps at the inverter input can go a long way towards reducing radio frequency interference. (Note that good inverters already have these.)
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Capacitor Role in a PV System
    calbiker wrote: »
    What may *appear* as a battery capacity deficiency, is most likely an inverter cabling deficiency. I bet the cold cranking amps of the battery is more than sufficient to cover the surge. Cable resistance is the problem. Use short, big cables.

    Cal

    you are right that insufficient battery cables can also cause this pumping action when a battery has sufficient ah capacity to begin with. if cables are lossy and battery capacity is not optimal this problem can grow exponentially out of hand very quickly.

    all here do need to remember that a battery is not infinite in its abilities and going from no load, to half loaded, to fully loaded from an inverter for example will cause an ac waveform super-imposed above ground on the dc voltage and can look like 12.5v no load, 11.9v half loaded, and 10.8v fully loaded as an example of an undersized battery capacity and/or bad battery cables. this is ripple ac voltage from a dc battery and would directly be synced frequency-wise with the frequency the load is pumping up an down at. now upping the ah capacity so that this drops no more than .3v from no load to full load reduces the ac ripple significantly. no capacitor will filter out this pumping action in that first example without getting huge, but it would theoretically be more doable with the smaller ac ripple voltage. there may be a point in there with the small ac ripples where filtering somewhat with a cap could be cheaper than adding more battery capacity, but that's an indeterminate animal for most people that is easily dealt with by going with properly sized batteries in the first place for they certainly won't last long being drawn down that far to produce this kind of ac ripple.

    this is also along the lines solar guppy was talking about with having a minimum battery capacity for the larger inverters and it would be true of all inverters to one degree or another by scaling.
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: Capacitor Role in a PV System

    Also, don't forget, RE deep cycle batteries are designed for capacity, not starting surges like car batteries. While they may have hundreds of amp hours in them, they cannot be delivered instantly, regardless of the cable size.

    Exception: if you drop an expensive wrench across a pair of terminals.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • SolarPowered
    SolarPowered Solar Expert Posts: 626 ✭✭✭
    Re: Capacitor Role in a PV System
    mike90045 wrote: »


    Capacitor doesn't have to be in the inverter. If you can externally wire a battery cap (capacitor) to meet the demand of the inverter watts/(farads). It may extend the life of the inverter, and as well the batteries and "prevent" the internal inverter capacitors from running hot. Hence less heat may also increase inverter efficiency by margins of up to 1~2%.

    Big reason why all the audio freaks with their 1000+ RMS watt amplifiers use them is to extend the life of the amp,and draw enough power, without cutting the supply from a low Ah battery that has to supply current to additional devices or extensions of a vehicle, such as lights for driving at night.

    (hypothetical) say you have a 240v parrallel inverter (2 inverters) set up, 1 battery bank 3O/T conductors in series to batteries, lets say you use a dryer with 240v, or need to run a 30 amp 240v heat pump. That's significant demand at AMP draw for the inverter to pull from the batteries, a common heat pump alone uses capacitors for start up, why not at DC end? Capacitors rapidly release current needed just as in the car audio world when an amplifier desires wattage for low Hz bass. Same concepts apply, supply and demand of energy in proportion to the demand it is needed.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,433 admin
    Re: Capacitor Role in a PV System

    Welcome to the forum SolarPowered,

    A few comments from my experience:
    Capacitor doesn't have to be in the inverter. If you can externally wire a battery cap (capacitor) to meet the demand of the inverter watts/(farads). It may extend the life of the inverter, and as well the batteries and "prevent" the internal inverter capacitors from running hot. Hence less heat may also increase inverter efficiency by margins of up to 1~2%.

    I am not sure, but usually you do not get very much ripple voltage from a 12 volt battery bank. So external/low voltage capacitors are not very useful unless they are very high capacity (Farads). Remember that stored energy is =0.5*C*V2. So you need a difference between the high and low voltage to draw/store energy in a capacitor (they are not batteries that store energy chemically).

    Look at the front end of a typical switching power supply (for a computer) front end. Typically the operating voltage of the input storage capacitor is the sqrt(2)*240VAC=339 volts peak (nominal, near 380 VAC peak). And say the capacitor operates down to ~180 VAC (240 Volts peak) (don't remember exact numbers--been too many years). The difference in energy storage would be:
    • (339v)2 - (240v)2 = 57,321v2

    Same thing with 13.2 volts to 11.5 volts for a 12 volt battery bank:
    • 13.22 - 11.52 = 41.99v2
    • 57,321v2/41.99v2 = 1,365 times more energy per unit capacitance in the "high voltage" front end of a capacitor storage element

    Yes, you could use ~Farad's level capacitors for the filtering on a battery bank vs ~1,000 uF's of a typical AC power supply. But this is not usually the best use of components. Electrolytic capacitors are usually the most unreliable/subject to age and heat degradation of any standard electronic component.
    Big reason why all the audio freaks with their 1000+ RMS watt amplifiers use them is to extend the life of the amp,and draw enough power, without cutting the supply from a low Ah battery that has to supply current to additional devices or extensions of a vehicle, such as lights for driving at night.

    Looking around:




    Capacitor Farad Rating
    Total System Wattage


    Under 1 Farad
    0-499 Watts


    1-1.9 Farad
    500-999 Watts


    2-2.9 Farad
    1000-1499 Watts


    3-4.9 Farad
    1500-2499 Watts


    5+ Farad
    2500-Up Watts



    Usually steady state loads (such as lights) would not affect the surge capabilities of a storage battery. The alternator would typically supply the "base loads" of the vehicle system and the battery (bank) would supply the low impedance surge capabilities required for the audio system.
    (hypothetical) say you have a 240v parallel inverter (2 inverters) set up, 1 battery bank 3O/T conductors in series to batteries, lets say you use a dryer with 240v, or need to run a 30 amp 240v heat pump. That's significant demand at AMP draw for the inverter to pull from the batteries,

    Yes, single phase inverters (120 or 240, or paralleled if sync'ed) will draw a "sine squared" current wave form from the battery bank. Nominally, we size the battery bank to supply that "ripple" current (keep battery temperatures low, and ensure that ripple current does not draw voltage so low that the battery "micro-cycles" between charging/discharging 120x per second--for a 60 Hz inverter).

    Typically, we have used 100 AH @ 48 volts per 1kWatt of inverter rating (or 400 AH @ 12 volts; 200 AH @ 24 volt battery bank). Note this is for flooded cell batteries--but for other reasons we also use for AGM and solar array/charging source power too.

    Another advantage is that this allows the battery bank to supply "surge" power for starting loads (such as pump motors) for multiple cycles to multiple seconds (or longer)--which capacitors cannot do (again, rating requirement of around 2kW of surge per 100 AH @ 48 volt battery bank).
    a common heat pump alone uses capacitors for start up, why not at DC end?

    A standard heat pump uses capacitor(s) to provide a "rotating magnetic field" to provide rotational torque for turning the rotor of the motor (single phase and split phase power cannot create rotating magnetic fields to start an induction synchronous type motor to rotate--you either need a starting/run capacitor to provide the 90 degree offset or a poly phase source--like three phase power to do that).
    Capacitors rapidly release current needed just as in the car audio world when an amplifier desires wattage for low Hz bass. Same concepts apply, supply and demand of energy in proportion to the demand it is needed.

    In the end, short/heavy cables with appropriate battery bank sizing is usually a better idea.

    Another problem that can occur with capacitors "hanging" at the end of a cable is oscillations (LC Resonance circuit, aka Tank, or LC Oscillator). Usually just not worth the trouble.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • john p
    john p Solar Expert Posts: 814 ✭✭✭
    Re: Capacitor Role in a PV System

    Using big caps between battery and inverter is one of the most endless arguements you can have. And in the end they achieve NOTHING. Wrong ..they use up your money. if you want great surge power in a 12v or 24 v supply just parallel batteries.... Super caps etc are short lived toys. Forget you ever heard of them for any solar use.
    Read my post #16.
    Now get back to work all of you and do something useful.
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Capacitor Role in a PV System

    i tend to agree with john that a cap would be pointless to use for what feeds it is the battery. a cap may be useful for a few seconds depending on the loads and after that it's totally the battery. only good solution is more battery capacity in the first place.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,433 admin
    Re: Capacitor Role in a PV System

    I should also add that you have P=V*I problems...

    A Farad size capacitor would need to handle an average current of:
    • P=V*I
    • I=P/V=1,000 W* 1/0.85 inverter eff * 1/10.5 volt minimum = 112 amps RMS

    Vs that 1,000 watt 120/240 VAC computer power supply capacitor storage element:
    • 1,000 W * 1/0.85 * 1/339 volts filter circuit = 3.47 amps RMS

    (the above may not be exactly correct--but close enough for discussion).

    Remember that Power also equals I2R.

    The "resistance" of a 12 volt system vs a 339 vac system would be:
    • 1122 / 3.472 = 3,615 time less resistance in copper traces, capacitor connections, capacitor internals, etc. just to have the same I2R thermal losses between 10.5 and 339 volt power system voltages.
    • ln (3,615) / ln (2) = 11.8 or approximately 36 awg difference in wire gauge to input of high voltage vs low voltage capacitor (i.e., you would need very nearly 2/O to 4/O awg or heavier wiring on the input Farad capacitor and to the plates inside) to manage the ripple current.

    Presumably the "foil" in a Farad level capacitor would not be able to manage the ripple current either unless it was hugely thicker which would make the equivalent capability capacitor huge and expensive too.

    I agree with John P--I don't think typical audio capacitors will do much for a real power system.

    Also, most audio systems flat out lie about their power output--By a factor of 5 or more. That 1,000 amplifier--may be closer to 200 watts.

    On the other hand, that 1,000 watt off grid power inverter may be capable of up to 2,000 watts for a few seconds or longer... Or upwards of 5-10x the "real" output power of a typical consumer audio amplifier.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • SolarPowered
    SolarPowered Solar Expert Posts: 626 ✭✭✭
    Re: Capacitor Role in a PV System
    BB. wrote: »
    Welcome to the forum SolarPowered,


    Typically, we have used 100 AH @ 48 volts per 1kWatt of inverter rating (or 400 AH @ 12 volts; 200 AH @ 24 volt battery bank). Note this is for flooded cell batteries--but for other reasons we also use for AGM and solar array/charging source power too.

    Another advantage is that this allows the battery bank to supply "surge" power for starting loads (such as pump motors) for multiple cycles to multiple seconds (or longer)--which capacitors cannot do (again, rating requirement of around 2kW of surge per 100 AH @ 48 volt battery bank).




    -Bill

    Nice to meet you Bill.

    I appreciate the welcome!

    From my experience what you mention is infact pretty on par AS factual.
    I can tend to disagree when it comes to DC 12V inverters @ AC 10,000watt (5,000) Watt RMS, in parallel (2 inverters), 4.23kWh solar (18 panels), 3 combiner boxes-6 string , inventec 235watt panels, 3 outback 80AMP MPPT controllers, bank of 4 AGM 31 trojans, in series using 3 O/T conductor, to (2) 10,000 watt max surge inverters, 5,000 watt continuous.
    I've done exactly as you just mentioned with 12V, 400Ah (4) AGM trojan 31 batteries, with parallel dual inverters (240V). In my personal opinion when under heavy load maxing inverters, 12V inverter's harvests and converts DC/AC in almost just as an efficient manner, to that of a 24V inverter, when using capacitors .
    Under normal system use without ( capacitor ) most 12V inverters are inverting at 90~91%, 24V can harvest and invert more efficiently at roughly 94% efficiency, regardless of conductors, and this has more to do with the internal capacity within the 12V inverter, bussing, sizing, etc. Capacitors re that added kick under heavy load conditions in my opinon.

    Now the solar generator that myself and a few others have engineered and been working on for the last year, needed to maintain that the DOD rate in elapsed time for AGM becomes less significant under heavy load conditions (exceeding 25 AMP's), please understand this is not a constant load of 5000 Watts, per inverter. Its a construction use generator that may use 5000 watts maybe for about 15~45 minutes max, and probably on average uses 1.2kWh per hour through out a total 8 hour work day, (for lap top, AC/heating, and a 1200watt microwave at lunch time). the generator has saturadys and sundays to fully charge.

    1.) AGM batteries tend to fall flat on power roughly at 75% DOD (depth of discharge), then take longer to charge based off that discharge. GEL batteries well that's debateable at 65% DOD.

    2.) Capacitors tend to prevent the DOD of AGMS from occurring more periodically and frequently keeping the batteries from running hot, as well serves as an advantage in parallel configuration, to allowing inverter capacitors to perform at lower temperatures.

    I.m not saying its a practical investment, how ever for the one time purchase, it seems to get the job done.

    12V capacitors are debateable as it takes 2 capacitor banks at 20 fared to make any considerable change to the efficiency of the harvest/inversion efficiency of a 12V inverter. A cost difference that is almost so small by $120 that most would just consider getting another battery to add to the battery bank.
  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Capacitor Role in a PV System
    niel wrote: »
    i tend to agree with john that a cap would be pointless to use for what feeds it is the battery. a cap may be useful for a few seconds depending on the loads and after that it's totally the battery. only good solution is more battery capacity in the first place.
    With my background and decades of experience in electronics/electrical, I too have to agree with Niel, BB and John.
  • PNjunction
    PNjunction Solar Expert Posts: 762 ✭✭✭
    Re: Capacitor Role in a PV System

    What about a capacitor on the input to the charge controller?

    Would a large cap be of any benefit to a normal pwm or mppt charge controller on the input? I kind of doubt it because I don't see it recommended, but had to ask.
  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Capacitor Role in a PV System
    PNjunction wrote: »
    What about a capacitor on the input to the charge controller?

    Would a large cap be of any benefit to a normal pwm or mppt charge controller on the input? I kind of doubt it because I don't see it recommended, but had to ask.

    A relatively small one might absorb some surges that might occur between the + and - of the controller input during lightening storms, but other than that, there would be no advantage, as when the sun hits the panels, the capacitors would have to charge up before the voltage was high enough to be useful to the controller, and on the other end, when the sun goes out, some small charge would still be available for a very short time while the caps discharge. The end result would be identical, except for short delays in the beginning of battery charging, and again at the end of battery charging. What I would be concerned about however, would be the relatively huge stored energy in the caps that the input of the controller would have to deal with. Normally the controllers only deal with whatever the panels can supply at any instant, but with a large cap on the input of the controller, the instantaneous energy available could be equal to having many times the panels for which the controller was designed. Could the controller handle such available instantaneous power? I guess that would depend on the controller. A shunt type definitely could suffer serious damage, depending on the size of the caps.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Capacitor Role in a PV System
    PNjunction wrote: »
    What about a capacitor on the input to the charge controller?

    Would a large cap be of any benefit to a normal pwm or mppt charge controller on the input? I kind of doubt it because I don't see it recommended, but had to ask.

    Nope.
    PV's are a current source, not a Voltage source. It is normal for array Voltage to fluctuate. Capacitors are used to stabilize Voltage (mainly). Not much point putting one on a PV.

    Some have reported success using them on turbines, but I rather doubt that as well because they'd have to be almost as big as a battery to have any effect.

    As far as inverters go, the company that built it already put caps on the input sufficient for the design. Additional ones would be redundant.