Solar Panel Questions?

stmarstmar Solar Expert Posts: 328 ✭✭✭
Every time I think I have a decent deal it falls through or does not seem like the right fit. I have a few questions:
1. Why do they make panels with lower voltage when 35 seems to be what you need?
2. Does being grid tied, not interactive, make a difference in the 35 necessity?
3. How do you size your controller, what values do you add/divide/multiply to stay within your controllers specs? Specifically talking about the Prostar-30 PWM.
4. How many watts of array can a 400ah bank take? (24 volt) During a sunny day my controller pulses quite a bit so do I need more array?
5. What is the difference, advantages, disadvantages between mono and poly panels?

Here is what I have now on my Morningstar PS-30:
12 X Solarex MSX-64: 64 max watts, 21.3 voc, 4 isc, 17.5 volts, 3.66 amps

My controller never shows anything near 30 or even 20, most of the time it is mid to low teens during the day.

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Solar Panel Questions?
    stmar wrote: »
    1. Why do they make panels with lower voltage when 35 seems to be what you need?
    2. Does being grid tied, not interactive, make a difference in the 35 necessity?

    The less-than 35 Vmp panels are designed for grid-tie systems which do not use the same Voltage that off-grid or battery-based systems use. Batteries & charge controller demand one set of minimum/maximum array Voltages, grid-tie another set. Most central inverters operate in the 300 to 400 Volt range: like twelve 30 Vmp panels in series.
    3. How do you size your controller, what values do you add/divide/multiply to stay within your controllers specs? Specifically talking about the Prostar-30 PWM.

    Charge controllers are usually sized by output current: the ProStar 30 can handle 30 Amps output at either 12 or 24 Volts. The array Vmp would be 17.5 or 35 respectively, but ultimately it is the array Imp that matters for the current out on a PWM controller as it is the same going in. So 30 Amp controller on 12 Volts is roughly (30 * 17.5) 525 Watts, but the specific panels may be, say, 17.7 Vmp and 7.9 Imp so you could really only use three such panels in parallel before exceeding the charge controller's current limit. Most controllers, even PWM type, can handle a bit more than their rating so in this case four panels would probably work. Curiously there are 150 Watt panels with the same Imp of 7.9 but Vmp of 18.9: same number of panels would work, but you would not have any more actual charging power.

    Use of an MPPT type controller changes this.
    4. How many watts of array can a 400ah bank take? (24 volt) During a sunny day my controller pulses quite a bit so do I need more array?

    400 Amp hours @ 24 Volts typically can take 40 Amps input, and may take more than that (or less) depending on the specific batteries. Generically: 40 Amps * 35 Vmp (for a 24 Volt system) = 1400 Watts. But you can't put that much through a 30 Amp controller.

    It is normal for a charge controller to pulse; it's how they work. However your definition of 'pulse' may be different. They pulse in that they turn on/off rapidly in order to regulate Voltage for Absorb and Float stages. If this is happening it's what should happen. If there's something else going on it may not be.
    5. What is the difference, advantages, disadvantages between mono and poly panels?

    Monocrystaline panels are slightly more efficient than poly or multicrystaline. This results in higher Watt yield per square area. They also tend to cost more. Otherwise the differences are not particularly significant.
    Here is what I have now on my Morningstar PS-30:
    12 X Solarex MSX-64: 64 max watts, 21.3 voc, 4 isc, 17.5 volts, 3.66 amps

    My controller never shows anything near 30 or even 20, most of the time it is mid to low teens during the day.

    Well 12 * 64 = 768 Watts, but most important is the 3.6 Imp * 12 = 43 Amps. The charge controller couldn't pass all that current even if it were available, and it may have damaged the controller if it were. The actual current will depend not only on what is possible for the panels to produce but also what the batteries demand.

    You need to check some things, starting with whether or not your batteries really are charged. Hopefully they are flooded cells and you can get a hydrometer and take some Specific Gravity readings. If the batteries aren't needing the full available current (30 Amps) to recharge they won't take it.

    The second thing to test is the panels themselves. One at a time, in full sun, check the Isc with a digital multimeter. Each panel should be able to put out near 4 Amps into the meter set on DC Amps and across the panel. Only one panel at a time! Most meters can only take 10 Amps DC.

    It would be good to check the array as a whole to see if there are any wiring problems too, but without a clamp-on DC Ammeter this becomes a bit tedious as you have to disconnect each panel in turn and see if there's any change in output during charging.

    Finally you need to check the charge controller. The clamp-on meter is a big help there because you can use it to check current flow when the controller is bypassed. Otherwise you can only go by increase in battery Voltage without the controller and that is not very accurate.
  • stmarstmar Solar Expert Posts: 328 ✭✭✭
    Re: Solar Panel Questions?

    "You need to check some things, starting with whether or not your batteries really are charged. Hopefully they are flooded cells and you can get a hydrometer and take some Specific Gravity readings. If the batteries aren't needing the full available current (30 Amps) to recharge they won't take it."

    I have Lifeline AGMs so can't check sg. They are fairly new.

    I am thinking that my array is not putting out it's full potential so hopefully the controller is okay, I have not seen any error codes thrown. I will try and go through the array and see what readings I can gather and see if what I have on this controller is okay.
  • stmarstmar Solar Expert Posts: 328 ✭✭✭
    Re: Solar Panel Questions?

    If my array was pumping out too many amps what would happen? I have seen no adverse reaction and like I said it never gets over 20 amps even on sunny days. Reason I ask is that it may take me a while to really take it apart and check the individual panels.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Solar Panel Questions?
    stmar wrote: »
    If my array was pumping out too many amps what would happen? I have seen no adverse reaction and like I said it never gets over 20 amps even on sunny days. Reason I ask is that it may take me a while to really take it apart and check the individual panels.

    It can't actually "pump" too many Amps, but if it was at full illumination and the load on the charge controller was high enough that the current flow was greater than the charge controller is designed to handle the controller would heat up, possibly to the point of component failure (hard to predict because we never know how 'over-built' a device is or how good it is at dissipating heat which is a major factor in handling current).

    The two things which affect the current most are supply (potential Amps) and demand (possible Amps). If the panels don't have enough sun on them or there's a fault with the array then the supply is affected and the current potential is reduced. If the load is high resistance (battery in a higher SOC) even if the supply is there the demand isn't so again the current will be lower than maximum.

    This is not the same as with a high-end MPPT controller where a current limit can be set.
  • stmarstmar Solar Expert Posts: 328 ✭✭✭
    Re: Solar Panel Questions?

    The Morningstar ProStar-30M displays "Disconnects & Protections", high temp disconnect and overcurrent protections among others. Would there not be a display or disconnect if there had been more power than the controller was rated? Just trying to figure out if I need to expedite my system review or even disconnect a few panels.
    If I should disconnect some panels what would I need to look for in new panels for compatibility if I wanted to use the older ones that I disconnect? I would use a new controller for the disconnected old ones and the new ones.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Solar Panel Questions?
    stmar wrote: »
    The Morningstar ProStar-30M displays "Disconnects & Protections", high temp disconnect and overcurrent protections among others. Would there not be a display or disconnect if there had been more power than the controller was rated? Just trying to figure out if I need to expedite my system review or even disconnect a few panels.

    Hopefully a high current situation would shut down the controller from heat before anything fries, but there are no guarantees. In general they'll take 10%-20% over.
    If I should disconnect some panels what would I need to look for in new panels for compatibility if I wanted to use the older ones that I disconnect? I would use a new controller for the disconnected old ones and the new ones.

    If you disconnect panels you won't want to be putting new ones on the same controller. If you want to shift some to another controller and add more of the same you'll want the Vmp to be close for parallel connections and/or the Imp to be close for serial connections (two panels in one string). It is usually easier to find panels with similar Vmp and there is more tolerance of difference there as PV doesn't care much what Voltage it runs at so long as it is allowed to produce current. Differences in Imp in series will cut the power to the lowest number.
  • CDN_VTCDN_VT Solar Expert Posts: 492 ✭✭✭
    Re: Solar Panel Questions?

    in Reading this thread , you do have 6 strings of two panels in series to make up the 12 X Solerex MSX-64 charging 24Vdc bank ?
    Max amp including the 25% overload that MS Pro 30 say(( "Capable of 25% overloads")) is 37.5 amps , your max panel output on the best day without any losses is 43.09 amp.
    Only seeing max under 20 amps leads me to thinking you have a panel wiring to controller problem . For the way I have wired mine , I trip each breaker for each string of 2 panels in series and see how much of a drop I get , Or I can use a DCV amp clamp meter to check each string has similar amps while under load or supplying power for charging.

    Another thing to check is that one set of panels are not reversed wired into the mix.

    Just some of my thoughts

    VT
  • stmarstmar Solar Expert Posts: 328 ✭✭✭
    Re: Solar Panel Questions?

    Yes; 12 X 64W @ 24 VDC
    If it is supposed to generate that much power then there is an issue so I will do some research and see what I can find. I forgot to mention that I have a 30 amp breaker between the array and the controller so hopefully that should protect the controller to a point. I have never had the breaker trip.
  • stmarstmar Solar Expert Posts: 328 ✭✭✭
    Re: Solar Panel Questions?

    Does voltage (24 vdc) have any bearing on the Imp (3.66 amps)? Trying to get an understanding before I start testing components.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Solar Panel Questions?
    stmar wrote: »
    Does voltage (24 vdc) have any bearing on the Imp (3.66 amps)? Trying to get an understanding before I start testing components.

    "Sort of".

    24 Volts is nominal system Voltage. In reality battery Voltage may run from as low as 21 (not recommended) to as high as 32 (during EQ). When the batteries are in a lower State Of Charge they will also be lower in Voltage and demand more current. So it is more likely you will see the maximum current of the panels (Imp) at the lowest SOC of the batteries.

    It is necessary to have the factors come together to see the maximum panel output: they have to have full, direct sun on them so that they could produce their full power and they have to have enough load (either low batteries or other demand) to require the highest current. If you want to go for full power (not just current) they also have to be cool enough that the Vmp doesn't drop.

    This is why when we test panels individually we eliminate as many variables as possible by checking for the Isc in full sun. There's no greater load than a short circuit, it won't hurt the panel, and it will demonstrate if it is capable of its maximum potential (it is unlikely you'd get Vmp and not Imp as panels are a current source; if they can produce Imp then Voltage is merely a function of the resistance on the output).
  • stmarstmar Solar Expert Posts: 328 ✭✭✭
    Re: Solar Panel Questions?

    Any idea how the cover works on these junction boxes? There are two screws and what look like hinges but there is resistance when I try and open it. I don't want to break anything and I am sure it is something simple. To get to the wiring I am sure it would have to open compeletely.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Solar Panel Questions?
    stmar wrote: »
    Any idea how the cover works on these junction boxes? There are two screws and what look like hinges but there is resistance when I try and open it. I don't want to break anything and I am sure it is something simple. To get to the wiring I am sure it would have to open compeletely.

    You've lost me there.
    Why would you need to take the junction boxes apart? Are there no leads coming from them? Are the panels wired from one junction box to the next? That is not normal.

    The junction box covers the internal panel connections between segments and the bypass diodes for the segments as well as the attach point for the leads. There should be no reason to take them apart.

    The leads should go to a common connection point such as a combiner box. Usually they have MC3 or MC4 connectors on them. Very old panels may not. Ordinarily you just disconnect the panels at the connection points to test them individually.

    If you could post a picture of what you're dealing with it may make the situation clearer.
  • PhotowhitPhotowhit Solar Expert Posts: 4,996 ✭✭✭✭
    Re: Solar Panel Questions?
    stmar wrote: »
    Every time I think I have a decent deal it falls through or does not seem like the right fit. I have a few questions:
    1. Why do they make panels with lower voltage when 35 seems to be what you need?
    You might be charging a 12 volt battery...Lots of 12 volt systems out there.
    stmar wrote: »
    2. Does being grid tied, not interactive, make a difference in the 35 necessity?
    Actually need much higher voltage.
    stmar wrote: »
    3. How do you size your controller, what values do you add/divide/multiply to stay within your controllers specs? Specifically talking about the Prostar-30 PWM.
    You size them to your needs, you have a 12 - 64 watt panels, They are 12 volt nominal panels designed for charging a 12v battery bank with a PWM charge Controller. The Prostar 30 should work fine with these panels, Since you have a 24 volt system you will use the panels in strings of 2. In strings of 2 they will produce the same amperage and double the voltage so each string will produce 3.66 amps at 35 volts. 6 strings will be 3.66 x 6 = 21.96 amps at 35 volts..
    stmar wrote: »
    4. How many watts of array can a 400ah bank take? (24 volt) During a sunny day my controller pulses quite a bit so do I need more array?.
    Check the specs on your batteries, I think Lifeline AGM's can take higher than standard charging rates, standard charging rates for flooded lead acid batteries are 5-13% of the batteries capacity..
    stmar wrote: »
    5. What is the difference, advantages, disadvantages between mono and poly panels?.
    Mono tend to have slightly smaller foot print for their output.
    stmar wrote: »
    My controller never shows anything near 30 or even 20, most of the time it is mid to low teens during the day.
    I wouldn't expect it to produce 30, your maximum potential is 3.66 amps x 6 strings(24 volt system) = 22 amps, normally you will produce less than this... Once the battery is out of bulk charging the amps passing through will be reduced, so your state of charge becomes a factor.

    These Solarex MXS64 Panels were popular in the late 90's and may be showing their age a bit, but should be functional on into the future, they have a junction box on the back that you make your connections inside. I suspect they have the screws as well as a latch of some sort. likely a slot that you can push a screw driver into to release.
    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
  • stmarstmar Solar Expert Posts: 328 ✭✭✭
    Re: Solar Panel Questions?

    Thanks, that answers a lot of questions. As you say they are probably showing their age at 15 plus years. I will go through the array and check the components and when I find the right deal on additional panels and controller I will be ready to act.
  • PhotowhitPhotowhit Solar Expert Posts: 4,996 ✭✭✭✭
    Re: Solar Panel Questions?

    Dang computer is having a brain fart and won't let me do a link and I have no time to restart it,

    Here's an address for a PDF of your panels;

    http://www.solarelectricsupply.com/media/custom/upload/Solarex-MSX64.pdf

    Since these panels may have not been changed in 15 years, once you open the J-box you might clean the terminals and apply some dielectric grease and cut and expose some new wire or clean the leads and reattach. Be careful and don't change the wiring! if there are some damaged jumpers or bad corrosion replace the wires or jumpers but these can be setup as 6 volt nominal panels as well, so play with the wiring at your own peril!

    I looked quickly for a wiring diagram but had no luck, I've seen one back when I was searching for a Photowatt diagram so it's out there...
    This might be a photo of your Jbox opened, I don't see a latch or pressure link but perhaps this will help;

    Attachment not found.
    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
  • stmarstmar Solar Expert Posts: 328 ✭✭✭
    Re: Solar Panel Questions?

    That is the box, maybe the hinge has to have a little pressure to pop it open, it stops just as it opens a bit. I will be careful and see if I can figure them out, sure don't want to break anything this old. Good tip on the dielectric grease and making sure the connections are viable. I was happy that the controller was not over amped.
  • stmarstmar Solar Expert Posts: 328 ✭✭✭
    Re: Solar Panel Questions?

    I saw a Kyocera 108 watt 24 volt solar panel with a max voltage of 43 volts and 3.35 amps. Would that be too high a voltage for adding to my system?
  • PhotowhitPhotowhit Solar Expert Posts: 4,996 ✭✭✭✭
    Re: Solar Panel Questions?

    Your looking for the VMP(Volts Maximum Power) number, 43volts sounds like a VOC(Volts Open Circuit) I suspect it will be similar to your other panels in series, You want the Vmp of the Kyocera panel to be close to the Vmp x 2 (since your doing strings of 2 panels) or the Solarex panels.

    If it is close you could add the single panel as you would a string of the other panels.

    Does that make sense?
    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
  • stmarstmar Solar Expert Posts: 328 ✭✭✭
    Re: Solar Panel Questions?

    It does show VMP = 43 volts and that is the most I have ever seen. It shows the VOC = 33.8. Seemed strange to me since I had not seen such a high voltage and did not know how it would work. If I went with another controller would I need to be as sensitive to matching the VMP?

    Kyocera 108 Watt 24 Volt
    G721-2W
    Polycrystalline Solar Panel
    Manufacturer Specifications:
    Maximum Power: 108.2 watts
    Maximum Power Voltage: 43 volts
    Maximum Power Current: 3.35 amps
    Open Circuit Voltage: 33.8 Voc
    Short-circuit Current: 3.20 amps
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Solar Panel Questions?
    stmar wrote: »
    It does show VMP = 43 volts and that is the most I have ever seen. It shows the VOC = 33.8. Seemed strange to me since I had not seen such a high voltage and did not know how it would work. If I went with another controller would I need to be as sensitive to matching the VMP?

    Kyocera 108 Watt 24 Volt
    G721-2W
    Polycrystalline Solar Panel
    Manufacturer Specifications:
    Maximum Power: 108.2 watts
    Maximum Power Voltage: 43 volts
    Maximum Power Current: 3.35 amps
    Open Circuit Voltage: 33.8 Voc
    Short-circuit Current: 3.20 amps

    It is not possible for the Vmp of a panel to be higher than the Voc. The listing is wrong. I suspect the Wattage is wrong too because if you multiply 3.35 Imp * 43 Vmp you get 144 Watts, and if the Vmp is actually 33.8 you get 113 Watts.

    Notice the Isc is lower than the Imp, which is also impossible.

    Moreover I could not find any listing for Kyocera 108 Watt panels (never heard of that size from any company) and I doubt these are genuine KD panels. The whole E-bay listing (the only place it shows up I could find) is suspicious. Search for the alleged model number turned up nothing from Kyocera, just the E-bay listing again.

    I wouldn't touch these with a 40 foot power pole.
  • PhotowhitPhotowhit Solar Expert Posts: 4,996 ✭✭✭✭
    Re: Solar Panel Questions?

    Well it took about 2 seconds to find the wacko's who are unable to write down the specs correctly, It's Solar Blvd who also goes by minidiscmini on eBay. They regularly call panels with vmp of 26-30 '24 volt' panels....

    They just have the numbers backwards, Short circuit voltage is as high as you can with out introducing some type of voltage converter, So it's hard to have a maximum voltage lower than your working voltage!

    You need to match the VMP pretty close for strings of panels. You can also use a separate controller,but if your panels are reasonable close to your controller and batteries at 33.8 you should be okay for all but the hottest days.

    to add to 'Coot's obsevations 3.2 amps x 33.8 volts = 108.16
    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
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Solar Panel Questions?

    Yep.
    But Kyocera's model numbers are usually "KD" + the Wattage so they should be "KD108" if they are Kyocera panels.

    I would not trust these as being real Kyocera panels. I would not trust a seller who can't even get Vmp/Voc and Imp/Isc straight either.
  • stmarstmar Solar Expert Posts: 328 ✭✭✭
    Re: Solar Panel Questions?

    I thought everything on the internet was true, lol. I thought something sounded weird about these so thanks for confirming that and adding to the knowledge base.
  • PhotowhitPhotowhit Solar Expert Posts: 4,996 ✭✭✭✭
    Re: Solar Panel Questions?

    They may be real, made specific for some relay station or such, but there are better options I think...
    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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