How to add an external gfdi

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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #32
    Re: How to add an external gfdi

    What brand & model GT inverter is this again? I went back through the posts and didn't see it mentioned by name.

    1.8 kW seems a bit small for a GT inverter. Whereas it might peak around 15 Amps AC output (and shouldn't exceed it) it needs 1800+ Watts on the input side to do so. It will also have a minimum start-up Voltage and a maximum input Voltage. On top of which it will have a set of parameters for the output dictating how high and low the AC Voltage can be and its frequency tolerance. There have been several cases on the forum where certain things arise which through the specs off not at first, but once the inverter starts to function. Low line Voltage due to high resistance to the grid for instance; the inverter can push the Voltage too high causing it to think there's no grid connected.

    Seems like you have to put meters on the in and out and watch what's going on when it pulls this stunt.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,606 admin
    #33
    Re: How to add an external gfdi

    I believe it is this Exeltech GT inverter:

    XLGT Overview
    Made in America, EXELTECH XLGT SERIES GRID-TIE INVERTERS are Transformerless, which means greater efficiency, lower cost, and less weight. The XLGT SERIES grid-tie inverters weigh only 14 lbs. Ultra lightweight, yet rugged enough for the most extreme indoor/outdoor environments, the XLGT Series grid-tie inverter is housed in a NEMA 3R enclosure for maximum environmental safety and protection. The XLGT Series, a cost-effective solution to tie into the grid with ease.

    Pure Sine Wave AC
    Made in the USA
    XLGT
    - 1800 Watts AC output
    - 200 to 600 Vdc Input

    96.5% Efficient
    - Compact
    - Simple one person installation
    - Natural convection cooling
    - Built-in AC/DC disconnect
    - ETL Certified to UL1741

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • solarvic
    solarvic Solar Expert Posts: 1,071 ✭✭✭✭
    #34
    Re: How to add an external gfdi

    Judging from the link you provided for your inverter I am wondering if the output of your panels are high enough to keep inverter turned on. your panels have + 10%-5% output tolerance @stc. If you have some wireing loss, cloudy or hot conditions you might not be getting high enough voltage to inverter. You should have 9 or 10 panels to get the voltage up. Just a guess but when the panels heat up the voltage might be too low. Solarvic
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #35
    Re: How to add an external gfdi

    I kept missing post #1 for some reason? :confused:

    I agree with Vic: you've got eight 224 Watt panels, that's 1792 Watts by nameplate. With typical derating that would be only 1379 Watts. Moreso, the Vmp on those panels is 28.9 times 8 = 231 Volts. That's just above the minimum for that inverter, and it would only occur under "best conditions". It's possible that the array is climbing above "turn on" Voltage, but then when the inverter loads it the Voltage drops and it shuts down again. This will not occur all the time, only when conditions are "just right" (or "just wrong").

    I think ten of those panels would be more suitable for this inverter.
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  • davidwillis
    davidwillis Solar Expert Posts: 104 ✭✭
    #36
    Re: How to add an external gfdi

    It should run fine with my 8 panels. They are rated for app 36VOC, and 29 Max power. That puts me at 288VOC, and 232 maximum power. It's range is 200-600V, so I am in that range.

    I do have a couple more panels I could add, but that would put my power over 1800W. Currently I have 8*224=1792W, 9 panels would put me just over 2000W, and 10 would put me at 2240W.

    It just seems strange to me that it works better with low light, but shuts off when the light is the brightest. It is still working now (really cloudy, and getting dark) But it is only putting out about 400W.

    Here are the specifications:
    Attachment not found.
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  • davidwillis
    davidwillis Solar Expert Posts: 104 ✭✭
    #37
    Re: How to add an external gfdi

    Sorry, I was typing when you posted that last one. I could easily add two more panels if you think that would fix it. But just as a note. I am getting up to 13 Amps with 8 panels, and the max for the inverter is 15. I am afraid it would go over that with 10...

    p.s. I called the company, but apparently there was no one there that was familiar with this inverter, and I need to call in the morning.
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  • davidwillis
    davidwillis Solar Expert Posts: 104 ✭✭
    #38
    Re: How to add an external gfdi

    hmm... it is interesting. It is raining now and obviously cloudy, and evening 6:45pm. I checked the inverter, and it is putting out 1.08 A, but the voltage on the panels are 148VDC. So I think I see what you guys are saying, with more sun, the inverter actually pulls the voltage down more, and maybe goes too low..??? Even though I did not see it go under 220, and it should work down to 200, maybe it is causing the problem.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #39
    Re: How to add an external gfdi

    Keep in mind that Voc is irrelevant to power production. It's only importance is to make sure the maximum Voltage input of the inverter is not exceeded. When you're talking power, you're talking Vmp. Note the "minimum PV start-up Voltage" on the inverter specs (third line). It says 230. Your array has a Vmp of 231, and that will be under best conditions. This is very borderline.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,606 admin
    #40
    Re: How to add an external gfdi

    Assuming your panels are running closer to 95F + 40F rise, based on Vmp-coeff -0.52 %/oC:
    • Vmp-hot = 29 Vmp + 29 Vmp * ((95F+40F-75F STC) * 1/1.8 F/C * (-0.0052 /oC)) = 24.0 volts

    And for your 8 panel string array:
    • 8 * 24 volts = 192 Vmp-array-hot

    So, with a 10 panel string, you are looking at a 240 VDC Vmp-hot based on my above numbers... Your Ambient may be higher than 95F, and your temperature rise could be as high as 60F or more... which would depress your Vmp-array-hot even more...

    If you live in an extreme environment (high desert with cold nights/mornings and hot days), the ratio between Voc-cold:Vmp-hot can almost be as high as 2:1

    A panel running at 185F (maximum rated temperature):
    • Vmp-hot = 29 Vmp + 29 Vmp * ((185F-75F STC) * 1/1.8 F/C * (-0.0052 /oC)) = 19.78 volts
    • 230 Volts minimum start / 19.78 Vmp-hot = 11.6 = 12 panels in series

    So, a worst case setup would require ~12 panels in series. It all depends on your local ambient and how much cooling your array will receive (i.e., mounted flat against roof vs tilted for get air underneath).

    A lot of vendors have string calculators to help with these estimates.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • davidwillis
    davidwillis Solar Expert Posts: 104 ✭✭
    #41
    Re: How to add an external gfdi
    Cariboocoot wrote: »
    Keep in mind that Voc is irrelevant to power production. It's only importance is to make sure the maximum Voltage input of the inverter is not exceeded. When you're talking power, you're talking Vmp. Note the "minimum PV start-up Voltage" on the inverter specs (third line). It says 230. Your array has a Vmp of 231, and that will be under best conditions. This is very borderline.

    So maybe I am a little confused on this. I thought the minimum start-up voltage was the Minimum voltage to turn on the inverter, but then once on, I thought the inverter would run until it hit 200v (since the operating range is 200-600v). However it shut off with the voltage at about 220v.

    I really don't like the idea of throwing 2688W (12 panels) of panels into an inverter that can only put out 1800W. I could easily increase the angle of the panels though. I had it planned to have them flat during the summer, and then incline them during the winter. The roof they are on is only about 15 deg. However I think increasing the angle even during the summer may help keep them cooler.

    By the way, today when I was having problems the temperature was about 70 deg, but the sun was bright.
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  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
    #42
    Re: How to add an external gfdi

    Looks like excels site of array sizing , for a close match to your panel, I found the BP3220T. the table calls for an 11 panel array....http://www.exeltech.com/pvpanel.htm

    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,
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #43
    Re: How to add an external gfdi

    The thing is, a panel does not really put out its rated power. And as it does put out power it generates heat which, ironically perhaps, reduces its power output. With your array "on the edge", so to speak, once it starts putting out power and heats up its power output drops - below the threshold that keeps the inverter running. So the cycle repeats. It is important to remember this will not happen all the time.

    Being able to maintain actual (as opposed to rated) Vmp above the inverter's operating threshold is important.

    Using ten of the 224 Watt panels gives a rated array of 2240 Watts, but in reality its output will average roughly 77% of this (depending on a number of factors including temperature) or 1724 Watts. That the inverter will turn into AC output, further reduced by its conversion efficiency.

    So in practice 2688 Watts would be around 2000 Watts, which could maintain full inverter output under good conditions.

    Just my opinion, but an increase to ten panels would result in marked performance improvement here.
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #44
    Re: How to add an external gfdi
    Cariboocoot wrote: »
    The thing is, a panel does not really put out its rated power. And as it does put out power it generates heat which, ironically perhaps, reduces its power output.
    You confused me... I thought that for a panel in the sun, it is hotter with no load, and cooler with a load.

    That makes sense to me thermodynamically because the sun has a certain radiant energy and when that energy hits an unloaded panel, the panel converts that energy to heat. When you attach a load to the panel some of the sun's radiant energy is converted to electrical energy, not to heat.

    Am I wrong about this?
    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • davidwillis
    davidwillis Solar Expert Posts: 104 ✭✭
    #45
    Re: How to add an external gfdi

    I don't know a lot about this (as you can probably tell). But I do know that photovoltaic solar panels convert light to electricity (not heat). In fact heat hurts voltage, and lowers output.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #46
    Re: How to add an external gfdi
    vtmaps wrote: »
    You confused me... I thought that for a panel in the sun, it is hotter with no load, and cooler with a load.

    No, it's the other way around. A panel producing no power (disconnected) will be at ambient temperature plus whatever solar thermal collection it gets. Connect the wires up and current flows; inevitably current means heat.
    That makes sense to me thermodynamically because the sun has a certain radiant energy and when that energy hits an unloaded panel, the panel converts that energy to heat. When you attach a load to the panel some of the sun's radiant energy is converted to electrical energy, not to heat.

    Am I wrong about this?
    --vtMaps

    The difference is that the panel is converting light energy to electrical energy, not thermal energy to electrical energy. The byproduct of the action is that inevitably some of that electrical energy turns into additional thermal energy within the panel.
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  • davidwillis
    davidwillis Solar Expert Posts: 104 ✭✭
    #47
    Re: How to add an external gfdi

    It doesn't look like I am going to be able to add the panels for a while, it is raining, and I don't want to carry panels on a wet roof.

    I do think you guys are correct though, I think adding more panels will fix it. I may have to get some micro inverters, and cut back down to 8 in the winter and use the micro inverters. Otherwise I would wast a lot of power.
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  • davidwillis
    davidwillis Solar Expert Posts: 104 ✭✭
    #48
    Re: How to add an external gfdi

    Ok, the sun came out a little, so I decided to see how it was working. It was putting out about 5 amps, and the DC voltage was jumping a lot between 230 to 265. Is that normal? It would hang around 245, then quickly drop down to 230, then up to 260, then back to 245. It is cold right now (about 45 deg, and the sun is weak), so I am sure it is not the heat (I bet they are not over 50 deg). While I was checking(for about 5 min), it restarted twice.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #49
    Re: How to add an external gfdi

    The array Voltage is probably "jumping" because the inverter is turning on and off. It senses "high enough" Voltage (Voc) and turns on, whereupon the load of the inverter draws the array Voltage down below shut-off and the cycle repeats. Depending on the exact lighting conditions it will stay on for some time, but it's operating on the edge of its Voltage threshold which makes it very volatile.
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  • davidwillis
    davidwillis Solar Expert Posts: 104 ✭✭
    #50
    Re: How to add an external gfdi

    It cleared up for a little bit, so I put up another panel. Not much sun, but with 9 panels my Voc is 307. When running the inverter it was 220-280. But light was very low. I hope to get the last panel up tomorrow (if the weather is ok), and see how it works.
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  • solarvic
    solarvic Solar Expert Posts: 1,071 ✭✭✭✭
    #51
    Re: How to add an external gfdi
    I do think you guys are correct though, I think adding more panels will fix it. I may have to get some micro inverters, and cut back down to 8 in the winter and use the micro inverters. Otherwise I would wast a lot of power.
    I think you won,t need the little inverters for winter when you add the extra panels. As Cariboocoot explained to you the inverter has losses and probably never will output more than 77% of the solar input. Experience will be your best teacher. :Dsolarvic:D
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #52
    Re: How to add an external gfdi

    Even with ten panels in series you'd be in no danger from high Winter Voc if that is the concern:
    36.6 * 10 = 366 * 1.3 = 475.8 which is still below that inverter's 550 Volt max operating.
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  • davidwillis
    davidwillis Solar Expert Posts: 104 ✭✭
    #53
    Re: How to add an external gfdi
    Cariboocoot wrote: »
    Even with ten panels in series you'd be in no danger from high Winter Voc if that is the concern:
    36.6 * 10 = 366 * 1.3 = 475.8 which is still below that inverter's 550 Volt max operating.

    I am not worried about that. I am just looking at the BP3220T panel on exeltech's website. They recommend 11 of them, which will produce 1872 Watts when hot, and 3201 Watts when cold. So it is a good match when hot, but I just feel like it is wasting a lot of the panels potential when it is cold. If the panels put out over 3KW, and my inverter only utilizes 1.8Kw, that is not very good.

    So my thought was that I could remove some panels, and use micro inverters on them when it is cold. That way the energy they produce would not just be wasted all winter.
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  • solarvic
    solarvic Solar Expert Posts: 1,071 ✭✭✭✭
    #54
    Re: How to add an external gfdi

    The info you got from exeltech string chart is wrong. I checked that BP panel on fronius string chart for an IG-2000 inverter which is only a 500 volt inverter and it list 11 panels rated at 2416 watt. Derating that to 77% gives you 1860 watts out of your inverter which should be just right for that inverter. If it was me I would use 11 panels and not worry a bit. Install the 11 panels and see what kind of output you get in the very best conditions and if you think it is too much you could just disconnect one when it got many degrees below zero. :Dsolarvic:D
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #55
    Re: How to add an external gfdi

    Don't worry about it.
    Temperature will affect the Vmp & Voc, hence the 1.3 factor in my array Voc calculation. That is "worst case" number we use up here in the Great White North. Apply it like this: Vmp 28.9 * 1.3 = 37.5 * 7.58 Imp = 285 Watts maximum per panel. Times ten panels is 2850 Watts. Times eleven panels is 3135.
    The likelihood of the power ever reaching that level is slight, as you need below zero temps to achieve it. Once the panels start producing they warm up.
    Even if you did "switch out" a panel to a micro, that will only output its maximum Watts. So putting 285 Watts on a 200 Watt micro inverter still only gives you 200 Watts. Never mind the legal ramifications of such a system install.

    I think you'll be happy with ten panels.
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  • davidwillis
    davidwillis Solar Expert Posts: 104 ✭✭
    #56
    Re: How to add an external gfdi

    so far so good... I havn't had time to hook up anymore panels, but with 9 it is running at 9A @ 125vac, and the panels are staying steady at 270VDC. It will be interesting how it works with more sun. If the weather is still good this afternoon, I will try installing the 10th panel.
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  • davidwillis
    davidwillis Solar Expert Posts: 104 ✭✭
    #57
    Re: How to add an external gfdi

    Well if low voltage is the problem it will take more than 9. I was watching it, and it was running at 260VDC, and it restarted. I am starting to think this is not the problem, or this inverted does not have a range of 200-600 like it says. It was no where near 200VDC, when it restarted. I plan to mount the 10th panel tomorrow, so we will see.
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  • davidwillis
    davidwillis Solar Expert Posts: 104 ✭✭
    #58
    Re: How to add an external gfdi

    I have 10 hooked up now, and the sun is out. It is producing 14.5 amps, and the array is holding at around 280VDC. It did restart once I know of, but it is not happening as often for sure.
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  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
    #59
    Re: How to add an external gfdi

    Well? or is it too soon to say BINGO!!

    or do you need 1 more to stop the shut down process?
     
    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
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  • davidwillis
    davidwillis Solar Expert Posts: 104 ✭✭
    #60
    Re: How to add an external gfdi

    I hooked up all my solar panels (a total of 12). I was planning on using 4 of them for battery charging for another project. With 12 I have not seen it shut off at all, and the voltage is around 350 or so. It goes up to 15 amps output even when cloudy, but I feel like I am not utilizing my panels very well (almost 2700W of solar panels only putting out 1.8kw).

    So I guess this was the problem, but it doesn't make sense to me that the inverter won't just work at any voltage over 200. It should say you need 300-600VDC, not 200-600VDC.
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  • solarvic
    solarvic Solar Expert Posts: 1,071 ✭✭✭✭
    #61
    Re: How to add an external gfdi

    Why don,t you try 11 panels and see if you still get 1800 watt output? Another suggestion, Did you use heavy enough wire from panels to inverter and what is the length from panels to inverter? If you have too small of a wire you would lose some voltage. Maybe you needed all the 12 panels to overcome the voltage drop. I know some people are parinoid about putting thier location on thier particulars but it would make it easier about trying to give them advice. Temperatures and location give posters more info to help diagnose thier problems. What might be right for my location would be altogether than someone living in Florida, Per Say. If you livedSomewhere like in Canada where they might get -40F 12 panels mght be too much but if you lived in Florida you might need all 12 panels just to get your inverter to work. :Dsolarvic:D
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