To diode or not to diode

I have 10 120 watt 44 volt panels I am hooking up in parallel. They will be on the roof with pretty even sunlight except early morn and later afternoon. Do I diode them or not is the question.

Comments

  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: To diode or not to diode
    Tooltime wrote: »
    I have 10 120 watt 44 volt panels I am hooking up in parallel. They will be on the roof with pretty even sunlight except early morn and later afternoon. Do I diode them or not is the question.

    Welcome to the forum Tooltime!
    Re your question on diodes, if you have a proper charge controller, diodes won't be necessary, and in fact will somewhat reduce the wattage available from your panels because of the inherent voltage drop across the diodes. If you're thinking of what might happen if one panel is under shadow while the rest are producing, there will be no problem, as the panels are in parallel, thus the voltage on it's terminals cannot exceed it's voltage rating.
    Rather than diodes, you should definitely consider fuses in line with each of the 10 panels, such that if one of the panels develops a short circuit, the other 9 panels cannot dump their power into that panel and so start a fire.
  • Tooltime
    Tooltime Solar Expert Posts: 45 ✭✭
    Re: To diode or not to diode

    Thank you for your quick reply. I will look into getting fuses.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: To diode or not to diode

    Ten 120 Watt 44 Volt panels? :confused: That's unusual, even if that Voltage rating is Voc.

    What do you expect to use for a system Voltage? What do you plan to use for a charge controller?

    As is, they would work for a 24 Volt system on a PWM controller. Any other system Voltage will require different panel configuration and an MPPT controller to work efficiently. In fact for a 1200 Watt array you should plan on using an MPPT controller anyway. The current output would be over 30 at the panels' Voltage level (120 Watts / 36 Vmp {assumed} = 3.3 Amps each). That puts it out of the realm of most PWM controllers.

    With MPPT you could run strings of two panels in series and five of the strings in parallel. This reduces the array current and increases its Voltage thus reducing the Voltage drop between array and controller. After that, the MPPT function would allow you to charge any standard system Voltage.

    Just something that needs to be checked.
  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: To diode or not to diode

    Excellent points as always Cariboocoot, you're obviously more awake than I am. :D
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: To diode or not to diode
    Excellent points as always Cariboocoot, you're obviously more awake than I am. :D

    Impossible, Wayne; it's three hours earlier here. :D
  • Tooltime
    Tooltime Solar Expert Posts: 45 ✭✭
    Re: To diode or not to diode
    Ten 120 Watt 44 Volt panels? :confused: That's unusual, even if that Voltage rating is Voc.

    What do you expect to use for a system Voltage? What do you plan to use for a charge controller?

    120 watt Avancis PowerMax panels

    Here is the specs of the charge controller. It is the all in one inverter,charger, and charge controller. When I have extra money built back up, I will looking into a stand alone controller. Until then, this is what I have to work with


    Rated Voltage: 24V
    Input Voltage Range: 30-55Vdc
    Rated Charge Current: 60A
    Max DC Load: 15A
    No Load Current: < 10mA
    Bulk Charge: 29.0V (default)
    Floating Charge: 27.0V (default)
    Equalization Charge: 28.0V (default)
  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: To diode or not to diode

    Can you supply the make and model of your controller please?
  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
    Re: To diode or not to diode
    Tooltime wrote: »
    120 watt Avancis PowerMax panels

    Rated Voltage: 24V
    Input Voltage Range: 30-55Vdc

    Errrr, you have a problem, because those panels have a Vmp rating of 42.8V and a Voc of 58.3V which could fry your controller. Assuming your panels are these 120W Avancis powermax strong modules: http://www.avancis.de/en/cis-solar-modules/powermax-strong/

    As wayne said, more info on the controller would be good.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: To diode or not to diode

    The controller is part of the inverter, guys; one of those infamous all-in-one-so-nothing-works-all-that-well units.

    Since it is a 24 Volt unit with a V max in of 55 it may not even have any MPPT function but just clips any extra power.

    As stephendv said, that Voc @ 58 exceeds the V max in of 55; that is a no-go.
  • Tooltime
    Tooltime Solar Expert Posts: 45 ✭✭
    Re: To diode or not to diode

    http://www.theinverterstore.com/3000-watt-pure-sine-solar-inverter-charger-24-volt.html.

    Carrbootcoot Has already pointed out the errors of my ways in an earlyer tread. I am just trying to pick my way through the mess. I know the charge controller is the problem and unless someone can point me in the direction of a controller that is a lot less then a $500 outback I am just trying to put it together for right now. I only paid $90 a panel for 10 panels.
  • Tooltime
    Tooltime Solar Expert Posts: 45 ✭✭
    Re: To diode or not to diode

    Attachment not found.

    Here is the panels, looks like the VOP is to high.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: To diode or not to diode

    Summarize for simple solutions.

    1200 Watt array consisting of ten panels with a Vmp of 44 Imp 2.7 to be used on a 24 Volt system.
    Basic problem: Vmp of array is about 9 Volts higher than it needs to be, Voc of panels exceeds existing controller input.
    Easy solution: lose the power difference using a PWM type controller that can take the 58 Voc without burning up.
    Total current: 28 Amps, so at least a 30 Amp controller. ProStar 30 without panel: http://www.solar-electric.com/ps-30.html $115. Xantrex C35: http://www.solar-electric.com/tracc35solch.html $85

    Downside: loss of power difference of 28 Amps * 9 Volts or about 252 Watts. To get that back you'd have to spend about $400 on a TriStar MPPT 45.

    I'd go with the C35 and sacrifice the power.
  • Tooltime
    Tooltime Solar Expert Posts: 45 ✭✭
    Re: To diode or not to diode

    OK. problem is solved! I will order the C35 controller today. I will be moving into the place on Monday. Right now the Generator will keep the batteries up till the solar is in place. I am guessing the the C35 will not require diodes?? I thought I had to go with the outback. Lesson learned. FYI, By winter I can hope to have the right controller and another 1200 watts on the roof.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: To diode or not to diode
    Tooltime wrote: »
    OK. problem is solved! I will order the C35 controller today. I will be moving into the place on Monday. Right now the Generator will keep the batteries up till the solar is in place. I am guessing the the C35 will not require diodes?? I thought I had to go with the outback. Lesson learned. FYI, By winter I can hope to have the right controller and another 1200 watts on the roof.

    Almost never are blocking diodes needed. :D

    All the panels will be in parallel (fuse each) and feed the C35 which will then connect to the batteries (another fuse/breaker). You'll still get the Imp from all panels, but you won't get the additional charge current that an expensive MPPT type controller would provide. If you double the array size you almost certainly will have to upgrade to one of the 'big' controllers: the more PV, the more worthwhile the MPPT function.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: To diode or not to diode

    WAIT! I was looking at the wrong spec sheet! :cry:
    You need the C40 to handle the 58 Volt input, not the C35!
    And darn it that's more expensive: http://www.solar-electric.com/c40.html
    $112

    The C35 & C60 are only good for 55 Volts (common failing among low Voltage controllers). For some reason only the C40 was designed for 48 Volt systems and thus able to handle input up to 125 Voc.
  • Tooltime
    Tooltime Solar Expert Posts: 45 ✭✭
    Re: To diode or not to diode

    I just sat down to order and thought I would check the thread first. Glad I did.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: To diode or not to diode

    My fault: the numbers are all in very small boxes and I have very old eyes. :blush:
  • animatt
    animatt Solar Expert Posts: 295 ✭✭✭
    Re: To diode or not to diode

    Also not sure what your planned usage for the inverter is. I have a similar inverter(low frequency large transformer). It is a 2000w model with out charge controller.

    This is a backup inverter for me but for real usage I really like it. That is if I am running nice size loads I feel it does very well powering them. It has great surge capacity due to the large transformer. Although I never put a scope on power so not sure how clean of a sine wave it produces.

    BUT that large transformer also is the reason for its greatest setback/negative. That being idle power draw. Just sitting idle power on it consumes roughly 55watts. 55x24=1320 watts a day to have it sitting there idle. I would venture a guess your uses more. I saw a 4000 watt version on ebay that consumed about 85 watt.

    That said if your loads permit it you could put it into standby mode. This bring my units consumption down to around 25 watts( can not remember exact figure). That is a good bit of electrical savings but really depends on your loads. It obviously would not keep stuff with timers working properly if it goes into standby. When in standby it pulses the transformer. You can hear small surges. If there is a load it full wakes up.

    I think the fan does not come on unless you have a medium size load on it which is nice. My main inverter a cotex 1500 watt inverter seems to have fan blasting everything it provides a small amount of power. But that is alot smaller and lighter, and idle draw of about 18 watts.

    Sometimes "the inverter store" has some items on ebay. I think it is refurbished stuff. But I picked up a 1000w low frequency model for $70 shipped to house. For me worth it as a backup to my backup. Although most stuff now goes for a bit more money. I mention this here for people that stumble onto this thread into the future.
    Back to my 2000w inverter it is 24v, and powers my 13k or 15k rooftop ac unit on motorhome. IT does it without blinking where the cotek stumbles. The cotek is only 1500w so I really did not expect much from it anyway. The ac unit use about ~1300w when running so surge I know is a good bit higher.

    I have had up to 3000w running off the inverter for about a minute. Although that was in cooler weather. I turned loads off as I did not want to push inverter any harder.

    I have also powered tools I used for working on motorhome. Circular saw, drills, angle grinder and a few other things. It did wonderfully. That said it is a backup. I have both inverters wired to the battery bank. So if I need high power loads I switch over to the low frequency inverter.

    I have my refrigerator running in the motorhome and it will not work correctly in power saving mode. I plan to use the low frequency inverter during construction of my house in the future. This will low better fuel usage. While generator is running it can charge the batteries instead of what normally happens on a job site where a generator is running 8 hours but with lots of times where there is no power draw. And really generator will only come up with heavy expected loads or low batteries. Otherwise generator can stay off and inverter can deal with intermittent loads like air compressor etc.

    Sorry to ramble. My main intention was to bring up the power usage point of that inverter. I like the inverter by usage scenario is key.