Oops, I think I made a boo-boo there.

robert1701
robert1701 Registered Users Posts: 12 ✭✭
edited April 2020 in Solar Beginners Corner #1
Hello, This is my first post.

I would like to make and off grid installation but do not have a lot of money, so I bought 10 secondehand solarpanels and ordered a cheap solar charger controler in China. See pictures below.

But now I have read that the controller can only handle a maximum of 50 Volts input from the solar panels and these panels give more.

Where can I buy another cheap controller which can handle this higher input voltage and doesn't cost and arm and a leg?




Comments

  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    Welcome to the forum Robert

    Those are oddball panels with a VOC of 78.4V, your only option would be to use a MPPT but due to the voltage the panels would need to be in parallel only for most controllers, be aware there are a lot of fake MPPT controllers, the price will be the indicator, the lower priced true ones such as EPEVER run around $200 for a 40A  version.

    Thin film panels have a shorter lifespan than crystalline type, typically around 10 years so it may be worth testing their output before making any decisions, being that they're used. 

    Sorry that I can't offer a better solution, it's a pity you didn't post before the purchase, but as they say hind sight is 20/20




    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery with Battery Bodyguard BMS 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
  • Photowhit
    Photowhit Solar Expert Posts: 6,002 ✭✭✭✭✭
    Your mistake, might be even worse!
    Thin film panels often contain Cadmium and considered hazardous waste. 
    Not sure what 'cheap' was, but 10 cents a watt is what one seller has been trying to get for used thin film panels;

    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • robert1701
    robert1701 Registered Users Posts: 12 ✭✭
    edited May 2020 #4
    Mmm. I think I bought the panels for about ¢27.5 per Watt. Also, I have no idea how old they are.
    I had a MPPT controller in mind, so the 75 Volt panels in parallel should give me a lot loading hours a day.
    Finding a cheap MPPT controller seems to be a bit difficult. Still have to find batteries also.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    MPPT (and generally) solar controllers are rated for maximum output current. Remembering that Power=Voltage*Current, if you have 2x battery bank voltage (24 volts vs 12 volts), the "power" (wattage) would be double...

    For example, (using their numbers), 400 Watts @ 30 amps:
    • P=V*I
    • V=P/I= 400 Watts / 30 amps = 13.33 Volts battery charging voltage (12 volt bus)
    • V= 800 Watts / 30 Amps = 26.67 Volts battery charging voltage (24 volt bus)
    This is all approximate, because battery charging voltage runs from ~10.5 volts to ~15 Volts... So actual charging power varies too.

    Nominally, assuming this is a good quality & well designed MPPT solar charge controller, our calculation for the maximum "cost effective" array would be (if 24 volt battery bank):
    • 30 Amps charging current * 29.0 volts charging * 1/0.77 solar panel+controller derating = 1,130 Watt (std or marketing numbers) array
    Now, there is the working voltage for the array... If 75 Volt Vmp panels, then the Imp-array would be around:
    • 800 Watts / 75 Volts Vmp = ~10.67 Amp Imp array (manual's specifications)
    • 1,130 Watts / 75 volts Vmp = 15.07 Amp Imp array ("our" deratings")
    MPPT charge controllers efficiently take high voltage & low current, and efficiently down convert to low voltage & high current needed to charge the battery bank.

    Most MPPT charge controllers will accept an "over sized" array and will never output more than their rated output current (long term, there are possiblities of outputting more than rated current during short periods of time, such as when doing MPPT "sweeps").

    The 0.77 derating factor is based on the fact that companies use room temperature for cell temperature when defining test conditions. However, while the test condition is ~25C, real panels run +20C or hotter (i.e., 45C) under full sun, hot ambient, low wind conditions). This causes the Vmp-array (in real life) to drop a lot. To as low as ~81% of the panels Vmp-std rating).

    For most installations (unless sub zero conditions), they will rarely output more than ~77% of their rated power (another 5% loss for controller efficiency, dusty panels, etc.).

    Note that if you are in sub zero (F) conditions, then panel Voc (voltage open circuit) does rise--Leading to an issue that needs to be checked--The Voc-cold for your local conditions (Caribbean island, vs Alaskan mountain range) could exceed the controller's Vpanel-max input rating (100 VDC?). Thin film panels have different temperature factors vs crystalline silicon panels. Details matter here.

    I don't know anything about this brand, so following their specifications/limits is always a good place to start.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • robert1701
    robert1701 Registered Users Posts: 12 ✭✭
    Most controllers are made for 12-24V solar panels it seems. Buying a Controller which can handle this 60-70V operational input from the solar panels seems to be rather expensive.
    Will In have to sell my 10 solar panels and look for second hand 12V ones to end this misery?

  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    For an MPPT type charge controller (which are more expensive than PWM type)--A 100 VDC max input (and Vmp~30-60+ volts for 12/24 volt battery banks) is about standard.

    To a degree, it is a tradeoff between "expensive" MPPT charge controller and "cheap" GT/non-standard panels, vs a "cheap" PWM controller and more "expensive" Vmp=18 or Vmp=36 volt panels).

    There is a problem in that some(?) PWM charge controllers are labeled MPPT "branded"--Obviously not good. And even some cheap MPPT controllers can have issues with not working correctly... So it is a bit of a gamble.

    Generally, large systems (say >800 Watts) tend to favor MPPT controller + "GT" non-standard panels. And smaller system (less than ~400 Watts, tend to favor PWM controllers with Vmp~18 volt "battery voltage" friendly panels).

    And why I suggest that folks 1) look at their loads closely--Solar power is not cheap, 2) do several paper system designs to get the basics, and 3) start to pick and price actual hardware and possibly go back to earlier steps if too expensive, does not work, etc.. And lastly 4) buy hardware.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • robert1701
    robert1701 Registered Users Posts: 12 ✭✭
    As I bought 10 of those 140W solar panels, I should get 1400W on a good day, so a MPPT controller it should be.
    With all panels parallel, it will almost be 25A, also on a good day.
    I will have to use the electricity mostly when the sun shines or I will have to place  more than a few batteries I think.

  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    edited May 2020 #9
    Since Vmp for your 140 Watt panels is ~62.3 volts... For a 12 or 24 volt battery bank, you need an MPPT controller to get even a fraction of the "true" panel(s') output power... PWM controllers are Array current in = Battery current charging:

    Vmp~62.3 volts, 2.25 Amps, then for a 12 or 24 volt battery bank, the charging energy for 10 panels in parallel series (assuming a generic PWM controller would not burn out with the high Voc from your panels):
    • 10 parallel panels * 2.25 Amps Imp = 22.5 Amps (PWM "perfect solar day/angle" harvest current)
    • 22.5 amps * 14.75 volts charging (12 volt flooded cell Lead Acid Batteries) = 332 Watts "ideal day peak" (12 volt bank)
    • 22.5 amps * 29.5 volts charging (24 volts) = 664 Watts "ideal peak" (24 volt bank)
    With a MPPT charge controller, roughly, the harvest on an "ideal-nominal day/time" would be:
    • 1,400 Watts Pmp * 0.77 typical panel derating = 1,078 Watts (panel derating and MPPT losses)
    • 1,078 Watts / 14.75 volts charging = 73.1 amps charging (MPPT @ 12 volt bank)
    • 1,078 Watts / 29.5 volts charging = 36.5 amps charging (MPPT @ 24 volt bank)
    Thin film panels are a bit different vs Crystalline Silicon panels--But the above is "close enough for government work).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • robert1701
    robert1701 Registered Users Posts: 12 ✭✭
    edited May 2020 #10
    So, than I'll have to find and order a 'decent' MPPT controller, most probably abroud, because, in all probability, nobody in my country uses and offgrid installation.
    (Some years ago our goverment subsidised installing a home solar installation connected to the grid. A few years later, a new government saw a pit in the budget as a result of this and decided that an additional €100 had to be paid annually together with of electricity Bill to cover this. So, People like me, who have no solar panel installation at all, are paying for the subsidised part of our neighbours' installation. Great!)
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Note, on my post #9... I made a typo, assuming your panels are all in parallel (not series).

    Actual array configuration does depend on the MPPT solar charger you eventually purchase.

    Your region (guessing on IP address) is not great for solar (Antwerp Belgium, fixed array, facing south):

    http://www.solarelectricityhandbook.com/solar-irradiance.html

    Antwerp
    Average Solar Insolation figures

    Measured in kWh/m2/day onto a solar panel set at a 39° angle from vertical:
    (For best year-round performance)

    JanFebMarAprMayJun
    1.38
     
    2.20
     
    3.03
     
    3.83
     
    4.49
     
    4.29
     
    JulAugSepOctNovDec
    4.29
     
    4.23
     
    3.29
     
    2.38
     
    1.50
     
    1.07
     

    Realistically, "good sun" is 3 or more hours per day... That gives you decent harvest from February through September. An example of a 1,400 Watt solar array (correctly connected with an MPPT solar charge controller would be):
    • 1,400 Watts * 0.52 off grid system with AC inverter typical efficiency * 3.0 hours of sun per day (long term average) = 2,184 WH per day
    Depending on the cost of power--Say $0.30 per kWH (higher US rate):
    • 2.184 kWH per day * $0.30 per kWH = $0.66 per day
    That is assuming you use 100% of your harvested energy per (March) day--Which you generally do not... You have to decide the cost of the system (emergency backup power outside of winter, summer cabin, etc.) vs the value to you.

    And yes, while government subsidies have really made solar panels cheap (mostly built overseas these days), Grid Tied solar, and green energy programs in general, have been on the back of subsidies paid by taxes and higher energy bills--With the subsidies pretty much going to the green energy companies that lobbied for the subsidies.

    In the USA, off grid homes usually do not get any subsidies, or smaller ones such as "no state sales tax" on solar components (5%-9% typical US state sales tax, but it does vary from 0% to 10%+).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • robert1701
    robert1701 Registered Users Posts: 12 ✭✭
    edited May 2020 #12
    I'm thinking about maybe making it a mobel installation. I then can use it at the summer cabine and somewhere else if I need it. I could make it foldable on a trailer and even put a generator on it in case the batteries die or for when there just isn't enough sun.
    This way I don't have to apply for a permit from the city. You need a permit for everything here.
  • robert1701
    robert1701 Registered Users Posts: 12 ✭✭
    I thought I could use this controller.
    The Victron Blue Solar MPPT 100/30
    Max. 100V 30A, but if I read the specs, it's only 440W at 12V it seems.

  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Permits for everything is always a pain...4

    Anyway, the spec. sheet says:
    1a) If more PV power is connected, the controller will limit input power.
    1b) The PV voltage must exceed Vbat + 5V for the controller to start. Thereafter the minimum PV voltage is Vbat + 1V.
    2) A PV array with a higher short circuit current may damage the controller.
    440 Watts is a "nominal" maximum output... But you can use a larger array if you do not exceed 35 Amps Isc-array.

    If you use our deratings:
    • 35 amps * 14.5 volts charging * 1/0.77 panel+controller derating = 659 Watts typical "max" cost effective array.
    • 440 Watts / 35 amps = 12.57 volt Vbatt
    12.57 volts seems to be a "low battery" charging voltage to define 440 Watts as the max output...

    I don't know anything about the Victron controller family (I am not in the business), but in general they seem to make good equipment.

    -Bill

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • robert1701
    robert1701 Registered Users Posts: 12 ✭✭
    Maybe it would be better to put some batteries in series and make a 24v or 48v system.
    I also found this online. An inverter and solar controller in-one and more:
    If I had loads of money, there would be no problem, but now I have to look for a good solution and it has to be cheap too.
    I still have no batteries also.

  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    It is hard to say... It could be an OK multi-function unit (AC inverter, AC charger, Solar Panel charger). There are some specifications that I have a quibble with--But it could still work OK for you (charging voltages seem to be a bit on the low side for flooded cell lead acid batteries). The DC stuff could be adjustable--I did not look for a manual. The solar panel input voltage--Need more details there. (website did not display well on my little Chromebook).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset