My PV project and Inverter ON/OFF control by the load.

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remtzi
remtzi Registered Users Posts: 3
in Solar Beginners Corner #1
Dear forum members,
I decided to build 12V PV (off-grid) system on the roof of my house. The PV stuff in my country is rather expensive. I bought less expensive (but certified) equipment directly from China. I am going to install the system in the spring. I made a small cheme and would like to show you and ask for your opinion. The system consists of:
1. 16 x Sungold Solar SGM-90W monocrystaline 17V/90W solar panels;
2. 2 x WELLSEE WS-MPPT60 solar MPPT 12V 60A controler;
3. 1 x PROSTAR DTA 6000A 12V 6000W Inverter;
4. Self made Inverter ON/OFF control by the 220V load;
5. Traction lead acid battery pack 12V/400Ah(I am going to buy it from my country)

Attachment not found.

The total PV theoretical power is 1440W. I expect to supply the battery about 1000W. One charge controller is not able to supply the total current and I decided to separate the panels in 2 groups, 8 panels each. In the group the panels are connected in parallel. Each of the groups is connected to the PV input of the MPPT controller. The outputs of the controllers I am going to connect in parallel to the battery.
I need to supply AC load with power about 600W for 5 hours in the evening.
The inverter 12V/6000W consumes about 2A without load. It is rather high consumption and I decided to build a control circuit which will OFF the inverter when the load is below 15W. Similar approach is used in some industrial inverters. I add Undervoltage protection of the battery. The inverter has such a protection but In my device I can adjust the ON and OFF voltage thresholds. I assembled the scheme on an experimental board and it works OK.
Attachment not found.
I adjusted the resistor R5 so when all the home devices are in Standby, the inverter is off. The power is about 15W. When I turn on a CFL lamp or something else, in couple of seconds the inverter turns ON. When I remove the load, in couple of seconds the inverter turns OFF and devices are powered from the power grid. The problem was to shild the sensing transformer from the AC magnetic field of the AC relay-it swithched the AC load between the power grid and the inverter output.
I like this forum very much and would like to know your opinion before I start building my PV system.
Best regards
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Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #2
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    Re: My PV project and Inverter ON/OFF control by the load.

    The Vmp=17.0 volts is a touch on the low side. And the Wellsee controllers do not (appear to) operate in a "real and useful" MPPT mode.

    I would set the system up as is... And if you cannot reach peak charging current needed on hot days to keep the battery bank well charged... Then you should reconnect the solar array in series parallel (at least 2 panels in series for Vmp>34 volts) and get a good quality MPPT type charge controller.

    If it is difficult for you to get parts--You may want to get one or two spare PWM controllers (non Wellsee) for emergency spares. I am not sure how well these controllers will work for you in the long term.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • n3qik
    n3qik Solar Expert Posts: 741 ✭✭
    #3
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    Re: My PV project and Inverter ON/OFF control by the load.

    It would be smart to also put a fuse inline with each panel. And some at the battery/inverter.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #4
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    Re: My PV project and Inverter ON/OFF control by the load.

    nice to see somebody designing their own stuff. i do think you will have a bit of excess pv capacity for that battery. usually the max is about 13% that we recommend, but some can take higher current rates and you should check with the battery manufacturer on that max. in any case a high charge rate, if capable, will induce higher maintenance as you will need to add distilled water more often and more cleanings of the battery tops.
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