Selection of Inverter for Solar Power Plant

Inverter:- Inverters are important part of any solar installation; they are the brains of the solar plant. Although the inverters main job is to convert DC power produced by the solar panel into usable AC power. Inverter having inbuilt monitoring system .This intelligent solar inverter also matches the required frequency, volt etc with electrical grid to run our load to be used at household and commercial premises.

As in practically solar field during cource of operation of inverter it takes normally 15-30secs to trace grid parameters like voltage ,Frequency etc after that it starts generate AC power. These inverters are fully automatic and intelligent inverter with inbuilt protections which protect the complete solar system and solar panel from any fault.

For Selecting Inverter go to the Link: https://drive.google.com/drive/folders/1LKiy_WragGqidvIxn9ePwIrMbzMq3gRt?usp=sharing

• Selection of Inverters:

• Before buying solar inverter, few points should be clear.

• Types of Inverter

• Technology – PWM or MPPT

• Feature – Remote Or Web Monitoring

• Brands – Delta, Luminous, SMA, Huwaei etc.

• Warranty – 2 years or 5 years

• Types of Inverter:
• 1.      String Inverter(SCB/SMB not required & also DCDB not required ,String inverters are most preferable now a days).

• 2.      Central inverter(SCB/SMB is required & also DCDB required , go to the technical parameter almost all parameters are same as compare to the String Inverters but main difference is that the Central Inverter having only one MPPT option where String inverter having multiple MPPT option).

• 3.      Micro inverter(This is the latest technology in solar sector. The main advantage of micro inverters in that each panel is monitored and optimized individually to generate maximum power. Solar panels can generate different amounts of power due to a number of reasons such as shading, dirt and mismatch etc.).

• 4.      Hybrid inverter(Traditionally the term hybrid referred to two generation sources such as wind and solar but more recently the term “Hybrid solar” refers to a combination of solar and battery storsge which unlike off-grid system is connected to the electricity grid).

• Technology – PWM or MPPT

In PWM technology the current is drawn out of the solar panel  at just above the “Maximum power current” of panel but output voltage as the output inverter voltage, whereas

With an MPPT controller the current is drawn out of the panel at the panel “maximum power current” and voltage as take as “Maximum Power Voltage”.(think of an MPPT controller as being a “smart DC-DC converter”)

Let us consider an Example of Znshine Solar-335watt module ,the technical parameter specification is given below in the image

     From the Module “Maximum Power Current”(Imax)= 8.91 A

                                      “Maximum Power Voltage”(Vmax)=37.6 V

                                       “Maximum System Voltage”=1500 V

      And also take a Inverter of Huawei model no- SUN2000-185KTL-INH0

                                             “Maximum input voltage(DC)”=1500 V

                                              “Full-load MPPT voltage range(DC)”=880-1300 V

                                               “Rated input voltage(DC)” =1080 V.

                                                “Rated output voltage(AC)”= 800 V

Here a string having 32nos. of module are connected in series then output Imax=8.91 A & Vmax=1203 V

Case-1:(For PWM technology based inverter)

Output Power =9.10A×800 V=7.28 kw

Here amps will be slightly higher than the maximum power amps, say 9.1A

Case-1:(For MPPT technology based inverter)

Output Power =8.91 A×1203 V=10.74 kw

However this is overly optimistic as the voltage drops as temperature increases; so assuming the panel temperature rises to say 30°C above the standard test conditions (STC) temperature of 25°C and the voltage drops by 4% for every 10°C, i.e. total of 12% then the power drawn by the MPPT will be 8.91A × 1058 V = 9.43 kw i.e. 22% more power extract than the PWM technology.

   Protection of Inverter:

1.      Input DC switch

2.      Input reverse connection protection

3.      PV string fault detection

4.      Anti-islanding protection (Anti-islanding protection is that a purely grid-tied PV system will only operate when the power grid is active. If there is a power outage the inverter will shut off and although the solar panels may still be generating power)(

5.      DC surge protection  (It protect surge current and voltage that come from DC side)

6.      AC surge protection (It protect surge current and voltage that come from AC side)

7.      Residue current monitoring (RCMU) (It detect these currents and disconnect the circuit from the source automatically when the values of these residual currents exceed the predefined limits)

8.      Overvoltage category

9.      Output overcurrent protection

10.   Insulation resistance detection.

String inverter

Fault in Inverter

Fault in Inverter