Some Important Parameters (Technical Aspects) Need To Be Compared Before FInalization of Any Make of Solar Grid Tie Inverters

Many Solar Designer asked to me in which parameters we can select the solar inverter so as to i am sharing my experience with others.

First of all as per site climate if the irradiation graph is parabolic curve(radiation vs. time) than Central/Monolithic inverter shall be used in comparison with Modular type Inverters.

Basic Parameters(Protection) Provided By Inverter Manufacturer:

DC Overvoltage, AC Overvoltage, DC Fuses, AC Short Circuit, DC Short Circuit, Frequency Out of Voltage, Voltage out of range, DC inverse Polarity, Ground Fault, Negative Grounding(GFDI), Insulation monitoring, HVRT, LVRT, Anti Islanding, AC output Breaker.

These all basic protection provided by inverter manufacturer but out of above these two, Insulation monitoring relay & AC output breaker type need to be confirmed from our end.

1) Output Breaker Type: Some manufacturer provided MCCB in place of ACB so please confirm this point from manufacturer itself. 

2) Insulation Monitoring Relay: Inverter is equipped with Insulation Monitoring Relay but please confirm the make of this relay. To save cost many manufacturer provided simple ABB etc. make relay in place of Bender realy which is more sensitive for insulation failure.

Apart from that below technical aspects is very important to freeze inverters:

1) Maximum Efficiency: Higher Efficiency will affect Higher generation

2) Auxiliary Consumption:Lower Consumption will affect  Higher Generation. This is divided into three sub categories which are:

• Check how many fans are provided with inverter to cool inverter and the consumption of it, if VFD is with FAN then surely you will save some amount of generation
• When inverter is running in the daytime at that time IGBT cards need some aux power, this is called Control Circuit Consumption. Some manufacturer plays in this they directly take this consumption from the DC Bus of the inverter and this extra power is not included in provided max efficiency of the inverter so please confirm with manufacturer.
• At night time inverter will be in sleep mode but taking some amount of power from Grid this is called Standby Consumption. 

3) Output Voltage: Due to Higher output voltage you can save some amount of cable runs from inverter to transformer so as to reduce cost.

4) Fresh Air Requirement(m3/h): This is required as low as possible to avoid any extra filtration unit for cooling purpose.

5) MPPT Voltage Range: Window of MPPT voltage shall be wide enough(550-950V). Many manufacturer provided with 600-850V in that case at higher temperature (at noon) series voltage will reduced say 580V as voltage is indirectly proportional to temperature then at this instance you will loose fare amount of generation so please check.

6) Temperature Derating : Check with inverter manufacturer graph of temp vs. output KVA of inverter so that you will know output KVA will start derating from which temp. Many manufacturer play with this case, they say output of inverter is 990KVA but from 25deg C  onwards output KVA will derated to say 900KVA upto 50deg C.

7) Shut off temperature: At which temp inverter will shut off means max temp rating upto which inverter will provided some amount of output in terms of KVA.

 8) Power factor(0.8 lead to 0.8 lag) & Reactive Power Compensation: Generally inverter is fixed at unity power factor but this shall be adjusted as per grid manually as well as sense grid and shall be automatically adjusted. This is very important aspect, belive me if inverter will feed reactive power to grid then u will loose some amount of active power generation and if in signed copy of PPA government officials mentioned that reactive power generation at our premises, which will directly feed to grid causing some amount of penalty so double loss will be there. Also note as inverter is directly connected to trafo and accordingly sense power factor at this level only, but at grid main meter power factor will be different in comparison with at trafo level because in between both(inverter trafo & main meter at grid), cable capacitance and trafo inductance is not included. For sensing power factor at main meter some manufacturer is providing reactive power controller which is connected directly in between inverter to main meter via RS485 cable to sense actual power factor of the plant for better reactive power compensation.

So that's all, this is my experience for selection of solar grid tie inverter, if any point kept as per your experience to finalize inverter please tell me, thank you.