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Why micro inverters are future?


Short and briefly



  • allows to install small PV systems, solar electricity already from single solar panel
  • allows different PV panels orientation, extrem flexible in system design
  • allows simultaneously usage of different PV panels technology (Poly/Mono/a-Si...)
  • best system performance under partial shading (affects single PV panel)
  • best system performance under long cable distances (low DC losses)
  • easy and quick system expansion, possibly at any time


The micro inverters are an excellent solution for small PV systems up to ~3kWp. Above this power-class an string-inverter will be probably cheaper, today and in the future.


Because the micro inverters and in general the regulating technology ist the most important component in the whole PV solar system, we offer only proven, solid and high quality products. Exclusively as official and authorized distributor (eg. Power-One, AEconversion).


We offer micro inverters in 230V/50Hz and 110V/60Hz typology. Ask us in case of individual requirements. We care about world-wide customer requirements, inter alia from Mongolia / Iran / Turkey / Switzerland / Iceland / Caribbean / USA...

 

Power-One Micro Inverter



 

If we can be helpful, contact us.

International Sales Team

PVshop.eu

 

 


 



Technical aspects



While designing PV system based on micro inverters, you have to consider two important aspects:


  • the system safety (grid and inverter)
  • the system efficiency

 


Safety (local grid)



system safety means mainly automatic disconnection of PV inverter, when missing the local grid (50Hz synchronization). The inverter will try within short period to gain the 50Hz frequency in the local LV grid, and if this will be not possible (due technical work, failures etc.) the inverter automatically disconnects itself from the local grid, as protection against creation of dangerous power-islands. This type of protection is also called an anti-island protection in the local LV grid. If the grid synchronizations 50Hz comes back, the PV inverter begins to transmit 230V/50Hz electricity into home/office/factory or directly into the local LV grid, depending on system design.


This kind of protection is generally regulated by national LV grid operator and its regulations and requirements (parameters). The most common requirement is the two-stage disconnecting structure within the micro inverters:


  1. internal disconnector (often based on internal software)
  2. integrated MSD (Monitoring Switching Device) physically galvanic disconnector.

The MSD is the most important disconnector. As an physical and galvanic disconnection device, subject to the national and local LV grid requirements and parameters. The MSD can be already integrated within the inverter (according country specific parameters, so called Grid-Codes) or will be additionally required as an external device within the whole PV system. That may depends on the micro-inverter (model and its equipment) and the local LV grid regulations.


Safety (Inverter)



It is not allowed to exceed the max DC input voltage of the inverter. That can destroy every inverter. The most dangerous here is the Voc, which may appear while inverter disconnected or not working. The inverters max DC input voltage, corresponds to by 10-15% reduced Voc as defined in the PV panel datasheet.


Example: if the inverters max. DC input voltage is 45V. The proper max connectable voltage (from PV generator or single PV panel) should be reduced by 10-15% of the given Voc in the panels datasheet. The reduction depends on PV panel temperature coefficient and increases under low temeprature (then e.g. instead of defined in the datasheet 37Voc may appear 41Voc and more).


So for an inverter with 45Vdc max input voltage, an panel with 37Voc would be an excellent solution.


Several combinations in different cable wiring (in series or parallel) allows to create different PV generators (single or dual panels based). But the DC input voltage, can never exceed, the allowed inverters parameters (Vdc max). 



Efficiency



Efficiency come from the miro-inverter parameters and its technology, an important aspect here is the inverters MPPT-starting voltage range. An PV panel should be choosen this way, that inverters input MPPT-starting voltage range, will be reached by the PV panel so quick as possible.


That can be problematic if you choose eg an 180Wp PV panel to a 250Wdc micro inverter. That would be an mismatching in the system efficiency and it will work, but the micro inverter will reach probably very seldom his max efficiency. And in case of 60-80Wp PV panel the required starting input voltage will be never reached.


In turn an slight oversizing the micro-inverter, eg. 260Wp PV panel connected to an 250Wdc micro-inverter is an quite smart solution, if not exceeding the allowed voltage and current, within the inverter. Optimal for each inverter is to bring him at its maximum power, where his efficiency is the best and highest.


Against slight exceeding the power (Wdc) and current (Idc) PV inverters are able to protect them self (goes into the derating), but against exceeding the max allowed voltage (Vdc) not.





Short description of the micro-inverters advantages




Small PV systems


The Micro-Inverter is ideal for the use in small PV-systems, since it starts converting solar energy from just a single module.

 



In contrast, the string-inverter typically requires 200V input voltage, which has the consequence, that at least 8 modules are required to build up an classical PV-string.




Different PV panels orientation


With micro inverters, a PV-system is an efficient system even with different module orientations. Because of the individual connection of each micro inverters with the PV-modules, the highest possible performance (individual MPPT) can be achieved. The modules operate independently from one another. 





Thus, the total return is much higher compared to systems using string-inverters because there, the module performing the worst power, limits the performance of other modules and the whole PV-string.




Different PV panel types and technology


At different modules, which have different benefits from each module, the maximum possible power is taken (individual MPP tracking). With a micro-inverter modules which operate independently and the total yield is therefore significantly greater than that of a string system.

 
 



System expansion


With little effort, each system can be transformed and expanded with additional modules depending on needs and available capital. 



It does not matter whether the PV-system consists solely of micro inverters or the new PV-module is added to a string-based system. With the micro inverter, you have all the freedom to expand your system at any time.

 
 



Partial shading


The micro inverter will increase the energy harvested, by eliminating sources causing high energy losses. In case of a shadow, snow, dirt, leaves or other obstructions on a PV-module in a system using central- or string inverters, the energy harvest of the entire string drops dramatically. Due to the individual connection in micro inverter based systems, a shadow on one module does not affect others modules or the whole string and therefore has only a minimal effect on the systems energy yield. In addition, in systems using micro inverters, the PV-modules are not affected by the tolerances of other modules, letting each operate at its maximum. In conventional systems, the central- or string-inverter perform MPPT for the whole PV generator, leaving some modules working below their Maximum Power Point. Micro inverters vary the electrical operating point of each module individually, maximizing the available power from each module.




 

Long distances (small losses)


For string systems, large distances between the modules lead to high losses in the PV lines. In systems with micro inverters, the voltage is transmitted with lower losses. 





The high DC current in an PV system must first go through a long path through the system until it is converted in the string inverter into AC current. Due to the long distance and the high current, a lot of the performance is lost.



 


The DC current from PV module is converted directly at the module and transmitted as AC current. Due to the high voltage, hardly any AC power is lost.






 

If we can be helpful, contact us.

International Sales Team

PVshop.eu



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