Comparison of String and Microinverter

Summary

A comparison of string inverters and micro inverters in the summary tab, highlighting the key differences between these two types of inverters and how these differences reflect their distinct functionalities and characteristics. The summary also includes an explanation of the terminology related to inverters used in the tab, providing clarity on their application and significance.

String Inverter	Micro Inverter

Key Differences

• Reflection (IAM) - Slight difference between string and micro inverter seen above of .1%. A micro inverter manages the Mppt of an individual (or small group) of solar panels and can react independently to variations in incident light angles caused by shading, tilt, or other factors. String inverters keep a consistent Mppt across all panels and thus inconsistencies in panel placement and angles of incident from perhaps an uneven roof will cause more losses
• Module Mismatch - Heavily influenced by string inverters as soiling or shading can affect the total systems power output. Negligible for micro-inverters. 
  • Module mismatch is set at a constant 2%, aligning with SAM's default value, which is intended to account for typical variations in real-world conditions. One might wonder why module mismatch isn’t set higher, given potential shading or other factors. The 2% represents the average variation between panels due to factors like manufacturing differences. Even when shading occurs, it is often assumed that all panels experience similar conditions, resulting in a relatively uniform performance loss across the array.
• DC-Wiring - DC wiring losses refer to the energy lost as electrical current travels through the wires connecting the solar panels to the inverter. The string setup has longer wire runs due to the centralized inverter. The increased resistance from longer wires can lead to greater voltage drops
• AC-Inverter Efficiency - The inverter efficiency deviates from model to model however string inverters are generally more efficient. String inverters are engineered to manage higher power levels as it is based from a centralized unit and larger inverters generally have a cooling system

Terminology

MPPT: Maximum power point tracking involves finding an ideal voltage that maximizes the power output of the panel. This is usually 75% of the VOC (Open circuit voltage).

VOC (Open Circuit Voltage): The maximum voltage produced by a solar panel when it is not connected to any load. It indicates the potential voltage under ideal sunlight conditions and is affected by temperature and the panel's design. Voc is crucial for ensuring compatibility with inverters and other system components

Irradiance: Power of sunlight reaching a surface per unit area, typically measured in watts per square meter (W/m²). It represents the amount of solar energy that strikes a photovoltaic (PV) panel's surface at any given moment and hence relates to energy produced

Shading: Physical blockage of sunlight. Since string inverters are connected in series, shading on one panel can significantly impact the performance of the entire string, making these systems more affected by shading than micro inverter systems.

Soiling: Refers to dust and dirt accumulation on solar panels as it reduces light absorption and thus efficiency.

Module Mismatch: Essentially the ‘weakest link effect’ for solar panels in which the performance of the entire string is determined by the weakest panel.