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Inverter Technology
22 May 2014
When the sun hits a solar panel on your roof it produces Direct Current (DC); however, Alternating Current (AC) is the standard power needed to run electrical equipment in your home or business. An inverter is an electrical device that is designed to convert DC to AC. There are two key types of inverters used for solar power system installations; string inverters and micro-inverters.
 
STRING INVERTERS
 
A string inverter is the most conventional type of inverter used for photovoltaic arrays. It is a single unit (about the size of a meter box) which connects to one or more ‘strings’ of solar modules. All the panels are wired together – combining the output of the solar arrays – which is fed to the inverter, which then converts DC to AC and feeds the power to the house and the grid. Most string inverters have an efficiency of 95% or higher.
 
Diagram: Solar power system with a string-inverter.
 

MICRO-INVERTERS

Micro-inverters are smaller inverters mounted on the back of each solar module in an array. Each micro-inverter is rated to handle the output of a single module. They convert DC to AC on the roof and feed power to the house and the grid. 
 
Diagram: Solar power system with micro-inverters

 

ADVANTAGES OF STRING INVERTERS
 
Cost
A system with a string inverter is likely to cost less because there is only one inverter, whereas micro-inverters require multiple inverters. This is especially relevant when dealing with commercial and utility scale systems.
 
System Size
It is more practical to configure a larger system with string inverters as you would require far fewer inverters.
 
Reliability
String inverters are an established technology with proven reliability, while micro-inverters are a relatively new development and reliability is not yet proven. As micro-inverters are mounted on the back of panels on the roof, they are exposed to the elements. The inverter’s performance and life may be affected by these conditions.
 
Failure Rate
Inverters are the most common point of failure in a photovoltaic power system. Many micro-inverters introduce a higher chance of component failure. Replacing a single central string inverter is also far easier than replacing a micro-inverter behind a solar module on the roof.
 
Monitoring
PowerSmart’s string inverters come with an integrated monitoring display on the face of the inverter. Micro-inverters require a separate communication box that communicates with each inverter and monitors performance.
 
 
ADVANTAGES OF MICRO INVERTERS
 
Flexible Design
A micro-inverter system is more flexible as there is no string configuration required. Each panel is independent (with its own inverter), and therefore the modules within a single installation can be placed at different orientations without affecting output of the whole system.
 
Redundancy
The performance of the whole array is not affected when there is a loss of output from one panel (for example due to shading).
 
Safety
Micro-inverter systems are commonly considered safer for installers because there is no high voltage DC power.

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