Download Module 8 Inverters

Fall 2009
Module 8
Inverters
Inverters
• Converts the DC power produced by the solar
modules into AC power used on the utility grid
History
• Inverters have been the weaker link in PV
systems
• Early inverters were unreliable
• Early inverters were inefficient which
penalized an entire system
Inverter Types
• Square Wave
• Modified square wave
• Sine wave
Square wave
• Step-function or “square” alternating
current output
– Considerable harmonic distortion
• For small resistive heating loads
Modified Square Wave
• Complex circuits used to switch DC into
AC.
• More appropriate for operating a wide
variety of appliances
• Still noise will be picked up by sensitive
equipment
Sine Wave
• High quality wave form
• Most common inverters today
• Little harmonic distortion
The wave…comparison
Inverter manufacturers
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SMA (Sunny Boy)
Fronius
Xantrex
Outback
PV Powered
Kaco
Enphase – Micro Inverters
The Guts
Some examples
Enphase Micro-Inverter
All Installed
Installing SMA
Optional Inverter Features
• Remote control operation and datamonitoring
• Load transfer switch-allows system to
meet critical loads during power failure
• Series and Parallel connectivity for
multiple inverters
• Individual module performance monitoring
Ideal Inverter Features – now
standard
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Maximum power point tracking (MPPT)
Low harmonic distortion
Near perfect Sine wave shape
Ground Fault Protection
AC/DC disconnects
Weatherproof enclosure
Specifying an inverter
• Grid Tied:Watts Output AC-computed STC
rated watts of PV panels
• Stand-Alone: based on peak load
• Input Voltage-usually between 75 and 480
VDC, called the window or range
– Insure that the voltage will not drop or exceed
this range because of climatic conditions or
inverter will not function
• Output Voltage:120, 240, 208, 480
• Frequency: U.S. is 60Hz
Specifying an inverter
• Grid Tied:Watts Output AC-computed STC
rated watts of PV panels
• Stand-Alone: based on peak load
• Input Voltage-usually between 75 and 480
VDC, called the window or range
– Insure that the voltage will not drop or exceed
this range because of climatic conditions or
inverter will not function
• Output Voltage:120, 240, 208, 480
• Frequency: U.S. is 60Hz
Grid Tied Inverter Sizing
• Sized based on the amount of watts we pass
through the system at any one time
– Size of inverter is the labeled watts
• an SMA 3000 is a 3000 watt inverter
– The most power that will pass through this inverter is 3000
watts
– If the output is 240 volts, the current will be 12.5 amps
» 3000W ÷ 240v = 12.5 amps
String Sizing Software
And sized by…
• PV system component package (grid tied)
• The Grid Tied PV system will be based on
other factors
– Budget
– Roof Size
– Rebate/Tax incentives