- Types of Solar Inverters
String Inverter
A string inverter connects several solar panels in series to form a “string.” Multiple strings can then be connected to the inverter.
Advantages:
Lower cost than microinverters
Simple installation and maintenance
Good efficiency
Suitable for residential and commercial systems
MPPT can optimize different strings
Disadvantages:
If one panel/string has a problem, that string’s output can be affected
Shading can reduce production
Usually installed in a location away from individual panels
Central Inverter
A central inverter is a large inverter that receives power from many PV strings and converts the combined DC power into AC.
Advantages:
Suitable for large-scale solar plants
Lower cost per watt for large installations
High power capacity
Easier centralized maintenance
Disadvantages:
A failure can affect a large portion of the plant
Requires higher-voltage DC cabling
Shading/mismatch can affect groups of panels
More difficult to install and replace because of its size
Microinverter
A microinverter is installed with an individual solar panel, converting that panel’s DC electricity into AC.
Advantages:
Each panel works independently
Better performance with partial shading
Panel-level monitoring
No high-voltage DC running through the system after each panel
Good for roofs with different orientations
Disadvantages:
Higher cost
More electronic devices on the roof
Maintenance/replacement can be more difficult because equipment is installed near the panels
- On-Grid vs Off-Grid Inverter
On-Grid Inverter
An on-grid (grid-tied) inverter connects the solar PV system to the utility grid.
Solar panel → DC → Inverter → AC → Home/Grid
Normally, it does not provide backup power during a grid outage unless the system has special backup/islanding functionality and appropriate equipment.
Off-Grid Inverter
An off-grid inverter is used in a system that operates independently of the utility grid.
Typical system:
Solar panel → Charge controller/inverter → Battery → Loads
A battery is generally required to supply energy when solar power is unavailable.
Hybrid Inverter
A hybrid inverter can combine solar, battery and grid operation.
Solar + Grid + Battery → Inverter → Loads
It can be useful when you want both grid connection and battery backup.
- Important Solar PV Terms & Full Forms
Abbreviation Full form Meaning
PV Photovoltaic Converts sunlight into electrical energy
DC Direct Current Current produced by solar panels
AC Alternating Current Current used by most household/grid loads
Voc Open-Circuit Voltage Maximum voltage of a PV module/string when no load is connected
Isc Short-Circuit Current Current when the PV output is short-circuited
Vmp Voltage at Maximum Power Voltage at which the panel produces maximum power
Imp Current at Maximum Power Current at which the panel produces maximum power
Pmp Power at Maximum Power Maximum power produced at the MPP
MPP Maximum Power Point Operating point where PV output power is maximum
MPPT Maximum Power Point Tracking Inverter/controller function that keeps the PV system near its maximum-power operating point
MCB Miniature Circuit Breaker Protects circuits from overcurrent/short circuit
MCCB Molded Case Circuit Breaker Higher-capacity protective circuit breaker
SPD Surge Protective Device Protects equipment from transient voltage surges
PWM Pulse Width Modulation Method of controlling electrical power using pulses
STC Standard Test Conditions Standard conditions used for PV module ratings
BOS Balance of System All PV-system components other than the modules themselves
D.C. Direct Current Same as DC
A.C. Alternating Current Same as AC
Important relationship
The basic power equation is:
P = V × I
At maximum power:
Pmp = Vmp × Imp
For example, if a panel has:
Vmp = 40 V
Imp = 12.5 A
Then:
Pmp = 40 × 12.5 = 500 W
- Voc, Isc, Vmp, Imp — Easy Way to Remember
Think of a solar panel like this:
Voc → voltage with NO load
Isc → current with SHORT circuit
Vmp + Imp → normal operating point for maximum power
And:
MPP = Vmp × Imp = Pmp
A typical panel’s Voc and Isc are not the same as its operating voltage and current.
- MPPT vs PWM
MPPT — Maximum Power Point Tracking
MPPT continuously adjusts the operating point so that the solar array can extract as much available power as possible.
MPPT = better utilization of available PV power
PWM — Pulse Width Modulation
PWM is a switching/control technique. In solar charge controllers, a PWM controller generally connects the panel more directly to the battery, so the panel voltage is pulled closer to battery voltage.
For many modern PV systems, MPPT charge controllers provide better energy harvesting than PWM controllers, especially when the PV voltage is significantly higher than battery voltage.
- MCB vs SPD
MCB
MCB = Miniature Circuit Breaker
Main purpose: overcurrent and short-circuit protection.
SPD
SPD = Surge Protective Device
Main purpose: protection against voltage surges, such as transient surges caused by lightning or switching events.
So remember:
MCB → overcurrent/short circuit
SPD → surge/overvoltage protection
- String vs Central vs Microinverter
Feature String Central Microinverter
Size Medium Large Very small
Installation String level Plant level Panel level
Typical application Residential/commercial Large solar plants Residential/commercial
Panel-level MPPT Usually no No Yes
Shading tolerance Moderate Lower Excellent
Cost Medium Low per watt at large scale Higher
Maintenance Relatively easy Centralized Panel/roof level
Failure impact String/inverter section Large section Usually one panel
Monitoring String/system Plant/system Panel level
Easy memory trick
Central inverter = MANY panels → ONE BIG inverter
String inverter = GROUP of panels → ONE inverter
Microinverter = ONE panel → ONE small inverter
- Very Short Revision
Before an interview or exam, remember these:
Voc = Open-circuit voltage
Isc = Short-circuit current
Vmp = Voltage at maximum power
Imp = Current at maximum power
Pmp = Maximum power
MPP = Maximum Power Point
MPPT = Maximum Power Point Tracking
MCB = Miniature Circuit Breaker
SPD = Surge Protective Device
PWM = Pulse Width Modulation
PV = Photovoltaic
DC = Direct Current
AC = Alternating Current
On-grid = connected to utility grid
Off-grid = operates independently of utility grid
String inverter = several panels/strings connected to an inverter
Central inverter = large inverter for many PV strings
Microinverter = inverter at individual-panel level
