Technical
SOLAR INVERTER SELECTION CRITERIA

DEPAR SOLAR TECHNICAL ARTICLES

SOLAR INVERTER SELECTION CRITERIA, Central vs String Inverters (or Multiple Small Inverters)

 

Solar panels produce electricity as direct current (DC) and Inverters convert DC current to alternating current (AC) power that is used in our everyday devices or systems in businesses or at our homes.  Individual solar panels are connected in series to form strings.  When using a central inverter, the DC power produced from each string runs along wires to combiner boxes where they are connected in parallel with other strings.  From there, the DC power is then run into the central inverter and converted to AC power. When using string inverters, each and every string has its own inverter that converts the current to AC and let the power carry on its voyage. Here there is a list of various criteria whether to use a central inverter or multiple small inverters while deciding about our system design.

 

 

 

 

Central Inverter

 

 

String / Multiple Small Inverters

 

 

System Availability

 

Single failure results in loss of the whole or substantial amount of energy.

Single failure results in a small loss of output generated by the single unit.

 

Initial Cost

 

Lower

Higher

 

Installation Cost

 

Lower

Higher

 

DC Watt Unit Cost

 

Lower

Higher

 

Balance of System Cost

 

Higher

Lower

 

DC Wiring Complexity

 

High: Requires combiners, recombiners, and dc disconnects.

Low: Combiners and disconnects typically included with inverter.

 

AC Wiring Complexity

 

Low: Single AC Output

High: Requires AC collection system with panel board

 

Installation Weight

 

High: Requires heavy equipment, crane etc.

Low: Can be installed by two-man crews

 

Warranty Period

 

5 years: extensions available at added cost.

10 Years standard: extensions available at added cost.

 

Warranty Service

 

Onsite by trained technician

Replacement by installer

 

O&M Servicing

 

Whole system needs to be shut down for the service period.

Each string or array can be shut down for maintenance or servicing purposes.

 

Ongoing Maintenance

 

High ongoing maintenance cost because of cooling and air circulation.

Low ongoing maintenance cost. (No fans or air filters)

 

MPPT Accuracy

 

Single MPPT point for up to hundreds of strings.

Individual MPPT points for up to several strings.

 

Multiple Array Orientations

 

Not recommended

Individual Inverters (or MPPT input) for each array orientation.

 

Array Layout

 

Limited: all strings must be equal length

Each inverter can have different array configuration.

 

Multiple Solar Panel Types

 

Nor recommended

Different Solar Panel types can be used within a single system.

 

Subarray Fault Detection

 

Difficult

Easy

 

Monitoring & Scada

 

Difficult

Easy

 

Energy Yield

 

Good

Typically 1% or 1.5% higher

 

Performance (comparison)

 

Requires additional data acquisition hardware and software

Easy to compare output and performance of multiple inverters

 

Interconnection flexibility

 

Must be ordered for a specific grid configuration.

Configurable for multiple grid configurations.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

This Depar Solar Technical Article study can be used in your risk analysis / assessment for a feasibility study or can be a helpful piece of paper for your academic or business studies.
This article by Omer Muhtaroglu had been released on October 2013 (updated March 2017)

 

 

 

 

 

 

 

 

 

 

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