SOLAR INVERTER SELECTION CRITERIA

Technical / SOLAR INVERTER SELECTION CRITERIA

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)