CHOOSING THE RIGHT INVERTER
By Bryan Thomas (Guest Editorial)
When purchasing a PV package, don’t overlook the importance of a top quality string inverter
Modern residential and small commercial Photovoltaic (PV) systems can be confusing. It can be difficult to understand what all the components are, what each component’s role is and what features matter most. But a small PV system can be grouped into three primary categories.
PV Solar modules: These capture sunlight and convert it to direct current (DC) electricity.
PV String Inverter: This component converts the DC electricity to alternating current (AC) household electricity and communicates system information to the end user.
Balance of System (BOS) Components: These include PV module racking, conduit, disconnects and other infrastructure.
Many solar modules today are only differentiated by their physical dimensions and power output—or specialty features such as the product’s integration with a roofing system. The BOS components also are relatively static in terms of their impact on overall system performance. This leaves the string inverter as the most flexible variable in a PV system.
Recognizing this, purchasing the right inverter is an important step in the solar PV process. The three key factors in a string inverter are reliability, efficiency and access to the unit’s performance data.
Reliability. Consider the reliability track record of the inverter manufacturer. Fancy, long warranties are a nice perk, but if the company isn’t as old as the warranty, proceed with caution.
Efficiency. Next, compare the inverter’s California Energy Commission (CEC) weighted efficiency percentage. This efficiency measure was developed by the CEC, and is the standard for measuring how efficient an inverter is at inverting DC electricity into AC electricity. A lower number indicates that more solar energy is lost to heat and not converted to AC electricity. Today, string inverters can and should achieve 97% CEC efficiency at a minimum—meaning you need not settle for lesser performance.
Access to Data. Finally, don’t forget to consider how you will access the inverter’s performance status and keep track of the PV system’s energy production information. The latest string inverters can be monitored for free from various Web sites. For example, Advanced Energy has integrated ZigBee wireless monitoring. Installation consists of making a quick connection with a ZigBee wireless gateway from the user’s broadband internet. Inverter production information and system status is then presented on
MyPVPower.com, completely free.
The PV string inverter is by far the most critical component of a PV system and has seen an incredible evolution in reliability, performance, and system design over the last 10 years. When designing any PV system, be sure to evaluate the string inverter based on reliability, efficiency and access to inverter performance information. GB
About the Author: Bryan Thomas is a product manager for AE Solar Energy (
www.aesolarenergy.com).
62 01.2012
www.greenbuildermag.com
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