Solar Inverter Reliability

A grid-tied solar inverter performs a range of complex functions from the extraction of DC Power to managing the safety of the Solar Power Plant. It comprises 100+ electric components backed by firmware. In addition to the inherent build quality, the grid conditions and the environment in which solar inverters are operating have an impact on their reliability. In this blog, we discuss the importance of solar inverter reliability and general guidelines on how you can go about choosing a reliable solar inverter.

Why Inverter Reliability?

As per independent research by Electric Power Research Institute (EPRI) inverter failure accounts for ~50% of solar plant's lifetime maintenance cost. Typically a solar inverter company along with the support of an installer takes 1 week to 1 month time to fix an issue associated with a solar inverter. This leads to significant power loss and revenue loss for the end customer or project developer. A 2 -3 weeks inverter shutdown in a year accounts for almost 5% energy/revenue loss for the customer. If the product is not under service warranty, the customer has to pay for the service to both the installer and the manufacturer.

Complete Failure vs. Part Failure

The complete failure of a solar inverter rarely goes unnoticed as it will lead to a complete shutdown of the Solar Plant, and a significant revenue loss for the customer. However, part failure of an inverter that goes unnoticed might have a significant impact on the long-term production, and safety of solar power plants:

1. Errors - We have noticed that certain inverters trip at voltage ranges lower/higher than the voltage limits set inside the inverter. This leads to energy loss during peak/off-peak hours. Similar errors may not persist for a long period but will have an impact on power production

2. Deration of Inverter Power: Most of the string and central inverters experience efficiency deration with the increase in internal temperature. This tends to increase with age, as the effectiveness of cooling or heat sink goes down. This efficiency deration leads to power loss during peak sun hours.

3. Failures of components that are meant for safety: The failure of the DC arc detection, and dc insulation failure detection circuitry might lead to the long-term risk of fire and electrocution

Service for inverter failure

The effectiveness of service provided by inverter manufacturers is very important for both the end customer and the solar installer. Good quality solar inverters connected to the internet can be debugged remotely, and certain issues can be fixed through firmware updates.

A specific part replacement or a refurbished inverter replacement may not guarantee the complete remaining useful life/design life for the product. This is because a specific part failure may have an impact on other inverter components as well, and this will reduce the overall design life of the system. So when we are calculating lifetime cash flow projections for a solar power plant, it is better to factor in an inverter replacement cost after the inverter warranty period.

The response time and resolution time for service issues by inverter companies should be an important consideration for solar inverter selection.

How to ensure inverter reliability?

Follow standard design and installation practices

Following the design and installation practices as per the solar inverters installation manual will ensure the reliable operation of solar inverters. Proper sizing of surge protection devices and regular monitoring of the status of surge protection devices is very important.

Choosing a reliable manufacturer

All inverter brands are not inverter manufacturers, and all manufacturers don't have the same build quality. The extent of testing done by the manufacturer, and the warranty offered by them are indicators of reliability. The service network of the manufacturer and their response time to issues also matters. The credit rating of the manufacturer is also important when we consider long-term serviceability.

Choosing a suitable grid-tied inverter architecture

Solar grid-tie inverters are generally classified into string/central inverters, optimised string inverters and micro-inverters. In general, micro-inverters are considered to be more reliable than optimised string and string inverters. (Read our blog on different inverter architectures here)

Understanding the inverter design

The design of inverter components, its cooling mechanism and IP rating also play an important role in its design life. Enphase microinverter's attribute their long life to design aspects such as a fully potted IP67 enclosure, no moving parts, low voltage operation, and lowest heat dissipation per sq-mm of surface area.

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At Cares Renewables, we are focused on delivering quality solar solutions to our customers and partners. Please leave a comment, if you have any queries on this blog. Write to us at info@caresrenewables.com, for your solar requirement.