Inverters are crucial components of a solar power plant—converting the DC power from PV modules to AC power for the utility grid and also typically serving as the ‘central intelligence point’ of a project. “Inverter performance, operation and reliability impact project value and return on system investment,” says Michael Mills-Price of DNV GL’s product qualification and testing team. “Inverter testing provides a benchmark to help solar project financiers, developers and EPCs compare and select inverter products.”
Solar inverter standards vary globally and by geographic region. Mills-Price explains that most inverters go through third-party testing only for conformance to these safety standards. “Most nationally recognized testing labs focus on evaluating inverter products for safety—that it’s not going to result in electrical shock or fire,” he said.
Manufacturers also self-test their products, but Ray Hudson, solar service leader at DNV GL, said testing varies significantly from one manufacturer to another. “Each manufacturing facility has different levels of capability and skill.”
DNV GL provides global independent solar advisory and testing services for the entire solar project life cycle. This includes its third-party inverter testing which was launched last October. DNV GL’s solar product qualification team (formerly PVEL) tests residential and commercial inverters in its Berkeley, California, laboratory. Using methods such as thermal and accelerated life testing in environmental chambers, the team analyzes whether or not an inverter is likely to meet the life span its manufacturer has estimated.
Unlike most nationally recognized testing facilities, DNV GL goes beyond the laboratory qualifications with its field testing facility (which is located at the former PV-USA facility) in Davis, Calif. Here, inverters are installed and tested directly in the field, experiencing “under the sun time” and their operation and performance is assessed while connected to an actual solar array.
“These tests are meant to complement the safety and interconnection assessment of other nationally recognized labs,” Mills-Price said, referring to tests for adherence to UL 1741, IEEE 1547, and all of the international IEC standards.
“A number of inverters have gone through our testing service since it was launched during Solar Power International last year,” Hudson said. “We’ve seen some interesting findings through testing on actual systems that have not shown up in laboratory tests.”
Qualification time can vary depending on system size and other factors, but typical inverter testing at DNV GL takes six to eight weeks if the lab and field testing occur in parallel.
One caveat, Mills-Price warns, is that inverter tests are not meant to put an exact date on inverter failure or predict exactly how much energy will be harvested for a given solar installation. There are a number of other factors that play into that larger equation. Instead, he said testing helps reduce the risk of out-of-the-box failures while providing a series of metrics to analyze performance against what the manufacturer provides in their data sheets. “These tests provide a means to reduce operational and management risks associated with PV systems,” Mills-Price said.
Mills-Price also points out that inverter reliability and performance is only going to be stretched with emerging interconnection requirement changes. “We’re requiring inverters to ride through a number of transient events much more than two or three years ago,” he said. “We’re also asking them to provide reactive power support under these conditions and pushing them on the AC-grid and connected side. This only increases the importance of evaluating inverter reliability and performance.”
As new inverter manufacturers enter the market, and others consolidate or exit, additional independent testing can help minimize project risk, Hudson adds. “Testing can provide confidence that the inverters you’re using have the functionality you expect,” he said. “We view that as beneficial to the financial and technical success of solar power plants.”
5 levels of inverter testing
DNV GL’s inverter qualification services includes five levels of testing:
Level 1: Functionality—Will the inverter work?
Level 2: Safety—Can the inverter be operated safely in the field?
Level 3: Performance—Will the inverter perform as expected when connected to a solar array?
Level 4: Robustness—Will the inverter meet expectations in a real-life field application?
Level 5: Reliability—Will the inverter last?
Did you know?
DNV GL specializes in global independent solar advisory and testing services for the entire solar project life cycle. This includes feasibility studies, energy production assessment, design review, construction and commissioning monitoring, support in grid interconnection, providing system design assistance, supporting environmental and permitting, and performing asset management services after projects are complete. DNV GL also offers technology reviews for inverter, module, mounting system and tracker manufacturers to support the bankability of their components. DNV GL supports buyers and investors through rigorous testing for both PV modules and inverters, as well as, product certification and batch testing for specific projects.
Listen to the full interview in this podcast.