Eternal Sun’s Large Area Steady State Simulators (LASSs) appear to represent a major advance in solar panel testing because they allow test labs to do a combination of things that they have not been able to do before.
First, explained Eternal Sun Business Development Manager Clemens Bauer, they allow climate-variable testing while the modules are exposed to light.
And, added CTO Stefan Roest, they are designed to allow continuous readings of the module’s performance in real time.
According to PV Evolution Labs CEO Jenya Meydbray, this would be the first test chamber on the market with both of these capabilities. Some test chambers, he added, offer a wiring option that makes continuous real-time climate variable readings possible, but only in a dark test chamber.
Eternal Sun is an outgrowth of research at the Netherlands’ Delft University, Bauer said. The goal of the research, Roest said, is to measure performance as exactly as possible under realistic conditions.
The company's marketing literature explains it this way: “The climate chamber solar simulator allows you to carry out I-V curve measurements to determine the basic parameters of your PV modules: power output, efficiency, open circuit voltage, short circuit current, resistances, etc. This can be done under various circumstances. Irradiance, temperature, and humidity can be changed by computer control. [...] The setup also enables light soaking, preconditioning and hot-spot endurance tests.”
As documented in GTM’s series on module testing, bankability rests on panels’ ability to withstand extremes of temperature, humidity, light, electrical load and weather conditions over time. According to Roest, Eternal Sun’s line of LASSs can accurately induce the condition extremes while providing the ability to read the modules ongoing, real-time performance under both the standard one-sun equivalent of 1,000 watts per square meter, as well as under the much more intense 1,366-watts-per-square-meter irradiation level.
Measuring every watt of performance reduces uncertainty for investors, Bauer said. The bankability of a module brand comes from the reduced risk that is proven in testing.
The climate chambers now in use by module test providers like Underwriters Laboratory (BRK:A) and Intertek (ITRK), Roest said, “cannot see how modules’ performance changes second to second.” The degree of precision provided by the Eternal Sun LASSs allows module manufacturers and would-be purchasers to see precisely when a module’s performance changes rather than whether it performs according to promise, for example, after 200 hours of humidity testing but not after 400 hours.
“There is no protocol,” Roest said of testing in Eternal Sun’s climate chamber. “You just keep the test running with all the factors and continuously monitor all the electrical parameters of the module and keep going until you get the data you need.”
“This can go as far as creating a performance matrix,” Bauer added, “giving indications on yields at all kind of conditions.”
Roest referenced an Eternal Sun simultaneous long-term performance and weathering test with Netherlands solar developer TNO that lasted 7,000 hours as evidence that the Eternal Sun climate chamber advances bankability evaluation of modules by making more accurate lifetime performance predictions possible.
Other module testers do not think lab performance provides conclusive lifetime service predictions. As TUV Rheinland’s Richard Bozicevich recently observed, “No lab tests necessarily reproduce what the module would be subjected to in the field.”
Accelerated laboratory testing methods are part of identifying bankability, according to Fraunhofer USA Center for Sustainable Energy Systems senior technical staffer David Meakin. “But does a test for 1,000 hours relate to one year, ten years or 1,000 years? Depending on the material, it can be any one of these. We understand some of the acceleration coefficients, but not all of them. The other part is what we observe in modules that have been in the field for a long time. Sometimes we have to rely on accelerated testing because we don’t have twenty years to wait to see what happens.”
The service life question is different, said PVEL’s Meydbray, adding that more data was provided, but it is not necessarily an improvement on the data quality in a way that illuminates the question of service life.
Eternal Sun markets its LASSs as well as its testing service. The test chambers are available in two standard sizes, 0.4 meters by 0.4 meters and 1.5 meters by 1.5 meters. The larger one, at approximately $100,000, is priced competitively with standard flash-testing devices, according to Bauer.