Experts with a sense of tradition

Since May 1982, the Laboratory of Energy, Ecology and Economy (LEEE) has investigated how energy, ecology, and economics can be most effectively integrated. Its annual outdoor solar module measurements have made LEEE an institution of international importance to the PV industry. However, as they often produce different test results than module manufacturers, and since they publish these conflicting figures, LEEE employees are not always met with the greatest enthusiasm. 

© PHOTON International. Yellow in the line of duty: Many of the 20-year-old modules in the 10 kW solar power system have built up a conspicuous yellow film over the years. Yet they still function as well as before.

The »LEEE News« is definitely not an imposing publication. Even so, when the inconspicuous pamphlet comes out every few months, PV planners pay attention.

The »LEEE News« provides a short summary of topics that are intensely discussed at many industry conferences: the results of outdoor module tests conducted on the roof of the LEEE. Currently, 12 modules -- five with polycrystalline silicon, four monocrystalline, two amorphous, and a CIS variety -- are under examination. And, unfortunately, as is often the case, the first published results come across like a revelation. The power ratings for modules provided by manufacturers are drastically different from the control measurements (see table).

The cause for this discrepancy between product rating and reality lies in the peculiarities of the market. Power remains the deciding characteristic of a solar module. But it cannot be measured with total accuracy, and more importantly, there are always slight variations within a module production series, even if exacting care is taking during the production process. As purchased modules usually deviate negatively from their rated power, there is increasing suspicion that module manufacturers consciously »fudge« their numbers to increase profits.

«Typical planners do not have the chance to test their modules,« says Domenico Chianese, current director of LEEE. »We provide them with information they can use to orient themselves.« Although LEEE is not the only laboratory that tests solar modules in outdoor experiments, no one has been at it with such comprehensiveness and for as long as this group of Swiss scientists. Moreover, nobody but LEEE publishes its results along with the names of the module manufacturers.

Module tests are just one aspect of LEEE's work; the real objective of the laboratory is to conduct scientific research, not act as a consumer protection agency. However, it is a tradition of the Lugano laboratory to strive for the integration of theory and practice.

	©  LEEE-TISO   Just a few rooms in the extensive complex of buildings at the Scuola Universitaria Professionare della Svizzera Italiana (SUPSI) serve as LEEE-TISO's headquarters. However, to compensate, the photovoltaic experts have spread themselves out on the complex's roof, where solar modules are everywhere.

The laboratory in its present form was established in 1979 as an initiative of the energy and environment authorities in the Swiss canton of Tessin: »Ticino Solar« (TISO) is dedicated, through the use of its grid-connected solar power plant, to demonstrating the practical possibilities of PV as well as research. The Swiss federal government provided financial support, and on May 13, 1982, an on-grid system, the first of its kind in Europe, came on line. The system of 288 Arco Solar ASI 16-2300 polycrystalline modules has a power of 10.65 kW (an additional 252 modules with 9.32 kW were added in 1992). In 1985 the Swiss Federal Office for Energy (BfE) agreed to provide further financial aid for a long-term study of the 10 kW system, and as early as 1987, the Swiss scientists constructed a 4 kW system with thin-film modules - also financed by the BfE.

The installation of the system 20 years ago not only marked the official birth date of TISO, but also the beginning of PV applications in Switzerland. Today, the still small institute, with just five permanent staff members, is organizationally and physically located in the Scuola Universitaria Professionare della Svizzera Italiana (SUPSI). This university is the home of LEEE, with which TISO was combined as one of two sub-departments in 1999. The majority of the current annual LEEE budget of around 700,000 CHF ($540,000) does not come from fixed grants (the Canton of Tessin, as the supporter of SUPSI, covers a third of the budget), but rather from third-party funds of different contractors.

© PHOTON International

The LEEE-TISO module test facility en detail.

comprehensive examination of TISO's now 20-year-old PV system. And the cheerful final results of the MTBF study were that although the modules have yellowed over the years, they still produce a healthy dose of electricity and will probably continue to do so for another 15 years (see PI 5/2002, p. 28).

The unexpected results of the inspection surprised many experts. But a comparison with the compulsory climatic test according to IEC 61215 produced several inconsistencies. The test's prescribed 1,220 climatic cycles between -40 and 85°C, as well as the 6,000 hours below 85 °C at 85 percent humidity, did not cause any significant damage to the laminate that encapsulates the solar cells. However, under more practical conditions, 92 percent of the modules began to delaminate. Yet surprisingly, this delamination, which makes it possible for moisture to penetrate to the cell, failed to negatively affect cell function. On the other hand, the IEC test showed that the Tedlar film on the backside of the modules was beginning to peel off, which in serious cases could develop into a significant security risk. Over the past 20 years, the modules on the roof of LEEE-TISO have been spared such mishaps.

The MTBF Project is thus another proof of just how important tests and experiments under practical conditions can be. Nevertheless, the laboratory's pure research work also leads to advances; for two years now, the institute has a solar simulator at its disposal, and in Feb. 2001 LEEE-TISO received accreditation for the execution of current-voltage measurements on solar modules according to IEC 60904-1. The institute is planning to buy a temperature chamber soon.
 

Naturally, the new testing device will also be available for use by module manufacturers. Chianese sees no cause for concern that this could impinge on TISO's neutrality: In the course of accreditation, the laboratory underwent an examination, and today the commercial orders make up just a small part of its work.

Module tests, on the other hand, do take up a great deal of the lab's resources. Two generators of each module type are included in every test line at the TISO test facility, each with its own inverter, with which the modules' Maximum Power Point (MPP) is measured. Earlier tests were even more elaborate. For instance, the first examinations in 1990 included six modules of each module type: Three were tested in the MPP range, one under open-circuit voltage, one under short-circuit current, and one was used as a reference module.

	© data: LEEE-TISO; graphic: PHOTON International The current (eighth) test series of LEEE-TISO was started in June 2001: Pn means rated power; Pa means the power before the test; P0 is the power measured after four days; P3 is the power measured after 3 months (all measurements conducted under STC conditions).

But this method required an unreasonable amount of work and space. Also, it failed to provide fully representative results, since the modules were acquired from the manufacturers to cut costs at LEEE. But Chianese says that the manufacturers were more careful with the products given to LEEE than with those of their normal customers: »We always received the very best quality modules« -- even though that is not exactly what the experiment required. Today, two modules of a certain type are purchased on an anonymous basis. This often annoys manufacturers, who argue that such a random sample is not representative and that modules purchased anonymously could happen to be on the lower end of the natural production-quality deviation. »But that's the responsibility of the manufacturer's quality control,« Chianese counters. »It's not our job to control the methods of their production.«

Jochen Siemer
© PHOTON International, May 2002