Solar power generation is one of the fastest growing industries in the world. This year, shipments of solar modules globally will exceed 7.8 gigawatts. Taking an average output of 200 W/module, this represents 39,000,000 modules per year. A growth rate of 30% per year is expected over the next several years. One reason for that growth rate is that Germany and Japan recently announced plans to exit nuclear power generation, and photovoltaic (PV) installations are one of the most attractive solutions for filling the generation gap.
Life Expectancy Doubts
But there is a problem. Solar power users expect modules to last between 25 and 30 years, but there is little data to support this expectation, and there are no recognized test standards in place to validate these assumptions. The current standards do not come close to the 25-year benchmark.
Companies have internal test methodologies, but there are no generally recognized standards. Warranties for manufacturing defects are typically 5 to 10 years, while efficiency warranties are between 10 and 25 years. Almost all of these warranties are based upon internal testing, which is held as "company secret" for competitive advantage.
In addition, there is little traceability. So what happens in 5 or 15 years if a module goes bad? Solar installations are multigenerational. Some of the companies manufacturing and installing solar power now might not be around in 25 years. What then?
Most solar modules generate DC electricity, which is fed through a junction box to an inverter, where that electricity is converted to AC and then fed into a home or business or directly to the grid. A typical home array is feeding approximately 2.5 kW constantly while the sun is shining. There is no way to turn it off except to cover the array. In the wide range of applications for solar power globally, solar modules can be exposed to temperatures exceeding 65C (149F) and down to as low as -60C (-76F). In addition, humidity has been identified as a significant contributor to module failures in tropical climates. Additional failure mechanisms based upon the location of an installation include atmospheric salt exposure, corrosion from pollution, extreme weather conditions, and exposure to ammonia in rural installations where livestock is kept.
A two-day conference was held recently in conjunction with the Intersolar conference and exhibition in San Francisco. Organized by Japan’s Institute of Advanced Industrial Science & Technology (AIST), the National Renewable Energy Laboratory (NREL), the Solar Engineering and Manufacturing Association, and PVTECH (the Japanese solar power research association), more than 170 industry participants met to discuss the issues related to quality assurance and long-term reliability.
The meeting included representatives from the major test laboratories, national and international research institutes, module manufacturers, suppliers, the insurance industry, system operators, and other industry stakeholders.
Michio Kondo, representing AIST, outlined that organization’s seven-year test methodology and reported a failure rate ranging from 0.5% for some manufacturers up to 6% for others. Later, a representative from one of the world’s largest solar investment firms documented a 10% failure rate for inverters within the first seven years of operation.
Field failures in solar power installations reported include cell cracking, junction box de-lamination, module delamination, diode failure, junction box and gasket cracking, glass breakage, and soldering defects leading to circuit failure. One utility-scale user has reported six fires in seven years in 50 MW of modules. Solar power generation requires the same safety factors as other forms of power generation. That same user expressed his concern that a major fire might occur within the next few years if this issue is not addressed.
The IEC test standards used and those from UL and TuV are primarily fire safety standards and simulate approximately five years of harsh environment usage. None of these tests is performed while the device is under power; all are static tests. Many manufacturers perform additional tests and also benchmark their products versus their competitors. However, no national or international standard or long-term test methodologies yet exist. The test specifications and standards for the materials and components are similar to those for modules.
Another factor affecting long-term reliability is the drive to reduce the cost per watt. In the crystalline module market, the price of cells represents 70% of the total cost of the manufactured product, and profit margins are thin. Module prices have fallen by as much as 25% in 2011, and manufacturers are desperate to reduce costs of materials while improving manufacturing efficiency. This has resulted in efforts to utilize new and less-expensive materials that in some cases may meet the current standards but are not as effective in the long run. A large number of field failures have been traced directly to materials and manufacturing processes.
The solar power supply chain is a long one, and the chain of responsibility is complex. Governments require safety and code compliance. Insurance companies and manufacturers provide warranties and liability and other forms of insurance. Repair and maintenance providers 10 or 20 or even 30 years from now will demand a safe and reliable product upon which to work.
With 40,000,000 new modules being deployed every year, it is incumbent upon all of the key stakeholders to act rapidly to develop and implement the methodologies and test methods to simulate long-term exposure under harsh conditions.
The working group is a good first step, but the industry is taking unacceptable risks until a generally recognized standard is formed. The module PV QA Forum has formed a task force to tackle these tasks, but it will take widespread industry participation to meet the challenge.
Materials suppliers, manufacturers, test laboratories, and other stakeholders must participate to develop standards for materials, modules, and inverters. A second meeting took place in Hamburg, Germany, in conjunction with the EUPVSEC exhibition in September (after this article was written); follow-ups were scheduled in September for San Francisco, at APEC, and in Taipei in October.
—Matthew Holzmann is the president of Christopher Associates Inc., a supplier to the solar power industry, and president of the Solar Engineering & Manufacturing Association.