Wednesday, May 1, 2013

Convergence of PV materials, test and reliability: What really matters?

SEMI, USA recently hosted the seminar on 'Convergence of PV Materials, Test and Reliability: What Really Matters?
Reliability in growing PV industry
Speaking on the importance of reliability to a growing PV industry - Sarah Kurtz, principal scientist,
Reliability group manager, NREL, said that confidence in long-term performance is a necessity in the PV industry. Current failure rates are low. There is need to demonstrate confidence so that failure rates will stay low. There has been exponential growth of the PV industry so far. PV is a significant fraction of new installations. It now represents a significant fraction of new electricity generating installations of all kinds.

How does one predict the lifetime of PV modules? There has been a qualification test evolution for JPL block buys. Most studies of c-Si modules show module failures are small. Internal electrical current issues often dominate.

The vast majority of installations show very low PV module failure rates (often less than 0.1 percent). There has been evidence that PV is low risk compared to other investments. To sustain the current installation rate, we need to demonstrate confidence that justifies the annual investment of $100 million or so.

Critical factors in economic viability of PV
DuPont has broad capabilities under one roof. It offers materials, solar cell design, and processes integrated with panel engineering. Speaking about critical factors in economic viability of PV - materials matter, Conrad Burke, global marketing director, DuPont PV Solutions, said that material suppliers have a distinct advantage to view trends. The industry can expect consolidation among large PV module producers and large materials suppliers.

There is an increasing dependence on materials suppliers for processes, tech support and roadmap. There is renewed attention to long-term reliability and quality of materials in PV products.

There is a race for survival among panel producers. There are dropping prices for solar panels, and quality is getting compromised. There are reduced incentives in established markets. The market will continue to grow. Key factors that determine investment return for PV include lifetime, efficiency and cost.

When materials fail, the consequences are dire. There are failures such as encapsulant discoloration, backsheet failure, glass delamination, etc. Average defect rates in new-build modules has been increasing. Significant number of PV installations do not deliver the projected RoI. The system lifetime is as important as cost and incentives.

Solar cell power continues to improve. There have been improvements from metal pastes and processes. Performance loss impacts the RoI. The US Department of Energy hired JPL to develop 30-year PV modules. Recent cost pressures have led to the dramatic changes in module materials and a lack of transparency.

Analyzing modules from the recent service environments show performance issues. Certification does not mitigate risk. Tests do not predict the actual field performance. He showed tier-1 solar panel manufacturing problems from China, Japan and the USA. Backsheet is critical to protect solar panels. Few materials have lengthy field experience. We will continue to see drop in prices for solar panels and opening of new markets. Focus for PV module makers will remain efficiency, etc.

Standards to assess PV module service life
Speaking on developing the methodology and standards to assess PV module service life, John Wohlgemuth, principal scientist, NREL, said that we would like to have a set of accelerated stress tests that can be performed on PV modules. PV modules today are typically qualified for or certified to IEC 61215 for crystalline solar modules, IEC 61646 that examines all parameters responsible for the ageing of PV modules and IEC 62108 for CPV modules.

Qualification tests should be fairly successful as the PV industry has been growing rapidly. Why aren't material tests adequate? In most cases, they are applied to new materials, not aged or stressed materials. These are generic material tests.

There is the International PV Module QA Task Force and the WG2 Materials Group. The PV QA Task Force has three groups looking at the guidelines for manufacturing consistency, testing for thermal and mechanical fatigue, and testing for humidity, temperature and voltage.

Task Group 4 looks at the testing for diodes, shading and reverse bias. Task Group 5 looks at testing for UV, temperature and humidity. Task Group 6 looks at the communication of PV QA ratings to the community. Task Force 7 looks at wind and snow loading. Task Force 8 does the testing of thin-film modules. Task Force 9 tests CPV modules.

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