A program is underway at Sandia National Laboratories to predict long-term reliability of photovoltaic (PV) systems.
The vehicle for the reliability predictions is a Reliability Block Diagram (RBD), which models system behavior.
Because this model is based mainly on field failure and repair times, it can be used to predict current reliability, but it
cannot currently be used to accurately predict lifetime. In order to be truly predictive, physics-informed degradation
processes and failure mechanisms need to be included in the model. This paper describes accelerated life testing of metal
foil tapes used in thin-film PV modules, and how tape joint degradation, a possible failure mode, can be incorporated
into the model.
The continued exponential growth of photovoltaic technologies paves a path to a solar-powered world, but requires
continued progress toward low-cost, high-reliability, and high-performance PV systems. High reliability is an essential
element in achieving low-cost solar electricity by reducing operation and maintenance (O&M) costs and by extending
system lifetime and availability, but these attributes are difficult to verify at the time of installation. Utilities, financiers,
homeowners, and planners are demanding this information in order to evaluate their financial risk as a prerequisite to
large investments. Reliability research and development (R&D) is needed to build market confidence by improving
product reliability and by improving predictions of system availability, O&M cost, and system lifetime. Universities,
industry, National Labs, and other research entities can be most effective by working together and in complementary
ways. The Department of Energy supports a variety of research projects to improve PV-system reliability. These
projects and current reliability issues for each PV technology are surveyed.
Despite significant growth in photovoltaics (PV) over the last few years, only approximately 1.07 billion kWhr of
electricity is estimated to have been generated from PV in the US during 2008, or 0.27% of total electrical generation.
PV market penetration is set for a paradigm shift, as fluctuating hydrocarbon prices and an acknowledgement of the
environmental impacts associated with their use, combined with breakthrough new PV technologies, such as thin-film
and BIPV, are driving the cost of energy generated with PV to parity or cost advantage versus more traditional forms of
In addition to reaching cost parity with grid supplied power, a key to the long-term success of PV as a viable energy
alternative is the reliability of systems in the field. New technologies may or may not have the same failure modes as
previous technologies. Reliability testing and product lifetime issues continue to be one of the key bottlenecks in the
rapid commercialization of PV technologies today. In this paper, we highlight the critical need for moving away from
relying on traditional qualification and safety tests as a measure of reliability and focus instead on designing for
reliability and its integration into the product development process. A drive towards quantitative predictive accelerated
testing is emphasized and an industrial collaboration model addressing reliability challenges is proposed.