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Partnerships for enhanced engagement in research (PEER) SCIENCE
Cycle 3 (2014 Deadline)

PRESSA: Photovoltaic Reliability Evaluation in Sub-Sahara Africa

PI: Gabriel Takyi (, Kwame Nkrumah University of Science & Technology
U.S. Partner: Christiana Honsberg and Mani G. TamizMani, Arizona State University (ASU)
Project Dates: September 2014 to February 2019

Many countries are procuring and installing large numbers of photovoltaic (PV) modules for various grid-tied and stand-alone applications. These modules need to be evaluated to ensure that they will meet the safety requirements (both electrical and mechanical), meet the nameplate rating requirements (rating tolerance shall be minimum), and be reliable and durable for at least 20 years. Because consumers decide to purchase modules based on their "$/watt" ratio as per the nameplate rating, it is critical to ensure that the rating is accurate. In this PEER project, the nameplate rating will be verified by the principal investigator's laboratory in Ghana before procurement decisions are made by investors and the government of Ghana.

The lifetime of PV modules is dictated by failure modes and degradation rates. PV module manufacturers typically provide 20-year warranties, but there are two problems. First, due to the dynamic nature of the investors’ decisions, many manufacturing companies do not last longer than a few years, rendering the 20-year warranty useless. Second, most manufacturers provide a 20-year warranty due to heavy competition in the industry but do not have substantiated evidence to justify these long warranty periods. Based on the experience gained in the U.S. partners' laboratory at ASU, it has been demonstrated that the majority of modules do not meet warranty requirements, and most manufacturers are no longer in business to make good on warranty claims when they are made. Three of the major failure/degradation modes in the climatic conditions prevalent in Ghana are solder-joint degradations/failure; encapsulate browning; and high relative humidity/rain-related degradation. In this PEER project, samples of PV modules will be evaluated for the above failure and degradation modes both in the field and the laboratory.

Two major impacts are expected with regard to purchasing decisions by various stakeholders, including the government of Ghana and Ghanaian investors and consumers. The first impact is related to nameplate rating verification. The stakeholders can purchase the modules based on their independently measured power provided by the Ghanaian researchers rather than their manufacturer rated power. The second impact is related to the lifetime of the modules in the field. An extensive evaluation of PV modules is required to predict module lifetime under various climate conditions. In the proposed limited-budget PEER project, the entire lifetime-related research cannot be performed, but a few key reliability studies will be carried out in the laboratory and in the field to identify the major failure modes using less expensive, non-destructive tests.

Summary of Recent Activities

During this reporting period ending, the PI focused on undergraduate and postgraduate student supervision. The research being carried out by PEER students include:

BSc Final Year:
1. Effect of angle of inclination on power output of solar PV modules installed at Knust, Kumasi
This research work is on the evaluation of five angle of incidence (0, 5, 10, 15 and 20) on power output.

2. Performance evaluation of 11-year old PV module of different technologies installed at KNUST
Under this work, different PV technologies (mono-crystalline, polycrystalline and thin film)modules installed in Ghana, a hot humid country in Sub-Sahara Africa is evaluated

MSc Final Year
1. Field study on the prevalent degradation forms for PV modules operating under various climatic conditions in Ghana.
The research investigates the effect of the different climatic conditions in Ghana on PV module current and power drop. The work tries to establish a correlation between the drop in performance and the observable physical defects.
2. Project on risk priority number (RPN). The student is visiting the 2.5MW Solar PV Plant at Navrongo to collect data.

3. PhD Research work
Some interesting results have been achieved in the PV modeling work. We are currently comparing real field life conditions to STC conditions. PV module certification testing standards such as IEC 61215 have been quite successful in reducing infant mortality but do not reveal much in terms of the actual long-term on-field reliability. The current work seeks to carry out an assessment of the real life conditions to which modules are exposed to in order to develop a more meaningful approach to predicting the actual field life of PV modules. A high-resolution data (5 minutes interval) which focused on temperature variation and thermally-induced stresses observed during thermal cycling was recorded and stored for the calculation of ramp rate. The module ramping (heating and cooling) rates also vary across the test years with the maximum ramp rates significantly above STC rates of 100 C/Hr

The PI is working on his final report.

PEER Cycle 3 Grant Recipients