The power plants based on renewable sources face various acceptance difficulties mainly due to high initial costs and low overall efficiencies. A way to improve performance of these systems is to utilize more than one type of source of energy chosen to provide some degree of complementarity. An interesting, albeit improbable, combination is obtained using hydroelectric and photovoltaic energy, taking advantage of the complementarity between these two types of sources coupled to reservoir and/or battery storage. This paper discusses energy complementarity in time and proposes a numerical dimensionless index, evaluating this energy complementarity between two types of energy sources, in the same or in different locations, or between two sources of the same type in different locations. In the end, the results of the application of this index to the solar and water availabilities over the state of Rio Grande do Sul, in southern Brazil, is presented in the form of maps. r

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Photovoltaic modules long-term reliability is a key requirement to keep this technology a commercially interesting option for energy production. The investment return on PV generation system depends, among other factors, on the peculiarities of the system on efficiency reduction caused by environmental action. Technical standards suggest laboratory tests for the qualification and a better understanding on module degradation behavior. Nevertheless, some degradation modes can only be observed after years of field operation. This paper presents the main signs of degradation on crystalline silicon photovoltaic modules caused by outdoor exposure after a period of 15 years in an installation in the city of Porto Alegre, the southernmost state capital city in Brazil. The electric analysis demonstrated that the modules kept 90.5% of their initial power, with an average of degradation rate of 0.7% per year. Some techniques helped the evaluation of defects caused by exposure of the arrays for long periods of operation, such as electroluminescence imaging and I-V curve testing. The most frequent defects found were browning (encapsulant darkening) and cell encapsulant delamination, leading to the anti-reflective layer deterioration. The junction box of one of the modules was detached, allowing the entrance of moisture and resulting in the disconnection of some of the module cells. The electroluminescence technique also provided a better understanding on modes of degradation. Despite the observed evidences of degradation along these 15 years, it can be said that the system remains within the expected operation limits.

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