Klaus Kiefer

System performance analysis and estimation of degradation rates based on 500 years of monitoring data

Fraunhofer ISE has been involved in monitoring of PV systems since the “1000-roofs-program” in the 1990s. In a few of these “old systems” equipment is still in place, metering PV electricity output and plane-of-array irradiation. The majority of ~300 PV power plants in our monitoring campaign today, however, is large-scale and built in the past 10 years. In this paper, we briefly review the historical development of the Performance Ratio (PR) and how average PR for newly built systems increased to almost 90%. This rather high PR of 90% only holds, however, if calculated by on-site irradiation acquired with c-Si reference cells and for climates comparable with those in Germany. Next, we use about 500 years of monitoring data on aggregate to perform an analysis of variations of the PR over time. To this end, data points at similar environmental conditions are extracted from long-term time series as to calculate so-called “rates-of-change” of the PR. Highly scattered “rates-of-change” are obtained, however, not allowing for the estimation of specific degradation rates on the system level yet. To this end, we finally revisit uncertainties of irradiance sensors and in particular revisit our irradiance sensor re-calibration data.

Complete PV power plant certification: New standards for quality assurance of large scale PV power plants

The quality of a PV system in terms of design, construction, safety and performance is crucial for the return-on-investment. Certification of modules, inverters etc. to international standards has provided a first level of quality assurance on the component level for a number of years but the industry also needs a standardized assessment on the completed PV power plant from design and planning through to execution and operation. VDE Testing and Certification Institute, a certification body with profound knowledge across the electrical and electronic industries, and Fraunhofer ISE, a leading applied research organization with more than 30 years of experience in the field, have now developed a complete power plant certification, creating a “VDE Quality Tested” label which is both transparent and simple yet customized to the plant under assessment. This establishes a new standard for quality assurance of utility scale PV power plants combining existing standards and established quality assurance procedures with the latest research results. The “VDE Quality Tested” certification is to state that the PV power plant meets the highest quality criteria as implemented, with an associated reduction in technical risks and with higher confidence yield forecast. This contribution provides an overview of the certification process itself, and explains especially the PV performance related steps (such as verification of module characteristics and performance ratio) based on field experience and concrete examples.

On-site performance verification to reduce yield prediction uncertainties

In this paper, we describe a number of quality assurance procedures for PV performance evaluations using data that has been acquired with commercially operating PV power plants. Summarized under the term “performance verification”, these procedures aim to make reliable use of data gathered by PV operators, despite inaccuracies in such data. To this end, short-term measurements with independent equipment and/or data sources are factored in. This ensures both meteorological and PV performance data gathered by operators have sufficient quality. Given a sufficient quality, site-adaptation of satellite based solar irradiation time series and optimizations of PV models may allow for significantly reduced uncertainties of yield predictions. This we anticipate to be of great interest to a broad range of PV stakeholders. The prerequisite for this, however, are appropriate quality of on-site sensors and strict maintenance of the PV performance monitoring systems in place.