The new term of the radiation-dynamic tracking efficiency describes the process of finding and maintaining the MPP during real weather conditions over an operating year. In this case, similar to the CEC rebate conversion efficiency, a typical radiation level for central Europe must also be assumed. Just as the CEC rebate conversion efficiency is derived from the weighted average value of the conversion efficiency at six selected outputs, the radiation-dynamic tracking efficiency can be determined from the weighted average value of the tracking efficiency in 13 characteristic radiation situations. However, the definition and reproducible replication of these operating conditions pose a great challenge and require a testing station that is far better equipped than a normal testing laboratory.
The innovative testing facilities at the SMA solar testing center, developed in-house over many years, made it possible – for the first time – to realistically simulate a PV array under the most diverse weather conditions and changes that often occur in the course of a day. This also made it possible to precisely determine the MPPtracking quality of an inverter, which led SMA to add the radiation-dynamic tracking efficiency analysis to its qualification standard in assessing inverters some years ago (see Weather at the touch of a button, page 7).
The benefits of this analysis become apparent when comparing the operational behavior of two inverters or MPP trackers. If it is still difficult to differentiate between devices under laboratory conditions (Euro ETA and US ETA), the individual strengths and weaknesses are clearly demonstrated with the remaining test results. The radiation conditions are divided into four groups: laboratory operation, static behavior, dynamic behavior and startup/shutdown behavior.