## 3 Results and Discussion
### Solar Inverter Concept  
The solar inverter plays a key role for EMEs of PV systems. Figure 4 shows a comparison of an inverter with module optimizers (SE) (Figure 4a) and a string inverter (K) (Figure 4b). The installation details were kept the same for Figure 4a,b: small-loop area behind the PV array (SLS), with functional equipotential earthing (W), zero distance between the string cables DC+ and DC\(-\) (R). These installation details were selected for the comparison of solar inverter concepts since they, according to theory [(23)], have the lowest impact on the emissions. Figure 3: MO_SE_SLS_W E-Z system measurement (pink) for the position B direction x, EMC limit line (purple), background to system margin \(P_{sys}\) category (dot: yellow, orange, green, blue, red), 3 representative sample background measurements (divers colors, see legend 22 xx). The MO_SE system in Figure 4a has 216 peaks above the highest background and 20 peaks were above the EMC limit. Whereas, the string inverters MO_K in Figure 4b has only 22 peaks above the highest background and 6 peaks were above the EMC limit. The MO_SE system has noticeably higher peaks then the K system, in the margin \(P_{sys}\) category 11-15 dB green, 16-20 dB blue, and \(>\)20 dB red. Figure 5a shows the frequency histogram of the MO_SE system. Figure 5b shows a zoom-in of the 13-20 MHz range, where many peaks are visible. Here is a clear repetitive pattern visible, with multiples of 200 kHz in the frequency range of 13.8-18 MHz; in none of the measured string inverter systems (F, K, and S) were such repetitive patterns visible. Figure 4: A comparison of inverter with module optimizers (SE) (a) and string inverter system (K) (b); both with monocrystalline half-cut modules with an aluminum frame (MO). Installations details were kept the same. The inverter with module optimizer system (SE) has noticeably higher peaks than the string inverter systems (K), as displayed in the horizontal bar graph in the top right corner of each plot. Figure 5: (a) shows the frequency histogram from system MO_SE_SLS_W; (b) shows a zoom-in of the repetitive pattern of 200 kHz. In summary, all MO_SE_yz system combinations showed 79-89 % more peaks than the three tested string inverter systems. Peaks have noticeably higher margins to the background (on average 90 %, 89 %, and 71 % more for the respected categories 11-15 dB, 16-20 dB, and >20 dB), regardless of loop area, earthing, or string cable distance. All MO_SE_yz system combinations have a visible repetitive pattern of 200 kHz. The prominence of the 200 kHz pattern varied slightly in the different system combinations. The most common frequency ranges were at 3.2-6.4 MHz and 12.6-21.2 MHz, with the second range being dominant in all measurements. The same 200 kHz pattern was reported by [6] for a module optimizer system from the same manufacturer in the frequency range 18-22 MHz. [PERSON] [17] reported 200 kHz and 100 kHz patterns in the frequency range 19-21 MHz and 33-35 MHz, the optimizer again coming from the same manufacturer. The measurement results in combination with earlier reports [6,17] indicate that MO_SE_yz system combinations increase the risk of interference with radiocommunication, while the tested string inverter systems (F, S, and K) do not. The string inverter system with one additional module optimizer (Tx) does not require optimizers behind every module. For the test, only one module was equipped with an optimizer. Such Tx systems showed no enlarged EMEs compared to the test string inverter systems (F, K, and S). However, [PERSON] [28] reported that Tx optimizers can result in interference and send out signal patterns with multiples of 50 kHz. The reduced number of Tx interference cases could be explained by the feature that module optimizers are only added to shaded modules and not to all modules. Interference from submodular optimizers was reported in [10]. Current submodule and module optimizer systems show undesirable high levels of EMEs.