Figure 1. Layout of the measurement

In the first configuration 6 modules distributed inverters were parallel connected. Figure 1 shows the measurements points A and B, where the background level have been determined, before making the measurements. The AC module inverters marked with letter A are referred in table 2 while those indicated with B refer to table 3.

The measurement at the cable LISN (point A, power delivery), refers to the open circuit test without the PV plant connected, figure 2.

Figure 2. Spectrum revealed at point A in figurel.

The signals in figure 2 around the marker between 10 and 30 MHz are found to be radio stations with the peak set at 21.3 MHz

The measure at point B with the PV plant connected to the DC part defines the background threshold, to be used as reference for the successive measurements. Figure 3 shows the optimal situation for the background threshold after making some adjustments to improve the layout of measurement.

Figure 3. Spectrum revealed at point B in figure 1.

Considering all the uncertainties of a measurement in a pre compliance procedure, we can assume the following considerations.

From the examination of figure 3 it seems that the background noise overcomes the limit line of the average value. The spectrum of the analyzer reports the behavior of the peak values and average. The EMC standard refers to the conducted limits in terms of quasi­peak and average value. The measurements are to be compared with the corresponding detectors.

In practice at first a fast measurement is performed, with the detector in the all range of frequency and then the points in which there was recorded the overflow are analyzed more carefully; only for those signals the measurements with the quasi peak detector and average values are made for the comparison.

As results from the table 9, reporting also the highest values, the quasi-peak values and the average values of the measurements are below the levels set by the standard EN 55011 (the signal at 7.199 MHz is very close to its limit value of 46 dB p. V), respectively listed in tables 7 and 8. Anyway demoduling the same signals we found they were radio station signals, so unavoidable during the measurements.

So we can conclude that the electromagnetic background interferes with the PV system but with values below the referring standard.

Signal	Freq (MHz)	Peak Amp (dBuV)	QP Amp (dBuV)	Avg Amp (dBuV)
1	1.444996	48.02	43.34	36.71
2	7.199402	42.37	41.70	45.47
3	9.830567	40.87	42.24	44.43
4	11.910258	44.70	51.00	47.59

Table 9. Referred to Figure 3.

Figure 4 reports the measurements of noises with the facade plant in operation. Each module is connected to its own inverter.

The plant presents 3 modules connected to the 3 type A module inverters and other 3 ones connected to the type B ones. All inverters were parallel connected. The power was of 206 W AC side.

Examining more carefully the figure 4 it results that the limit lines are both overcome by the peak values when the waiting time was set at 3 minute in several frequency ranges. During the measurement the max hold function reports only the maximum values during a preset interval.

Signal	Freq (MHz)	Peak Amp (dB|iV)	QP Amp (dB|iV)	Avg Amp (dB|iV)
1	0.8293	56.18	50.37	42.16
2	4.66743	66.06	59.51	48.31
3	6.93344	66.40	60.84	51.12
4	8.3192	63.26	56.43	46.75

Table10. Data referred to figure 4.

By looking in the ranges of frequency were there were the highest values, 4 more representative values are selected, so obtaining the table 10. In correspondence of the

frequencies 4.66743 MHz and 6.93344 MHz, even if just a bit, there is the overcoming of the limit values in term of quasi peak and average values.

Successively conducted emissions related to other configurations have been measured; in particular the inverter type A and the type B have been analyzed.

Configurations with 3 and 1 inverters have been compared and figures 5 and 6 refer to the case with the AC module inverter type В respectively.

Figure 5. Spectrum with 3 parallel type B module inverters.

Figure 6. Spectrum with 1 type B module inverter.

These configurations comply with the Standard within all the frequency range from 150 kHz to 30 MHz, where all the signals present values of quasi-peak and average below the maximum, and even for those whose values overcome the average curve, as reported in table 11.

Signal	Freq (MHz)	Peak Amp (dBpV)	QP Amp (dBpV)	Avg Amp (dBpV)
1	1.1117	55.35	51.63	43.91
2	9.8308	52.02	54.53	54.31

Table 11. Data referred to figure 5.

Figures 7 and 8 refer to the case of type A module inverters.

Figure 7. Spectrum with 3 parallel type A module inverters.

Figure 8. Spectrum with 1 type A inverter.

In these cases the limit values are just a bit lower. That happened for the signal at 4.2925 MHz in the case of 3 inverters and for the signal at 6.78 MHz for the one inverter, as shown in tabs 12 and 13.

Signal	Freq (MHz)	Peak Amp (dBpV)	QP Amp (dBpV)	Avg Amp (dBpV)
1	0.9933	56.38	50.57	42.06
2	4.2925	61.50	55.33	47.88
3	8.1618	64.57	58.39	49.37

Table 12. It refers to figure 7.

Signal	Freq (MHz)	Peak Amp (dBpV)	QP Amp (dBpV)	Avg Amp (dBpV)
1	1.199	52.723	48.607	41.609
2	4.3789	57.190	51.618	44.012
3	6.7863	60.734	56.445	47.95
4	9.8376	59.845	51.345	46.678
5	12.056	50.756	44.876	41.67

Table 13. It refers to figure 8.

From the comparison it results that the type B module inverter complies just a little more with the standard, respect to the type A, even if the differences are not so impressive.

Figure 9. Layout of measurement with the plant inverter.

The last case refers to the configuration where all the modules are series connected and connected to only one inverter, referred at table 1, as results from figure 9.

Figures 10 and 11 show the measurements respectively with the plant not in operation (open circuit), and in operation at power of 216 W.

From the figure 10 it results a threshold background more than acceptable, namely the 6 dB of attenuation are respected within all the measurements, since the highest values refer to the broadcasting radio stations.

From the figure 11 it results that the plant complies with the limit curve of the quasi-peak values while for the average level some doubts arise in the low frequency part between 150 kHz and 400 kHz.

Figure 10. Spectrum at open circuit conditions.

Table 14 shows the measurements of two of the more representative signals within the remaining interval, highlighting that they are largely below the considered limits.

Figure 11. Spectrum with PV plant connected.

Signal	Freq (MHz)	Peak Amp (dBpV)	QP Amp (dBpV)	Avg Amp (dBpV)
1	1.448229	48.53	44.32	37.54
2	5.304179	52.62	49.61	39.34

Table 14. It refers to figure 11.

Conclusions

Considering the not ideal conditions the measurements have been performed and the precompliance nature of them, it should be said that the revealed conducted emissions could reasonably comply with the Standard EN 55011, and so in all the configurations. So the supply of power from the PV facade to the grid happens in respect with the standard rule.

The configuration with only one inverter is more conservative respect to the diffused inverters case. For those the module inverter type B revealed just a bit less interfering of the inverter type A.

The measurements have showed that if there is an important background level, some signals can be captured from the PV plant, specially if long cables are present and particularly if they are put inside the buildings.

Those signals can travel along the cables of the electric wires in the buildings and acting as noises on appliance sensitive to the same frequencies.

From that it follows that the PV plant should be carefully designed in term of geometry and the frequencies of the transmitted frequencies should be analyzed.

This has been the first analysis and new surveys on existing BIPV applications are needed to be performed so to give answers to the following questions:

— what about the power size?

— what about the different responsiveness to the irradiance levels?

— what about the inverter types and configurations?

— what about the geometry?