As part of a research project between vandeSun (a brand of map energy & planning GmbH) and the Institute of Industrial Management at FH JOANNEUM, various solar roof technologies were tested under real-life conditions. The aim was to analyze the effects of shading on energy efficiency and to identify the most efficient solutions - in particular the PV roof shingle from vandeSun.

1 Background and objectives

Shading caused by buildings, trees or weather conditions is one of the biggest challenges for photovoltaic systems. The project investigated three technologies:

• Standard PV module
• PV roof shingle with integrated circuit
• PV roof shingle with bypass diode

The aim was to find out how these technologies react to partial shading and which ones deliver the highest energy yield under real conditions - a decisive factor for the efficiency of modern solar roofs.

2 Methodology

The tests were carried out in the Smart Production Lab at FH JOANNEUM in Kapfenberg. After a comprehensive analysis of the influencing factors such as light intensity, temperature and humidity, a detailed test plan was drawn up. The tests were carried out outdoors to ensure realistic conditions.

Figure 1: Roof shingle with integrated circuit

Figure 2: Roof shingle with bypass diode

Figure 3: Roof shingle with integrated circuit

3 Results

A total of 101 experiments were carried out with the different technologies to collect data. 34 with the bypass diode technology, 35 with the integrated circuit and 32 with the standard PV module. This shows that there is a balance between the various technologies and that no technology was favored. As already mentioned in Chapter 3, the experimental investigation was used to test two questions in a focused manner. On the one hand, the efficiency of a cell was analyzed in more detail, i.e. at what point this roof shingle no longer produces electricity. On the other hand, the efficiency of the individual technologies was compared with each other.

3.1 Efficiency of a cell

For this purpose, one cell was first completely shaded and then the degree of shading was gradually reduced. As can be seen in Figure 4, for example, with a value of 0.25 on the x-axis, a quarter of the cells are shaded and the rest are unshaded. The shaded power divided by the unshaded power is shown on the Y-axis. It can be seen here that at a shading of 25%, the roof shingle with the integrated circuit and the bypass diode switch off, as a constant power is produced from this point onwards. With the standard PV module, something only switches off at a shading of 50%, see Chapter 5.3. In a comparison of all three technologies, the integrated circuit is the most efficient, ahead of the bypass diode and the standard PV module.

Figure 4: Shading a cell

The same result is obtained if the actual power output is considered rather than a standardized value, as shown in Figure 5: Power output of a shaded cell. The roof shingle with the integrated circuit delivers a significantly higher output under the same conditions, both in shaded and unshaded conditions.

Figure 5: Shading of a cell (power)

3.2 Efficiency of the technology

To compare the efficiency of the two roof shingle technologies, integrated circuit and bypass diode, the individual shingles were shaded one after the other so that they switch off, as can be seen in Figure 6. The shaded output divided by the unshaded output is shown on the Y-axis and the number of shaded roof shingles on the X-axis. It is clearly visible that the difference is still minimal with one or two shaded roof shingles, but there is then a clear difference between the technologies. With five shaded roof shingles, the total output of the bypass diode is too low for the inverter and no electricity is produced. With the integrated circuit, this is the case with six roof shingles. If 4 roof shingles are shaded, the integrated circuit is more than 60 % more efficient than the bypass diode.

Figure 6: Shading individual shingles