The importance of a Photovoltaic glass in an irradiance sensor – Part 2

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YES, Sunmeter Pro irradiance sensor allows to calculate the performance of a photovoltaic system with a measurement precision around 2%!

The photovoltaic glass of the Sunmeter Pro

In a previous article we described the photovoltaic glass, one of the key features of our Sunmeter Pro. This glass is the microprismatic glass already used in the manufacturing of photovoltaic modules. We also claimed that this type of glass increases energy production by absorbing more sunlight thanks to its irregular and anti-reflective surface. Furthermore, we stated that with this type of glass the measurements of Performance Ratio (P.R.) of photovoltaic systems are more accurate than with smooth high transparency glass, for the simple reason that the Sunmeter Pro pyranometer is manufactured with the same glass as the photovoltaic modules. By choosing the same photovoltaic glass the photons transmission is similarly optimised for the production of electrons. In this second article we will show the results of real measurements in the field, providing quantitative support to our assertion.

Irradiance measurements for 3 Sunmeters Pro in red, yellow and green (with PV cell laminated on photovoltaic glass) compared to a Competitor sensor in blue (with PV cell laminated on smooth glass) versus time.

Can we demonstrate that photovoltaic glass of Sunmeter Pro is better?

In this workpiece we will compare the performance of irradiance sensors with smooth high transparency glass and our irradiance sensor with photovoltaic glass. First of all, we refer to Figures 1 and 2, in which the X-axis represents the time (during daylight hours) and the Y-axis the irradiance (power received in a given instant in a given area) in W/m2. Our Sunmeter Pro performance is represented by the red, yellow and green traces; the competitor’s sensor is shown with the blue line.

Irradiance measurements for 3 Sunmeters Pro in red, yellow and green (with PV cell laminated on photovoltaic glass) compared to a Competitor sensor in blue (with PV cell laminated on smooth glass) versus time. The time window has been reduced compared to Figure 1 in order to remove the effect of tree branches generating shadows.

We can observe that, in the undisturbed area in the window around 12:00, the irradiance recorded by our sensors is consistently similar to the competition. In particular (Figure 3), we can observe that the irradiance values in the time window around 12:00pm are similar – the two traces overlap – but they diverge as the angle of incidence of the sun rays increases.

• Competitor’s Sensor between 13:08 and 13:20 measures an average 2.7% less than Sunmeter • Competitor’s Sensor between 13:30 and 13:45 measures an average 3% less than Sunmeter • Competitor’s Sensor around 14:00 measures an average 4% less than Sunmeter • Competitor’s Sensor around 14:20 measures an average 4.5% less than Sunmeter • Competitor’s Sensor between 14:30 and 15:00 measures an average 5.5% less than Sunmeter

Moreover, as the field was not an ‘ideal field’ due to tree branches shadows in the morning before 10:10 and then again after 15:20, we have performed a 2nd order regression on both red and blue curves and we have extrapolated them to 16:15 (Figure 4). We can then estimate the difference between the two curves at 16:00 which is 52 W/m2.

Irradiance measurements for Sunmeter Pro in blue (with PV cell laminated on photovoltaic glass) compared to a Competitor sensor in red (with PV cell laminated on smooth glass) versus time. The time window has been reduced compared to Figure 1 in order to remove the effect of tree branches generating shadows.

Irradiance measurements for Sunmeter Pro in blue (with PV cell laminated on photovoltaic glass) compared to a Competitor sensor in red (with PV cell laminated on smooth glass) versus time. The time window has been reduced compared to Figure 1 in order to remove the effect of tree branches generating shadows. The blue and red curves have been interpolated within this time window and extrapolated to get irradiance values until 16:00. Here is also an extract of the table of measurements from a time window in the middle of the day with all the sensors included.

Click the following link to download the full pdf table: Compar_PVGlass-GlossyGlass_250319_093417

Conclusion

When measuring the performance of an investment fund in a given stocks & shares portfolio the benchmark must belong to the same equity portfolio; similarly an irradiance sensor must be built with the same materials as the photovoltaic modules. These modules are generating electricity, and their optical and photonic aspects are the key elements in such energy production. In particular, if we encapsulate the irradiance sensor cell with a different reflective material from the photovoltaic glass, the resulting optical (photonic) measurements will be different. It might be 3%, 5%, 6%…? When measuring the P.R. of a plant you want to be more precise! In conclusion, in this article we have observed and described that when the sun is low on the horizon the reflectivity of a non-photovoltaic glass will allow less photons to enter the sensor cell, resulting in a diminished irradiance value. As a consequence the performance will be over-estimated (the irradiance value is at the denominator in the PR calculation). The error will be larger the lower the sun is on the horizon, further from the perpendicular above the photovoltaic module.

What are other interesting features of the Sunmeter pro irradiance sensors?

Discover them in our White Paper freely downloadable from our website. Here is the link to all of our documents for download. The White Paper is the last in the list soluzionesolare.com/downloads/

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