SPF Testing – Solar Glass

The performance of thermal collectors and PV modules depends significantly on the glass used. The measurement and certification procedure developed at SPF is internationally recognized as a reference and evaluates the specific properties required for good solar glass

As a rule, special solar glass is used that is characterized by high purity. This achieves a significantly higher light transmission (= usable energy) compared to normal glass. Visually, however, good solar glass can hardly be distinguished from normal window glass.

The correct measurement of light transmission is very complex and requires special spectrometers and sensors. The measurement of structured glass is particularly demanding, since the angle-dependent transmission has a significant influence on the annual yield of solar systems.
The necessary infrastructure is available at SPF.

Testing and Certification

The SPF certificate for solar glass is available for PV and for thermal collectors (ST). The specific requirements for the optical properties are defined by the glass efficiency. This is determined on the basis of the following measured values:

Optical transmission
Angle factor (Incident Angle Modifier)
UV degradation

Glass efficiency and classification into performance classes Solar thermal (ST)

Untreated Glasses		One-sided AR treated glasses		Both sides AR treated glasses
class U1	η_GL ≥ 0.900	class Y1	η_GL ≥ 0.925	class X1	η_GL ≥ 0.950
class U2	η_GL ≥ 0.885	class Y2	η_GL ≥ 0.910	class X2	η_GL ≥ 0.935
class U3	η_GL ≥ 0.870	class Y3	η_GL ≥ 0.895	class X3	η_GL ≥ 0.920
class U4	η_GL ≥ 0.850	class Y4	η_GL ≥ 0.870	class X4	η_GL ≥ 0.890
No solar glass	η_GL < 0.850	no solar glass	η_GL < 0.870	no solar glass	η_GL < 0.890

Glass efficiency and classification into power classes Photovoltaics (PV)

Untreated Glasses		One-sided AR treated glasses		Colored Glasses
class P1	η_GL ≥ 0.940	class R1	η_GL ≥ 0.980	class P C	η_GL > 0.0
class P2	η_GL ≥ 0.925	class R2	η_GL ≥ 0.965
class P3	η_GL ≥ 0.910	class R3	η_GL ≥ 0.950
class P4	η_GL ≥ 0.890	class R4	η_GL ≥ 0.925
no solar glass	η_GL < 0.890	no solar glass	η_GL < 0.925

SPF Testing – Solar Glass

Testing and Certification

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