ASTM E434 is a standard test method for calorimetric determination of hemispherical emittance and the ratio of solar absorptance to hemispherical emittance using solar simulation.
ASTM E434 Calorimetric Determination of Hemispherical Emittance and the Ratio of Solar Absorptance to Hemispherical Emittance Using Solar Simulation
What is ASTM E434?
What is the Scope of ASTM E434?
The ASTM E424 test method covers calorimetrically determining the ratio of solar absorptance to hemispherical emittance using a steady-state method and calorimetrically determining the total hemispherical emittance using a transient methodology.
The operating temperature of a solar cell affects its performance and lifespan. To calculate total radiative heat transfer and, therefore, solar cell operating temperature in applications such as building-integrated photovoltaics, precise information on total hemispherical emittance as a function of temperature is required.
Materials and Substrates: This test method can be used to test any coating, given its structure remains stable in vacuum over the temperature range of interest.
Methods and Apparatus: Covers steady-state and transient measurements using apparatus elements like vacuum systems, cold shrouds, temperature sensors, and solar simulators.
ASTM E434 Sample Preparation and Equipment
Each specimen shall be drilled at the edge with a set of holes through which suspension strings are to be introduced for the ASTM E434 test technique, and the substrate is machined from flat stock to a size proportioned to the working area of the chamber.
The main apparatus elements include a vacuum system, a cold shroud within the vacuum chamber, temperature-measurement instrumentation, and a solar simulator.
ASTM E434 Testing Procedure and Requirements
ASTM E434 is a colorimetric test technique for determining hemispherical emittance and the ratio of solar absorptance to hemispherical emittance using solar simulation. In calorimetric tests of material radiative properties, ASTM E434 requires placing the specimen in a vacuum under simulated solar radiation with cold surroundings.
- The thermophysical properties of the specimen can be derived via an equation that relates heat balance concerns to measurable test parameters based on observation of the specimen’s thermal activity.Â
- To determine α/∈, the side of the specimen in question is exposed to a simulated solar source through a port with appropriate transmittance across the solar spectrum in a typical measurement. The radiant energy absorbed by the specimen from the sun and radiated by the specimen to the environment causes the specimen to reach an equilibrium temperature that is determined by the α/∈ ratio of its surface.
- The specimen is heated with a solar simulation source and then allowed to cool by radiation to an evacuated space chamber with an interior effective emittance of unity in the dynamic radiative method of determining total hemispherical emittance. The total hemispherical emittance of the test specimen can be computed as a function of temperature using information such as the specific heat of the specimen as a function of temperature, the area of the test specimen, its mass, its cooling rate, and the temperature of the walls.
ASTM E434 Results Analysis and Interpretation
The ASTM E434 steady-state equation calculates the ratio of solar absorptance (α) to hemispherical emittance (ε) by equating the absorbed solar radiation to the thermal energy radiated to the vacuum chamber’s cold shroud at thermal equilibrium.
Updated on September 4, 2026
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