Value chain · CLM-1418
In plain terms
The standard ground sunlight used to test solar cells adds up to about 1,000 watts per square metre, or 1 kilowatt, on a surface tilted towards the sun, under one fixed set of atmospheric conditions. It is a reference value, not what any site receives.
The claim as recorded
The ASTM G173-03 reference ground spectrum "Global tilt" (AM1.5G), integrated over its tabulated 280-4000 nm range, gives 1000.4 W/m2, that is about 1 kW/m2; the "Direct+circumsolar" column gives 900.1 W/m2. The reference conditions are one fixed atmosphere, absolute air mass 1.5, on a surface tilted 37 degrees toward the equator facing the sun.
Evidence behind this: T0-calculation: a trapezoid integral over wavelength of the held G173-03 table (CALC-132), on SRC-779 and SRC-780, both proposed T3.
Scope and limits
The tables cover 280-4000 nm only, and the standard's own text, which may state a total, is not held, so 1000.4 W/m2 is the integral of the tabulated band computed in CALC-132, not a number read from the standard. It applies to a plane tilted 37 degrees and facing the sun under the stated atmosphere; it is not the irradiance on a horizontal surface, nor typical noon sunlight at a given site or time. The AM0 column integrates to 1347.9 W/m2 over the same band; the reason it is below a full-spectrum solar constant is not shown in the held files (UNVERIFIED). T0 on a T3 input; single source, so conf is not HIGH (METHOD 3.2). Not independent of CLM-1417, whose source describes the same standard.
What it assumes
The integral of the tabulated 280-4000 nm band is taken as the standard's broadband value; trapezoid quadrature on the table's grid.
Where it comes from
This is the project's own working, shown in full:
, the page says the spectra describe terrestrial solar spectral irradiance "under one and only one set of specified atmospheric conditions", with absolute air mass 1.5, a 37 degree tilt toward the equator and the 1976 US Standard Atmosphere. SRC-780, columns "Global tilt" and "Direct+circumsolar" in W*m-2*nm-1 from 280.0 to 4000.0 nm. CALC-132: trapezoid integrals 1000.37 (global), 900.14 (direct) and 1347.93 (Etr) W/m2.
Cite this
energyaperture.com/c/clm-1418
CLM-1418, Energy Aperture, as of 2026-10-10.