Self-reference procedure to reduce uncertainty in module calibration

This paper presents a composite measurement approach that capitalizes on complimentary strengths of 3 different test beds to significantly reduce uncertainty in I- V parameters for secondary module calibration. This approach addresses PV manufacturers' need for reduced uncertainty in the calibration modules that provide the basis for their module power ratings. This new method enables NREL to reduce uncertainty for secondary module calibration in commercial c-Si modules from
$\pm 3.2\%$
to
$\pm 0.7\%$
for
$\mathbf{I}_{\mathrm{SC}}$
and from
$\pm 3.3\%$
to
$\pm 1.1\%$
for
$\mathbf{P}_{\mathrm{MAX}}$
. This new module self-reference, or MSR procedure is based on the sensitivity of module voltage to temperature plus the uniformity of outdoor sunlight. By calibrating module
$\mathbf{v}_{\mathrm{oc}}$
in thermal equilibrium on a flash simulator we provide an accurate gauge of junction temperature for subsequent measurements. By calibrating
$\mathbf{I}_{\mathrm{SC}}$
outdoors in natural sunlight we enable the module to serve as its own reference device in setting the intensity of a continuous simulator, effectively eliminating the impact of spatial non-uniformity and spectral mismatch on the I-V measurement. These procedures significantly reduce measurement errors due to temperature uncertainty, spatial non-uniformity, and spectral mismatch.