Photovoltaic modules are rated at standard test conditions, STC, but in real life operation they are exposed to very different conditions. The power of a module and its device parameters are obtained from the current-voltage characteristic (I-V curve) of the module but the curve varies with irradiance and temperature conditions. The I-V curve is transformed from real operational conditions to STC and vice versa with translation equations. In this paper we investigate the fundamental nature of the translation equations and show that they introduce consistent bias in the power and device parameters, obtained from the translated I-V curves. We show that the nature of the translation equations forces the device parameters to transform from one to another set of irradiance and temperature conditions by algebraic transformations, which are derived in this paper. Validation of our findings is given for the series resistance. Our findings have significant implications for the assessment of module degradation.

光伏模块在标准测试条件 STC 下进行评级，但在实际操作中，它们暴露在非常不同的条件下。模块的功率及其器件参数由模块的电流-电压特性（IV 曲线）获得，但该曲线随辐照度和温度条件而变化。IV 曲线通过转换方程从实际操作条件转换为 STC，反之亦然。在本文中，我们研究了平移方程的基本性质，并表明它们在从平移的 IV 曲线获得的功率和器件参数中引入了一致的偏差。我们表明，平移方程的性质迫使设备参数通过代数变换从一组辐照度和温度条件转换为另一组辐照度和温度条件，是在这篇论文中推导出来的。对串联电阻的研究结果进行了验证。我们的发现对评估模块退化具有重要意义。