Photoacoustic (i.e., photocalorimetric) measurements on photovoltaic devices can directly yield their energy conversion efficiency. This is illustrated for a Si solar cell, for which case excellent agreement is found with normal electrical measurements. In addition, the photoacoustic spectra under load and at open‐circuit conditions are reported and compared with the cell’s spectral response. Together, such measurements can provide information on the wavelength dependence of the cell performance as well.