The micromechanical photothermal spectroscopy system and method includes a cantilever assembly having at least one cantilever thermal sensor extending from a support. The sensors may be simple bimetallic sensors, or may include microchannels made from two materials having different thermal expansion coefficients for analysis of microfluids. A beam of infrared light is separated out from solar radiation by gratings and filters, and is at least partially projected on the cantilever sensor(s). Heat released from the analyte by absorbance of infrared light results in deflection of the cantilever sensor(s), which is measured by a deflection detector. A filter wheel permits tuning of the sunlight-based infrared light beam to plot a spectrum of absorbance as a function of wavelength or wave number characteristic of the analyte. The deflection detector may be optical (using a laser and position sensitive detector(s)), or may use piezo-resistive material embedded in the sensor(s).