Chemoorganoheterotrophic organisms use the energy that is chemically linked to nutrients for biosynthesis, maintenance of the structures, replication and growth. The attainable growth efficiency [1] as well as the growth rates [2] are determined by thermodynamic rules and can be calorimetrically monitored in real time. This is of great practical importance if, for example, microorganisms are to be used as producers in the chemical industry. Interestingly, despite the impressive successes of biothermodynamics and calorimetry in the area of chemoorganoheterotrophic energy conservation, non-chemical energy sources for microbial growth (e.g. light and electricity) have been largely neglected. Here, the energy of photons and electrons allows the microbial reduction of CO2 and make bio-reactions feasible which are thermodynamically not allowed. Potential reasons for this surprising lack of knowledge are challenges to develop the required tailor-made calorimeters and to quantify very low energy conversion efficiencies in case of photosynthesis. For these reasons, new photocalorimeters and bioelectrocalorimeters were developed and tested. In the case of light energy, it is now possible to determine the efficiency of energy conservation as a function of light intensity and environmental conditions in real time with an accuracy which is not accessible by other methods. This was successfully confirmed for two examples: Microalgae of industrial (Chlamydomonas reinhardtii) and ecological (Phaeodactylum tricornutum) [3] importance. In the case of electrical energy, we succeeded with our calorimeter in quantifying previously unknown energetic burden for growth on electrodes (i.e. microbial electrochemical Peltier heat).[4] Numerous applications of the new calorimetric techniques are conceivable