In an effort to replace fossil fuels by more sustainable solutions, the demand for green hydrogen hasgrown significantly over the last few years. This has raised the interest in electrolysis and has boostedits development. Water electrolysis produces hydrogen and oxygen from water using direct current,nowadays often with an electrochemical efficiency of around 80%. Although much effort has beenmade to reach such high efficiencies little research has been done on the excess heat produced byelectrolysis. This thesis intends to cover this topic, mainly focussing on Proton Exchange Membrane(PEM) electrolysis. All of the inefficiencies of the electrolyser translate into heat and it is the objective ofthis research to investigate how much of this heat can be extracted and contained for use in a separateapplication. Furthermore, in the second part of this thesis, the available applications are studied in anoffshore and onshore production scenario to better understand potential of this heat.In order to accurately simulate the thermal behaviour of a stack of PEM cells an electrochemical andthermal model was created representing the average largescalePEM electrolyser of today. Furthermorea basic integrated cooling system was designed in order to assess how much heat can be extractedfrom the stack and at what temperature. The system consists of separate channels for coolingwater inside the bipolar plates that separate the individual cells. It was found that well over 90% ofthe heat produced by the stack can be extracted in the form of cooling water at a few degrees (<3표퐶)below stack temperature without impeding the performance of the stack. The largest contributor to heatbeing lost, was found to be the production of water vapour on the anode side of the cells which can bereduced significantly by operating with an elevated pressure in the anode chamber (5 bar).In the onshore case study it was found that an electrolyser is very well suited to be connected to adistrict heating network. The low temperature heat serves well for applications such as space heatingand/or water heating. In an offshore scenario the excess heat can serve to aid in thermal desalinationhowever it proved to be more difficult to find an adequate application for the full amount of producedheat.In conclusion, the models presented in this thesis have shown very satisfactory results in terms potentialof excess heat. It has proved to be a very interesting field of study and more indepthresearchas well as broader studies on possible heat applications can be conducted to fully understand thepotential of excess heat from electrolysis.