The operational modes of high-temperature (HT) electrolyzers are developed and explored. The benefits and operational limitations of using the HT electrolyzers are discussed. HT electrolyzers have difficulty in receiving heat which must come from electrical resistance in operational modes such as isoelectric point if there is no high temperature heat from external processes available. Low temperature electrolyzer cells can easily use water at ambient state but HT electrolyzers need additional heat for the evaporation of supplied water. Pressurization of the system is an option to reduce the demand of evaporation. Any electric heating as microwave, electromagnetic radiation and heat pumps which could be possibilities for introducing heat to HT electrolyzers are discussed in this context. The implications on the performance of HT electrolyzers and larger systems containing HT electrolyzers operating around the isoelectric point are discussed. It can be easily shown by thermodynamic evaluation that only an optimized system design and integration can deliver reliable solution. Energy supply scenarios, such as hydrogen production and supply, are discussed with respect to these larger systems. An outlook to possible electrochemical production systems is given as well.