Inthe transition to decarbonizedenergysystems, Power-to-Gas (PtG)processes have the potentialtoconnecttheexistingmarketsforelectricityandhydrogen. Specifically,reversible PtGsystemscanconvertelectricitytohydrogenattimesofamplepowersupply,yettheycan. Our reversible power plants reach up to 80% efficiency in electricity conversion, making them twice as efficient as conventional systems. Specifically, reversible PtG systems can convert electricity to hydrogen at times of ample power supply, yet they can also operate in the. Specifically, reversible PtG systems can convert electricity to hydrogen at times of ample power supply, yet they can also operate in the reverse direction to deliver electricity during times when power is relatively scarce. Here we develop a model for determining when reversible PtG systems are.