Comparing electrolyser costs reveals clear trade-offs. Alkaline systems are cheapest to buy & last longest but are slightly less efficient. Proton exchange membrane systems cost more because of rare metals yet respond quickly to wind & solar & produce very pure hydrogen. Solid oxide high-temperature systems are the most expensive to build but use about a third less electricity, making them cheapest where free industrial or nuclear heat is available. Because electricity makes up most of the cost of green hydrogen, power prices matter more than technology choice