If power is free, difficulty would be 10x of what it now and no body profit other then manufacturer.. so its still the same..

You are somewhat missing the poin... if power was free, as in power "in general", no one would need to work because automatization would be widespread enough for most jobs to be redundant, so an economy can't and isn't necessary when humanity has reached free power (post scarcity). Geothermal tecnology is pretty much free power.