I have never understood that sentiment. If you define long term energy storage as being able to discharge at max power for a day or a week you are penalizing s

I have never understood that sentiment. If you define long term energy storage as being able to discharge at max power for a day or a week you are penalizing superior storage technologies for no reason. Let's say that you have two technologies that have the same cost per KWh, the same round-trip efficiencies, etc. Now let's assume one of them has a maximum discharge rate of C/100 so that at maximum power it lasts for 100 hours. Let's assume the other technology has a maximum discharge rate of 1C, so at maximum power it lasts for 1 hour. For the same price, you could have either a system that only works for long term storage or a system that would be considered "short term" storage even though it has the same capacity and the same price as the long term option. There may be some exceptions, but generally whenever you have short term storage you automatically have the option of long term storage as well by just discharging at a lower rate.