What is the difference between prana, qi (or chi) and kundalini?
First let us try to relate to concepts from the same tradition - prana and kundalini. Prana has been translated as the ``vital breath'' and ``bio-energetic motility''; it is associated with maintaining the functioning of the mind and body. Kundalini, in its form as prana-kundalini, is identical to prana ; however, Kundalini also has a manifestations as consciousness and a as a unifying cosmic energy. One could ascribe these same aspects to prana as well so past a certain point these become distinctions without differences.
From the subjective standpoint of an individual actually experiencing the awakening of kundalini I have found three completely different opinions:
The first opinion is that a pranic awakening is only a prelude to a full kundalini awakening. Tibetan yogins that I have encountered consider the activation of prana (Tibetan: rlung) as merely a prerequisite for the activation of kundalini (Tibetan: gTummo). What's attractive about this viewpoint is that it explains the difference between the experience of simply having pleasant sensations in the spine and the much more powerful experience of having a ``freight-train''-like full kundalini experience.
The second opinion, espoused by Swami Shivom Tirth for example, is that prana and kundalini are absolutely equivalent and that it is not meaningful in any way to describe a difference between kundalini rising and prana rising. When posed with question as to how to distinguish between pleasant sensations that show some pranic-activity in the spine and the much more powerful experience Swami Shivom Tirth said that the difference is not in the nature of the activity but in the consciousness that observes it. If the consciousness that experiences the pranic activity is seated within the spine (or more correctly, the central channel, known as the sushumna), then the experience is felt much more powerfully.
The third opinion, espoused by the modern hatha yogin, Desikaran, is that pranic awakening is the true experience to be aimed for and kundalini is actually an obstruction. Desikaran sees the kundalini as a block in the central channel and thus the kundalini must be ``killed'' to make way for the prana. This is the most unusual view of the three.
The Chinese concept of qi (or chi) can be safely identified with the Indian concept of prana.
If all this seems confusing - don't worry, you're in good company. My conclusion is that these are all different terminologies for dealing with a common set of experiences. Any one of these viewpoints is adequate for describing the full range of experiences. What is probably more relevant is to distinguish two different experiences which are often confused. In one an individual experiences some pleasant energizing electric energy running along the spine. This experience itself brings about a wide range of experiences and results in vitality and sensitivity.
Another very distinct experience is the experience of kundalini entering the sushumna and rising up the spine. As soon as kundalini enters the sushumna this experience will completely overwhelm ordinary waking consciousness. From the moment that kundalini enters the sushumna there will no longer be a distrinction between the subjective consciousness which experiences and the object of experience. This experience much more profoundly transfigures consciousness.