Asceticism can be considered. It involves positive solitude and self-improvement practices. It is usually a religious discipline but not necessarily, it is also a life-style.
Asceticism describes a lifestyle characterized by abstinence from worldly pleasures, often for the purpose of pursuing spiritual goals.
http://en.wikipedia.org/wiki/Asceticism
There are two types of asceticism, relative and ultimate, and each of these having mundane and spiritual varieties:
[Asceticism edited by Vincent L. Wimbush Professor of New Testament and Christian Origins Union Theological Seminary, Richard Valantasis Professor of New Testament and Christian Origins Iliff School of Theology]
Also, solitude is often used in positive sense as opposed to loneliness and isolation. But to be more specific, you can consider the phrase positive solitude which is self-explanatory. Wikipedia mentions the positive psychological effects of solitude as below:
Another proven benefit to time given in solitude is the development of self. When a person spends time in solitude from others, they may experience changes to their self-concept. This can also help a person to form or discover their identity without any outside distractions. Solitude also provides time for contemplation, growth in personal spirituality, and self-examination.