Can I Recite Aloud When I Pray Alone?
Question

What is the ruling on reciting out loud in prayer for one who is praying alone? Is it permissible to recite silently?
Praise be to Allah.Reciting out loud in Fajr prayer and in the first two Rak`ahs of Maghrib and `Isha’ is Sunnah for both, one who is leading the prayers and one who is praying alone . If a person recites silently there is no sin on him, but he would be  neglecting an act of Sunnah .
If the person who is praying alone thinks that reciting silently helps him to focus more in prayer, then that is O.K., because it was narrated that when the Prophet (peace and blessings of Allah be upon him) prayed at night, sometimes he would recite aloud and sometimes he would recite silently, as was reported by `Aishah (may Allah be pleased with her).
For one who is leading the prayers, the Sunnah is always to recite out loud , following the example of the Prophet (peace and blessings of Allah be upon him) and because that enables the congregation to benefit by hearing the words of Allah, whether the prayer is obligatory or supererogatory. 
And Allah is the Source of Strength.