From The Vault
Solar Powered is a Fallout 3 Perk.
You gain an additional 2 points to Strength when in direct sunlight, and slowly regenerate lost Health at a rate of 1 HP every 10 seconds. Unlike Night Person, which operates both indoors and out, this perk only operates outdoors. It is in effect between 6 AM and 6 PM.
One must beware that due to the strength increase when the perk is in effect, if he is within 20 pounds of being overencumbered, he will become overencumbered upon entering any indoor area as well as after 6PM.
The usefulness of this perk is negligible if you plan on getting the Almost Perfect perk from Broken Steel. At 9, your character will only gain 1 point of Strength, and a well-built character would save his Strength bobblehead so as to get Strength to 10. With that aside, 1 HP every 10 seconds only outside between 6AM and 6PM.