The two billionaires with substantial solar stakes are Christy Walton and Zhu Gongshan of China.

FORBES: World's Greenest Billionaires 2013

The U.S. tops the ranking with 44 fresh faces, including the richest newcomer, Christy Walton, who inherited her fortune from her late husband, John.

FORBES: New Faces

Joan Vehik, Alice Walton, Christy Walton, Helen Walton, John Walton, Martha Whetstone, Carl Whillock, Margaret Whillock, Susie Whitacre, Caroline Whitson, Heather Whitson, Turner Whitson, Donna Axum Whitworth, J.

CNN: AllPolitics - Guest List

Christy Walton, the richest of the new billionaires in 2006, took on her fortune from her husband John, who died last June and was himself a Wal-Mart Stores heir.

FORBES: Magazine Article

Christy Walton, the richest of the new billionaires in 2006, took on her fortune from her husband John, who died last June and was himself a Wal-Mart Stores (nyse: WMT - news - people ) heir.

FORBES: Women We Envy