Yuma Sun: The challenge is the economy; the opportunity is clean energy. More and more Americans realize the challenges we face are connected. Our overreliance on fossil fuels is the leading source of global warming emissions, pollutes our air and water and exposes consumers to the price spikes of a global fuel market. We need to repower America by shifting to 100 percent homegrown clean electricity, cut our dependence on oil in half and dramatically cut global warming pollution — moves …