The term “grid” suggests a certain uniformity to the power system’s structure, but the network more closely resembles a patchwork quilt stitched together to cover a rapidly expanding nation.

The United States doesn’t yet face the critical shortage of power that has left more than 600 million people in India without electricity this week

But the U.S. grid is aging and stretched to capacity. More often the victim of decrepitude than the forces of nature, it is beginning to falter. Experts fear failures that caused blackouts in New York, Boston and San Diego may become more common as the voracious demand for power continues to grow. They say it will take a multibillion-dollar investment to avoid them.