BENGALURU -- It took three months of research before 25-year-old finance professional Sagar Agarwal took the plunge into rooftop solar, joining an initiative widely recognized as the largest of its kind in the world. But despite being a resident of Lucknow, which in April became the Indian city with the most residential solar installations, he was left frustrated by the friction he encountered -- a situation mirrored across the nation, whose lopsided rooftop solar rollout threatens to impinge on energy