In March, the world passed a major energy milestone, adding its third terawatt of solar power. It took nearly seven decades, after the invention of the silicon solar cell in 1954, for the world to install 1 terawatt of solar capacity, conceivably enough to power the entire United States. BloombergNEF expects installations will continue apace, with the world hitting 9 terawatts of solar power by 2036. Analysts project that, by that date, poor countries will have installed more solar power than rich countries, China notwithstanding. The first terawatt of solar was installed largely in wealthy nations, as governments subsidized renewable energy, Bloomberg reports.