“Berkshire will always be building.” So said Warren Buffett in his latest annual letter to Berkshire Hathaway shareholders in February. Most people might imagine he means adding to Berkshire’s dozens of company holdings or the $144 billion in cash he calls a “financial fortress.” But he was actually referring to clean energy. Buffett has had exposure to clean energy since the early 2000s, and in last year’s letter, he called it one of the “four jewels” of Berkshire Hathaway. A 30-fold Increase F