Tesla’s energy business could become $20 billion to $50 billion more valuable if Elon Musk’s plan to build 100 gigawatts of yearly solar cell manufacturing capacity in the United States pans out, analysts at Morgan Stanley say. “The solar opportunity is underestimated,” Musk told analysts on Tesla’s Q4 earnings call last month. “We think the best way to add significant capability to the grid is solar and batteries on Earth and solar in space,” he added. As Musk sees opportunities in the solar manufacturing…