Google parent Alphabet is spinning off a little-known unit working on geothermal power called Dandelion, which will begin offering residential energy services. The announcement Thursday took the wraps off one of the secretive projects at the Alphabet unit X, known notably for its work on self-driving cars and internet balloons. Dandelion chief executive Kathy Hannun said her team had been working for several years “to make it easier and more affordable to heat and cool