By Nichola Groom LOS ANGELES (Reuters) – In a first on Monday, an online marketplace will allow U.S. homeowners to weigh options for going solar as easily as they can compare prices for airline tickets. Geostellar, a startup backed by power producer NRG Energy Inc, is seeking to become the Expedia or Orbitz of the solar industry — a one-stop shop where consumers can not only compare the benefits of leasing solar panels versus buying them outright, but ultimately sign up to install a system. Solar players including NRG, No. 1 U.S. …