Greenpeace said yesterday that it has purchased $241,000 of stock in the Royal Dutch/Shell oil company in an effort to pressure the company to build a huge solar panel production plant. The group bought the minimum stake required so that it has the right to communicate with fellow shareholders ahead of the company’s annual meeting on May 9. Greenpeace recently commissioned a study from the consulting firm KPMG that found that Shell could get a 15 percent return on investment in solar energy. Greenpeace is mounting a similar campaign to get British Petroleum to make big investments in solar.