Wall Street Journal: Some of the biggest energy hogs in a company sit in front of workers everyday: their PCs. For a company that has 10,000 personal-computer desktops, for example, just leaving most of them turned on all night can cost more than $165,000 a year in electricity bills, while spewing more than 1,380 tons of carbon dioxide into the air per year, estimates a 2007 report by the Alliance to Save Energy, an advocacy group in Washington, D.C. That’s roughly the amount of greenhouse gas …