The following logos have been sized specifically for use on Powerpoint Posters. Whenever possible, use the vertical color logo. If the vertical logo doesn't work well with your layout or you have to reduce it in size so that the "United States Department of Energy" line becomes so small that it's difficult to read, then use the horizontal color version. If you're using it in a document that will be printed only in black and white, use the grayscale version. Only use the black version if the you are placing the logo on a screened background on which the screened "ball" is hard to distinguish.
When you click on the "Download" link, the logo will appear in a new tab and display at its actual size. Right click on top of the image and select the "Save image as..." option from the menu and save the file to a folder where you can find it for future use.