Most cheapest energy
HOW we can save energy and in what way we can produce energy by cheapest way.
Who is "we"? As in the world population? The US? You?
There are a thousand sites dedicated to energy use. https://www.google.com/search?q=saving+energy+tips&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla:en-US:official&client=firefox-a