Do you know how much does a single web search costs?. The cost in not measured just in dollars, its in terms of power consumption. 
The searches which we do on the search engines like Google, yahoo etc are powered by millions of computers which are packed into warehouses. These computers are integrated together to form a single system which helps the searchers to obtain required content. According to laws of Thermodynamics, it wastes energy.
First law states that to do any work, it needs energy, i.e, to work done to move electrons across silicon wafers. The second law states that some of the input is lost usually in the form heat. 
When we hit a search & successfully get the required content we become happy, but in the server due to the thermal motion of atoms agitates air molecules behind the CPU racks which heats them. Hence thereby requiring computer fans & air conditioning units used to remove the heat produced from the warehouses.
IT research firm, Gartner estimates & says that Google's data centers have around million servers in which each server draws electricity of 1 Kilowatt power. So, keeping this estimates, Google's engine utilizes around 1 million Kilowatt-hours & moreover, Google search engine serves up to 10 million search results per hour across the globe.