Energy efficiency refers to any method where less energy is consumed to attain the same amount of useful output. There are opportunities for energy efficiency measures at all levels of energy use, from household appliances to large-scale industrial projects.  Across the board, energy-efficient products reduce energy costs and decrease reliance on energy imports. Similar to renewable energy sources, energy-efficient products and processes reduce greenhouse gas emissions, but given the price of renewable energy, energy efficiency is sometimes the cheaper option for reducing greenhouse gas emissions.