Energy Performance Contracting (EPC) is about guaranteed savings. When equipment or facilities are upgraded to improve energy efficiency under an EPC, the energy savings that result are guaranteed by the contractor for the term of the contract (usually 5-7 years). If the savings fall short, the contractor makes up the difference.
Because savings are guaranteed, they can be used to pay off the capital cost of the project with very little risk, even over longer payback periods of five, six or even ten years.
You get the benefits of the upgrades immediately - better comfort or lighting levels, reduced greenhouse gas emissions, often lower maintenance costs - but you use future savings to pay for them. After the project has been paid off, you get to keep all the savings.
Australian Energy Performance Contracting Association