Overnight cost is a measure of cost which compresses all the costs involved in creating a new power plant over a period of time into a single measure – as if the power plant suddenly appeared “overnight”.
In cases where the development and construction period is short, the overnight cost might closely equate to the total of development, equipment and installation costs. For other projects, where the pre-operations part of the project is lengthy, there can be significant other costs such as financing (interest etc.) which accrue too. These should be included within a measure of overnight cost.