Energy efficiency projects often have a life of 10 to 50 years because measures continue to provide returns long after the initial investment has been repaid.

Applying a short pay back standard to a long-lasting measure is false economy, and can cause measures with much larger life cycle savings to be rejected.

'Return on investment' is a better concept than 'pay back' because it acknowledges that the financial benefits start flowing immediately, instead of after the pay back period has elapsed.