Sustainability
Embodied Energy Payback
What to compare before estimating energy payback.
What to compare before estimating energy payback.
Making and installing equipment takes energy. An energy payback assessment asks when the cumulative energy generated or saved offsets the energy invested, using the same energy accounting basis on both sides.
A comparison needs a defined product, site, operating pattern and alternative. Energy payback, carbon payback and financial payback answer different questions.
Compare the energy invested in the installed system with its expected generation, using a consistent energy accounting basis. Location, shading, orientation and manufacturing assumptions affect the result.
Compare systems delivering the same useful heat. Use the heat pump’s seasonal performance, the alternative heater’s fuel use and a consistent basis for electricity and fuel.
A battery shifts when electricity is used and loses some energy in the process. An assessment needs to show how charging and discharging change energy use compared with operating without storage.
Compare lamps delivering similar light output. The lamp being replaced, hours of use and replacement frequency determine the energy saving.
Compare the energy invested in the materials and installation with the heating or cooling energy saved in that building. Climate and the existing fabric matter.
A wallbox supplies electricity to the vehicle. To assess an energy saving, define a different charging setup or compare the vehicles and journeys in a wider transport assessment.
For an example of how a study defines its boundaries and assumptions, see the IEA PVPS lifecycle assessment guidelines for photovoltaics.