How much money will it save? This Sciendirect publication calculates a yearly saving of only €4. So it seems not worth it. But their model uses a temperature window of -16 to -27 Celsius and assumes a freezer that has a 4h safe food storage capacity in case of power blackout. However my freezer has a 17h safe food storage capacity and we can widen the temperature range to let's say -32 Celsius, so we might save €24 per year.