Defrost your freezer (or the freezer compartment of your fridge) regularly as ice builds up. In fact, just 2 mm of ice means the appliance consumes 10% more energy. For example, if your fridge consumes 2kWh/day, monthly derfosting may save you at least 73 kWh/year.
No investments, just creating an electricity saving habit.
How to reduce the power consumption of my refrigerator and freezer?