What does a 50 W fan cost to run?
50 W ÷ 1,000 × 8 hours × €0.20/kWh = €0.08 per night.
At eight hours a night for 30 nights, that is 12 kWh and €2.40 in electricity. This is an estimate assuming a constant 50 W draw. Your actual power setting and tariff can change the result; standing charges and other bill items are excluded.

