You do pay for the electricity cost. Assuming the Rpi consumes 10W and is on 24/7 and your electricity cost is $0.15/kwhr : 365d * 24h * 0.01kW * $0.15 = $13.1

You do pay for the electricity cost. Assuming the Rpi consumes 10W and is on 24/7 and your electricity cost is $0.15/kwhr : 365d * 24h * 0.01kW * $0.15 = $13.14/yr in electric costs.