The Raspberry Pi is a series of small single-board computers, very cheap, and very useful for hosting simple servers such as VPN server or DNS server that will contribute to strengthen your security and privacy.
Power consumption of a Raspberry Pi
A 700 mA power supply on 5v, which makes 5v*0.7A = 3.5 Watts at the max for the B+ model.
I measured the real power consumption at 2.8 Watts.
Evening 2.8 Watts x 24 hours x 365 days = 25kWh per year.
At the EDF rate of 0.1452 euros per kWh, running one (or more) servers on the Raspi will cost us 3.56 euros per year.