UPDATE. Our property is quite well lit at night. The infrared lamps built into the cameras do a good job, but they also consume quite a bit of electricity, about 20 Watts each. I wondered how the cameras would perform without the infrared lamps, so we took one down, opened it up, disconnected the lead to the lamp, reinstalled the camera and waited for dark. As you can see below, the cameras perform quite well without the infrared.
So we will be disconnecting the infrared lamps from the other cameras for a saving of about 20W X seven cameras = 1.7 kWh per night or P17 per night or P510 per month.