Those dells pull about 30W at near-idle. Let's assume 40W given an extra NIC and the workload running. US domestic power averages about 12.3 cents per kWh. So

Those dells pull about 30W at near-idle. Let's assume 40W given an extra NIC and the workload running. US domestic power averages about 12.3 cents per kWh. So 36 bucks a year versus 8 bucks per year for the ERL.