I'm sure much has been discussed about power usage on the cMP, but I wanted to run some everyday numbers on my cMP 4,1 just to see the costs of operating the machine 10 years later. With the passage of time, efficiency gains in technology might lead us to think that these old machines are going to hit us in the pocket book when it comes to energy consumption, but just how much does it cost? Are machines from 10 years ago really so inefficient to consider replacement? Is tossing what works for something newer more environmentally friendly? Well, those questions were the purpose of my testing! Not long ago, I got myself a Kill-A-Watt meter, so now my questions can be answered! First off, I'm running an updated version of the 4,1. I've flashed it to 5,1, installed a W3690, pulled the spinning drive for an SSD, added an RX 580, and updated to Mojave. Since I can't effectively use my Mac without a display, my measurements will include my monitor--a very modern LG 27" 4K IPS display. I may eventually measure the display just to be able pull it from the results. Assumptions: I let my machine sleep after 15 minutes of idle, and I don't turn it off. Sleep is a big contributor, as it will be the state of my 4,1 probably 80-90% of the time throughout the year. I allow the monitor to also go to sleep. For these results, I'm assuming approximately 20 hours of the day my machine will sleep. The other 4 hours of the day will be mixed use. I rarely load my machine (no games, rare encoding), so I don't expect heavy load usage rates very often. I will be generous and say I load my machine for 1 hour a day and it idles for the other 3 hours. I'll use the average US national rate of $.12/kWh to estimate a yearly cost and this site to do my math. Results: Sleep: 5W, or 37 kWh per year ($5) Idle at desktop: 142W, or 155 kWh per year ($19) Heavy workload: 315W, or 115 kWh per year ($14) So for my use case, my 4,1 Mac Pro with display costs me about $38 a year to operate. I'm actually quite surprised that the idle power draw was so low. The energy efficiency of such an old machine is commendable. I think my usage is being quite generous to the high side--I probably am overestimating my usage by at least 10%. I'll run a few other household items and see how they compare. I have a late model PS4 Pro attached to a 48" UHD that I'm curious to measure as well.