It's outrageously low. They're also fancifully assuming cpu tdp = electrical power, cooling = 0w, and another 0w to the motherboard/network cards. And each box has 1 non-redundant, schmuck-grade $80 psu, as well as a consumer grade mobo. This would never be anywhere near their uptime.
CPU TDP is accounted for, the CPU linked in the blog post draws 65w and that is used in the electricity calculations.
I did realize that I completely forgot about RAM, when I get back to a computer I'll have to make some updates, but it won't materially move the numbers, there's 33% margin of error between the number in the spreadsheet and $2 / TB / Mo.
The $80 PSU is what I could link to from Newegg, I do have experience in industrial electronics, and I know from firsthand experience that you can buy a 10+year PSU at 93% efficiency for well under $80 at 300 watts. At that level, you're going to be able to request all the required cabling as well, which means you're getting a much better price than the $7 per cable linked in the post.
95% uptime means 18 days of downtime per year. Consumer grade PSUs and mobos do much better than that.
You included tdp but tdp /= actual electrical power. Intel approximates it from base clock (practically all consumer motherboards ignore the tdp/boost spec). AMD uses voodoo to calculate tdp, it's a pure marketing number with no basis in power usage. To make matters worse, motherboards typically go nuts with voltage on consumer boards, and power draw can vary wildly depending on what instructions you're using. There are a crap load of x86-64 extensions.
Yes, you forgot ram. And network chips, motherboard power delivery losses, motherboard power usage, cabling losses, etc. I'd guess it would total 50-100w, but feel free to current clamp the psu rails to get a realistic number.
As for the 95% uptime, I agree with you. I wasn't considering how much breathing room that actually provides, I was just going with my instincts.
