How Much Does it Really Cost (Electricity kWh) to Self-Host A Site?

I installed my new APC BR1500LCD this evening.  The unit has a nice LCD display on the front which tells me the exact wattage (among other things) flowing through the UPS.  Based on my previous experiment as described here, I calculated that the server connected to the UPS consumes about 240 W of energy.  As it turns out, my calculations were a little high.  Assuming the BR1500LCD is accurate, the server actually uses closer to 200 W when idling (which is even better, meaning I can extend my battery life even further than I thought because it uses less wattage).


HOW MUCH DOES ALL THIS COST?

OK, so the ammeter from my experiment said that the server uses about 240 W.  My new APC UPS says the server uses about 200 W.  For the sake of this post, I'll assume the actual wattage is somewhere in the middle: 220 W (0.220 kW).

If this system is online for one hour, that means it uses 0.220 kWh's (kilowatt hour) of electricity from my utility company.  According to my last utility statement, electricity costs me roughly $0.12 USD (12-cents) per kWh.  To find out how much it costs to run the system for a single hour:

0.220 kWh * $0.12 = $0.0264 USD (about 3-cents) per hour

OK, it costs 3-cents (rounding up) per hour to run my server.  Well, my server is never on for only an hour, so lets multiply this out to compute the cost for a whole month (assuming a month is 30-days):

$0.03 * 24 hours = $0.72 USD (72-cents) per day

$0.72 * 30 days = $21.60 USD per month

So it costs me roughly $21.60 per month to keep kolich.com online 24/7/365.  Now I can answer some of these questions ...

• What percentage of my total monthly utility bill goes to keeping kolich.com online 24/7/365?  My monthly utility bill includes gas, and electric.
  
  My utility bill is about $60 USD a month, on average.  So $21.60 of $60 is about 36%.  Roughly 36% of my monthly utility bill goes directly to keeping my server hardware running.
  
  
  
• In terms of electricity costs only, how much does it cost me per month to keep kolich.com running 24/7?
  
  $21.60 USD per month.
  
  
  
• If I only turned on the server when I was actually in my home, how much would I save per month?  This doesn't make sense for a web-server, but most folks have some type of desktop computer they only turn on when they are actually using it.
  
  Assuming I'm only in my home, awake, for about 8 hours a day, my electricity costs for kolich.com would shrink to $7.20 USD.  So, that's over $14 USD of utility savings per month.  For some, this might be a big deal.  But generally, $14 to keep a server online 24/7/365 is well worth the expense.
  
  
  
• If I "upgraded" to an equally powerful yet more energy efficient box, how much would I save per month?
  
  I've included a graph below that gives you a rough idea how much leaving a piece of equipment on 24/7 actually costs.  The graph assumes your utility company charges you $0.12 per kWh.  If I was concerned about the costs, I might be able to "upgrade" to a more energy efficient box to save roughly $5-$10/month.  In my opinion, the hassle of migrating to another server isn't worth the $5 to $10/month savings.
  

Here's the Excel spreadsheet I used to make these calculations and build this graph.

Enjoy.