A better formula to calculate power costs

[taltamir]

A good rough estimate for those unwilling to do the math is 1$ per 1 watt per 24/7 on device... I do the math before every purchase.

But you can derive a better formula:
1 watt * 1kilowatt/1000 watt * 24 hours/day * 365 days/year * 0.07$/kilowatthour = 0.6132 $/year @ 1 watt @ 7 cents per KWH.
many people pay more for their electricity though... at a more realistic 11 cents per KWH you do:
1 watt * 1kilowatt/1000 watt * 24 hours/day * 365 days/year * 0.11$/kilowatthour = 0.9636 $/year @ 1 watt @ 11 cents per KWH.
1.0512 $/year @ 1 watt @ 12 cents per KWH.

But actually... 1.0512 / 12 = 0.0876. Thats the ratio that is always what you get when diving the above results, you can use to build the following equation:

For an always on device (24/7): year power cost in $/year = 0.0876*E*P
where E = Power in watts
where P = Cost per Kilowatt hour in Cents

so 30 watts in a place that cost 14 cents per KWH will give you: $/year = 0.0876*30*14 = 36.792 $/year.

to convert this to a machine that is on X out of 7 days, multiply this value by X/7. To convert it to a machine that is on Y hours per day multiply by Y/24.
To convert this to a value for a machine that is on Z hours per week multiply it by Z/168

So a machine that is on 40 hours per week will cost to operate per year:
$/year = (40/168)*0.0876*E*P

Generic formula:
$/year = M*0.0876*E*P
where E = Power in watts
where P = Cost per Kilowatt hour in Cents
where M = Multiplier based on how many hours per week, days per week, or hours per day the machine runs. Use 1 for this value if it is on 24/7/365.

 

[SpeedEng66]

my power company sends me a bill every month they calculate it for me
heh

Im no math wiz or anything but a pc for example will use more watts while under load and less when in idle.. how can you really calculate something that can fluctuate so much?

 

[taltamir]

my power company sends me a bill every month they calculate it for me
heh

Are you sure they aren't showing you the cost per KWH calculation rather then how to calculate the yearly cost in $s of various devices?

Im no math wiz or anything but a pc for example will use more watts while under load and less when in idle.. how can you really calculate something that can fluctuate so much?

1. This work for non computer devices... ex: stereo, TV, etc... they typically have more stable power consumption.
2. For a PC that is alternating, measure the power consumption at the wall at idle and at load. Calculate the consumption at load based on how many hours a day it is at load status (on average), and how many hours in idle status. EX: computer A takes 80 watts at idle, 140 watts at CPU load, and 250 watts when loading GPU as well (playing a video game), and 5 watts while off.

Formula is $/year = M*0.0876*E*P
If you do some timing for a week or maybe longer and get your daily averages you can calculate it like so
$/year = M*0.0876*E*P + M*0.0876*E*P + M*0.0876*E*P + M*0.0876*E*P
where you can take factor out P (the M and E are different for each instance and cannot factor out) to get:
$/year = (M*0.0876*E + M*0.0876*E + M*0.0876*E + M*0.0876*E)*P
where each instance of the formula uses the different data, if you play games 2 hours a day, idle for 4, load for 2, and it is off for 16 hours
$/year = (2/24*0.0876*250 + 4/24*0.0876*80 + 2/24*0.0876*140 + 16/24*0.0876*5)*P

 

[FortressDewey]

Perhaps use this calculator and then up the results by 10% to cover for any miscalculations. http://www.matthewb.id.au/power/computer_power_consumption_calculator.html

Good luck

 

[taltamir]

The calculator you linked is used to predict how much power (in watts) you draw from the wall based on component selection. So if you give it your components, it will tell you that your idle power is X and your load power is Y etc...

My calculations is to calculate the COST of electricity if you already KNOW your wattage consumption. I recommend using a real measuring device such as the kill-a-watt meter rather then an estimator tool on some random website.
I OWN one of those tools and I have recorded my real power consumption at the wall, I do not need any "estimator" tool for something best measured.

Besides, even if it was a real power COST calculator; why would I use a black box 3rd party calculator when I know exactly how to calculate it myself? I derived the formula, I am sharing them now.
I am not even asking how to do the stuff but sharing a better formula for calculating it yourself (accurately)