Power Factor and CO2 Emissions

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timm333

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Electrical Design Engineer
I am trying to figure out how to calculate the kVAR of power factor capacitors based on CO2 emissions. If the CO2 emissions (in Lbs/MWH) are known and the required minimum power factor is known, then how do we calculate the size of the capacitors in kVAR? Thanks.
 
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I don't think the numbers are directly connected.

Your CO2 emissions depend upon real power consumption (Lbs/MWh).

Your capacitors alter reactive power, which is energy shuttling back and forth between parts of the grid without being consumed. Reactive power does not directly consume energy and does not directly cause emissions.

Reactive power does increase losses in the grid, and those losses are real power with real emissions. But that is indirect. Adding capacitors does not reduce reactive power, it simply makes it circulate more locally thus reducing losses. (Actually if you put capacitors at a distant location relative to the load the serve you might increase losses.)

Capacitor size is based upon the reactive needs of the load, not power consumption or generator emissions.

Jon
 
As Jon mentioned, I think CO2 emissions and kVAR are generally not directly related, unless as part of some weird method of calculating CO2 emissions, they related them.
Since the zero energy crowd is unregulated and become pretty creative in their calculation methods, someone may have whipped up a CO2 calculation from VAR, but generally it is based on W + indirectly VAR.
 
timm333 said:
I am trying to figure out how to calculate the kVAR of power factor capacitors based on CO2 emissions. If the CO2 emissions (in Lbs/MWH) are known and the required minimum power factor is known, then how do we calculate the size of the capacitors in kVAR? Thanks.
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The short answer is that you cannot do what you want.

What you could do potentially, is calculate how much energy was saved by using power factor capacitors. Basically you can reduce the I squared r losses in the wiring feeding your loads because power factor capacitors can reduce the current level in those wires. It's not a whole lot, and I don't know how you'd ever get any kind of reliable numbers to use. You probably just have to make them up like so much of this kind of stuff is with a lot of assumptions and speculation about such things.

Once you figure out how much energy was saved should not be real hard to work backwards from there and figure out how much CO2 was avoided. Not sure why it matters to you unless it's just an attempt to look green by selling snake oil in the form of capacitors. There are plenty of people doing that already.
 
It looks that we can calculate it indirectly. The standard value of CO2 emission is 0.85 Lbs/kWH as mentioned at this link: https://www.eia.gov/tools/faqs/faq.php?id=74&t=11

Let’s say the load is 1000 kW at power factor of 0.75 and if we increase the power factor to 0.9 then we will have to add capacitors of 397 kVAR and we will save 222 kVA. But the problem is that active power will still be same (1000kW). If we are able to convert kWH to kVAH then we will be able to calculate that how much CO2 will be saved by saving 222kVA. How do we convert kWH to KVAH in this case? What do you guys think about it?
 
Capacitors do not eliminate reactive power flow. They simply redirect it. So you are not 'saving 222 kVA'. That 222 kVA is now flowing between the capacitors and the load rather than on the transmission line.

You see indirect savings because when that 222 kVA flows on your transmission line it causes real losses. You need to calculate the real losses on the transmission line caused by the reactive power that had been flowing on the line. You also need to calculate any new real losses in your capacitor system. The net reduction in losses is a net reduction in kWH.

In other words you cannot convert kVAH to kWH. You can only calculate the losses (in kWH) caused when so many kVAH flow on a given component.

If you had a zero loss transmission line, then the reduction in power factor would result is zero real energy savings.

-Jon
 
timm333 said:
It looks that we can calculate it indirectly. The standard value of CO2 emission is 0.85 Lbs/kWH as mentioned at this link: https://www.eia.gov/tools/faqs/faq.php?id=74&t=11

Let’s say the load is 1000 kW at power factor of 0.75 and if we increase the power factor to 0.9 then we will have to add capacitors of 397 kVAR and we will save 222 kVA. But the problem is that active power will still be same (1000kW). If we are able to convert kWH to kVAH then we will be able to calculate that how much CO2 will be saved by saving 222kVA. How do we convert kWH to KVAH in this case? What do you guys think about it?
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It does not work that way. You save some energy but it is solely the I^2R losses in the conductors that has a slightly higher current when the power factor is lower for the same real power.

As a practical matter, it will be very difficult to calculate the savings in even a remotely accurate way because of all the assumptions one would have to make.
 
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