Power factor

ispookie666

What effect would power factor have on battery storage systems (read as Inverter + Battery)? Is this purely academic or does this affect the usable power which can be extracted from batteries?  

I have noticed the power factor (on EM115 meter for Givenergy) to range from 0.2 to 0.9, the lower values when the power consumption or generation is low.  

Heedtheadvice

Not sure this will answer your question but might help......or yet again might confuse!

.....and I hope I am not teaching you to suck eggs!

Power, at any particular time can be calculated as the instantaneous potential difference in a circuit ( voltage )  multiplied by the instantaneous current (Amperes) i.e. P= VxA

For a dc system (battery and the like) at any moment that is a straight forward calculation VxA.

However for an Alternating Current system the voltage and current have a varying i.e. sinusoidal waveshape. For a purely resistive source and load the voltage and current waveshape (the sine wave) are identical in time so that simple formula works there too VxA.

For some cuircuits with a significant amout of capacitance and/or inductance (usually in combination with resistance) then the current waveform is not in time with the voltage, it can lead or lag, i.e. is not synchronous and is therefore out of phase. That means that the instantaneous values need to be know through that phase relationship and the amplitude given a correction factor to take account such as Vx cos(phase angle) A. The greater the time difference the bigger the phase angle.

Normally synchronous voltage and current is zero time difference and therefore zero angle, so cos of the angle is 1. So power is Vx 1 x A. but as the phase angle between the two waveforms increases the power is reduced according to the cosine value reaching zero at 90degrees (where the instantaneous voltage is max but current is zero....or current max voltage zero etc.). That angle is known as the phase angle and the figures quoted are the cosine values i.e. the Power Factor.

So at 0.9 power factor, the power is 90% of what it would be fir synchronous Voltage and Current waves and 0.2 just 20%. I am assuming therefore that at low generation just 20% of potential power (if it were in phase) is produced and thus there is a big efficiency loss at low generation levels.

The batteries being DC should still have the same storage capacity so I guess it is just the conversion that becomes less efficient.

I would hope that somebody who knows the particular derivation of the figure you quote knows better!

ispookie666

@Heedtheadvice I sort of understand the power factor and its always good to refresh the knowledge.  
I do know that domestic premises are not charged for kVA or kVAR.  

Suppose the inverter battery has a limit of 3000VA and you are using roughly 2000VA, following this you turn on another load.  If the Apparent power goes above 3000VA will the meter register this?  or will it only register Actual power?

Maybe I'm talking porkies 

Heedtheadvice

Never mind the non answer I gave...

I am not even sure I understand your question!!

What do you mean by apparent power?

Which meter are you considering?

gefnew

Could this help in your quest.
What is Power Factor? | How to Calculate Power Factor Formula | Fluke

Heedtheadvice

What a great explanation! Never did want all that froth!

ispookie666

Thank you for the nice analogy.