Energy measurement kVARh

Sterlingtimes

My household electricity meter measure reactive energy in kVARh as well as active energy in kWh.

Is there any value to me in knowing my kVARh usage? The reactive energy (import and export) is approximately half of the associated active.

Strider590

It's basically about power factor, the phase shift between voltage and current when powering inductive or capacitive loads. This phase shift is wasted power, because (due the way meters work) you pay for more than you actually use.

Power Factor = kWh / (square root (kWh squared + kVARh squared))

Generally speaking if your power factor is less than 95%, you'd consider power factor correction (big device full of capacitors) to negate the phase shift.

In a residential property, unless you've got secret high powered industrial machinery working 24/7 in your basement, you'll never see a problem.
Things like fluorescent lights have a poor power factor, but come with correction capacitors already fitted.

grumbler

AFAIK, residential customers don't pay for the reactive power, but commercial customers can be charged extra.

ChiefGrasscutter

KVahr is a 'better' measure of the current flow into your house.

KVA is the Volts times the amps
KW is the volts times amps times power factor
All large industrial supplies are measured in KVAhr and not KWhr
You can see that if you have a load which has a zero power factor then the KW will be zero and the meter will not record that the load is using a lot of current....which has to be generated.

So measuring by KWhr under records the true energy use unless the pf=1 at all times.

Until homes get charged like industrial supplies then it is only a passing interest to you of your home's overall power factor.

Sterlingtimes

Thank you, Chief, grumbler and Strider, for your most helpful responses.

I will do some arithmetic when I have read my meter this evening.

In terms of export of solar produced energy, is the export kVARh meaningful?

grumbler

ChiefGrasscutter wrote: »

...

So measuring by KWhr under records the true energy use unless the pf=1 at all times....

Not quite correct.
It does measure the true energy used by the house, but ignores the extra losses in the supply cables between the house and the generator caused by the reactive component.

agrinnall

I did some work on electricty use with some businesses a couple of years ago, and looking at an example bill I can see that out of a total monthly charge of over £13,000 the reactive power adjustment was £82.