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I know that VA is the unit of apparent power (combination of real and reactive power) and Watt is the unit of real power only. So, I think it is more precise and accurate to express electrical power in VAs not in watts. But that does not happen. What is written on some generators is 40 Mega-Watts. And I've heard the president saying that the government added some mega watts to the electrical grid.

Why don't they express electricity in VAs instead of watts? Is that because the customers pays for the real power only and not for the reactive power?

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    \$\begingroup\$ Because it is the International System of Units: en.wikipedia.org/wiki/International_System_of_Units \$\endgroup\$ Commented Nov 1, 2015 at 19:53
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    \$\begingroup\$ Because you get billed for Watts, not for VAs \$\endgroup\$ Commented Nov 1, 2015 at 19:55
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    \$\begingroup\$ @codo so is A and W/A \$\endgroup\$ Commented Nov 1, 2015 at 20:39

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Because it costs the generating companies 1:1 to supply you with watts, with real power.

While it is not free for them to supply you with VA, because that extra current needs bigger cables and transformers, and causes larger voltage drops, which cause increased losses in the distribution network, it does not cost them 1:1, and in the limit of a very meaty network indeed, it doesn't cost them anything.

So charging you for watts charges you for your power use, which is fair. Charging you for VA would, to the extent that VA exceeds watts, charge you for their distribution choices, which is not fair.

Obviously they don't install very meaty indeed networks, so the VAs still cost something to shift. That is why you have power factor correction mandated in many loads these days, to get the VA down towards the actual real watts.

Neither is more precise and accurate, each has its own domain of applicability.

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    \$\begingroup\$ Plus a dishwasher is the only reactive consumer in a household. Heaters of any kind are much more common. \$\endgroup\$ Commented Nov 1, 2015 at 20:41
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    \$\begingroup\$ @Vorac - What a strange comment. Much of the load in a dishwasher is an electric heater. If you're looking for an example of a domestic motor load, then a vacuum cleaner is a better example. \$\endgroup\$ Commented Nov 1, 2015 at 21:36
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    \$\begingroup\$ Or a power drill for home repairs. But still cooking+hot water are by far the most often used appliances (I didn't think of a vacuum, I don't own one). \$\endgroup\$ Commented Nov 2, 2015 at 8:25
  • \$\begingroup\$ It's the big number appliances that get the attention, so PCs and flourescent lights. The former have been mandated to have Power Factor Correction power supplies for some time now. Tubes require a PFC capacitor (for old ballasts) or PFC corrected inverters. \$\endgroup\$ Commented Nov 2, 2015 at 8:46
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Watts can be used to power your kettle, run your TV, refrigerator and power your hi-fi. You get billed for watts. However, some appliances will take more than just watts - they'll take reactive power (VAr) and although this doesn't contribute to lighting a lightbulb or actually turning a fan, this reactive power is taken all the same.

This means that the electricity company have a small dilemma - the current that flows thru their cables to you house is bigger than the actual current needed to do work via your appliance and this is a dilemma because the wires have to be thicker to take that extra current.

So, in some case your utility company will make charges (to certain customers) based on their watt-hour usage and their reactive watt-hour usage.

Luckily, most househoold customers only get billed for watt-hours used.

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While a powerstation generates onto the grid VA (and the source of the power is watt's), the general population does not understand VA.

If the president/politician/CEO started a press conference and started the speech with "We have added a 40GVA generator to the grid), there would be a lot of questions from the reporters.

There are those with an electronics background that do not know there is a difference and those that out of habit/laziness use watt's and VA interchangeably. The general population stand no chance of understanding the specifics of leading and lagging, they just care about their cooker, aircon, heater working when they need it and with a reasonable amount of energy security.

Put it down to colloquialism (like ibuprofen being referred to as a painkiller when it is actually an anti-inflammatory drug)

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