Terminology.. phased power, apparent power, active power?

[CaliSunHarvester]

The following screenshot is from the SmartESS app. It has been confusing me since day 1.



In my world of ignorance, Voltage * Current = Energy, aka V*A = W.
Now I read that VA is not quite the same as W. Apparent power vs phased power?

And why is the first leg labeled "A" and the 2nd is "2"?

In my simple mind, leg 1 uses 90W and leg 2 uses 66W, total should be 156W.

But no, the total is 38W.

90VA + 66VA =? 38W

I wish the POCO would calculate like that when they bill me.

 

[CaliSunHarvester]

Here is another screenshot with advanced math:



Solar input 1340W
House consumes 52W
Battery receives 1340W - 52W =?? 1530W

 

[Madco]

I'm not really sure what is going on with the SmartESS App, but a couple of things:

1. Voltage * Current does not equal energy. The product of voltage and current is power in DC and apparent power in AC. DC power is measured in watts and apparent power is measured in VA. There are three components of apparent power - real and reactive (imaginary power). Real power is power that actually does work. Reactive power is power that circulates to create magnetic fields in motors, as an example, and is measured in VAR. You might want to search "power triangle" to get a better understanding of apparent, real, and reactive power as they are vectors.

2. Energy is the product of power and time and is measured in Wh, or more typically, kWh. An important thing to keep in mind is that as far as billing is concerned, it is the real power you pay for, not the apparent power.

So, in your first post the 90VA + 66VA = 156VA. That won't equal 38W because VA is apparent power and W is real power. The two are related by power factor (which is pretty low from the numbers). The only time apparent power will equal real power is when the connected loads are all resistive, loads like electric heaters. If there are any inductive loads like motors, microwave ovens, etc. or capacitive loads like computer power supplies, LED lights, etc., apparent and real power will not be equal. BTW, both compact florescent and LED lamps have incredible poor power factors, so if you're "lamped" with those, that make explain why you're seeing 156VA apparent and only 38W real.

 

[CaliSunHarvester]

You made it suddenly clear to me. And yes, the load was probably just some lights as it was early in the morning.

So their power factor would be 38/156 = 0.24

Pretty sure we didn't cover this in school:

 

[Madco]

Good deal, glad I could help!

With inverters, it's a crapshoot as to what happens with the reactive power. Ideally it would be returned to the battery but that depends on the circuit design. I have a feeling that with it is just dissipated as heat with most if not all of the less expensive units!

 

[CaliSunHarvester]

just dissipated as heat

Definitely creating a lot of heat. Outside temperature was 40 last night, but the electrical shed didn't drop below 72 and it is 79 right now.

It's amazing heat from such little consumption. The inverter itself also consumes about 100W. I mean 100VA. But it's DC. So the same, right?

 

[Madco]

Yea, it consumes 100w.

The heat dissipation is interesting. My system has the batteries co-located with the inverters in a small 6'X8' shed, insulated to R11 in the walls, R32 "ish" in the ceiling, and no insulation in the floor. It sits on deck blocks, so it has around 12" of ground clearance. I purposely designed the building to be as small as possible to ease both the heating and cooling requirements.

I leverage the dissipation to heat the shed by winter. The interior temperature falls to 35F with an outside temperature of 5F. An 18" exhaust fan handles heat removal in the summer (temps up to 105F). Our record low temp is -18F, so I run a small electric heater on those occasions to keep the LiFePO4 batteries above freezing. Funny thing, that -18F temperature has occurred twice in the last three years or so. Hard to rationalize that with all the global warming!

 

[CaliSunHarvester]

Temperature and humidity of the last 24h.
I was afraid of both and overbuilt probably. Thinking of funneling that nice heat into the house. The shed backs to a walk-in closet, unfortunately. The house has no central heat which is totally fine 350 days a year. Today is one of those 15 other days. Feels like 60 inside.

 

[hwy17]

I wish the POCO would calculate like that when they bill me.

Good news, they do. Residential power is metered in real watts and you do not pay for VA / power factor.

Large industrial power does get billed for their power factor.