AC versus DC load calculations and resistance

Gullo

I'm new here, and I have a question that's interesting to me.

In 2016, I had a very large residential Schneider based solar project installed. This year I upgraded it to super size. I experienced this same phenomenon in both systems...

Before the first install was started, 5 years of electricity bills were examined and load calculations were done on my load center using an eGuage (a fun little device if you have or are willing to afford one). Peak loads and inductive loads and every circuit on the property were analyzed and probed and calculated...

The very rough super over simplified numbers worked out something like this

Winter, about 20 kWh/day ----  Summer about 35 kWh/day  --- During both seasons, my overnight loads ranged between 16 and 24 kWh.

So I bought a 109.2 kWh battery (2100 Ah), which according to my preferences would have given me something similar to an 85% to 90% SOC every morning - or viewed another way, a regular nightly discharge of 10% to 15%. Sure a cloudy day or a few in a row would use some battery, but for my purposes 109 kWh was way more than enough.

I know that there is some voltage drop from the array to the charge controllers, and some conversion loss from PV-DC to Battery-DC and then from Battery-DC to AC and then from AC back to DC at the actual devices/loads, and that was not accounted for in the load calculations because it was thought to be too minimal to be bothered with considering that I'm using such a huge battery.  

Nevertheless, in my 2016 installation, I noticed immediately that I was averaging more than 30kWh per day in winter and as much as 55kWh in summer. There were other more pressing problems with the system, so I didn't have time or inclination to find out what was up. Then I upgraded this year...…… and my averages bumped up even more, and I bought my own eGuage.

For those who don't know, an eGuage uses permanent CT clamps on the circuit wires and measures the electricity directly at the breaker.

Here's my basic starter question... Why does my AC eGuage regularly report an immediate total load of less than 800 Watts while my Schneider equipment reports the same load as between 1600 and 1800 Watts?

Once again, I know that there is conversion and voltage drop and I have a sense of the difference between real power and apparent power, but none of those accounts for double the consumption.

And speaking of apparent power, I wonder very seriously about resistance. Am I actually dissipating as much energy as I'm consuming? That would suggest a very serious and dangerous problem. Is it possible the Schneider load calculation as represented in the Gateway or the Combox is so inaccurate that it's twice the load as an eGuage installed right at the circuits? How does the Schneider even calculate those load representations? Is it normal for the Schneider equipment to indicate one load (Right this second, Schneider says my load is 1.5kW, and my eGuage says my load is 776W) while any other measurement device is indicating only half the load that Schneider sees?

If I chase the tail of those thoughts, the most concerning one is, what if there's so much resistance somewhere that I'm actually dissipating just as much energy as my loads are consuming? How could that be? And since the eGuage is reading what I know to be my normal averages right at the load center, IF the Schneider load representation is right, AND the resistance notion is right, then the resistance is on the Schneider side -

SOOOOOOO I wonder if maybe AC Loads or AC Grid or DC cabling is not torqued correctly - I wonder if something has impedance that I'm unable to figure out. I wonder a million things, but for now, I'm asking. Does anyone else have experience with the difference between two different load calculations of the same load? I mean my Schneider is ONLY providing the load that is called for by my load center, so they should be similar even if there is a conversion from DC to AC worked into the calculations...

Any thoughts?  

Gullo

….. I forgot to mention. I Do have eGuage CTs in the PDP at the AC load side of the breakers. those results are much more similar to the readings that I get at the load center CTs. At this moment, Gateway shows 1.6kW, eGuage PDP AC Loads side shows 1254W and eGuage Load center shows 797W...

1600

1254

797

Yet all three of those reads is basically a representation of the house's TOTAL load. The reads are just from 3 different locations.

The eGuage is reading total load at the load center, and it is reading the total AC load of all inverters, and Gateway is reading what it reads to tell me loads.

jonr

I'd take a known load and find out which of your measurement systems are accurate. Set up correctly, they should all be pretty close.

Gullo

Jonr -

That's a good idea. I have 4 XW+ inverters

I think I would turn off all circuits in the Load center except a receptacle breaker, plug in a light, turn it on, and read the load. I suppose I could find a 200W incandescent bulb out there somewhere still. Would that work? Any other suggestions?

BB.

You can use an electric heater as your test load.

Resistive electric heaters are very close to 1.0 power factor.

Bill

Estragon

A portable electric heater ~12-1500w might be a good test. Some loads could be PF of .5, but seems unlikely whole house loads would be anything like that. A heater would be mostly resistive (except fan motor, if any), so PF near 1.0

One thought... could the CT be set up such that it's only seeing 1/2 of a split phase, or showing 240v amperage times 120v for kva?

mike95490

microwave ovens have a lousy PF to use for testing

alcoppa

I have tried to read all of the posts, The one that caught my attention was that your night time usage is as much as 24 kw. I was wondering why the monthly night time use would be around 1000 kw a month. That seems excessive to me. Al

alcoppa

Get an old hanging light fixture or an over the mirror bathroom fixture that uses 4 or 5 light bulbs and screw in 5 60 watt bulbs or 2 40 watt and 2 60 watt. Regular edison bulbs are basically a resistive load. Al

alcoppa

Sorry, but I looked at th numbers to fast it is just over 700KW-hrs at night. That still seems a high number.