ECN Forum Forums General Topics of the Trade General Discussion Area metering (net) and load shedding application

It exists and has been connected and working for a couple years now. As someone said, they have just been manually guessing...sunny day run the dryer or hot tub, etc.

As far as setup...Im not good at describing but here goes.
High voltage from road to pole transformer/pole (utility owned). Secondary of transformer has like 3 feet of wire then connects to the 2 "services", the "load" going underground to the disconnect in the shop, the "generation" to a meter on the pole and to its disconnect in the shop. The CT for the bidirectional meter is on that 3 feet beside the transformer, the CT wires run down the pole to the meter. So I would have to go up the pole within about a foot of the transformer with my CTs to get a net reading that way. Not happening.

I came across a watt transducer called Wattnode http://www.ccontrolsys.com
Was thinking of using one of these with a pair of CTs by each disconnect to get a pulse output (equivalent to watts).
Then I would need a instrument that can use those two pulses, combine them and give a relay output based on my settings.

Any ideas?
Im looking at a programmable relay BB Electronics TECO SG2 http://www.bb-elec.com/product_multi_family.asp?MultiFamilyId=39&Trail=158&TrailType=Main
Not sure if it suites...probably fancier than needed anyway.

All right, you probably cannot get access to PoCo metering CTs.

Is there an monitoring output of the inverter that will provide a output KW signal in realtime? If there is, half of your work is already done.


WAIT A MINUTE !!!

How does the customer hook up a load to the inverter output before the generator meter?

Does the generation meter have some sort of one way clutch that prevents it from spinning backwards? I hope so or else you are buying power at 60 cents per KWHr when the inverter can't support all of the additional load.

Does the inverter service count as a separate service? Does it share a neutral and earth with the main service?
How do you power any loads off of the inverter panel?

Something sounds wonky about this setup.

Im not doing very well describing this...I'll try my hand at a diagram

Pole Transformer
|
|
PoCo CT ---(CT wire)--> bi-directional meter
|
|(top of pole)
|---(underground)-> load disconnect ---> subpanels
|
|
Generation meter
|
|(underground)
solar disconnect
|
|
Solar array

both disconnects are in the shop. As you can see the generation meter measures all solar production, the bi-directional measures what leaves from the solar and what is brought in from utility. The difference between the solar generation and what leaves is what is used on-site at cheap.

I'm going back to confused again (or still)

Try posting this image of the layout:

http://s10.postimage.org/vvmnel37d/layout_diagram.jpg


upload images

I believe you are overthinking this. Perhaps this model will make more sense.

Every KWHr leaving the inverter meter costs you 6 cents. Every KWHr leaving the property earns you 66 cents. Every KWHr entering the property costs you 20 cents.

Property is a net exporter of energy? You earn 60 cents/KWHr. Property is a net user of electricity? It costs you 20 cents/KWHr. Every KWHr you generate and use on site costs you 6 cent/KWHr.

Assuming KWHr meters are read once a month, there is no need to read the meter in real time. If you use 10 KWHr during a 24 hr period and generate 10 KWHr during the same 24 hr period, your net cost is 60 cents. It doesn't matter when you use the energy.

If you hook your load up to the inverter panel upstream of the inverter meter, AND you consume more energy than the inverter can put out. Your energy cost will be either be 14 cents a KWHr if the inverter meter runs backwards, or 20 cents a KWHr if the inverter meter does not run backwards. If you consume less energy than what the inverter puts out, your energy costs will be 0 cents per KWHr.

Sorry, I'm confused...Doesn't make sense, seems really complicated.

This is it:

1) Every KWHr leaving the generation(inverter) meter earns 60cents. 100% of the energy the inverter outputs. That's a given regardless of what the load is doing and whether property is exporting or importing.

2) Every KWHr that leaves the generation meter, but does NOT pass through the bi-directional meter (not exported), and used on site in real-time costs 6cents.

3) Every KWHr that is imported (consumed) costs 20cents.

This is not like net ACCUMULATIVE metering. It is bi-directional. If 10kwhr is exported that day and 10kwhr imported that night, the meter knows 10kwhr exported and 10kwhr imported, and charges for all 10kwhr imported at 20cents. Basically we don't want the energy reaching the bi-directional meter.

Example (24hr time period):
Inverter produces 60kwhr, then 60kwhr is recorded on generation meter.

40kwhr is exported, 30kwhr is imported. 40kwhr export, 30kwhr import is recorded on bi-directional.

Customer is paid $36.00 (60cents x 60kwhr)
Customer is charged $6.00 (20cents x 30kwhr imported) plus $1.20 (6cents x 20kwhr used real-time[60kwhr generated - 40kwhr exported]). Total charged $7.20

Does that help at all??

I'm sooo confused!! My head is hurting.
Seems that we do this with a line tap (or backfed CB) and a net POCO meter. With a solar production meter on the inverter output.

Lol...Ya it's like that except it's not a net meter but a bi-directional meter. I wish I could delete "net" from the subject, that might be what threw off some people. I meant net/surplus real-time KW, not POCO net Kwhr meter.

If it's any consolation, only the few first ones got hooked up this way. They don't allow this anymore.

"They don't allow this anymore."

To that I say....thanks!!