Author Topic: MTU1 on the service mains, before solar tap?  (Read 2210 times)

MoreCowbell

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MTU1 on the service mains, before solar tap?
« on: April 18, 2013, 01:36:49 AM »
Hello,

I'm very much a layman so excuse any incorrect language.

I'm having a large PV system installed, and the electricians were kind enough to install my TED 5002-G in the process.  Because it's a larger solar setup, they weren't able to use a typical breaker, instead they used a combining panel, which then "tapped" into the incoming service power line before hitting my 200Amp main breaker.

The electrician installed the CT on the incoming service line BEFORE the solar panel tap.  He will return to finish the installation tomorrow, and will place the other CT on the solar generation end.

Is this correct?  Currently, the TED with one connected CT is correctly reporting my energy usage.  (It's actually pretty amazing to see how accurately it displays changes when I flip a light switch, etc.)  However, when I briefly turned my panels on, the TED went from reporting about 1.1kW (with slight fluctuations) to reporting 5kW, which I believe is the amount being sent BACK to the utility.  Does that CT differentiate between power coming and going? 

That is, how do I know whether I'm:

GENERATING 6.1kW and using 1.1kW, resulting in:
MTU1 showing 5kW
MTU2 (solar) showing 6.1kW

or:

GENERATING 6.1kW and using 11.1kW, resulting in:
MTU1 showing 5kW
MTU2 (solar) showing 6.1kW

Is there some way to show the DIRECTION of power flow at MTU1, or will we need to move the CT from before the solar tap to between the solar tap and the 200A breaker.

I appreciate the help!

John

MoreCowbell

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Re: MTU1 on the service mains, before solar tap?
« Reply #1 on: April 18, 2013, 01:53:00 AM »
I thought a visual might help.  Here's a pic of the CTs installed in my panel:

(img removed for bandwidth conservation reasons)

you can see the solar taps connected after the CTs, right on top of the main breaker.

Thank you.
« Last Edit: April 18, 2013, 11:35:21 PM by MoreCowbell »

pfletch101

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Re: MTU1 on the service mains, before solar tap?
« Reply #2 on: April 18, 2013, 06:08:31 PM »
The first MTU (variously referred to as MTU0 and MTU1!) should be on the utility feed and the second (MTU1/MTU2) should be on the solar feed, with their red dots pointed in the same direction relative to the panel (all toward or all away from). In Footprints setup, MTU1 should then be set to 'Adjusted Load' and MTU2 to 'Generation'. With these settings, the MTU2 readings should always be negative (even if the panels are in darkness and the inverter is actually drawing standby power), and the MTU1 readings (shown as 'Net' on the Footprints display) should shown the flux to/from the utility mains, with a positive sign meaning that power is being drawn from the utility and a negative sign meaning that you are sending power to the utility.
Peter R. Fletcher
TED Pro Home - main MTUs monitoring utility and PV Solar feeds; 2 Spyders monitoring selected individual circuits

n8huntsman

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Re: MTU1 on the service mains, before solar tap?
« Reply #3 on: April 21, 2013, 09:17:21 PM »
Sounds correct to me.  You want to be able to measure the flow of electricity from each of the two sources, the utility company and your solar array.  To do this you need to have one set of clamps coming off of the solar supply and the other set of clamps needs to be on the utility side, before your solar feed.  Doing it this way will allow you to monitor the supply from each source seperately.  Footprints will show you the sum of the two, as well as each source individually.  The sum will be your overall household usage.