Energy Products

New Microgrid Installation

edited November -1 in Energy Products
As promised, I’m reporting back with an update on our new solar microgrid installation. The installation and initial testing were completed last week - we're proud new Powerwall owners!

Here are the project highlights with a few embedded photos:

- Our new residential microgrid includes thirty 320-watt Hanwha QCELL solar panels in two strings for roughly 10 kW of power generation, a single 10 kW SolarEdge HD inverter w/optimizers, Tesla energy gateway, new microgrid breaker panel, and an array of 3 Powerwalls providing over 40 kWh of energy storage with 21 kW of peak power capacity and up to 15 kW of continuous power capacity.

- The local power company does not support net-metering, only dual-metering. This limitation required a slightly different "zero-export" system configuration in order to achieve our objectives for a fully self-powered home that will also operate during utility grid outages. The zero-export featured works fine so far - we don't send any energy to the grid and we rarely expect to consume any energy from the grid.

- The project installation took a week. It was started and completed on-time by a competent local Tesla reseller in NC.

- The quality of the rooftop installation work was excellent. The mostly-black panels look great on the charcoal-black roof, which has a due-south orientation. The panel layouts were very well done, the wiring is invisible, and we expect the roof penetrations will be trouble-free.

- The interior installation of the Powerwall array, energy gateway, inverter, generation panel, and integration with our main electrical breaker panels was also very well done. Perhaps most impressive was the fact that the overall microgrid system worked correctly the first time it was activated for testing. The Tesla mobile app came online immediately, showing normal Powerwall operation without a hitch. A few pictures of the (unfinished) electrical room are shown here:

- Based on the first day of initial system testing and Powerwall charging it appears the solar generator will easily meet its 10 kW power specs. On a mid-December day, with the sun fairly low in the sky and high clouds partially obscuring the sunlight, we saw consistent generation in the 5-6kW range and peak generation in the 8-9 kW range during the middle of the day, with roughly 37 kWh of total daily generation. I expect these numbers will increase substantially on longer days with full sun in the spring/summer time frames.

- Based on data from the Tesla energy gateway during the first day of generation and Powerwall charging, all power flows were shown correctly. All solar energy was directed to the Powerwalls until they charged to 80-90% by late afternoon, during which time all energy consumed from the grid was directed to power the home. After charging the PWs, the home automatically switched to self-powered mode with the home drawing 100% of its energy from solar/PWs and zero energy from the grid. Perfect so far.

- Here are some Tesla mobile app screen shots of first-day operations. Note the times:

Initial system power-up in the morning. Low Powerwall charges out of the box, low solar generation. All solar generation routed to charge the Powerwall array, all home consumption from grid power:

Generation and PW charging improving by mid-morning.

Stronger generation and good charging progress by early afternoon, self-power mode in progress:

The critical zero-export functions of the system also seemed to work well as we saw inverter generation reduced to match the home consumption in real-time and did not see any energy from solar or PWs flowing back to the grid.

No more sun after 5pm - home is self-powered:


  • edited December 2019
    Thank you for the update. Your Powerwalls are stacked front to back. I know they do not require much maintenance but how easy is the access to the one next to the wall should it need it? Thanks again.
  • edited December 2019
    Turns out Tesla provides vertical separators mounted between each Powerwall on the right and left sides to hold everything in place when stacking them together. A short steel wiring nipple is also installed between the units near the left side where all the wiring is connected.

    To remove or replace the PW near the wall, one would snap off the left side covers, loosen the nipple nuts, unplug the CAN bus connectors, loosen the #10 AC wiring, and then move the front units out of the way. Would not take long for a trained tech. Maybe 30 minutes to disassemble and an hour to reconnect.
  • edited December 2019
    Thanks for sharing your experience and the photos of your system. I'm curious to know what your solar panels look like on your roof: are these standard PV panels or do you have Tesla roof tiles?
  • edited November -1
    Thanks for sharing your experience and the photos of your system. I'm curious to know what your solar panels look like on your roof: are these standard PV panels or do you have Tesla roof tiles?
  • edited December 2019
    PS: can you share photos of your roof and the panels?
  • edited December 2019
    "The critical zero-export functions of the system also seemed to work well as we saw inverter generation reduced to match the home consumption in real-time and did not see any energy from solar or PWs flowing back to the grid."

    How does that work exactly?

    When my system is off grid and the battery pack is full, the solar system does not exactly match the power needs of the house.

    My two Solar Edge inverters are either on generating solar or they go into a 300 second pause mode waiting for the battery SOC to decline a bit from home consumption. There is no matching of solar power to home demand unless it is simply by chance for a few seconds that it happens.
  • edited November -1
    I agree with @PapaSmurf. It’s pure coincidence that your house was using the exact amount of power the solar was producing. Especially when the grid is up, the PW doesn’t control the solar inverter. The solar inverter is controlled by frequency shifting. If the grid is up, this can’t be done.
  • edited December 2019
    On my PV/Powerwall installation, if the grid is down, the PWs are full, and there is sun on the PV, the TEG does its magic:

    The PV is disconnected from everything by the TEG fiddling with the PW's output frequency, which the inverter interprets as a bad grid, so it shuts down. The house gets power from the PWs, but at a frequency slightly off 60Hz. When the PW charge is below a certain threshold (I don't know what that threshold is), the TEG then tells the PWs to go back to 60Hz, which causes the inverter to decide that the grid is good again, and it reconnects the PV to charge the PWs back to full. Rinse and repeat, until the sun goes down, or the grid comes back. If you're monitoring things via the app, it looks really weird, if you don't understand what's going on.
  • edited December 2019
    Responding to a few posts:

    Our Hanwha panels are standard 320 watt black PV models - not Tesla Solarglass. They look great on our charcoal black roof - will look for a photo and post it. Due south exposure.

    The latest SolarEdge inverters have a zero-export option, which I assume was created at least in part to address dual-metering situations like ours where unlike net-metering the local utility stipulates that no energy may by sent back to the grid.

    The TEG, PWs and inverter work together to throttle-back the inverter output as described by gregbrew.
  • edited December 2019
    Interesting side note. Previously, when the grid went down, the PWs would take over, and my UPS/Power Conditioners would trip because of a sometimes not-so-clean transition to the PW battery power. Then, the UPS would not re-enable itself to run from the house power because house power was too far out of its 60Hz frequency spec. So, during a grid failure, my UPS would cause my server to eventually lose power due to the UPS battery dying, even though there was usable power coming from the PW. It seems that I wasn't alone. You can read about people's UPS becoming useless after they installed PWs.

    It appears that Tesla was listening, and "fixed it" with a firmware upgrade. Now, when the grid fails, the PWs provide power closer to 60Hz (61.5Hz-ish IIRC). This seems to be enough to keep most UPS happy, but out of spec enough to trigger inverters to sense a bad grid and shut off the PV feed as needed. My UPS are happy during grid failures now.

    Sweet, huh?
  • edited November -1
    Good to know! My UPS backup worked just fine last time... but I’m already on 1.41.2...
  • edited December 2019
    Thanks for sharing and the pictures.
    If you are getting so much generation in Dec, you will be getting a bunch more in the summer months. Will you be sending excess back to the grid?
  • bpbp
    edited December 2019
    The installation of our panels/PW has been completed, awaiting PTO (Permission To Operate) from the utility.

    We've told our installer we will not make the final payment on the system until we've been able to verify the system will properly transition to off-grid operation, our UPS systems work while off grid, and everything continues to work when grid power is restored.

    If 1.41.2 fixes the off grid 60Hz problem, then we shouldn't have any problems with the off grid test. But want to make sure we've verified everything works now - rather than discovering during the first outage that something isn't right...

    Hopefully we'll get PTO and the off-grid test completed by the weekend...
  • edited December 2019
    @charlesj - if your question was in response to my posts the answer is no. Unlike utilities that support net-metering, no energy can be sent back to the grid in a dual-metering scenario like ours.

    You're right about more generation in the peak spring/summer months, but our consumption will also rise during those months. New construction projects are always a bit tricky as there is no consumption history to help zero-in on the ideal system sizing.

    In this case, with help from 4 years of operating history with a 14 kW solar generator on another home, we're pretty confident that a 10 kW generator with 3 PW2s should get us pretty close to a fully self-powered microgrid with little (or ideally no) energy pulled from the grid.

    We'll see what happens. We've only seen one day of operations - will report back after we get a few months under our belt.
  • edited December 2019
    Good luck bp - exciting times!
  • bpbp
    edited December 2019
    Our installer is hoping we'll get PTO next Monday, which is essentially the last full workday before the end of the year for many people - so if we miss Monday, it's possible PTO could stretch out past year end.

    However, in reading the IRS tax form, all that's required to file for the 30% tax credit in 2019 is to have the installation completed, which has been done, only awaiting PTO and our final "off grid" test. Evidently paying for the system in 2019 is not required to get the credit this year.
  • edited December 2019
    Has anyone order solar panels directly using the Tesla website? I put in my order last month and was told I would be receiving the Hanhwa QCell 315 panels and Delta inverter. I was not given a choice on either products. I'm based in Hawaii.
  • bpbp
    edited December 2019
    Our installer provided us several options on panels - we ended up with 44 LG 350W panels, coupled with 4 PowerWalls.
  • edited December 2019
    Thanks @Patrick for your excellent summary and pictures of your installation and recent experiences. I live in Edmonds, WA with 13.2 kWh solar PV system installed in 2012 (240 W Itek Panels with Bluefrog APS microinverters). We installed 2 PW2's in June 2018 and have been operating as a microgrid for ~9 months of the year. We have net metering here and export around 60 percent of our excess solar back to grid. I am envious of the amount of solar you are generating in December. We do not do very well between November and mid February with December being the worst. This year we are only generating around 6 kWh/day, which is insufficient to charge our PW2's this time of the year, so we are reliant on the grid to fill in the rest. We generate a lot of solar during the summer here by comparison (up to 65 kWh/day during July). Thanks again for reporting on your experiences. You are right these are exciting times, and it is great to see others that are serious about reducing their carbon footprints and becoming more self reliant.
  • edited December 2019
    @Tesla-David - Always glad to share our learnings on the journey to a fully self-powered lifestyle! Glad your system is still running well.

    Regarding December generation - not yet sure how this will play out over time with only one full day of generation under our belt so far prior to inspections - but seeing about 37 kWh on a fairly nice day was certainly encouraging. That said, I’m fully prepared for numerous days of low generation on cloudy and rainy winter days.

    Will report back as we gain more experience.
  • edited May 18
    @Patrick Which installer did you use? I'm in North Carolina as well and am considering solar.
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