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Solar Microgrid Project

Solar Microgrid Project

Hello,

Wanted to thank everyone who responded to our recent questions and comments regarding solar microgrid components, including panels, inverters, gateways, and battery storage arrays. We’ve made our decisions and we expect our new microgrid to come online before the end of 2019.

Will share a few details on our choices in case they will help others:

Technology

- Hanwha panels, SolarEdge string inverter, Tesla Powerwall 2 battery array

Microgrid Capacity

- Generator power = 10 kilowatts

- Generation plan = average 1.1 megawatt hours per month (NC location, less sun than FL)

- Max energy storage = 40 kilowatt hours (three PW2 units, gateway)

- Max continuous storage load = 15 kilowatts

- Max peak storage load = 21 kilowatts

- Projected utility grid offset = 100%

Financial Summary

- Turnkey pretax installed price was roughly $53K

- $26K for the generator elements and $27K for the Powerwall 2 storage system

- After-tax pricing works out to about $39K all-in

- Monthly payments are roughly $190/month with 100% financing (just adding $39K to the final mortgage amount)

- Projected electric bill with no microgrid was roughly $300/month.

- Assuming no surprises, we’ll be saving roughly $1,300 per year, ever year, starting immediately after the microgrid installation

- Increase in home value = roughly $40K.

- Home equity increase starts at $600/yr, grows annually as mortgage is paid down

Fun Factors

- Our first turnkey microgrid project with Powerwall storage

- First fully self-powered solution, we rarely expect to pull energy from the grid

- Net-metering was not offered by local electric utility, only dual metering. Found creative zero-export inverter configurations as a workaround to allow direct microgrid to connect to the grid with no net-metering

- All equipment consolidated in basement electrical room

- Lead the market transition to renewable energy rather than follow - ambassador for others

- Save $$$

Based on all the feedback here we avoided dealing with Tesla direct and engaged a local Tesla reseller instead now that Powerwalls are readily available. Will report back early next year with installation results.

Wishing blue skies and free megawatt hours to all!

Pat

gregbrew | 26 September, 2019

I applaud your moving to green energy, but how is your system any different than any other with PV and Powerwalls?

Patrick | 27 September, 2019

Thanks Greg.

It's not much different at all, with the exception of a) using this type of microgrid design with a local utility that does not offer net-metering (dual-metering only), and b) being something new for this region as Powerwalls have only recently become available here.

The biggest challenge by far was putting together a microgrid that can operate in a dual-metering utility environment. Sounds like we'll be one of the first in this regard.

gregbrew | 27 September, 2019

Dual metering is not uncommon. It depends on the utility. I started with a dual-metering setup with my PV system and batteries (not SC or Tesla) in 1999. (I drove EVs then, too.) SCE changed it out to a single bidirectional meter, and upgraded my main panel to 200A in about 2009...on their dime. Woo-hoo!

Patrick | 29 September, 2019

Interesting.

Hope TVA and their co-ops in NC/GA/TN ultimately move to a simple net-metering system at some point in time.

Their version of dual-metering requires any private solar generator to feed all its energy directly to the grid - not to the home where the generator is installed. This means the entire system is useless during a grid outage - a total non-starter.

Crazy - thus our zero-export solution.

Just curious - how did you deal with your dual-metering situation at the time?

gregbrew | 29 September, 2019

The second meter simply measured what was going out to the grid, because they didn't have meters that could measure flow in both directions. How can your utility possibly know what portion of the PV energy your house is using? Your PV and PWs are on the inside of the meters, such that the only thing the outflow meter can measure is the *excess* PV that isn't consumed by the house. I'm not sure that I clearly understand the architecture of your PV/PW system. Any chance you could provide a diagram?

Tesla-David | 29 September, 2019

@Patrick, congratulations on your microgrid project and thanks for reporting, and keep us posted. I live in Edmonds, WA with 13.2 kWh solar PV system with 2-PW2 batteries operating in self powered mode since June 2018, and this year we have not drawn any grid energy since mid-February, and are exporting about 60 percent of our solar energy back to grid. We have Net Metering here, and are paid for our excess production ($0.54 kWh), which has helped us pay off our solar system installed in 2012. Our solar will be fully paid off this year, and our electric bill last year was $188 for the entire year with all electric home, and two Tesla's. I love hearing about others interested in living off grid and being more self reliant. Way to Go!

Patrick | 30 September, 2019

Greg - similar arrangement here with dual metering which creates the issues I mentioned above. Not ideal for microgrids. Will post a diagram once our design is finalized.

Tesla-David - hello again and thanks. Have been admiring your success! Anxious to join you and go fully self-powered on the new project. Will report back with results.