*Aloha Wrenches,*
*I thought I'd share my own experiences with the Powerwall as my company is now launching a program to add PW to existing NEM systems since the vast majority of them do not have storage which means that if the grid goes down, so does their PV system. (With the exception of the SMA SB line and their Secure Power Supply.)* *And no, I'm not a shill or toadie for Tesla.* *marco * *I wanted to walk my own talk. Before we launched adding Powerwall to existing Net Energy Metered solar electric systems, I wanted to make sure that what was promised on paper would work in the real world. I added Powerwall to my NEM system last year and have been monitoring and testing it during normal grid-on and grid outage modes. And I’m very pleased to report that Powerwall has performed flawlessly and as expected.* *When used in a NEM system, Powerwall is programmed to be in “Backup” mode. When utility power is on, Powerwall stands ready in a full state of charge for any power outage. During normal grid-on conditions, my Powerall takes about .6 kilowatt-hours every other day to stay fully charged. Over the course of the month, this Powerwall’s electricity consumption comes to about 9 kWhs or about $3/month at the current HELCO R rate.* *I have turned the utility power off to my home on a number of occasions in order to experience how Powerwall would perform in a simulated grid outage. When the grid goes down, my house effectively becomes a self-generating micro-grid. That is, my photovoltaic system (solar modules and inverters) and Powerwall (battery storage and integrated inverter) form a power grid with energy being created and stored and then consumed by my electric loads.* *Several things I noted from my simulated grid outages:* *· I purposefully overloaded Powerwall by turning on my electric dryer and electric oven at the same time. As expected, since the maximum output of Powerwall is 5 kilowatts, it shutdown. Meaning that all the power in my house went off. Within seconds, Powerwall reset itself and the power came back on, with the dryer and oven having shut down after the power went off. If power does not come back on after your Powerwall trips off, you will need to turn off those high-power loads and reset Powerwall by turning its black on-off switch, located on the right side of the unit, from on to off and then on again. The important takeaway: during a utility outage, you will need to be careful as far as operating heavy electric loads, especially 240 volt appliances both from the perspective of overloading your Powerwall and rapidly drawing down the battery capacity, especially at night.* *· The magic of frequency shifting. Without getting into too much techno-talk, this is the story of frequency shifting. Normal utility frequency is 60 hertz (Hz). PV inverters require the utility frequency to be at or near 60 Hz in order to operate. During a grid outage, Powerwall effectively establishes grid quality power (120/240 volts at 60 Hz), allowing a micro grid to operate with solar providing power to your house loads (during daylight hours) and charge Powerwall as needed. During the day with the loads being met by your PV system and Powerwall being at or near full state of charge (97-100 percent), Powerwall will shift the frequency from 60 to 66 Hz in order to turn off the PV inverter(s). That is, the PV inverter(s) see the frequency out of spec and shut down as they’re expected and required to do. Why? Because with Powerwall at or near full and the house loads being met, there’s nowhere for any additional solar generation to go. Powerwall will wait for its the state of charge to drop below 96-97 percent before shifting the frequency back to 60 Hz which allows the PV system to restart and generate solar power again. This frequency shifting can take place repeatedly over the course of the day depending on load demands, solar potential and Powerwall state of charge and is perfectly normal and does not damage the PV inverters.* *· **66 Hz and home appliances: when Powerwall is at 66 Hz, some of your house loads may be affected. What I and other Powerwall owners have noticed, while not a comprehensive list, can include: electronic clocks running fast, motors sounding different (microwave, washing machine, pumps), uninterruptible power sources (UPS) not charging and going into back-up power mode, appliances having a computer behaving unusually.*
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