How to get power from A grid-tie solar system, when utility company cut off AC power?

[cdm889]

I am a new member of this forum, I live in Northern California, was an electronic engineer, retired 7 years ago. I owned a Tesla solar system 3.9KW grid-tie solar system using Delta Solivia 5.2 TL inverter. Every time my utility power company (PG&E) does often power shut down due to weather or other emergencies. When we lost AC power, my solar system will do an automatic shutdown (to prevent the power company repair crew from electric injury from the grid-tie solar system).

When the above happened, it is quite ironic that the sun still shining, and we could not get any benefit from using my solar power system. I got a quote which is $15,000 to add a backup battery system, it is way over my budget, any advice?

[SunEagle]

Hello cdm889 and welcome to Solar Panel Talk

As of now the only way to use a solar pv system when the grid is down is to have a hybrid inverter and batteries. Or you can disconnect manually from the grid and use a generator.

There are other types of grid tie inverters that allow you to use a small portion of the pv system but they also need to be something like the SMA with secure power option. Even then if you get a passing cloud your power will falter. If you want a continuous power supply I only know of either a battery system or generator.

[solarix]

In selling solar for many years, I always cringed to hear people realize the down side of grid tied systems.
"You mean that when the grid goes down, even though I just paid all this money for solar, I'm going to be out of power just like my neighbors?"
That is a big reason why we use the SMA Sunnyboy system with its Secure Power Outlet that provides enough daytime power to run a fridge and other small stuff.
When they added that feature 5 years ago, I figured all the other inverter makers would come out with something similar - no one else has.
Other than that, you have to double (or more) the cost of your solar system by adding a hybrid inverter and batteries in order to be independent.....
You see, grid tied solar without batteries is what made solar do-able 15 years ago. Simple, reliable, durable, efficient, cost effective. All that goes away when you add batteries.

[SunEagle]

In selling solar for many years, I always cringed to hear people realize the down side of grid tied systems.
"You mean that when the grid goes down, even though I just paid all this money for solar, I'm going to be out of power just like my neighbors?"
That is a big reason why we use the SMA Sunnyboy system with its Secure Power Outlet that provides enough daytime power to run a fridge and other small stuff.
When they added that feature 5 years ago, I figured all the other inverter makers would come out with something similar - no one else has.
Other than that, you have to double (or more) the cost of your solar system by adding a hybrid inverter and batteries in order to be independent.....
You see, grid tied solar without batteries is what made solar do-able 15 years ago. Simple, reliable, durable, efficient, cost effective. All that goes away when you add batteries.

I guess I am surprised that the OP was not told what would happen to the pv system if the grid went down. But maybe the sales person just didn't care.

[J.P.M.]

I guess I am surprised that the OP was not told what would happen to the pv system if the grid went down. But maybe the sales person just didn't care.

Why would a sales person divulge information that might kill a sale ?

That would mean some integity on the peddler's part wouldn't it ? Good luck on that.

OP: similar to the old addage "physician, heal thyself", since you were an electronics engineer, maybe doing a little homework before you signed on the dotted line would have been in order.

[heimdm]

If we look at a generator solution... that uses an Transfer Switch (automatic or manual/interlock), to shutdown the grid feed in, and then the generator provides power until you either shut it down or in the case of an automatic transfer switch commands the generator out of service. How much power (peak & continous) do you need to run the stuff you want to use during an outage? If you have natural gas or propane, adding generators to those are fairly simple. Battery costs are high and the supply chain issues has only made it worse.

What is your budget?

[cdm889]

Thanks for all the advice. I appreciated!

I think a battery pack like Tesla Powerwall (starting $15k +) would solve this dilemma, but this high cost is not justifiable for a couple-hour-long power shutdown unless I want to go completely off-grid. Even the SMA Sunnyboy inverter is a good concept but not an option Tesla Solar offers. A power generator is more likely to work as Mr. heimdm suggested. I think for my appliances, like 1 refrigerator, 1 Microwave oven, 2 TV and few lamps, 1500 Watt power generator is OK.

Don't try this wild idea, I have an interesting thought: When I turn off the AC main switch, so no AC power going back to the power grid, then can I briefly connect the generator to house wiring (without turning off the Solar inverter's AC switch)? This "AC present" signal may trick and trigger my Delta inverter think it should not do the "automatic shutdown solar system" as there is AC power. Thus, I can still harvest solar power when the power is shut down. (Once triggered, the Generator should be disconnected to prevent AC power from going back into the genaerator, it will be damaged as it is designed to generate power, not to receive power).

It sounds good, since I don't know how this "automatic shutdown circuit" works, it may or may not work at all, also this trick may damage the inverter or void the solar system warranty, Don't try it period. I will not advise anyone to try it. Just a wild idea for Internet discussion only.

[peakbagger]

You need a battery in the loop and hybrid inverter. Some folks have successfully gotten the former Solar City branded hybrid inverters built by Delta to generate AC without a Tesla battery attached. There are some You Tube videos of people doing it. They are (or were) cheap on Fleabay. At best its kludge and smoke may reward your efforts..

[Ampster]

.... A power generator is more likely to work as Mr. heimdm suggested. ........

Don't try this wild idea, I have an interesting thought: When I turn off the AC main switch, so no AC power going back to the power grid, then can I briefly connect the generator to house wiring (without turning off the Solar inverter's AC switch)? This "AC present" signal may trick and trigger my Delta inverter think it should not do the "automatic shutdown solar system" as there is AC power. Thus, I can still harvest solar power when the power is shut down. (Once triggered, the Generator should be disconnected to prevent AC power from going back into the genaerator, it will be damaged as it is designed to generate power, not to receive power).

It sounds good, since I don't know how this "automatic shutdown circuit" works, it may or may not work at all, also this trick may damage the inverter or void the solar system warranty, Don't try it period. I will not advise anyone to try it. Just a wild idea for Internet discussion only.

The concept you are describing is known as AC coupling and it is essentially what aTesla Powerwall does as well as how hybrid inverters are able to work with Grid Tie inverters which peakbagger described. The GT inverter uses a complex algorithm to test if the grid is attached and presents the infinite load that the GT inverter needs to work. There is also a process in AC coupling that allows the GT Solar to vary its output depending on loads but that needs a battery to act like a buffer as loads change. A generator output is to dirty and it does not have the programming to control the GT inverter.

You are correct that it is a wild idea and I also would not try it either because you will most likely release the smoke in your GT inverter and/or your generator.

A generator, as heimdm suggested, is your most cost effective solution to feed your loads through a transfer switch properly wired to your electrical panel.

[Mike90250]

A GT inverter is not likely to sync and accept a ordinary generator ( feather in the wind RPM governor ) But it's likely that a inverter generator could meet the Fq Stability requirement and depending on the house, loads & generator, possibly meet the Grid Impedance requirement, and go on-line, trying to raise the "grid voltage" by half a volt, in order to "sell" to the grid. When the sell exceeds your house loads, the GT inverter is now pushing power into your generator, likely resulting in smoke release.

[heimdm]

A GT inverter is not likely to sync and accept a ordinary generator ( feather in the wind RPM governor ) But it's likely that a inverter generator could meet the Fq Stability requirement and depending on the house, loads & generator, possibly meet the Grid Impedance requirement, and go on-line, trying to raise the "grid voltage" by half a volt, in order to "sell" to the grid. When the sell exceeds your house loads, the GT inverter is now pushing power into your generator, likely resulting in smoke release.

You definitely want to check out the documentation for your given inverter. For example with Solar Edge, they have an alternate power source mode (https://www.solaredge.com/sites/defa...ge-sources.pdf). As Mike90250 and Ampster mentioned there are definite things to keep in mind when trying to get the inverters to power up in an off-grid situation.

[cdm889]

I would like to get the information of the Tesla solar system's roof installed "Rapid shutdown", i.e. RSD unit, to find what is the logic behind it.

In the meantime, I will just buy a Portable Sinewave AC power generator (about 1K watt) that is based on Lithium Iron Phosphate (LiFePO4) battery, to support my internet router, a freezer, a refrigerator, TV, and some lamps.

[Ampster]

I would like to get the information of the Tesla solar system's roof installed "Rapid shutdown", i.e. RSD unit, to find what is the logic behind it.
......

I don't think links are allowed on this forum but if you Google or search for the term "NEC RSD" you will find information on the regulation. How Tesla actually does that may be proprietary but Tesla, Enphase, Solaredge, Tigo and others all have products or devices that allow systems to comply with the requirement. As far as I know NEC adopted RSD in 2017 but each jurisdiction has their own schedule about when it was implemented. Some jurisdictions may not have uet implemented RSD so your may want to check with your local building department.

[Mike90250]

........
In the meantime, I will just buy a Portable Sinewave AC power generator (about 1K watt) that is based on Lithium Iron Phosphate (LiFePO4) battery, to support my internet router, a freezer, a refrigerator, TV, and some lamps.

Just because it can power 1kw of load, you also have to ask "How long can it power it ? " It may be only 20 minutes, or as much as 2 hours. read the data sheets carefully !!

[calgeorge]

The main reason that grid-tied systems stop working when the utility power fails is that your inverter has to synchronize frequency with the grid. Without a grid, the inverter doesn't have a reference frequency to match up with.

If your inverter allows you to disable selling power back to PG&E, you could feed 60 Hz power into the grid connection with anything that can produce a sine-wave at the proper frequency and voltage.

Your inverter will use the PV input for the power and synchronize it to the input. You would need a manual (or automatic) transfer switch to disconnect from the grid during this operation.

If your inverter doesn't have a way to disable selling back to PG&E, then your reference power source would have to be able to deal with receiving power on it's output terminals.