Usable A/C output question

[LeeLewis]

There is something that is not very clear to me in terms of generation of usable power. I'll try to explain.

I have a 10KW system that feeds power to the power company.
Each panel has its own inverter and therefore the AC voltage is being combined.
So basically, the system is feeding AC voltage into the grid when it generates more than we are using.
I would like to use some of that power to charge my own batteries, but before it gets to the meter.

The part I don't understand is the amount of usable power depending on the amount of sunlight it is getting.

Is there something in the system that cuts off power if it is too low to be usable?
I mean, what if it's only generating 80V AC, how can that be used and does it ever happen or is there something that prevents power from flowing unless there is a certain amount of voltage?

So for example, if I needed 1000 watts to power my battery charger, if the voltage was too low, would that not potentially damage my charger?
Is it possible that my system was only ever meant to feed the grid and not be something I can use independently?
I have to believe the latter cannot be the case and that there is something I'm not seeing such as a combiner or something that controls all of this.

[heimdm]

Sounds like you micro-inverters. When the power out of the solar system it goes to the closest load for the most part. If that is something in your house say the dryer is running it goes there. If you don't need it and your neighbor does it flows up the grid and over to them. Since you have micro's your only option for your battery is AC coupled such as a powerwall. If you look at most of the grid-tied/hybird battery solution many of them have a dependence on production/consumption CT's. These are those magnetic donuts that go around the main electric feeds. These systems require to know how much power is being produced or consumed to determine where that energy will go.

When your power from the solar array drops below your needs, example, you are producing 80 watts of power and require 1500 watts of power, the gap will be filled in by the grid. The mention of low voltage cut offs, etc, that is usually in off grid or dc-coupled solutions. Since you are AC from the panel, everything if in the US is going to be 240v.

[bcroe]

There is something that is not very clear to me in terms of generation of usable power. I'll try to explain.

I have a 10KW system that feeds power to the power company.
Each panel has its own inverter and therefore the AC voltage is being combined.
So basically, the system is feeding AC voltage into the grid when it generates more than we are using.
I would like to use some of that power to charge my own batteries, but before it gets to the meter.

The part I don't understand is the amount of usable power depending on the amount of sunlight it is getting.

Is there something in the system that cuts off power if it is too low to be usable?
I mean, what if it's only generating 80V AC, how can that be used and does it ever happen or is there something that prevents power from flowing unless there is a certain amount of voltage?

So for example, if I needed 1000 watts to power my battery charger, if the voltage was too low, would that not potentially damage my charger?
Is it possible that my system was only ever meant to feed the grid and not be something I can use independently?

Your inverters are designed to feed the 240VAC line, never just an appliance. The
line fixes the voltage, the current from your inverters will vary with sunlight, power is
voltage X current. You will never see 80V with all connected in parallel at same voltage.

If you want to use some of your power, just connect the load at the inverter side of the
meter. Some of the inverter output current will go to your load, instead of the meter. If
the load is more than inverter output, the load will take all inverter output current plus
the rest from the line, thru the meter which you will pay for. Bruce Roe

[peakbagger]

Another way of thinking of an inverter is a bucket that is filled with a small hose. The small hose is fed from the solar panels via a MPPT circuit that is always looking at the solar panel sun input and adjusting the voltage and current to get the maximum amount of power out of the panel. Instead of marking the depth in the bucket with depth mark if with power produced. Once the "bucket" fills up to the overflow, power runs down the overflow to the utility. On the older Enphase inverter's I own there is LED that flashes when the inverter is running. The LED blinks at a different rate depending on how much power. If the sun is out and bright, the buckets are always overflowing so the power output is relatively steady, when its not sunny, the outputs are on and off. Unless there is a battery in the system to allow the system to ride over the ups and downs the loads are just not going to see steady power.

I only have four microinverters and an analog ammeter on the combined output of all four, when the panels are putting out low power, I can see the needle on the ammeter wiggle a bit everytime an inverter send out a surge of power.

[LeeLewis]

Thank you for all of this input. It seems however that I'm not asking my question properly and it's because there is something missing in how the whole thing works.
I think this comment is closest to what I'm trying to ask.

Your inverters are designed to feed the 240VAC line, never just an appliance. The
line fixes the voltage, the current from your inverters will vary with sunlight, power is
voltage X current. You will never see 80V with all connected in parallel at same voltage.

I think what you are explaining here is that this is a grid tied system. Meaning that the grid will take what ever it gets then add to it if needed or use it elsewhere if it's excess to us.
-What ever it generates and fed into the grid. If it is not generating enough, the grid doesn't care, it just doesn't use it.
-If the system is generating more than we are using in the house, the grid takes the excess (paying us a lower rate than we're buying from them) it and uses it, neighbor, etc.

I've built many DC to AC systems where I used banks of external batteries to power UPS's with generators that kick in after it warms up. Those I'm familiar with.
This solar system however, is something new to me and I need to learn it so I can maintain it on my own.

If the panels were putting out DC, it would be as simple as buying a properly sized inverter that would output clean power if/when the solar array is putting out some minimal amount of usable power.
Since each panel has micro inverters, it means I'm dealing with AC and when using AC, you need to have a solid voltage to prevent ruining electrical hardware.
If everything I've said above is clear to you, then we get to my question.

Because the system is putting out AC and if I didn't want to have it connected to the grid, what would I need to connect it to since that would not be an inverter.
Would it be some kind of controller that cuts off the solar AC if it is to low to be useful?

My thought is that since the power company pays us less than we pay them, I'd like to use what I need first, then send the rest to them when there is excess.
I would like to charge a bank of batteries which would be connected to a full time inverter that would output clean, usable AC.

[sdold]

My thought is that since the power company pays us less than we pay them, I'd like to use what I need first, then send the rest to them when there is excess.
I would like to charge a bank of batteries which would be connected to a full time inverter that would output clean, usable AC.

Typically there is a Net Metering" or NEM agreement with the power company, Imagine a meter that counts up when power flows from the grid to your house, and counts down (backwards) when power flows from your house to the grid. The power company compares the reading at the start of the year with the reading at the end of the year. If it's gone up, they charge you for that amount of power. If it's gone down (backwards) they pay you for the power you've sent them (at a reduced rate).

During the year ,sometimes the meter runs forwards (house using more than the solar is generating), sometimes backwards (house using less than the solar is generating), but the only thing that matters is at the end of the year when the meter says you used more than you generated (you pay for that) or you sent them more than you used (they pay).

Does that help? That's a typical simple net metering situation, yours might be different.

[bcroe]

My thought is that since the power company pays us less than we
pay them, I'd like to use what I need first, then send the rest to them when there is excess.
I would like to charge a bank of batteries which would be connected to a full time
inverter that would output clean, usable AC.

My Net Metering works as sdold describes (not all do). I just dump whatever energy
I can collect onto the power company line, usually in big hunks, for KWh credits. I
take back KWh credits (1:1) in a more continuous manner for my needs. To me
the PoCo is a free, infinite capacity, 100% efficient, zero maintenance battery.

If you want to use your own battery, you will not come anywhere near any of the
specs above, it will be a costly, high maintenance, limited capacity system, but
capable of off grid operation if you must have that.

Here the PoCo does not pay me $ at all. If I have excess generation at the end
of the year, they get to keep it for free. That does not bother me, given all I have
gotten over the year. Those extra KWh cost me nothing extra to generate.
Annual budget varies a lot but is something like 30,000 KWh generated, 28,000
KWh consumed. Bruce Roe

[Mike90250]

The micro inverters sit idle, waiting for 2 things. 1) Qualified, Stable, Grid power. 2) Sunlight enough to generate power to output

Any grid tie inverter has to "see" the Grid and "Qualify" it, before it will start outputting power. Generators are not frequency stable enough to be qualified, but an inverter generator might be. And then your 2kw inverter generator gets power fed into it from the micro-inverters and the thing fries.....

[LeeLewis]

I'm sorry I never got back to this. I'm not receiving the email notices and lost the tabs I had open.

Anyhow, I think the last comment is what I have been needing to understand.

First, to understand what I have, it's called a grid tied system? This means it's not really meant to be used stand alone, it must be connected to the grid.
The system generates power which offsets our power costs and that's all it does. The key here is that it isn't usable on its own unless I add another component otherwise, it's only a grid tied system. Am I understanding this right at this point?

>The micro inverters sit idle, waiting for 2 things. 1) Qualified, Stable, Grid power. 2) Sunlight enough to generate power to output

To confirm, you're saying that the system is not outputting any power unless it knows there is power from the grid?

>Any grid tie inverter has to "see" the Grid and "Qualify" it, before it will start outputting power. Generators are not frequency stable
>enough to be qualified, but an inverter generator might be. And then your 2kw inverter generator gets power fed into it from the
>micro-inverters and the thing fries.....

Ok, let's not fry anything then because this was an expensive system .

My goal is simple. I've been left hanging by the installer and want to learn how to take care of this system on my own. What I'd like to accomplish is that if the grid goes down, I'd like to be able to use the power being generated by the solar system. It would be a shame to have no power yet a 10KW system sitting there idle that I would be using.

I run two racks of computer hardware connected to a 10KW UPS. The UPS is connected to a transfer switch.
I have a NG generator that controls the transfer switch.
The geny comes on when it senses grid power is gone and about 30 seconds later, it trips the transfer switch.
When grid power comes back, it trips the transfer switch back then shuts down about a minute later.

Based on the input, as long as the solar system senses grid power, it generates. If grid power goes down, it stops feeding.
Because it is strictly a grid tied system, it doesn't offer any way of getting to use any power it generates and worse, it is functionally disabled in some way when grid power goes down.

Hopefully, I've got all of this correct now.

I guess I need two things which maybe is even a combined device.
1: Some kind of transfer switch that would continue to 'fake' the grid should it go down so that the solar system continues generating power.
2: Something that the solar feeds its AC into that would be intelligent enough to know if there is enough useful power to make it available otherwise, cut off the output. I suppose it would have a configurable way to select what you're after.
For example, if all I need is 120VAC at a usable 10A, then cut power if generation goes below X Amps.
Or maybe I need 240VAC at 40A. Power gets cut off should voltage go below X Amps.

Very much like an intelligent UPS and PDU for example.

So, if I'm on the right track now, what exactly am I looking for?
The solar goes into a breaker panel that has the city meter and the manager connected to it.
After that, connections go into two locked boxes owned by the power company. That means I get to play with anything before the locked boxes right?

[solardreamer]

My goal is simple. I've been left hanging by the installer and want to learn how to take care of this system on my own. What I'd like to accomplish is that if the grid goes down, I'd like to be able to use the power being generated by the solar system. It would be a shame to have no power yet a 10KW system sitting there idle that I would be using.

You are not alone. Many people include me want the same thing. Search the forum and you will see many posts about this.

I guess I need two things which maybe is even a combined device.
1: Some kind of transfer switch that would continue to 'fake' the grid should it go down so that the solar system continues generating power.
2: Something that the solar feeds its AC into that would be intelligent enough to know if there is enough useful power to make it available otherwise, cut off the output. I suppose it would have a configurable way to select what you're after.
For example, if all I need is 120VAC at a usable 10A, then cut power if generation goes below X Amps.
Or maybe I need 240VAC at 40A. Power gets cut off should voltage go below X Amps.

No transfer switch can 'fake' the grid. You need an independent power source that provides grid quality power to activate the grid-tied inverters. Other controls will be necessary for a practical solution as well.
Here is a recent thread (https://www.solarpaneltalk.com/forum...t-off-ac-power) that you may find helpful.

[LeeLewis]

I put 'fake' in quotes to mean maybe there is a transfer switch out there that has its own power supply that mimics grid power but knows if grid is gone so it transfers the load from the grid to my own output. Basically, making the solar system unaware that the grid is down to prevent it from stopping generation of power.

I didn't even know this was an issue until I posted this question. I never really cared since I didn't have to take care of it but now I want to understand it better and take advantage of it.

[oregon_phil]

Sorry if I'm the only one slightly confused.

Your #1 priority: You were left hanging by the installer and want to learn how to maintain the system on your own. Some of the system details lead us to believe you have microinverters, but we don't know the brand & model number of the microinverters. People can provide more insight to your system if you give more details.

Your #2 priority: Be able to use the solar system when the grid is down.

Other system variables: you have a NG generator and automatic transfer switch.

When your electrician wired in your NG generator and ATS, they must have taken into account the AC from your solar system. How is solar, NG generator and ATS wired from the meter to your electrical panels?

Similar to you, I have a 10kW solar array with SMA string inverter, NG generator and Automatic Transfer Switch. During power wildfire power outages, only my NG generator runs; solar is removed from the electrical circuit. I have a solar ready electrical panel that isolates the solar AC circuit. Your electrician could have used a power relay (load shedding relay) to isolate your solar AC circuit. O

I elected not to integrate solar into my wildfire backup solution because it would be very cost prohibitive. Besides, whenever I need NG backup power, the sun is obscured by smoke or snow/ice.

Also, my NG generator continuously monitors the grid to see if AC power qualifies over a 1 to 2 minute period. If AC power does qualify, then the ATS transfers power to the grid and the NG generator shuts down. As stated before, solar inverters qualify AC too. As Mike90250 pointed out earlier, your solar microinverters push power onto the grid raising the AC voltage. In my case it is 1 to 1.5VAC. If your generator is hooked up to this circuit, power will be trying to flow into your generator. Best case: generator and inverters shutdown. Worse case: generator and /or inverters burn out.

[solardreamer]

I put 'fake' in quotes to mean maybe there is a transfer switch out there that has its own power supply that mimics grid power but knows if grid is gone so it transfers the load from the grid to my own output. Basically, making the solar system unaware that the grid is down to prevent it from stopping generation of power.

There are multiple ways to do it. I suggest you read the previous threads to learn more.

I didn't even know this was an issue until I posted this question. I never really cared since I didn't have to take care of it but now I want to understand it better and take advantage of it.

You have plenty of company. Most solar owners don't know about this issue until they experience a blackout and start to care about it when they have to deal with hassles like throwing food out from freezers and restocking. Installers generally don't point out this issue unless they are pushing expensive home battery add-on's.

[LeeLewis]

Yeesh, the site just keeps timing my session out.

I'm not quite sure why there might be some confusion. I've never had to play with solar systems but now I want to better understand what I have.

It was simple to me at first. The system generated power, we got a cut in our bill, I didn't think twice about it. Within the first three years, our installer slowly started making it harder and harder to get anything done. He initially told me the problem was that the panels and inverters were no longer available because SolarBridge had gone under. It was a bit hard to believe that such an expensive system would start failing only three years into owning it. From that point on, he kept trying to get money out of me for parts but I was able to find used parts on ebay. Eventually, he left me hanging.

Thanks to this post, I now have a better idea of what I've got and based on the input. I now know I've got a grid tied system. I wasn't really aware of that before, as mentioned, because it simply never came up and it also answers why some of this setup was a bit of a mystery to me.

I'm more than happy to provide what ever information anyone wants. I'm not holding back, I just wasn't sure what I was looking for when I posted so didn't know what I should share.

First, let me clear something up. I installed the generator on my own. It is not tied to the house. It is connected to its own transfer switch which flips the power from house to a 10KW UPS when the grid goes down. This is for my computing hardware but when we have long outages, I do connect extensions so I can keep the fridge, furnace and some lights going. I don't care to hook it up to the house, too complicated of a run thanks to a dirt basement.

The UPS kicks in on power fluctuations and of course, complete loss. In the meantime, the generator senses grid loss and starts warming up. Around 30 or 60 seconds later, the transfer switch flips. At that point, the UPS gets its power from the generator until everything goes back to normal. The UPS avoids all of the computing stuff to crash.

The system is a 10.5KW one with SolarBridge p250lv-208/240micro inverters, mage 250 / 6 pl us ac panels and a SolarBridge manager, SPM-101 or 103. For some reason, the manager only shows 2700 watts being generated when it even shows anything. The installer left it all messed up so it's not getting the PLC data. I did hack into the manager and have access to the command line so started watching what it used to send to a couple of sites that were being used to remotely monitor my system. That's kind of useless to me right now. I need to find out why the system is no longer generating power because the 2700 watts is a false reading, our bill reflects this fact.

When it warms up, I'll start working through it and figure out what's not working and fix it. In the meantime, I figured it's time for research to see what I'll need to better use what I have. I want to get power from the system if the grid goes down. I could care less about getting credits from the power company, I'm more interested in harnessing what I have. I'm thinking I would use the power to charge batteries which in turn would run a UPS. I don't need it connected to the house, I'm find with just running some extensions as I do now with the generator. Once done, I would have the option of using the generator or the solar depending on what the conditions are.

So, from what I understand at this point, I have a grid tied system that only generates power when the grid is up. This makes sense now.
It means I have to add some hardware so I can have it continue generating power when the grid is down. It also means I should be able to play with this up to the breaker box that then goes to the power company which is locked.

Hope this all better explains what I've got, where I'm at and what I'm wanting to accomplish .

[LeeLewis]

I think I have all this figured out now thanks to learning that I have a grid tied system.
Looks like I just need to convert my system into a hybrid one.
Hardware needed, a charge controller, batteries, disconnect and a battery based grid-tie inverter or what I was referring to as a method to 'fake' the grid.

Or if I wanted to really get into this, I could see if I see if there's a way of changing out those Pantheon II micro inverters that keep dying, maybe even go DC?

Something along these lines at least.

Thanks for all of the input folks. It was very much appreciated and now I better know what I'm talking about .