How about this IDEA?

[ToneJ]

I have a SolarEdge system I designed and built myself. It's a SE7600US inverter and when I originally selected it they were advertising that it could be upgraded to to add a battery backup to it. (StoreEdge Upgrade) They never actually shipped their proposed upgrade but they did start selling the 7600 with the upgraded adapter box. So I currently have no upgrade path to their StoreEdge system without completely replacing my inverter.
So here's my idea, add an inverter (I'm thinking of the Powland) to only run when the grid is down while the SolarEdge runs when the grid is up. Both Inverters would be hooked up to the panels but only one would draw power at a time. I would put Y connectors in between the solar panels and the SolarEdge Optomizers so there would effectively be dual connections to the panels. I might have to install a relay to turn off the connection to the panels going to the off grid inverter so it doesn't try and draw power the same time as the SolarEdge system is. The hybrid inverter would only be hooked up to the essential circuits and the battery. When the grid is up it would feed thru to the essential circuits and charge the battery if needed. When the grid is down, it would power the essential circuit from the batteries or the solar. Does anyone see any problem with this scheme? The only thing I can think of is that the panels are tied together in an open series circuit and that might affect how the SE Optomizers work.

 

[Frank in Thailand]

Hello ToneJ,

Welcome to the forum.

I don't know the 2 inverter.
One is grid tied only.
The other one is hybrid, yes?

At the moment there is no battery, and no inverter that can use the the battery.

First thing:
2 separate AC source on one net/grid/group will not work (short, sparks, magic black smoke), unless specialy designed for this.
(Sensing eachother frequency)

It's easy enough to have a simple solar charger in y split with your current setup.
Yes, the controllers fight a little, and during the charge of the cells, your efficiency from the solar is lower.

Once the cells are charged, the "battery solar controller) goes to sleep and have no influence on the existing system.

Your current inverter can't run of a battery.
That S*cks that you can't buy that extension anymore.

Depending on your needs, buy the smallest inverter you think you can get away with.
This is emergency power, to keep the lights on and prevent the food in de freezer to spoil, yes?
Higher wattage inverter have also higher own power consumption, reducing the total "backup power" time.
Refrigerator and other motors need pure sine wave.
Heaters, lights, laptops, etc. Can use cheaper modified sine wave inverters.

I think an open door...
Did you contact the builders of your inverter if they have the extension somewhere?
Or that they can provide you with parts/schematic.
It should not be rocket science to build.
The solar is DC.

As crazy side step, you can feed the DC to the solar in....
If it's usually 115v (3 panels in series) providing 115 from solar or battery doesn't make a difference....

Pwm/mppt controller is effectively a buck converter.
And not that problematic to make/buy a boost converter.
Some diodes to stop a possible feedback loop and your all set.

It will work, ugly and cheap solution, but functional

 

[jasonhc73]

It will work.

The problem is that the Solar Edge will only curtail the panels when the limits of the inverter output are reached.

What are you going to do when you don't have that much load to use all the output from the panels?

It is very easy to put a 60 Hz AC signal on the line and let the SolarEdge work.

I use my "grid-tied" inverters, off-grid all the time. I turn them on with the off-grid inverter. The demand from the off-grid inverter is lowered by the production of the "grid-tied" inverters. My grid-tied inverters are set up to be relatively low watts and don't add more than what my loads are. My house seems to just sit idle using 800watts 24/7. In theory, my "grid-tied" micro-inverters are capable of 1400 watts, and the panels are rated 295W each, so 1180watts potentially. I've never seen more than 650watts out of them yet.

Ultimately when you connect a grid-tied inverter, there is never a situation (except in California) where the demand for electricity is less than the supply from the inverters, and even then, they are able to transfer the energy out to the transmission lines and moved across borders.

If you run the same system off-grid, you can very easily supply your house with much more energy than you are actually using. I am not at all sure what would happen if this situation happened.

The essence of solar panel setup.

The panel, Inverter, plug. Right now I am "off-grid" in my house. I have MPP-Solar inverters running my house through the main loads-panel wiring (back-feeding as any generator would). I connected one panel to one microinverter, the microinverter light turned red. (Island protection, meaning...

diysolarforum.com

 

[ToneJ]

The other one is hybrid, yes?

Yes.

2 separate AC source on one net/grid/group will not work (short, sparks, magic black smoke), unless specialy designed for this.
(Sensing eachother frequency)

I understand that. I'm thinking that the grid tie only works when the grid is up, obviously. Then the hybrid would only function when the grid is down. Maybe the other inverter would not be a hybrid but just a simple inverter with a transfer switch build in so when the grid is up it just passes thru, when the grid is down it switches to running off batteries. In that case then I would need some kind of solar charge controller hooked up to the batteries to charge them from the panels.

Did you contact the builders of your inverter if they have the extension somewhere?

I contacted the distributor that I bought the SolarEdge from, he's the one who told me they never built the upgrade unit. He contacted the Mfg and they told him that. SolarEdge's newer system requires a "Battery Interface" unit which about the same cost as the inverter so adding a battery to the newer system ends up being very costly.

This is emergency power, to keep the lights on and prevent the food in de freezer to spoil, yes?

Yes. So I understand that it doesn't need to be as powerful as the SE7600. I understand about AC coupling and it requires that your Hybrid inverter be as powerful or greater than the grid tied unit. So what I'm trying to come with is a cheap way to "kind of" do DC coupling. I don't think I realized that the Hybrid inverter would be trying to put the excess power back onto it's grid so that's why I suggested above that I just need and inverter/charger that is designed to feed thru (and charge the battery) when the grid is active and run off the battery when it's not. When the grid is down the relays to the alternate DC string would charge the battery too. I guess I would need a charge controller that shuts down when the battery is full.

I'm doing a lot of thinking out loud here but that is helping me think thru the issues.

Welcome to the forum.

Thanks. I wish I would have know about this forum 5 years ago when I built my system. Of course, maybe it didn't exist then. I actually started designing my system in 2007. Back then panels cost about $1000 each! Our power company (Rocky Mountain Power) has a rebate program based on a lottery that would give you up to $5k back. That in combination with the State & Federal rebates netted my system at only $3.5k. So my system paid for itself after about 4 years.

 

[ToneJ]

What are you going to do when you don't have that much load to use all the output from the panels?

Yeah, that's what I just replied to @fhorst about.

If you run the same system off-grid, you can very easily supply your house with much more energy than you are actually using. I am not at all sure what would happen if this situation happened.

I have heard that you can set up something to "dump" the load to. That might require some kind of active device to monitor what is going on and only turn on the dump load when it's needed and only to the level that it is needed. That is what I originally though about doing and evolved into this idea I'm referring to here.

 

[Frank in Thailand]

Solar panels are funny.
They don't have excess load or capacity or production.

A turbine needs to lose its generated energy, otherwise it burns.

Solar panels don't need this.

When your battery is fully charged, what do you think happens with the "excess" energy?
It's not there.
Like a water tap, it doesn't have to stay open.

If you plan on using addituonal inverter to power your grid when the main grid is down, you need to make a lot of security measures.

You don't want to electrocute the engineer working to repair your grid, and you don't want magic smoke the moment the grid starts working again

I can't be sure for your grid tied inverter, but most work when the grid is down, and provide only the energy of that is used.
The rest of possible power production is discarded.

As long as you don't make a sudden peak of 1500 watts, it will work.


Easy enough to test, flip your main switch and see what happens!

 

[jasonhc73]

Linemen have never been injured by "back feeding" the grid.

WHY?

Generators have been back-feeding houses, and the grid for a lot longer than solar panels have.

What do they(Linemen) do then?

They short the circuit to itself. That trips the generator's circuit breakers, they are not back-feeding the grid now.

 

[jasonhc73]

Solar panels are funny.
They don't have excess load or capacity or production.

A turbine needs to lose its generated energy, otherwise it burns.

Solar panels don't need this.

When your battery is fully charged, what do you think happens with the "excess" energy?
It's not there.
Like a water tap, it doesn't have to stay open.

If you plan on using addituonal inverter to power your grid when the main grid is down, you need to make a lot of security measures.

You don't want to electrocute the engineer working to repair your grid, and you don't want magic smoke the moment the grid starts working again

I can't be sure for your grid tied inverter, but most work when the grid is down, and provide only the energy of that is used.
The rest of possible power production is discarded.

As long as you don't make a sudden peak of 1500 watts, it will work.


Easy enough to test, flip your main switch and see what happens!

Off-grid inverters "curtail" solar panels when the battery is charged.
Grid-tied inverters only curtail solar panels when the maximum input of the MPPT is reached. There is no "full battery" for a grid-tied inverter to consider.
Some newer much smarter Grid-Tied with Battery backup has the capability to do "grid-stingy". These treat the grid like it is a generator, but operate practically like an off-grid inverter. Tesla Gateway and Sol Ark have these features.

 

[Frank in Thailand]

I'm sure the widows disagree with you.

As safety now the first thing lineman do is ground the cables so any backfeed won't kill them.

I truly wish you where right that no lineman got electrocuted at the job from some household or factory that didn't isolate their energy production from the grid.

Do yourself a favour and Google for it, to see the number of line workers that have died due to this.

 

[Frank in Thailand]

Off-grid inverters "curtail" solar panels when the battery is charged.
Grid-tied inverters only curtail solar panels when the maximum input of the MPPT is reached. There is no "full battery" for a grid-tied inverter to consider.
Some newer much smarter Grid-Tied with Battery backup has the capability to do "grid-stingy". These treat the grid like it is a generator, but operate practically like an off-grid inverter. Tesla Gateway and Sol Ark have these features.

Yes, you are probably right.
Your older type grid-tight inverter can't balance.
It gives out all it receives.

Perhaps selling this unit to some person that doesn't need off grid safety backup, and buy a hybrid is a better solution?

They probably will have higher efficiency, as the technology did advance a lot in the last 10 years.

I don't know how old your unit is, but it might make sense to use the right tools for the job and say goodbye to the older tools that aren't equipped to to the (new/advanced) job

 

[ToneJ]

If you plan on using addituonal inverter to power your grid when the main grid is down, you need to make a lot of security measures.

In my idea the additional inverter/charger only powers the essential circuit so nothing goes out to the grid. The transfer switch only connects to the essential circuit when the grid is up. The solar panels in that case are only charging the battery at the same time that the batteries are driving the essential loads. When the battery is full, I'm just guessing that the charge controller is backing off because the battery is getting full. I should create a drawing to it's easier to follow what I'm saying.

I can't be sure for your grid tied inverter, but most work when the grid is down, and provide only the energy of that is used.
The rest of possible power production is discarded.

The "optimizers" in the SolarEdge scheme act as a valve to the panels, they only pass the power that they are told to by the SE inverter. When the grid shuts down, the optimizers stop passing current. I think the SolarEdge inverter has to dump some power in the few seconds that the optimizers are shutting down. I think the NEC requires that they shut down in a given minute amount of time.

Perhaps selling this unit to some person that doesn't need off grid safety backup, and buy a hybrid is a better solution?

Yeah, I thought about that. I asked the dealer if he thinks there is a market for a used SE7600US. Haven't heard back from him. The newer unit that works with the Backup Interface costs more and the Backup Interface cost about US$1.5k or so. I think my idea is going to be a lot cheaper.

 

[pollenface]

I would use a seperate PV array for your hybrid inverter.

 

[svetz]

Does anyone see any problem with this scheme?

Yes.

You will definitely need a solution to decouple the house from the grid. Not only is it the law in most countries (for reasons mentioned above), if you don't you'll be powering your neighbor's gear and most likely trip the inverters.

Next is that grid-tied inverters act as current sources, these are different than the voltage sources most people are used to like: the grid, a battery, or an off-grid inverter. Voltage sources are "well behaved" in that they provide current as the voltage drops (they stabilize voltage). A current source tries to push current regardless of voltage, it's how it back-feeds the grid. To have a combined system, you need a "brain" that can throttle the output from the solar panels and an absorption mechanism that can handle surges while the panels throttle down.

These are well known problems (see video) and the solar industry currently has two solutions.

1. Toss the old inverter and switch to one of the new hybrid inverters (e.g., Sol-Arc) or a solution like Enphase's Ensemble.
2. Use an AC Coupling solution.

 

[ToneJ]

Yes.

You didn't explain the problem. (Thanks for your reply and taking the time to think about my idea)

1) The SolarEdge is grid tied and disconnects from the grid when needed. It takes care of itself.
2) The Inverter/Charger only connects the essential circuits to the grid when it is up. When the grid is down, it connects the essential circuits to the battery.
3) The solar charge controller is only hooked up to the battery and thus isn't hooked up to the grid. It only charges the battery when it needs to and I assume it will cooperate with the charger built into the Inverter/Charger. If not, then this could be one problem.
4) There are two different connections to the panels. Panels I assume act like a Voltage Source and will share the load with the SolarEdge Optimizers, they don't know what's changing the voltage or current, they're use to adapting to the changes. The solar charge controller is also use to changing voltage/current so I assume it will handle whatever changes it needs to.

So I guess my two biggest questions are 1) will the Solar Charge controller cooperate with the charger on the Inverter/Charger? And 2) will the Solar Charge Controller cooperate with the SolarEdge Optimizers?

 

[svetz]

The earlier post was to explain the problem with this approach: ​ Apologies if I misunderstood (I'm more visually acute).

If you're trying to do this... ​ ...to answer the question we'd need to understand the voltages/currents in series/parallel for the SCC and how they interact with the DC Optimizers attached on the Y splitters at those voltages and currents. While I don't have that knowledge....sorry..., someone else might.

So, what I'd suggest is drawing the missing pieces of the diagram on the right showing at least one string of panels, the voltage at each panel and the optimizer specs.

 

[ToneJ]

So, what I'd suggest is drawing the missing pieces of the diagram on the right showing at least one string of panels

Yes, the drawing on the right is what I'm talking about and yes I need to drawing the other pieces. What software are you using to do your drawing?

 

[svetz]

What software are you using to do your drawing? I used OpenOffice, but here's a link to other drawing tools member's like. As you're most interested in voltages and current flow, you might also consider a circuit emulator like this (see image right). It doesn't have a solar panel as a component, but using a battery and resistor should be close enough to ensure all the voltages/currents are correct. Two helpful formulas: Watts = VI and V=IR, where V is voltage and I is current.

​

 

[ToneJ]

Here's my diagram. The Panel & Grid should probably read "Load Center & Grid". Again, the top half is only active when the grid is up, the bottom half only hooked up to run off the battery when the grid is down. So I'm assuming the Charge Controller will be functioning when the battery isn't full, the same with the charger part of the Inverter/Charger. I'm also assuming that the Inverter/Charger can only work in one direction, it can't put power back to the Load Center & Grid. When the grid is up the transfer switch just passes on the AC to the Essential Loads. I'm assuming it can charge the battery if it needs it.

 

[svetz]

I suspect if you're going to run into trouble it will be the voltage/current that the optimizer sees from having the panels in series and parallel. Given those voltages/currents and the specs on the DC optimizer should tell you what's what. That's why I think you'll need to layout at least one string of panels and show the electrical details (e.g., voltages/current) for the wiring. That is, you need to demystify the "more panels" and "more Optimizers" for at least one string. For example here's three panels in series where each panel is 6V and 3 amps, what is the voltage at each of the optimzers?

​

Note: Voltage readings are not part of the circuit​

Does the "panel" in Panel & grid refer to more solar panels, or your load center?

 

[ToneJ]

That is, you need to demystify the "more panels" and "more Optimizers"

Just what it says, more panels in series, more optimizers in series. The number of panels in series before the optimizers would be less than the number of optimizers in series as the charge controller would be sized to the battery size. I was originally thinking that the series loop before the optimizers would only be connected when the grid is down, a simple DC relay. In that case when the Optimizers are "down", meaning that they are not passing much if any current, they do pass 1v each to let the SE Inverter know they are there. If the SE Inverter is down, I don't think they would be passing any current. I may have to stick a current clamp on the line and see for sure.

(not sure what the Panel & grid is... do you have microinverters too?).

I don't think you read my text. It should have read "Load Center & Grid". I originally put "panel" but realized it would be confused with the solar panels. It's the Power Panel or Load Center as some call it. No, no microinverts.