Can you stack hybrid inverters in a large PV system?

[TheMechE]

Why do people try so hard to over complicate things

my system and all D.C. Coupled systems have

Backup load
I
solar ------- CC------- DC bus-------inverter-------grid
I
Battery

the inverter can regulate how much int inverts and if it is a charger or inverter, thus it controls the flow of power
you can have multiple inverters and multiple CC on the system
ouback inverters can sync with each other and the grid
they can sync either in phase or opposite phase or with three of them for 3 phase.
if they are configured for in phase or out of phase with an auto-transformer then one can shut down if the load is less than the other can handle by itself.

That is cool. Thank you for the information. I will look into outback inverters since they can sync with each other. My concern was just that the system I was thinking about was really large and I don't know if there are limits for how many inverters can sync. I assume you meant that your system looks like this from what you told me before though.

...........................Backup load
...................................I
solar ------- CC------- DC bus-------inverter-------grid
...................................I
................................Battery

[ButchDeal]

That is cool. Thank you for the information. I will look into outback inverters since they can sync with each other. My concern was just that the system I was thinking about was really large and I don't know if there are limits for how many inverters can sync. I assume you meant that your system looks like this from what you told me before though.

..............................................Back up load
.................................................. .........I
solar ------- CC------- DC bus-------inverter-------grid
...................................I
................................Battery

it is like this
nearly all DC coupled bimodal systems are simlar

There are stacking limitations on the count of inverters that vary by model.

[TheMechE]

..............................................Back up load
.................................................. .........I
solar ------- CC------- DC bus-------inverter-------grid
...................................I
................................Battery

it is like this
nearly all DC coupled bimodal systems are simlar

There are stacking limitations on the count of inverters that vary by model.

Is there a known way to get past stacking limitations? Like with a very large system? Is there a controller that can accept many AC input signals and sync them all to output a single AC signal?

[ButchDeal]

Is there a known way to get past stacking limitations? Like with a very large system? Is there a controller that can accept many AC input signals and sync them all to output a single AC signal?

you can talk to outback or Schneider etc. on setting up a large system. It looks like the Radian is limited to 10 which would get you to 80kw of inverter. That would be enough for a 100kw array.

http://www.outbackpower.com/downloads/documents/Make_the_Power/radian_8048a_4048a/radianseries_8048a_4048a_specsheet.pdf

[TheMechE]

you can talk to outback or Schneider etc. on setting up a large system. It looks like the Radian is limited to 10 which would get you to 80kw of inverter. That would be enough for a 100kw array.

http://www.outbackpower.com/download..._specsheet.pdf

Thanks, just to make sure, something like that wouldn't convert the solar power to AC before converting it back to DC to put in the batteries right? It chooses either to convert it to AC or leave it as DC and charge the batteries. Or is this the one you use where the inverter and the CC aren't combined into one unit, so it can go to DC first then to the inverter?

[ButchDeal]

Thanks, just to make sure, something like that wouldn't convert the solar power to AC before converting it back to DC to put in the batteries right?

That would be AC coupled

It chooses either to convert it to AC or leave it as DC and charge the batteries.

DC coupled.

Or is this the one you use where the inverter and the CC aren't combined into one unit, so it can go to DC first then to the inverter?

Outback and Schneider use separate charge controllers.

Normally Outback would be DC coupled for a system like this but you could configure it any way you like. If you wanted AC coupled you would have to add on grid tie inverters and skip the charge controllers. I would recommend going DC coupled using Charge Controllers though.

[TheMechE]

That would be AC coupled


DC coupled.



Outback and Schneider use separate charge controllers.

Normally Outback would be DC coupled for a system like this but you could configure it any way you like. If you wanted AC coupled you would have to add on grid tie inverters and skip the charge controllers. I would recommend going DC coupled using Charge Controllers though.

Yeah, converting the DC to AC (AC coupled system) doesn't make sense to me because you lose efficiency when you convert back to DC. Definitely would want a DC coupled system.

[Mike90250]

....Is it a large zener diode to ensure energy only goes into the batteries and not out unless the grid goes offline? .......

I'm going to kneecap the person responsible for implanting in folks minds you need diodes in solar systems.

[ButchDeal]

I'm going to kneecap the person responsible for implanting in folks minds you need diodes in solar systems.

but if you don't have them then the power will flow backwards and the PV modules will glow light light bulbs...

[TheMechE]

I'm going to kneecap the person responsible for implanting in folks minds you need diodes in solar systems.

but if you don't have them then the power will flow backwards and the PV modules will glow light light bulbs...

I was talking about something like this. I mean, how else do you stop the batteries from being drained unless the equipment communicates which it sounds like it does?

http://i.imgur.com/4oVXbIs.png

[ButchDeal]

there is so much wrong with that drawing.
What is the grid tie inverter doing?
you don't connect batteries to the input on a grid tie inverter and you don't connect a charge controller to a grid tie inverter input.

[TheMechE]

there is so much wrong with that drawing.
What is the grid tie inverter doing?
you don't connect batteries to the input on a grid tie inverter and you don't connect a charge controller to a grid tie inverter input.

Thank you. I see what you mean. I revised the image. The problem is I need inverters that can handle a very large PV system (probably too large for hybrid inverters?) yet I also want to be able to function independently of the grid.

So I am seeing three scenarios here:
1. Grid-tie only (no batteries nor hybrid inverter needed. I can remove those from the image)
2. Hybrid system (all components in the image remain, including the zener diode?)
3. Pure off-grid system (remove grid-tie inverters from system)

I hate switches because they can fail and cause a lot of problems, but maybe this shows why I think I need the zener diodes so the hybrid inverter can choose whether to draw from the batteries or not.

I need to do more reading on MPPT charge controllers though. Can they always put 100% of the PV power into the batteries if the batteries aren't fully charged? Or are batteries picky and can only accept so much energy at once depending on their state on charge?

[ButchDeal]

I don't see a new image but also don't really understand they the zener diodes.

The hybrid inverter is going to draw the power it needs for the loads when off grid from the DC bus. In off grid it is either this or shut down. The power comes from Grid and/or battery but there is no choice the power is needed.

In grid tie mode the inverter inverters what is left over after any charging from the charge controllers. There is no need to "Control" the flow just regulate how much it inverters.
So if you are getting 5kw from solar and using 3 to charge the battery then the inverter can invert 2kw, problem solved no need for any diodes or switches.

[TheMechE]

I don't see a new image but also don't really understand they the zener diodes.

The hybrid inverter is going to draw the power it needs for the loads when off grid from the DC bus. In off grid it is either this or shut down. The power comes from Grid and/or battery but there is no choice the power is needed.

In grid tie mode the inverter inverters what is left over after any charging from the charge controllers. There is no need to "Control" the flow just regulate how much it inverters.
So if you are getting 5kw from solar and using 3 to charge the battery then the inverter can invert 2kw, problem solved no need for any diodes or switches.

The new image is in the old post. I just ended up replacing the old image with the new one. What you said makes sense. The inverter only inverts what it needs. The rest goes to the batteries.

What is to stop some of the energy from leaking out of the batteries and flowing unneeded into the inverter though (and then the batteries getting recharged from the output of the solar panel)? Wouldn't that be an efficiency loss and bad for the batteries? Here's an image of what I mean. I know the NET flow to the batteries is zero in this case, but couldn't there still be flow to and from the batteries?

http://i.imgur.com/x2bWPwv.png

What I'm trying to ask here is how do you know the inverter's source of power is 100% the PV panels and 0% battery energy? The way I see it, either the battery or the PV panel could supply energy to the inverter.

[Mike90250]

.......
What is to stop some of the energy from leaking out of the batteries and flowing unneeded into the inverter though (and then the batteries getting recharged from the output of the solar panel)? Wouldn't that be an efficiency loss and bad for the batteries? Here's an image of what I mean. I know the NET flow to the batteries is zero in this case, but couldn't there still be flow to and from the batteries?.....

Same thing that keeps your 100w light bulb from consuming 1800w when it's plugged into the grid.
Simple electrical theory, parts that are operating properly, consume a limited amount of power, not unlimited power.