Ongrid? Off Grid? I want both!

[Monsieur le Nudiste]

Hello Everyone,

I am planning to build a modular solar power system for my future house,
What I would like to do is to have a system that:

-Is modular (I'd like to start with just a few panels first, just enough to meet the minimum voltage of the inverter, then add panels progressively)
-can work off grid, with a battery backup (I can build the batteries myself, slowly adding capacity over the years)
-can also work grid tied, because obviously at the beginning I won't have enough power for the whole house

I'd like the system to work as follow:
-whenever there is sunlight, first charge the battery to 100% SOC then selling whatever is left to the grid.
-Once the battery is charged and there is no sun anymore, use the power from the battery until it is discharged, then go back using the grid.

I've seen a lot of people praising the Growatt inverters, especially the 5000ES ones. They seem to be quite modular, powerful enough and from what I've red so far people seem relatively happy with these. What I like about them is that they feature everything in a single unit (charge controller, inverter, etc.).
They seem pretty good to me, but I can't really find a clear answer as to how they work once grid tied. They have an input for the grid connection so I suppose they can work grid tied, but they are marketed as off grid, which I find a bit confusing.

Do you think it is possible to reach all these goals with a growatt 5000ES unit? How does it normally work once the grid is plugged on it?

Thanks a lot in advance for your answers!

 

[sunshine_eggo]

off-grid = no grid interaction, but it can RECEIVE input from the grid as backup to power loads or charge batteries.

grid-tie = grid interactive, i.e., can sell back to the grid. Note that you will need an agreement with your utility company and be subject to all their requirements.

Consider that NOT going nude may reduce your climate control energy demand. Often conservation is the most beneficial approach.

 

[Monsieur le Nudiste]

Haha, thanks for the reply!
It is clear for me now, I was a bit confused by the off grid-grid tied thing.
One more clarification: can a grid tied system work off grid?

I guess I can forget the Growatt ES5000 then, too bad

Does anyone knows a grid tied inverter that has similar specs?
5000 watts output or more, capable of being paralleled, battery backup and, if possible, affordable....

What system would you guys go for if you had to make a system that could behave as explained in the first post?

This system would be installed in China first, then after a few months/years I would move back to France and hopefully take it with me (we have similar grid characteristics in both countries AFAIK, 220-240V, 50-60Hz)

 

[Jordi]

Well, according to sunshine_eggo reply; the only disadvantage of Growatt ES5000 is that it can not sell the surplus to the grid. If you have a big battery and planning to keep a big battery capacity compared to the solar output; that should not be a problem. Totally not If you are planning to go 100% off-grid in the future. Most important for you at the beginning is to have the grid as back-up to support your small starting setup and so allow you to consume as needed, and that can be done with that Growatt ES5000. (so says sunshine_eggo, I am a noob)

 

[Monsieur le Nudiste]

Well, according to sunshine_eggo reply; the only disadvantage of Growatt ES5000 is that it can not sell the surplus to the grid. If you have a big battery and planning to keep a big battery capacity compared to the solar output; that should not be a problem. Totally not If you are planning to go 100% off-grid in the future. Most important for you at the beginning is to have the grid as back-up to support your small starting setup and so allow you to consume as needed, and that can be done with that Growatt ES5000. (so says sunshine_eggo, I am a noob)

Well, I just learned an other piece of information that makes your suggestion even more valid:
Apparently in France (where I'm planning to install this system), it is not allowed for an individual to DIY a solar system and then sell his production to the grid. You HAVE to get the system entirely installed by a certified professional (and not just your regular electrician, some stupid specific certification)... I simplify a bit, but that's basically the idea. You cannot just pass an inspection, that would make too much sense, it had to be ridiculously idiotic.
As usual, France is the very best at creating stupid laws to limit the possibility of individuals building things. I should have guessed it, it's a classic.

So I suppose that definitely rules out selling to the grid for me, the only option left is indeed off grid with a big battery.
Now the plan is pretty much what you said: go for a small off grid system with grid backup, then progressively increase production and storage until the day I could, hopefully, completely disconnect from the grid.

 

[Steve Fractals]

So I'm also about to go down this route. I was confused at first and still am a little.

From my research it seems I dedo need off-grid and then utilise the AC/Utility In on the inverter for grid backup.

The bit I'm struggling to get an answer for is if I wire it all as diagram below which shows that my only grid connection would be to AC-In on inverter and no other grid connections to the house (yes I know I will need a bunch of isolators), will the AC in of an off-grid inverter take 100% power from grid/utility and pass it to the AC out if no sun and batts are dead or will it just charge the batts only. I'm guessing I could set it for both options but can't get confirmation from the manuals. Also if inverter goes off then will it startup again from AC/Utility IN without any solar or batt power?

 

[Monsieur le Nudiste]

So I'm also about to go down this route. I was confused at first and still am a little.

From my research it seems I dedo need off-grid and then utilise the AC/Utility In on the inverter for grid backup.

The bit I'm struggling to get an answer for is if I wire it all as diagram below which shows that my only grid connection would be to AC-In on inverter and no other grid connections to the house (yes I know I will need a bunch of isolators), will the AC in of an off-grid inverter take 100% power from grid/utility and pass it to the AC out if no sun and batts are dead or will it just charge the batts only. I'm guessing I could set it for both options but can't get confirmation from the manuals. Also if inverter goes off then will it startup again from AC/Utility IN without any solar or batt power?

I'm obviously no expert, but I assume that is the whole point of having grid backup, to bypass the whole system whenever you have no sun/no battery left (but no doubt someone more qualified will have a better answer).

Your question brings another question to my mind: since the Growatts are rated at 5000W, does this power limit applies to the AC backup as well? or is it only the limit of the inverter part itself? How does this limit work exactly, is it only valid when totally off grid?

What happens when the total load of appliances is superior to whatever the Growatt can produce when you are plugged into the grid?
Can the growatt supply lets say 20% of the power from its battery and then the remaining 80% from the grid?

 

[Jordi]

Well, I just learned an other piece of information that makes your suggestion even more valid:
Apparently in France (where I'm planning to install this system), it is not allowed for an individual to DIY a solar system and then sell his production to the grid. You HAVE to get the system entirely installed by a certified professional (and not just your regular electrician, some stupid specific certification)... I simplify a bit, but that's basically the idea. You cannot just pass an inspection, that would make too much sense, it had to be ridiculously idiotic.
As usual, France is the very best at creating stupid laws to limit the possibility of individuals building things. I should have guessed it, it's a classic.

So I suppose that definitely rules out selling to the grid for me, the only option left is indeed off grid with a big battery.
Now the plan is pretty much what you said: go for a small off grid system with grid backup, then progressively increase production and storage until the day I could, hopefully, completely disconnect from the grid.

? it is the first time in my life I see a French person talking bad about France. I com from Spain, I think we are as good as France at doing stupid laws. We had for almost 5 years a tax for harvesting sun; as If the sun hitting Spain belonged to the government. At the end common sense won and the alteration was resolved.

I wish you all the best in your DIY endeavors and the only thing I can advice you is to read about expanding battery capacity and thus possible impact to your starting design; mixing old and new batteries is a thing and many people here will be able to help you on that; definitely not me.

 

[jvin248]

.

-Do you have a large well pump? I do and it makes system design a lot more challenging (needing a split inverter or two inverters)
-France must have a big group of lobbyists to get those laws in place. Seems the power companies in the US are not keen about buying power and so do their own limiting too (buy power for X and sell power for 0.5X or some reduced rate).
-Grid-tie systems seem to shut down when the grid goes down, Off-grid inverters can grid-tie and use solar when the grid is down, which is the whole point of having a solar system.
-Panels are 'relatively' cheap and easy to expand capacity. Inverters are expensive and often the limiting factor.
-Batteries I haven't gotten to yet.
-I'm taking the first approach of a manual panel switch just like using a gasoline generator for when the grid is down.

.

 

[Goboatingnow]

off-grid = no grid interaction, but it can RECEIVE input from the grid as backup to power loads or charge batteries.

grid-tie = grid interactive, i.e., can sell back to the grid. Note that you will need an agreement with your utility company and be subject to all their requirements.

Consider that NOT going nude may reduce your climate control energy demand. Often conservation is the most beneficial approach.

Grid tie does not automatically mean feed back either. Any decent solar should have the ability to grid tie

 

[Mattb4]

Grid tie does not automatically mean feed back either. Any decent solar should have the ability to grid tie

Actually due to two power sources in parallel it does mean feedback can occur. Whether DC in parallel or AC in parallel.

 

[sunshine_eggo]

The bit I'm struggling to get an answer for is if I wire it all as diagram below which shows that my only grid connection would be to AC-In on inverter and no other grid connections to the house (yes I know I will need a bunch of isolators), will the AC in of an off-grid inverter take 100% power from grid/utility and pass it to the AC out if no sun and batts are dead

Yes. It can also charge the battery. There are typically multiple options with most inverters.

or will it just charge the batts only. I'm guessing I could set it for both options but can't get confirmation from the manuals. Also if inverter goes off then will it startup again from AC/Utility IN without any solar or batt power?

If AC-in is available, it's unlikely the inverter will ever "go off" it properly configured.

 

[Steve Fractals]

Yes. It can also charge the battery. There are typically multiple options with most inverters.



If AC-in is available, it's unlikely the inverter will ever "go off" it properly configured.

Thanks, I had seen some manuals state that they can be set to use Solar first, then Battery and finally utility/grid and will mix so if load is say 1000 (for ease) watts and solar providing say 600 Watts and batteries 200 watts then it will use grid/utility for the remaining 200 Watts and assumed that meant it could equally do 100% from the grid/utility but I couldn't find that in any of the manuals or descriptions I read and thought it would be bonkers not to have that facility but wanted to check.

I get that the Inverter should never really go off if configured properly but I keep reading that if it goes into standby then it will take Solar or Battery to start it but I don't know if that phrase means that if no solar or battery then it will standby the inverter and just pass all AC-IN to AC-OUT etc. Can you or anyone else confirm what this standby mode means and if I'm right or wrong on my assumptions please?

 

[sunshine_eggo]

Thanks, I had seen some manuals state that they can be set to use Solar first, then Battery and finally utility/grid and will mix so if load is say 1000 (for ease) watts and solar providing say 600 Watts and batteries 200 watts then it will use grid/utility for the remaining 200 Watts and assumed that meant it could equally do 100% from the grid/utility but I couldn't find that in any of the manuals or descriptions I read and thought it would be bonkers not to have that facility but wanted to check.

I get that the Inverter should never really go off if configured properly but I keep reading that if it goes into standby then it will take Solar or Battery to start it but I don't know if that phrase means that if no solar or battery then it will standby the inverter and just pass all AC-IN to AC-OUT etc. Can you or anyone else confirm what this standby mode means and if I'm right or wrong on my assumptions please?

Most inverters with "standby" operation can still act as chargers from both AC or PV. The MPP Solar and Growatt units will still charge even if their power switch is off.

 

[Steve Fractals]

Most inverters with "standby" operation can still act as chargers from both AC or PV. The MPP Solar and Growatt units will still charge even if their power switch is off.

Thanks for that.

I wonder if you could help further.

I know this is an unlikely scensrio but I need to know for planning purposes. So for example, It's evening so no solar and I've been using my batteries, they go flat & my inverter switches to 100% Grid from AC-In but I then have a power cut with grid down so I'm defo now in the dark. Once the grid is restored will the inverter immediately fire back up off the Grid through its AC-In or will it just charge the batteries and then once batteries got some power it will then fire up off them?

 

[wattmatters]

One more clarification: can a grid tied system work off grid?

It depends. Most grid-tied inverters cannot, they require a grid frequency signal to operate - they are grid-following inverters. But these inverters don't operate with a battery either.

Those that do work with a battery are hybrid grid-tied inverters which work in concert with a grid isolation system - they connect to a battery and in case of grid outage will disconnect from the grid and then commence operating off-grid. When the grid signal returns they will go through a process of realigning their AC output frequency with the grid before reconnection.

These sort of hybrid grid tied inverters are expensive and are not normally the realm of DIY solar in most countries.

In any case, any generation source which can supply/energise the local grid will be subject to a variety of regulations and requirements (rightly so because it can be life threatening for grid workers). In Australia, where 1 in every 3 homes has a grid-tied PV inverter system, they can only be installed by suitably qualified professionals and require approval from the local distribution company.

The bit I'm struggling to get an answer for is if I wire it all as diagram below which shows that my only grid connection would be to AC-In on inverter and no other grid connections to the house (yes I know I will need a bunch of isolators), will the AC in of an off-grid inverter take 100% power from grid/utility and pass it to the AC out if no sun and batts are dead or will it just charge the batts only.

You can have the grid feeding the AC input of the all-in-one inverter, and that can be passed through to the AC output to power a home's circuits. How much power can be passed through in this manner is a specification limit of the AIO inverter. This may or may not be an issue depending on what the home is seeking to power. Often homes have some individual high power draw appliances which may not be suitable for powering via such an inverter. Large ducted aircon systems, electric hot water systems, sometimes ovens or induction stovetops.

You can set up two distributions panels, one which is fed from the grid only and one which is fed by the AIO inverter. One might be considered an essential loads panel and the other for non-essential loads. This way you can keep the loads the AIO is supplying within the pass-through and output limits of the AIO inverter, while other loads are only ever connected to grid power.

Thirdly, you can set up a transfer switch, so that the essential loads normally fed by the AIO inverter can instead be directly fed by the grid and no longer powered from the AIO inverter. This is an important option in case the AIO inverter is out of service for whatever reason. You do not want an essential loads panel which cannot also be powered by the grid if needed.

Your question brings another question to my mind: since the Growatts are rated at 5000W, does this power limit applies to the AC backup as well? or is it only the limit of the inverter part itself? How does this limit work exactly, is it only valid when totally off grid?

A 5 kW inverter will be rated to supply up to 5kW and no more, except for very brief surges beyond that (a few seconds).

When passing through grid power, how much power can be passed through will be a limited by the design of the inverter and you would need to check, but it would be wise to consider the limit for passing through power to be similar to the inverter's capacity to supply power from the battery. It is after all using the same terminals when supplying from either source.

What happens when the total load of appliances is superior to whatever the Growatt can produce when you are plugged into the grid?
Can the growatt supply lets say 20% of the power from its battery and then the remaining 80% from the grid?

If the load is greater than the inverter can supply, the inverter will shut down. Depending on the inverter it may seek to restart after a while, hopefully by then the load has been reduced and the inverter can resume normal operations.

While there are inverters capable of such blending of sources to power loads I very much doubt any off-grid model of Growatt is capable of this. Normally the choices with these Voltronic style off-grid systems are either:

i. Loads powered by battery and solar PV (if available)
OR
ii. Loads powered by the grid

In either scenario the solar PV can charge the battery, while in the latter the grid can also supplement the PV for charging the battery.

If you want full blending of power sources then you will need to look for different inverters. They will cost a lot more though.

 

[wattmatters]

I know this is an unlikely scensrio but I need to know for planning purposes. So for example, It's evening so no solar and I've been using my batteries, they go flat & my inverter switches to 100% Grid from AC-In but I then have a power cut with grid down so I'm defo now in the dark. Once the grid is restored will the inverter immediately fire back up off the Grid through its AC-In or will it just charge the batteries and then once batteries got some power it will then fire up off them?

It depends on the inverter. Too many combinations and permutations to answer.