Question about Solar + battery + grid

I can't seem to wrap my head around the complete system that is needed to manage the electrical switching side of a system with solar, battery and the grid.

I am in the stage of building a 48 Volt lithium battery using 18650 cells.
We are looking at solar panels with micro inverters (meaning 230V from the roof)
And I am connected to the grid.

I can't seem to grasp what I need as a system to manage all of that.
How does that system charge the battery from the panels, but not the grid?
How does my house use energy first from the panels, 2nd from the battery and lastly from the grid?
And when there is a power outage, how does the system decouple the grid from my house?

What hardware can be used for that?
How does it talk to each other?

Lots of question where I can't seem to get an integrated answer to.

Best regards,
Maarten

I feel your confusion - I had much of this 'lack of understanding in my gut' when I started my off-grid system. I'm off-grid and you want a hybrid system... but I can offer some 'laymen' level comments.

Electricity can flow simultaneously even when controlled by separate entities. For example,
- A charger checks the battery voltage and based on that - follows its internal wiring/settings... and will push max power till it nears top voltage and then less and less till the battery is charged.
- An inverter pulls electricity to create AC to power things. The inverter has its own operating range of min/max voltage and max power and will pull from the battery to meet the load demand.

These 2 things happen independently and simultaneously over a shared wires physically connected a battery! Electricity will go 'on the wire' from the charger and 'come off the wire' to the inverter with the battery operating as a buffer. In/out changes happed as fast as electrons can swizzle around - e.g. the speed of light basically. Electrons are really cool/easy in this regard - they simply flow to the demand as they are allowed.

In the same way, hybrid units can take in grid power + PV power... monitoring each one - and run a charger (power to charge the battery) and an inverter (power to loads) all simultaneously. It is sophisticated electronics - but nothing 'mysterious' - and the demand is high enough today that there are a good range of affordable products.

The difficulty is in picking the exact combination of features and matching operating parameters to meet your needs. For example, every unit that has PV input has a voltage range and a max power. This means the panels need to be hooked up to operate within the specs of the unit you purchase. Units typically settle on nominal battery voltages - such as 24v or 48v. On the AC side, the US is 240v/120v split-phase and elsewhere is 3 phase. When you hook to the grid - the key question is will you push power BACK to the grid... in which case you'll need permissions from power company and they may limit your equipment choices.

You could help get good responses on this forum by working up details. For example - you made a start with detail but folks will need a bit more to provide any specific equipment suggestions....

>I am in the stage of building a 48 Volt lithium battery using 18650 cells.
How many cells are you planning to use - 14s? - etc. This will lead to a specific battery 'Killowatt Hours' capability.

>We are looking at solar panels with micro inverters (meaning 230V from the roof)
OK we have 230v (good). How many panels (e.g. total 'Killowatt' capability) are you thinking?

>And I am connected to the grid.
Grid into your home only - or are you planning to also push/sell power back into the grid?

What kind/size of things do you plan to power? - e.g. lighting?, refrigerator?. power-tools?, cooktop?, AC?, electric car charging? .. The idea here is to arrive at a planned max "Killowatt' capability.

If your plan isnt to sell energy back to the grid you should ge an offgrid system.
If you plan for batteries and sell back to grid you should get a hybrid system.

microinverters are generally for grid-tie where you only sell to the grid and not use battery systems.

This is the simple answers and then you can make it alot more complex. The most important part is that if you plan to do any type of grid-tie system. That is Hybrid or grid-tie with 0 feed to greed you still need a permit And you might even need a permit for just mounting the panels depeding on where you live. Start there

Note that building diy batteries of lithium isnt 100% safe. It can be made "safe" but it can always fail

Now start dig into it and best source is to check the project section and see what fits you.

And one last tip: If something is cheap its cheap for a reason and dont forget that protection is the first thing to think about in this world.

First of all: Thanks for your replies!!


For 48 volts I am indeed planning to built a 14s pack. More specifically a 14s160-200p pack (19-24 kWh) (I might split them in 2 separate 14s packs for easy service, and the ability to stay "online")

I think we will get about 9-10 panels of 350W each 3.2-3.5kW.
The microinverters will be from Enphase. (microinverters have a longer life than a central inverter, so eventually cheaper, but it needs to work in the system of course

We are running on 230V AC, I live in the Neterlands.
We have a 'smart meter' so we can 'sell' back to the grid.
But only when the battery is full and I am not using any power, whenever possible batterystorage of course.

Peak power I am able to use with my grid-connection is 6250W.
But I estimate that with 'normal' operation and we are using the oven, fridge an AC this is ~3600W
So that would be enough for the battery to provide, the rest can come from the grid at the peaks.

I know a DIY battery can never be a 100% safe, that is why it will be located in the non-attached garage away from the house. But I will try to make it as safe as possible and service and monitor it regularly (I bought a FLIR camera to detected heaters for example).


I am looking at the Multiplus II from Victron as an all in solution (inverter/charger). I hope the ideal situation is possible in my house and where the hardware is located:
(I can't seem to embed pictures in the post)

My installation sounds very much the same.
I use the Sofar Mass Energy ME3000SP AC coupled charger/inverter.

chuckp said:

My installation sounds very much the same.
I use the Sofar Mass Energy ME3000SP AC coupled charger/inverter.

Click to expand...

Thank you for your reply!
Could you explain, or provide a schematic, on how you have put everything together?

Maarten said:

Thank you for your reply!
Could you explain, or provide a schematic, on how you have put everything together?

Click to expand...

Hi

Sorry totally manic at the moment, as Soon as I have a fe2 mins spare I’ll put something together for you.

Look at mine though i dont have microinverters but one large

People, thank you for all your advice. This forum really helps to gather smart people

daromer said:

If your plan isnt to sell energy back to the grid you should ge an offgrid system.
If you plan for batteries and sell back to grid you should get a hybrid system.

microinverters are generally for grid-tie where you only sell to the grid and not use battery systems.

This is the simple answers and then you can make it alot more complex. The most important part is that if you plan to do any type of grid-tie system. That is Hybrid or grid-tie with 0 feed to greed you still need a permit And you might even need a permit for just mounting the panels depeding on where you live. Start there

Note that building diy batteries of lithium isnt 100% safe. It can be made "safe" but it can always fail

Now start dig into it and best source is to check the project section and see what fits you.

And one last tip: If something is cheap its cheap for a reason and dont forget that protection is the first thing to think about in this world.

Click to expand...

I do not sell to the grid but I am not offgrid. I kept the grid connection so my system can perform like a much larger system. Anything over the max output of my inverters comes from the grid and the inverters continue to supply their max output. This means all surges and rare high loads are covered by the grid and the inverters keep on tooting. My system is sized to supply the majority of my loads. Not having to size my system to supply all of the surges and rare high loads made it so I could spend a lot less on batteries panels inverters etc.

Grid tie inverters with limiters do as I just explained. Also solark outback Deye Schneider to name a few all have these capabilities. They can use external CTs while in grid tie mode to limit the inverters output to not sell to the grid.
The purpose of the limiting external CTs is to avoid all the hoops, permits, much higher expense etc. What happens on your side of the meter is your business in my book

Cheap 4-life said:

I do not sell to the grid but I am not offgrid. I kept the grid connection so my system can perform like a much larger system. Anything over the max output of my inverters comes from the grid and the inverters continue to supply their max output.

Click to expand...

Interesting - to me, this is off-grid. Off-grid doesn't mean you ignore *incoming* Grid power but rather you don't connect/send power to the Grid. I use ATSs to switch back and forth automatically - so when my off-grid solar system runs out of power, the grid automatically takes over.

Cheap 4-life said:

This means all surges and rare high loads are covered by the grid and the inverters keep on tooting.

Click to expand...

If by surge you mean like a motor startup surge - I don't know of equipment would work back/forth with off-grid + grid for a 'surge' in amps. If you mean that off-grid does X circuits and you have extra Y circuits that are 100% Grid - then yes. For example, most of my house is ATS'ed but the Spa is 100% grid all the time.

Cheap 4-life said:

My system is sized to supply the majority of my loads. Not having to size my system to supply all of the surges and rare high loads made it so I could spend a lot less on batteries panels inverters etc.

Click to expand...

In my case - I took it nearly all the way (except for the SPA). 10% of my circuits are not on off-grid / ATS - but that's just because of diminishing returns on wiring and they don't consume very much. In a 'real emergency' I can easily add the remaining few circuits at the main panel by doubling up to off-grid circuits or just run a few extension cords to off-grid circuits.

I’m using grid tie inverters, so I’m certainly not offgrid. The other 4 hybrid inverters I mentioned, can also operate in grid tie mode (connected to the grid) and not send more power than the loads need therefor not feeding power into the grid-past the meter. They will not operate in grid tie mode unless the grid is present. While in grid tie mode my inverters and the 4 I mentioned allow the grid to supply the start up surges from a central heat and air unit and fridges etc. grid tie inverters don’t supply the surge amps for loads, the grid does. So this isn’t offgrid. Also the inverters I’m referring to while in grid tie mode do not shut off when the homes loads are more than the inverters max output. No transfer switch is needed or used. Ofcourse if the grid is down then transfer switches automatic external or internal or manual are used and then the hybrid inverters do as you describe. When offgrid (Unlike grid tie) the homes loads cannot exceed the output of the inverter. If it does the inverter shuts off as you describe. So this requires the setup to be sized for the high wattage surges from motors etc and for occasional high loads

CTs is to avoid all the hoops, permits, much higher expense etc.

Click to expand...

The 0 limiter do not get you away from permits. You still need to have full on permit to have a grid-tie system connected to the grid. No matter if you sell or not!! WAY to many people think this in legal and just to take an example its NOT legal in Europe.
In Europe you need to have permit as soon as you have something connected that can send back to grid. This so the Linesmen know what departments that potentially could have a fault and they disconnect it when working....

The 0 limiter is for those who does not get paid to send energy back while still having the permit. So please dont write or tell people this is legal because it aint in most places and beware that people read what you write! We want to be clear about whats legal here and what not.

daromer said:

The 0 limiter do not get you away from permits. You still need to have full on permit to have a grid-tie system connected to the grid. No matter if you sell or not!! WAY to many people think this in legal and just to take an example its NOT legal in Europe.
In Europe you need to have permit as soon as you have something connected that can send back to grid. This so the Linesmen know what departments that potentially could have a fault and they disconnect it when working....

The 0 limiter is for those who does not get paid to send energy back while still having the permit. So please dont write or tell people this is legal because it aint in most places and beware that people read what you write! We want to be clear about whats legal here and what not.

Click to expand...

I was unaware of this, thnx for the info!

After a bit of searching it seems that in the Netherlands you are required to register your solar panels or other electricity delivery systems here: https://www.energieleveren.nl/

Exactly And in some countries you are not even allowed to connect an offgrid inverter even though its just "input"... I agree that some rules is weird but the rule about grid-tie i agree on and we should highlight this since fact

(Yes i dont do all things legal either...) But for this forums sake we need to promote the legal aspects and highlight where the limits are

daromer said:

The 0 limiter do not get you away from permits. You still need to have full on permit to have a grid-tie system connected to the grid. No matter if you sell or not!! WAY to many people think this in legal and just to take an example its NOT legal in Europe.
In Europe you need to have permit as soon as you have something connected that can send back to grid. This so the Linesmen know what departments that potentially could have a fault and they disconnect it when working....

The 0 limiter is for those who does not get paid to send energy back while still having the permit. So please dont write or tell people this is legal because it aint in most places and beware that people read what you write! We want to be clear about whats legal here and what not.

Click to expand...

We have had this conversation before, but I understand you wanting me to be clear. As I explained using an inverter with zero export allows me to avoid the extreme hoops, cost, permits etc. Where I live I can’t even install a solar panel “legally”. To get permitted the cost of my setup would have been in the 10s of thousands. I know for some people it wouldn’t cost that much but it’s crazy where I live and where other people live. Maybe if it was the same way where you live you might feel differently. So yeah for ME and in MY book whatever happens on my side of the meter is my business as it should be. All grid tie inverters (and most hybrid) have antiislanding to protect lineman. The zero export is not just for people that don’t get paid to send power back into the grid. It is also for people that want to be self sufficient and want to save their own excess power in batteries so they have power stored for when the grids down.

But it doesnt make it "legal" (In EU and the places i have heard of). Thats the point here and i will continue to point the legal aspect out because there have been people thinking just because you 0-export its legal and totally safe. It aint and wont!

And no matter if it have antiilanding it can cause issues if it fails. Thats also mentioned in for instance the EU descriptions to why its a must.

0-export is not needed for those saving energy into the battery since those systems have SBU (All i have looked at so far) where it priotizes use from Solar, battery and then utility thus also charges in same order

Im not here to change your setup but its very much important that what we teach and or show also clearly shows the legal or illegal aspects.

Edit. Yes you edited while i wrote. Yes its just about the legal aspect and im a paint in the ,,,, sometimes

Cheap 4-life said:

(snip) When offgrid (Unlike grid tie) the homes loads cannot exceed the output of the inverter. If it does the inverter shuts off as you describe. So this requires the setup to be sized for the high wattage surges from motors etc and for occasional high loads

Click to expand...

Very nice thread. Yes, offgrid the maximum power cannot exceed inverter output, and in my case it's a problem because inverter can output 1.5 times more current than the grid (5KW vs 3.3KW). I don't want 5KW going around my wires, so I bought a current limiter that will trip when 3.3KW are reached.

This topic is interesting. I'd like to discuss mechanical UL listed ATSs (physically interlocked relays) vs 0 limiter systems. To me - a 0 limiter system (like this: https://www.ebay.com/itm/2241323088...1291&msclkid=6c6e115b173510f5d844719bcc111362 ) can be quite risky compared to a physically interlocked UL listed relay ATSs - because its a simple measurement and can easily measure 'wrongly'.... and allow power to out to the grid. On the other hand, physically interlocked relay ATS system seems a bit safer - because its physically (very unlikely/impossible) to send power to the grid unwittingly.

I'm not sure how hybrid (all-in-one/inverters) work but I assume they also use limiters? and therefore can be risky in the same way 0 limiters above - compared to mechanical ATSs as far as unwittingly allowing power to the grid?

I'd be interested in any comments on this.

Quick google search indicates that mechanical ATSs are legal in the U.S. - but may require electrician install in some jurisdictions.

Proper grid tie use islanding as cheap Said. Ie software based. And in many countries they talk about systems where the grid owner also can controll the output. Lets see how that goes.
Eya we Hall. It destroy the thread with all this