Question about Solar + battery + grid

Maarten

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Mar 14, 2021
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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
 

OffGridInTheCity

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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.
 
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daromer

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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.
 

Maarten

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Mar 14, 2021
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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)
 

chuckp

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Jul 29, 2018
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My installation sounds very much the same.
I use the Sofar Mass Energy ME3000SP AC coupled charger/inverter.
 

Maarten

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Mar 14, 2021
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My installation sounds very much the same.
I use the Sofar Mass Energy ME3000SP AC coupled charger/inverter.
Thank you for your reply!
Could you explain, or provide a schematic, on how you have put everything together?
 

chuckp

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Jul 29, 2018
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387
Thank you for your reply!
Could you explain, or provide a schematic, on how you have put everything together?
Hi

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

daromer

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Look at mine though i dont have microinverters but one large
 
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