Add Battery to Grid-tied Solar Edge

[Hedges]

The place I go to has giant high pressure propane tank that can fill my tanks without electricity.

???

Propane - Vapor Pressure vs. Temperature

Vapor pressure vs. temperature.

www.engineeringtoolbox.com

I don't know how you accomplish that unless you paint the tank black. Or light a bonfire under it.
Or make something like a captive air tank (bladder between the propane and a higher pressure gas.)

If the giant propane tank is any higher pressure than my little tank, then it contains incompressible liquid with no space for propane gas. I don't want to be anywhere around it.

 

[Richter12x2]

For the cost difference I see little financial justification for DIY.

BTW, are you sure you only need add batteries to your StorEdge? Most grid-tie inverters in the US only output 240VAC. If you want to run regular household loads you probably have to at least add an autotransformer sized (7.6KW in your case) for the inverter to get split-phase power which is additional cost.

That's what I was thinking. It does need an autotransformer, and a seperate critical loads box, but that'd be true of DIY also. Although it serves my house already or my sellback on netmetering would be higher, so instead of seeing like 4kW sellback, and 8kw bought, I'd expect to see something more like 24kW sellback and then 32kW bought... maybe the autotransformer is already there?

 

[Richter12x2]

???

Propane - Vapor Pressure vs. Temperature

Vapor pressure vs. temperature.

www.engineeringtoolbox.com

I don't know how you accomplish that unless you paint the tank black. Or light a bonfire under it.
Or make something like a captive air tank (bladder between the propane and a higher pressure gas.)

If the giant propane tank is any higher pressure than my little tank, then it contains incompressible liquid with no space for propane gas. I don't want to be anywhere around it.

My only thinking here is that basically a full propane tank is under pressure and an empty one isn't? So you wouldn't get as much as if you could do a full liquid fill, but you'd still be able to transfer to an empty tank.

 

[Ampster]

which seems to be easy enough to DIY on the StorEdge. The hardest part looks like just moving the critical loads to a subpanel, and that's just standard house electrical stuff.

The Storedge system uses a high voltage battery which is a lot more complicated than a critical loads panel. It is also a lot more dangerous at 350 volts than the nominal 48 volts DC in most hybrid inverters. The five little wires referred to above presumably are communication and voltage sensing wires. They communicate through a special interface board to the DC to DC converter inside the LG Chem battery to control charging and discharging. It is not a trivial task. It makes swinging loads to a critical loads panel seem like child's play.

 

[Ampster]

instead of seeing like 4kW sellback, and 8kw bought, I'd expect to see something more like 24kW sellback and then 32kW bought...

I am not sure I understand that math? When I added a hybrid inverter I was able to increase my sellback by a small amount, but not beyond the production of my solar panels. It is difficult to program most hybrids to sell off the battery to the extent of the above math. Most NEM agreements prohibit it.
However, load shifting can make a significant difference in terms of the economics of increasing consumption. I can go into details if needed but wanted to understand your example first.

 

[Hedges]

My only thinking here is that basically a full propane tank is under pressure and an empty one isn't? So you wouldn't get as much as if you could do a full liquid fill, but you'd still be able to transfer to an empty tank.

Unlike some other gasses, propane (and butane) liquefy at conveniently low temperatures. Both liquid and gas coexist at a single pressure - look at a transparent plastic cigarette lighter, or slosh a propane tank. Pressure simply tells you temperature of the contents.

It may be possible to get some transfer of liquid to the larger tank, but the gas in the small tank compresses and builds up pressure, resisting that. It is normally pumped in. I've seen an adapter to "try this at home, kids!", probably takes patience as the gas cools and condenses. It is important to leave some portion of gas in the tank. If you managed to fill completely with liquid propane, when temperature rose it would burst the pressure relief and drain.

Other gasses, like O2, can be done that way. One welding shop had a row of tanks of various pressures and refilled mine from those.

 

[Ampster]

I would consider DIY LiFePO4 which appears to be about $0.05/kWh of cycle.

That is roughly the math that I came up with when justifying my DIY system. DIY scales up better than the Storedge/LG Chem or the Tesla Powerwall if you just want to add incremental battery capacity.

 

[Hedges]

That's what I was thinking. It does need an autotransformer, and a seperate critical loads box, but that'd be true of DIY also. ... maybe the autotransformer is already there?

Page 17 of this manual appears to show the inverter (StoreEdge) acting as transfer switch for protected loads panel.
Autotransformer and battery connect to StoreEdge.

https://www.solaredge.com/sites/default/files/storedge_backup_installation_guide_NA.pdf

"Max distance between the battery and inverter is 70 ft / 20m"

 

[solar8484]

Unlike some other gasses, propane (and butane) liquefy at conveniently low temperatures. Both liquid and gas coexist at a single pressure - look at a transparent plastic cigarette lighter, or slosh a propane tank. Pressure simply tells you temperature of the contents.

It may be possible to get some transfer of liquid to the larger tank, but the gas in the small tank compresses and builds up pressure, resisting that. It is normally pumped in. I've seen an adapter to "try this at home, kids!", probably takes patience as the gas cools and condenses. It is important to leave some portion of gas in the tank. If you managed to fill completely with liquid propane, when temperature rose it would burst the pressure relief and drain.

Other gasses, like O2, can be done that way. One welding shop had a row of tanks of various pressures and refilled mine from those.

I don't know how they do it exactly but based on my observation it looks like the "Bleed Valve and No Pump" method described below.

Methods of Refueling Propane Tanks

Methods of Refueling Smaller Propane Tanks from Larger Ones. Here I am simply presenting some information that I have found in other places. My own propane supplier won't allow me to make the connections needed to use any of the techniques below, but your experience may be different. I take...

spaco.org

I guess I don't really care about how they do it as long as they can do it without electricity.

 

[solar8484]

That's what I was thinking. It does need an autotransformer, and a seperate critical loads box, but that'd be true of DIY also. Although it serves my house already or my sellback on netmetering would be higher, so instead of seeing like 4kW sellback, and 8kw bought, I'd expect to see something more like 24kW sellback and then 32kW bought... maybe the autotransformer is already there?

I doubt the autotransformer is already there. In grid connected mode the inverter is just syncing up to the grid 240VAC and the split-phase is done by POCO's transformer. You won't have that when not connected to grid.

 

[Richter12x2]

I am not sure I understand that math? When I added a hybrid inverter I was able to increase my sellback by a small amount, but not beyond the production of my solar panels. It is difficult to program most hybrids to sell off the battery to the extent of the above math. Most NEM agreements prohibit it.
However, load shifting can make a significant difference in terms of the economics of increasing consumption. I can go into details if needed but wanted to understand your example first.

What I meant is, power from the panels must go to the house first, so it must already support unbalanced load. Otherwise, you'd send the full 240V you generate out to the grid and then get the power back from the grid, wouldn't you, letting the grid handle the load balancing? I don't know, it's just a guess, but if I'm not seeing 100% of the generation go out . . .

 

[Richter12x2]

The Storedge system uses a high voltage battery which is a lot more complicated than a critical loads panel. It is also a lot more dangerous at 350 volts than the nominal 48 volts DC in most hybrid inverters. The five little wires referred to above presumably are communication and voltage sensing wires. They communicate through a special interface board to the DC to DC converter inside the LG Chem battery to control charging and discharging. It is not a trivial task. It makes swinging loads to a critical loads panel seem like child's play.

From the manuals, it still needs a critical loads panel, and the switching is done automatically in the storedge. The 5 wires are the RS485 communication wires for communication. My point is that it's already designed to do all of that, it's not complicated to hook up their battery to their system. It'd likely be VERY complicated to try to DIY a battery pack to do the same thing.

What I'm looking at is:

https://ressupply.com/documents/solaredge/SE7600A-USS2_StorEdge_Installation_Guide.pdf

https://ressupply.com/documents/solaredge/StorEdge_Battery_Wiring_Guide.pdf

https://ressupply.com/documents/lg_chem/RESU10H-R_Installation_Manual.pdf

 

[Ampster]

My point is that it's already designed to do all of that, it's not complicated to hook up their battery to their system. It'd likely be VERY complicated to try DIY.....

Exactly my sentiments.

 

[Hedges]

What I meant is, power from the panels must go to the house first, so it must already support unbalanced load. Otherwise, you'd send the full 240V you generate out to the grid and then get the power back from the grid, wouldn't you, letting the grid handle the load balancing? I don't know, it's just a guess, but if I'm not seeing 100% of the generation go out . . .

I'm pretty sure the inverter don't know nothing about imbalanced loads. It delivers all the watts it can to 240V. If your loads are imbalanced, it exports power on one phase and imports on the other with grid doing the balancing. If configured for zero export, measure current on both phases and vary wattage delivered up or down such that the sum is never net export. Watt hour meter measures net watts, sum of the two phases.

You ought to be getting 100% of available PV turned into AC, and the watts are either consumed by your loads or exported.

 

[klacol]

I have up and running a Solaredge Storedge SE7K-RWS with a coupled LG Chem RESU 10 battery in Germany for one year now. The battery is directly coupled to the Storedge inverter. I would like to extend the amount of storage and wonder, if I am bound to the batteries from Solaredge/LG.

My battery is announced as 48V Lithium-Ion Storage. That seems to be no high-voltage battery.

Does anybody know, if I can buy/build a 48 V - DIY Battery and integrate it somehow? These questions arise in my head:

1. Is a 48V DIY battery compatible with the Storedge SE7K-RWS?
2. Which battery management system should I use and would the BMS need to "speak" with the inverter?
3. How would I have to connect a DIY battery?
4. How would I configure the SolarEdge Dashboard with the new amount of storage?

Any help appreciated.

 

[Ampster]

As far as I know the battery and inverter are integrated by an interface card. I suspect the communication is proprietary. It may take a great deal of effort to figure it out.
In addition the chemistry of that battery is not the same as a typical DIY LFP battery.

 

[klacol]

As far as I know the battery and inverter are integrated by an interface card. I suspect the communication is proprietary. It may take a great deal of effort to figure it out.

Thanks, yes, there is a third cable (RJ45) between inverter and battery. I have asked at solaredge, if they support other batteries, than the LG Chem RESU X.