Layout advice and brand recommendations

[CelectricB]

Hi all,

We do MEP, civil/structural engineering and recently installed a small PV system at our office. We've drawn plans for an addition to the office and want to double the size of our PV system while also adding back up battery(s) (from 10 solar panels to 20). As it is currently, the PV system power is used by the building panel, and any excess energy sold back to utility with bi-directional meter.
To be clear about the functions/operations that we're looking for with the addition:
When all PV power is not being used by the building, it should fill the back up battery(s) before selling back to utility. Power from the back up batteries should be used before utility power, but only when the PV power is insufficient.

Any and all advice welcome, below are my main questions/concerns.

• Proprietary nature of Solar Edge: If we continue to use our inverter (and buy a second one for the new string of panels), it's my understanding the we would need to buy one of their smart meters in order to use "smart management" for the functions we need. Is this true, or is it simple enough to use a charge controller & inverter connecting the battery(s) to a separate breaker on the "Existing 60A MCB Panel"? (2nd photo)
• Will the battery inverter/charge controller need to be directly connected to the PV inverter or is it okay to put it on it's own breaker within the outdoor MCB panel?
• Buying a second identical inverter for new panel string vs one larger one for both strings?

 

[jaggedben]

You call it a 'backup' battery but you only describe functionality of using the battery for 'self consumption' to reduce utility imports. Please clarify if you actually want to have backup power capability in the event of a utility outage, as that will completely change your line diagram. Also please clarify if you want either or both functionalities to cover the indoor panel you show, and if that panel really also has another PV system.

Hi all,
...

• Proprietary nature of Solar Edge: If we continue to use our inverter (and buy a second one for the new string of panels), it's my understanding the we would need to buy one of their smart meters in order to use "smart management" for the functions we need. Is this true, or is it simple enough to use a charge controller & inverter connecting the battery(s) to a separate breaker on the "Existing 60A MCB Panel"? (2nd photo)

You have two options:
a) Use Solaredge inverters and supported battery ESS. This is a 'DC coupled' solution, where battery and solar array operate in parallel with the inverter. You can only do DC coupling with Solaredge.
b) Use an 'AC coupled' battery ESS with its own inverter/charger (same device), made by another manufacturer.
Whoever's battery inverter you use, you will use that manufacturer's supported metering, because it's the battery that needs to know when to charge/discharge.

There are only a handful of widely used products for option b that readily support use with Solaredge, as far as I'm aware. Tesla and Sol Ark are two.

• Will the battery inverter/charge controller need to be directly connected to the PV inverter or is it okay to put it on it's own breaker within the outdoor MCB panel?

That depends on the equipment you use.

• Buying a second identical inverter for new panel string vs one larger one for both strings?

If you go the Solaredge route I believe you'll need a new inverter(s). If you go another route, the second identical inverter will probably cost less out of pocket, and unless there are other considerations (e.g. available space) then it doesn't matter.

 

[CelectricB]

You call it a 'backup' battery but you only describe functionality of using the battery for 'self consumption' to reduce utility imports. Please clarify if you actually want to have backup power capability in the event of a utility outage, as that will completely change your line diagram. Also please clarify if you want either or both functionalities to cover the indoor panel you show,

and if that panel really also has another PV system.

Our main goal is to reduce utility imports (no back up power) on the "Existing Building Panel", there are essentially no loads on the outdoor 60A panel. Both panels are close and tapped off the meter. The "Existing Building Panel" should not have a PV system breaker, please ignore.
Sorry for the confusion, and thanks for the help!

You have two options:
a) Use Solaredge inverters and supported battery ESS. This is a 'DC coupled' solution, where battery and solar array operate in parallel with the inverter. You can only do DC coupling with Solaredge.

Would love to use a solaredge battery on the dc side (such as the LG Chem Resu7h). We are worried that since we do not have the Solaredge smart metering system, the battery would not operate in any mode but backup.

b) Use an 'AC coupled' battery ESS with its own inverter/charger (same device), made by another manufacturer.
Whoever's battery inverter you use, you will use that manufacturer's supported metering, because it's the battery that needs to know when to charge/discharge.

We're looking into an AC coupled solution because we're not confident we can find a Solar edge smart meter that is compatible (bought the inverter off ebay...). Just beginning to look into both solutions and really trying to get smarter and gain experience with solar.

Thanks again!

 

[jaggedben]

Adding a Solaredge meter to a Solaredge system is relatively straightforward.
You would need a different Solaredge inverter than the one you have, anyway, to support a dc coupled battery. And there's sure to be a meter available that goes with it.

 

[winnie]

Zeroth order question: have you done the math on the cost of electricity using a battery to maximize self consumption vs simply buying power from the utility when PV is not sufficient, and putting the battery investment into more PV.

Energy stored in a battery is _very_ expensive, usually more expensive than energy simply purchased from the utility. However this math is quite dependent upon the utility tariff structure.

My understanding is that at the present time PV is the _cheapest_ sources of electrical power when the sun is shining, but that energy stored in a battery costs far, far more. But utility rates are rising pretty rapidly, are different everywhere, and batteries keep getting cheaper. So you need to do the math afresh when looking at a new installation.

-Jon

 

[ggunn]

This ^^^

Typical of a few conversations I have had while manning a booth at solar trade shows in Texas:

Me: What do you want to accomplish with a PV system on your home?
Potential customer: I want to get off the grid.
Me: Is the grid available and reliable where you are?
Potential customer: Yes, but I want to stop buying power from the utility. I want to stick it to the man.
Me: The man does not care; you will be sticking it to yourself.

 

[jaggedben]

Current levelized cost of residential energy storage is in the neighborhood of $0.25 to $0.30/kwh, before or after solar+tax credit. That will likely sound like a deal in California and Hawaii. I don't believe it will in Texas.

 

[winnie]

I think those LCOE calculations assume maximal use of the battery resource, eg. charging and discharging 1x per day. If you size your battery to cover larger lulls in solar production, it gets used fewer times over the course of its life (or over the course of its amortization period) and the cost per kWh goes higher.

-Jon

 

[CelectricB]

Zeroth order question: have you done the math on the cost of electricity using a battery to maximize self consumption vs simply buying power from the utility when PV is not sufficient, and putting the battery investment into more PV.

We're mostly doing this project as a way to learn and gain experience in PV systems, not necessarily to maximize production or minimize cost.

 

[CelectricB]

Adding a Solaredge meter to a Solaredge system is relatively straightforward.
You would need a different Solaredge inverter than the one you have, anyway, to support a dc coupled battery. And there's sure to be a meter available that goes with it.

I may be missing something or misunderstanding, but our inverter does support dc coupled batteries. Hopefully, I'm not just being dumb. Here's some pictures of the tag, inside of inverter and installation manual.

 

[ggunn]

Adding a Solaredge meter to a Solaredge system is relatively straightforward.
You would need a different Solaredge inverter than the one you have, anyway, to support a dc coupled battery. And there's sure to be a meter available that goes with it.

From the inverter nameplate photo it appears that they have a StorEdge inverter.

 

[jaggedben]

I think those LCOE calculations assume maximal use of the battery resource, eg. charging and discharging 1x per day. If you size your battery to cover larger lulls in solar production, it gets used fewer times over the course of its life (or over the course of its amortization period) and the cost per kWh goes higher.

-Jon

I don't know why you'd oversize the battery that way.

You're actually correct that my BOTE number above didn't include a factor for cloudy days where the battery doesn't charge, but I think that factor would be an under 5% difference for a properly sized battery. I've done a slightly more involved model in a spreadsheet and come up with the same ballpark. Variation in installation quotes will likely be a bigger factor.

In any case, serious people use modeling software and enter consumption data to optimize battery size. And it comes out roughly the same.

 

[jaggedben]

I may be missing something or misunderstanding, but our inverter does support dc coupled batteries. Hopefully, I'm not just being dumb. Here's some pictures of the tag, inside of inverter and installation manual.

Correct, that inverter does support a battery or two. You should be able to connect a meter with RS485.
It's been a couple years since I've worked with that equipment so I can't speak to availability of the meter, but I believe Solaredge actually uses a rebranded Wattnode meter, if that helps.

 

[CelectricB]

Correct, that inverter does support a battery or two. You should be able to connect a meter with RS485.
It's been a couple years since I've worked with that equipment so I can't speak to availability of the meter, but I believe Solaredge actually uses a rebranded Wattnode meter, if that helps.

I appreciate the help & info!