PV Array and Battery size

[Grouch]

I have heard that the individual Li ion batteries are about the size of AA batteries; if that's true then no, but I'm pretty sure that some companies offer rack mounted stackable units that you can combine.

ah ok. Makes sense... if they are the size of AA batteries, then yeah no building on our own. Yes, I have seen Tesla and LG offer stackable battery banks... that's what you are referring to? like the Powerwalls by Tesla?

 

[jaggedben]

I'm trying to look it up on Google, I can't find anything on their battery selection.. it's the Exide 6E95-11... I guess it's lead acid.

So LG and Tesla batteries are Lithium Ion. Would lithium ion batteries be sold in a way where you can custom make a battery bank, such as in the example I gave in the link (for example, making a custom made bank that can offer multiple days of back up)? or is it industry standard to stick with the pre-made models that LG, Tesla, and other companies offer?

If you go this way I would recommend looking at Simpliphi and Fortress Power. No direct experience but they make lithium battery units designed to be like lead acid in terms of voltage, meaning they can be used with inverters designed for 48V DC systems, for example. Also they use LFP chemistry which is safer and longer lasting in most conditions, if treated right.

 

[Grouch]

If you go this way I would recommend looking at Simpliphi and Fortress Power. No direct experience but they make lithium battery units designed to be like lead acid in terms of voltage, meaning they can be used with inverters designed for 48V DC systems, for example. Also they use LFP chemistry which is safer and longer lasting in most conditions, if treated right.

What's the industry norm? do most designs use the pre-made battery banks such as what LG or Tesla offers (RESU-10H, Powerwalls, etc.), or do most designs use custom made battery banks? or is it a mix of both?

 

[jaggedben]

What's the industry norm? do most designs use the pre-made battery banks such as what LG or Tesla offers (RESU-10H, Powerwalls, etc.), or do most designs use custom made battery banks? or is it a mix of both?

Probably the norm tends toward real ESS like Powerwall, Resu-10H, or Enphase Encharge. It's important to understand that these are not just 'battery packs'. Powerwall and Encharge output and input AC, and Resu-10H does high voltage DC and must communicate with an inverter that supports it. One could say these are integrated 'smart' systems and you can mostly just follow the instructions to install them.

By contrast, lithium battery packs like Simpliphi or Fortress are 'smart' internally with battery management systems and internal overcurrent protection, typically, but they don't come with inverters or any decisions made for you about which inverters to use and how you integrate them into the rest of a system. There will likely be more for you to figure out on your own when it comes to inverter choices and configuration, and more ways you can screw it up even if you're relatively smart and responsible.

You do not want to be integrating bare lithium cells into a system. Or at any rate, that's the realm of developing and manufacturing product and getting it listed, rather than being in the installation business. That's a bit of a difference between lithium and lead acid.

 

[Grouch]

There will likely be more for you to figure out on your own when it comes to inverter choices and configuration, and more ways you can screw it up even if you're relatively smart and responsible.

Ha! Yeah, I knew this answer had to be in there somewhere. You start making your own battery banks, now you're on your own to choose an inverter... and good luck if it all works and communicates properly.

ok, understood.

 

[Joe.B]

If you do end up building your own I've been told that "marine" batteries are better than "car" batteries. Cost a bit more, but they are built to last and they are better at handling charge/discharge cycles. They can be drained completely and recharged many times, a process that usually kills regular car batteries.

 

[ggunn]

If you do end up building your own I've been told that "marine" batteries are better than "car" batteries. Cost a bit more, but they are built to last and they are better at handling charge/discharge cycles. They can be drained completely and recharged many times, a process that usually kills regular car batteries.

Actually, neither are good for solar or backup applications. Both are designed to deliver high current for a short time, while batteries suitable for backup or offgrid power are built to deliver relatively low current for extended periods of time. There are plenty of lead acid batteries available that are solar/backup specific, but I have seen electric forklift batteries used in these applications.

Repeatedly completely draining and recharging any lead acid battery will kill it. You only want to use the top 50% of a lead acid battery's total capacity.

 

[rainwater01]

...and how much cash you have to burn. Although I'm sure you could design an expandable system and add modules later.

That’s the cool thing about lithium batteries. When you’re using lead acid batteries if you add or replace batteries they’re supposed to be of the same make, model and age. With lithium batteries most of them I’ve read about allow you to add to them.

I’ve worked on several 48 volt stand alone systems with 48 6 volt lead acid batteries. That’s a lot of maintenance and a lot of battery cables. I could do the same thing with only 6 48 volt lithium batteries.

 

[tallgirl]

I have heard that the individual Li ion batteries are about the size of AA batteries; if that's true then no, but I'm pretty sure that some companies offer rack mounted stackable units that you can combine.

There are people who use standard prismatic cells or assemblies. Nissan Leaf cells are popular because they have a nice shape.

However, you don't ever want to mess around with Lion batteries unless you know how to build a BMS to go with them. For that matter, you don't want to make your own battery pack unless you know how to build a BMS. I've done experiments with NiMH thermal runaway and they runaway just fine. I was told they were easy to destroy, and they are!

 

[Sriram]

What he means is that your service's maximum interconnection will be determined in amps, and that will be proportional to the maximum AC wattage of inverters you may install (not DC rating of the panels). The constant of proportionality being the service voltage rating, for single phase.

E.g. 120/240V service, service conductor ampacity is 200A, maximum interconnected PV amps will be 160A or 200A depending on how you do it and the NEC year, and so the connected inverter rating(s) will be capped at 240V * 160A = 38.4 kW or 240V * 200A = 48 kW.

That's for a grid-tied system without any Power Control System (PCS). Under the 2020 NEC, with a PCS that limits the current going back to the grid, you could install more inverter power.

Cheers, Wayne

just one question for the above statement, if we are going for line side tap it's 200A and if we have 200MCB then it will be 40A of backfeeding, Can i know how you got that 160A?

 

[ggunn]

just one question for the above statement, if we are going for line side tap it's 200A and if we have 200MCB then it will be 40A of backfeeding, Can i know how you got that 160A?

The 20% rule does not apply to line side connections. The maximum output current of a supply side connected PV system is only limited by the NEC to the "size of the service", which only became defined as the ampacity of the service conductors in the 2020 NEC.

 

[Ozymandias]

Regarding 3., you can certainly get an idea from your current connected service billing, if this is an existing home. Based on our billing, we use about 30 kW-hr per day in the heating season, and 50 kW-hr per day in the cooling season. We'd need four (4) Powerwall II's at a cost of $7,500 each to cover one day's worth of electricity usage in the summer. That's $30,000, and personally a bit rich for my taste. To answer the OP more directly, you will not find any magic battery of the Powerwall type that will go for days. You could certainly use load shedding to extend your battery run time; we could use fans in the summer instead of AC, for example.

I just got a quote for one of my customers from a Tesla certified installer of $36,450 for two powerwalls! I assumed the going rate for a powerwall was $7,500-$10,000 + labor. Supply chain issues??
I'm out here in Missouri.

 

[gadfly56]

I just got a quote for one of my customers from a Tesla certified installer of $36,450 for two powerwalls! I assumed the going rate for a powerwall was $7,500-$10,000 + labor. Supply chain issues??
I'm out here in Missouri.

Not sure about supply chain, but it looks like the current MSRP of a Powerwall II is $9,250. How far away is the installer? If he's got significant windshield time or has to put his crew up overnight, you're going to be paying for that. Other than that: supply and demand.

 

[Ozymandias]

Not sure about supply chain, but it looks like the current MSRP of a Powerwall II is $9,250. How far away is the installer? If he's got significant windshield time or has to put his crew up overnight, you're going to be paying for that. Other than that: supply and demand.

Thanks for the figure. Both customer and installer are within city limits, when I suggested LG Chem as another option they flat out dismissed the product for issues related to warranty.

 

[wmgeorge]

I just ordered and received some LiFePO4 100 aH batteries not cheap, but from Renogy $449 shipped to my door and no sales tax and I might have gotten a extra 5% I forgot if I did or not. They can be discharged down to zero and stay charged for a long time, no fire danger when charging. Built in BMS and connect with a Bluetooth phone to check charge level or more.

 

[jaggedben]

I just got a quote for one of my customers from a Tesla certified installer of $36,450 for two powerwalls! I assumed the going rate for a powerwall was $7,500-$10,000 + labor. Supply chain issues??
I'm out here in Missouri.

The cost of the Powerwalls themselves and wiring them to breakers isn't anywhere near the full cost of a battery backup project. You have to install the gateway, run a (typically) 100-200A feeder to it, and then feed that to either a new or existing subpanel to back that up. Or intercept an existing feeder and splice it in jboxes to achieve the same. And then you likely also have to rewire loads, which may be relatively simple or may take as much time on the jobsite as everything I've mentioned already. You've got to do all of this in an organized fashion to avoid having the customer's power off longer than they expect. Hard to do all this at speed and volume and still deliver customer satisfaction.

So, roughly, take price of Powerwalls (plus tax?), add $1000 for the gateway equipment, add the going rate in your area for wiring up an EV charging plug (distance dependent) to account for wiring up the Powerwalls, add the going rate in your area for a service panel upgrade to account for the rest of the work, add a couple $K for some likely higher permit fees and for someone to draw plans (because the AHJ may want plans when they wouldn't for that other stuff) .... And there you have roughly the minimum price for a company that wants to stay in business doing this work. And that's for a simple project.

I'd say the number you quoted is a bit on the high side if it's a base price that doesn't include more than a simple job requires, and about right if the job requires more. If demand is high, they may be quoting high to separate out the customers who are actually serious.

 

[caribconsult]

I just got a quote for one of my customers from a Tesla certified installer of $36,450 for two powerwalls! I assumed the going rate for a powerwall was $7,500-$10,000 + labor. Supply chain issues??
I'm out here in Missouri.

I think the price you quote for the battery is about right, but the twin instalation sounds like it includes the gateway, panels, inverters, all the wiring and tubing, installation, etc. Is that correct?

 

[Ozymandias]

The cost of the Powerwalls themselves and wiring them to breakers isn't anywhere near the full cost of a battery backup project. You have to install the gateway, run a (typically) 100-200A feeder to it, and then feed that to either a new or existing subpanel to back that up. Or intercept an existing feeder and splice it in jboxes to achieve the same. And then you likely also have to rewire loads, which may be relatively simple or may take as much time on the jobsite as everything I've mentioned already. You've got to do all of this in an organized fashion to avoid having the customer's power off longer than they expect. Hard to do all this at speed and volume and still deliver customer satisfaction.

So, roughly, take price of Powerwalls (plus tax?), add $1000 for the gateway equipment, add the going rate in your area for wiring up an EV charging plug (distance dependent) to account for wiring up the Powerwalls, add the going rate in your area for a service panel upgrade to account for the rest of the work, add a couple $K for some likely higher permit fees and for someone to draw plans (because the AHJ may want plans when they wouldn't for that other stuff) .... And there you have roughly the minimum price for a company that wants to stay in business doing this work. And that's for a simple project.

I'd say the number you quoted is a bit on the high side if it's a base price that doesn't include more than a simple job requires, and about right if the job requires more. If demand is high, they may be quoting high to separate out the customers who are actually serious.

10-4.
Thanks for illustrating the process. The quote given to us was preliminary without a site visit and only a base figure without including any upgrades or rework; where l come in. We are still shopping around.

 

[Ozymandias]

I think the price you quote for the battery is about right, but the twin instalation sounds like it includes the gateway, panels, inverters, all the wiring and tubing, installation, etc. Is that correct?

Okay. Yes, it is a baseline quote without rework or upgrades included. We are adding it to the customer's existing array of 21.56kW, Fronius inverter at ground mount.

 

[ggunn]

10-4.
Thanks for illustrating the process. The quote given to us was preliminary without a site visit and only a base figure without including any upgrades or rework; where l come in. We are still shopping around.

One thing - a Powerwall installed as a partial home backup requires a lot more support equipment than one or more of them installed as a whole home backup, especially if there is PV of more than (IIRC) 7.6kW AC installed. I have seen a case or two where the extra gear was nearly as expensive as another Powerwall, meaning it was almost as expensive to get a single Powerwall in partial home backup as it would be to get two Powerwalls in whole home backup.