Battery Isn't Tied to All Roof Panels

[Jomby]

BTW, thanks for the schematic. That saves so much trouble and guessing. I am not an electrical engineer, but am a retired engineering that is researching whole house backup solutions for wildfires. So take my advice with a grain of salt and review all and anything with your electrician/inspectors.

What exactly did you tell that to your installer? Did the installer make you sign off on the technical design before buying materials?

**You want full house backup powered by the battery inverter and ALL solar panels.

As you stated, the current configuration doesn't work this way. A transfer switch needs to be on the "line" side main panel to isolate your entire house. But I think I know why your system is configured the way that it is. The SB 5.0 solar inverter generates 21 amps max at 240VAC. 2 X 21 amps = 42 amps for two inverters. Minimum breaker size is 1.25 x 42 amps = 52.5amps. The internal breaker in the SMA transfer switch is only rated for 50amps; this would be a violation.

The SMA transfer is not service rated, but this can have a work around.

The other thing that sticks out in my mind is that you have 125 + 30 = 155amps of PV/Battery generation breakers in your main panel. That leaves you 240- 155 = 85 amps left in your main panel. In other words, your main panel should have an 85amp max breaker on the top of the main panel.

Like I said, I'm not an electrician, so please check my math.

They asked for approval prior to submitting permit but I'm not experienced with electrical. What they described was that I c
ould run heat pump off grid using solar energy when grid was down but 15 panels to run heatpump and charge battery seems unrealistic. I'm monitoring system and it is around 17-19 kwh (partly cloudy days) total so taking half of that, I'm producing enough to charge the battery but not run any equipment. To me the problem seems like it would be that the configuration is insufficient to to anything beyond charge the battery.

[Jomby]

Now that I think about it, the 125amp breaker in the main panel may or may not be considered PV/battery generation if the transfer switch is set for zero export. So forget my statement above about the main panel breaker size.

If you look at the SMA transfer switch manual, it says 9.6kW AC max for the solar inverter. So my assumptions about your two inverters being greater than 50amp max was correct.

You also didn't say what kind of rapid shutdown and/or power optimizers you have installed. In other words, are all the panels facing in the same direction and is there shadowing at all?

Depending on your roof situation, you could get one larger inverter for all the panels in three strings using a SMA 7.7 -41 at 32amps/240 AC out to hook up to the transfer switch. This will work with the 50amp breaker. But then the entire transfer switch and additional shutoffs will have to be moved between the meter and main panel. The SMA has a lot of solar/battery functionality built in, but it is relatively brand new. I bet nobody has too much experience with it here.

Like I said, I was researching backup solutions for my house during wildfire seasons and have looked extensively at 200 amp transfer switches. These transfer switches are monsters compared to the SMA transfer switch. In other words, I doubt that the wire from your electric meter to your main panel will fit in the SMA transfer switch. Your existing wiring is probably aluminum.

Re-reading the SMA transfer switch installation manual, it says 3/0 to 300 kcmil copper wire will fit in the transfer switch. You push the power wire into the terminal block then slide a lever down to secure it. I'm used to seeing a massive bolt securing this connection, but it probably works.

I am not an electrician. You should have everything verified by and electrician and/or inspector.

Thanks Phil, so it's sounds like I'm stuck. Do you know if tesla powerwall has this limitation of being hooked to a limited number of panels? Longerterm perhaps tesla is a better solution?

[oregon_phil]

Read my last post. Did you get that agreement in writing?

They should have asked you about the locked rotor amps for your heat pump.

I also think you are mixing up Power (kw) and Energy (kwh).

How much power does it take to start your heat pump and air circulation system? It would be in your best interest to take a complete inventory of your electric devices. Make a spreadsheet.

At peak sun on your solar panels, you have the potential for 6 kW from your solar system and 6kW from your battery system. Whether or not 12kW will start your heat pump is another thing (12000 watts at 240VAC = 50 amps). But these are motors.

If your locked rotor amps is anywhere near 50 amps, your heat pump will not start. The newer inverter style soft start heat pumps will be much easier to start.

[oregon_phil]

I'm not sure why you are stuck. The equipment has to be changed and/or reconfigured. If you told the installer what you wanted and they didn't give you what you wanted, then you have grounds to go back to them. At this point, I would put my concerns on paper and go back to them. Otherwise you are going to think about this forever.

[Ampster]

,.......... Do you know if tesla powerwall has this limitation of being hooked to a limited number of panels? Longerterm perhaps tesla is a better solution?

Phil did not answer this part of the question and I can only give you a conceptual overview. This is more for the benefit of other readers, because your options may be limited by your contractual obligations.
The "better" solution is the one that meets your needs. Every system that integrates multiple components will have its own unique limitations. That is true, whether it uses AC coupling or a proprietary method like SMA may use. Tesla uses AC coupling and is actually an integrated inverter, transfer switch and battery with an integrated battery management system. The Powerwall does have limitations that are different than the SMA limitations but perhaps more easily addressed by adding additional Powerwalls. The best place to ask detailed questions about the capabilities of Tesla Powerwalls is on a forum populated by Powerwall users and installers.

Despite the title of this thread, the operative issue seems to be your contract with your installer. Phil has already asked the relevant questions about that contract. This technology is in a significant state of transition and you will never be satisfied if you try to compare what you have with what just came out today.

[oregon_phil]

Jomby, you dropped a lot of dimes for this installation. It doesn't do what you want it to do and it will probably bug you forever unless you get some answers. You want solutions to your problem, not to tell the installer what equipment to use and how to install it. It is unclear to me how many SMA battery inverters can be on the same AC line at the same time. Each SMA battery inverter can handle up to 3 batteries, however.

1. Write down what you want out of your system in very concrete terms; line item by line item. i.e. 1.I want to run my heat pump all night when the power goes out. etc.
2. Take inventory of every single electrical device in your house: voltage, amps, starting and running.
3. Figure out what devices are connected to the main panel and what devices are connected to the sub panel.
4. Sit down with your installer and go over every item in #1 to see if your needs are or aren't being met by the current installation.
5. What are the limitations of my systems and what do I need to do to fulfill every item in #1. How much will this cost me?

Good luck. Ask a lot of questions and get answers before moving forward. You never mentioned anything about your daily power usage or panel orientations. I think the heat pump is going to be your biggest issue. Since you are interested in whole house power backup during outages, for information sakes, look up how a gas generator, service entrance transfer switch and load shedding works. This will help you understand how other industries tackle the same problem. The equipment is pretty beefy.

[oregon_phil]

Jomby, One more thing and I'll let this one be. This might be helpful in your discussions with your installer.

Do a Google search for "SMA Energy System - For home energy management and backup power". This is an SMA marketing brochure that basically depicts you can run your home on solar and that home has one solar inverter and one battery inverter to run all the "heavy loads" of your home. Basically, this SMA energy system will run everything in your home. I think this is what you wanted. Like all marketing, it is misleading, but you can probably use this in your argument to get what you want. I want what you showed me in this brochure and this is not what I am getting.

Secondly, if you look at a picture of the Tesla gateway/transfer switch internal components, it is a very robust piece of equipment that has a service rated option. The brochure says it can handle multiple powerwalls (I think up to six).

Ok, that's it. Good evening.

[Jomby]

Jomby, One more thing and I'll let this one be. This might be helpful in your discussions with your installer.

Do a Google search for "SMA Energy System - For home energy management and backup power". This is an SMA marketing brochure that basically depicts you can run your home on solar and that home has one solar inverter and one battery inverter to run all the "heavy loads" of your home. Basically, this SMA energy system will run everything in your home. I think this is what you wanted. Like all marketing, it is misleading, but you can probably use this in your argument to get what you want. I want what you showed me in this brochure and this is not what I am getting.

Secondly, if you look at a picture of the Tesla gateway/transfer switch internal components, it is a very robust piece of equipment that has a service rated option. The brochure says it can handle multiple powerwalls (I think up to six).

Ok, that's it. Good evening.

Thank you so much Phil and Ampster. Where would I go to learn more about electrical concepts; kw power vs kwh energy etc?
*When writing down consumption inventory, the usage on the device is only when it is running, but how would I know how often and how long the unit is running? Example water heater shows 4,500 watts but maybe it only runs once every 3 hours and those would be brief except for when showering in morning? Heat pump may run for 45 minutes every few hours due to insulation of house etc.

[oregon_phil]

You can start learning with web searches.

For plug in items, you can measure power consumption, watts and energy used, kwh with a kill-a-watt device. Everything device in your subpanel flows through the SMA energy meter. You can learn how to use your existing equipment. Every piece of equipment and the energy meter. You will learn alot that way.

[Ampster]

There are also some good Stickies on this forum..

[oregon_phil]

I know the OP hasn't posted about this in two months, but I thought it might be beneficial for others regarding SMA high voltage battery inverters and interactions with SMA solar inverters. SMA posts installation and technical notes in various websites, blogs, etc. I also need to interpret SMA's specs a little better.

Tidbits of knowledge to share in order to correct my earlier assumptions.

1) SMA battery inverters are limited to one battery inverter per phase. The SMA high voltage battery inverter is 240VAC out while the SMA sunny islands are 120 VAC out (2 sunny islands for 240VAC). i.e. only 1 SMA high voltage battery is needed per installation.

2) The OP mentioned Tesla Powerwall vs the current SMA battery inverter solution. Tesla is a battery + inverter solution that you can chain up to 4 together; SMA high voltage battery inverter can accept up to 3 batteries in what they call a battery string inverter. Totally different methods. Interesting.

3) in either case, if you want whole house backup, some sort of automatic transfer switch is needed (SMA SUNNY BOY STORAGE AUTOMATIC BACKUP UNIT/ Tesla Backup Gateway)