Hi, I´m new to solar, don´t yet have a system, but have an ok idea about what I need

400bird

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I would like to do the same. Do you have any lithium batteries in your house? Laptops, phones, cameras, watches,
pacemakers, meat thermometer, heart rate monitors, bike computers, 18650 flashlights, power tools, electric toothbrush, electric razor, range finder, laser printer, a couple remotes, ... i'm counting easily over 40 just for these innocuous things in my house!

I'm guessing you have a LOT of lithium batteries in your house.

Th difference is all of those are small and portable and professionally engineered. If they start smoking it's something in theory you could hold at arms length and throw outside.
 

FrederikSchack

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The BMS can stop a cell that is shorted internally. Read some if the fire stories and do what you feel is right. Many of them had a BMS connected.
Ok, thanks I´ll take it very seriously and look more into the fire-risk of lithium. I did have two batteries (old ones), called something like BL-5 go bad (swelling), in two very different devices, but have had a wide range of devices with lithium and never heard about anybody I know having issues (considering the amount of devices people have). So my guess is that many iterations of development have made lithium safer. On the other hand you´re very right about the scale of the batteries makes the risk a much bigger issue, we clearly see that when a Tesla crashes, it's like fireworks.

I have a few reasons for keeping them inside. One is the heat outside in the summertime, we have days around 35 degrees. Another is that I don´t really have a good place for an enclosure outside. Third I would like to minimize what can be stolen from the outside of the house, I´m not entirely confident about having 7000 usd worth of batteries outside in an enclosure. Fourth, if they are operating at 48 volts, I wouldn´t like too long cable runs.

But I´ll try to evaluate the risk and see what I could do to minimize it.
 

FrederikSchack

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I almost fell off my barstool. My choice was War And Peace, Moby Dick, the entire Bible or your post :)

But seriously, that's pretty indepth and will probably take multiple thread to delve into and sort all the variables.

At least you already really know your infrastructure.


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When the interest teases me, then I dig fairly deep, but I see there´s a lot more to be uncovered here :)
 

FrederikSchack

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I just started drawing the solar system and started wondering about the grounding of the panels, I don´t see any issue with using the grounding from the breaker panel.

Do I need to design something for leakage of current in the solar panel circuit? The solar cells are generating electricity and as such there´s no real good place to put an RCD?


SolarSystem.jpg
 

FrederikSchack

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It suddenly hit me. The charge controller in the inverter only charges with 3000 watts, which means that whatever is produced above 3000 watt has to be consumed, to be utilized. This "excess" will mostly be in the middle of the day, so we would have to make sure to utilize this energy.

Now another thought hits me, maybe it´s better to have two smaller synchronized hybrid inverters, with each their battery bank, with the ability to absorb a bigger amount of power? This would give me full redundancy, as far as I can see and that would be desirable too.
 

DerpsyDoodler

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Certainly, I'm going to make a diagram when I come home 🙂

I would much prefer to have somebody to set up the system, especially in regards to warranty and I'm now speaking with a company that I was recommended, some of the best in Uruguay. They suggested a 6kW of panels and 4kW of inverter, considering the strong sun here (short path through the atmosphere at 85 degrees) and rarely a cloud in the summertime, I think that's going to overload the inverter a lot.

So definitely I would need to be in every step of the design and implementation.
Did they recommend a charge controller or inverter to go with the panel reconnendation?
 

FrederikSchack

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Did they recommend a charge controller or inverter to go with the panel reconnendation?
They just suggested this integrated unit with inverter and charge controller and nothing besides it. But I´ve told them that I don´t feel confident about that configuration and that I would like the Growatt SPH5000, if they can get it. So now they are looking into this unit.
 

DerpsyDoodler

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They just suggested this integrated unit with inverter and charge controller and nothing besides it. But I´ve told them that I don´t feel confident about that configuration and that I would like the Growatt SPH5000, if they can get it. So now they are looking into this unit.
What was the integrated unit? Micro-inverters? Did they provide specs or a spec sheet?
 

400bird

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It suddenly hit me. The charge controller in the inverter only charges with 3000 watts, which means that whatever is produced above 3000 watt has to be consumed, to be utilized. This "excess" will mostly be in the middle of the day, so we would have to make sure to utilize this energy.

Now another thought hits me, maybe it´s better to have two smaller synchronized hybrid inverters, with each their battery bank, with the ability to absorb a bigger amount of power? This would give me full redundancy, as far as I can see and that would be desirable too.

Yeah, if you wanted more solar to charge the battery you might need to add an extra solar charger controller wired to separate PV strings.

But, the Growatt also only produces 3000 watts from battery. Are you sure this would be enough?
It's also a high frequency inverter. It's not going to start a motor, like an air conditioner. I don't have any experience with this brand, but hopefully it will at least start the refrigerator compressor.
 

DerpsyDoodler

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Yeah, if you wanted more solar to charge the battery you might need to add an extra solar charger controller wired to separate PV strings.

But, the Growatt also only produces 3000 watts from battery. Are you sure this would be enough?
It's also a high frequency inverter. It's not going to start a motor, like an air conditioner. I don't have any experience with this brand, but hopefully it will at least start the refrigerator compressor.
I didnt realize it was high frequency. Strongly suggest you reconsider this choice. If you havent already, this is a point you should do some research on.
 

FrederikSchack

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Yeah, if you wanted more solar to charge the battery you might need to add an extra solar charger controller wired to separate PV strings.

But, the Growatt also only produces 3000 watts from battery. Are you sure this would be enough?
It's also a high frequency inverter. It's not going to start a motor, like an air conditioner. I don't have any experience with this brand, but hopefully it will at least start the refrigerator compressor.

Maybe you´re really going to save my ass here :D

I did come across the fact that it was a high frequency inverter in a video making a load test on a similar Growatt unit running on a 48V battery:

He does seem to be overexcited and probably sponsored. He appears to be running some heavy loads on it (29 minutes into the video), amongst it starting an air-compressor, running a vacuum and a miter-saw at the same time (although not cutting). The air-compressor already has a bit above 80 psi of pressure on it and from my own experience that can even be tricky to start on regular grid-power if it´s on a long extension cord.

I didn´t know about the disadvantage of high frequency inverters, so I´m going to dive into that.

At first I looked at amazon for reviews and they were generally positive, but now that I´m looking into it, there are other places on the Internet where there are many complaints.
 

FrederikSchack

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Yeah, if you wanted more solar to charge the battery you might need to add an extra solar charger controller wired to separate PV strings.

But, the Growatt also only produces 3000 watts from battery. Are you sure this would be enough?
It's also a high frequency inverter. It's not going to start a motor, like an air conditioner. I don't have any experience with this brand, but hopefully it will at least start the refrigerator compressor.
Ok, I´m not really finding any in-depth material about this topic regarding solar high/low frequency inverters.

I understand that high frequency inverters have a higher efficency, like this Growatt claims to have a 97%+ efficiency, but might have issues with start-up loads.

Whereas low frequency is more like grid-power or a high torque motor, but with much lower efficiency.

But how is the reliability of the two technologies in general?

I do know about high frequency modulation, which is used with great advantage in HiFi-systems and understand that it´s the same principle used in high frequency inverters.
 

FrederikSchack

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"The “modified sine wave” has detrimental effects on many electrical loads. It reduces the energy efficiency of motors and transformers by 10 to 20 percent. The wasted energy causes abnormal heat which reduces the reliability and longevity of motors and transformers and other devices, including some appliances and computers. The choppy waveform confuses some digital timing devices.

About 5 percent of household appliances simply won’t work on modified sine wave power at all. A buzz will be heard from the speakers of nearly every audio device. An annoying buzz will also be emitted by some fluorescent lights, ceiling fans, and transformers. Some microwave ovens buzz or produce less heat. TVs and computers often show rolling lines on the screen. Surge protectors may overheat and should not be used."

"Total harmonic distortion (THD) lower than 6 percent should satisfy normal home requirements. Look for less than 3 percent if you have unusually critical electronics, as in a recording studio for example."


The Growatt inverter is in fact a modified sine wave inverter, but promotes less than 3% THD.

Good that I´m more confused now, it means that I´m seeing the icebergs and not ignoring them :D
 

DerpsyDoodler

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Maybe you´re really going to save my ass here :D

I did come across the fact that it was a high frequency inverter in a video making a load test on a similar Growatt unit running on a 48V battery:

He does seem to be overexcited and probably sponsored. He appears to be running some heavy loads on it (29 minutes into the video), amongst it starting an air-compressor, running a vacuum and a miter-saw at the same time (although not cutting). The air-compressor already has a bit above 80 psi of pressure on it and from my own experience that can even be tricky to start on regular grid-power if it´s on a long extension cord.

I didn´t know about the disadvantage of high frequency inverters, so I´m going to dive into that.

At first I looked at amazon for reviews and they were generally positive, but now that I´m looking into it, there are other places on the Internet where there are many complaints.
It probably won't last as long as a low frequency inverter. According to some in the know, hf inverters will stress and tire out their components more quickly. Low frequency can handle "always on" applications better.
 
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Hedges

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Maybe you´re really going to save my ass here :D

I did come across the fact that it was a high frequency inverter in a video making a load test on a similar Growatt unit running on a 48V battery:

Key parameter to look for is surge wattage and duration.

The battery inverter I use, SI 6048US, is rated 5750W continuous (at 25 degrees C) and 11kW surge for 3 seconds.
Also 180A (at 120V) which would be 21.6kW for 0.060 seconds; that isn't to start motors, rather to trip circuit breakers in case of a fault, and leave other circuits running.

I've seen some HF inverters with 10 second surge rating. Others quote 10's of milliseconds, which won't start anything.
Probably depends on amperage capability of front-end boost circuit, which raises battery voltage to something above AC voltage.

There are also high-voltage battery inverters (e.g. Tesla Powerwall, SMA Sunny Boy Storage) which are HF design with 400V input. Apparently the small "400V" batteries from LG for SMA aren't really a 400V series connection of cells, rather a 48V battery with boost converter. So all together a HV inverter design, with boost circuit in the "battery" and buck converter in the inverter. That explains 6000W rating with 9000W surge.

Look at ratings of appliances you want to run. Whatever wattage the motor needs, assume 5x that to start. If it takes 2000W to run, assume 10kW to start, for something less than a second (I've measured about 0.18 seconds for a window A/C)
In the case of a refrigerator, much of its power rating is defroster heating elements, while motor draws 300W for older units, as little as 50W for some newer ones. A 2000W sine wave inverter should be sufficient for a refrigerator.

I don't know about longevity of HF battery inverters, but top name PV inverters are now transformerless (HF architecture). Durability is going to have more to do with quality of design than architecture.
 

FrederikSchack

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Key parameter to look for is surge wattage and duration.

The battery inverter I use, SI 6048US, is rated 5750W continuous (at 25 degrees C) and 11kW surge for 3 seconds.
Also 180A (at 120V) which would be 21.6kW for 0.060 seconds; that isn't to start motors, rather to trip circuit breakers in case of a fault, and leave other circuits running.

I've seen some HF inverters with 10 second surge rating. Others quote 10's of milliseconds, which won't start anything.
Probably depends on amperage capability of front-end boost circuit, which raises battery voltage to something above AC voltage.

There are also high-voltage battery inverters (e.g. Tesla Powerwall, SMA Sunny Boy Storage) which are HF design with 400V input. Apparently the small "400V" batteries from LG for SMA aren't really a 400V series connection of cells, rather a 48V battery with boost converter. So all together a HV inverter design, with boost circuit in the "battery" and buck converter in the inverter. That explains 6000W rating with 9000W surge.

Look at ratings of appliances you want to run. Whatever wattage the motor needs, assume 5x that to start. If it takes 2000W to run, assume 10kW to start, for something less than a second (I've measured about 0.18 seconds for a window A/C)
In the case of a refrigerator, much of its power rating is defroster heating elements, while motor draws 300W for older units, as little as 50W for some newer ones. A 2000W sine wave inverter should be sufficient for a refrigerator.

I don't know about longevity of HF battery inverters, but top name PV inverters are now transformerless (HF architecture). Durability is going to have more to do with quality of design than architecture.
That was very good information, thanks a lot :)

I´m going to go through all the heavy loaders and I´ll try to figure out what their surge rating is. I figure there is a constant base load, so if I add a constant base load, the highest surge rating and a good buffer (50%), then I´ll end up with a usable number.

I tried to look for a surge rating for the Growatt SPH5000, but they don´t advertise it, so that is probably not an impressive rating.

I have an induction cook top, that might punish the inverter well.
 
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