I'm confused about inverters. Brands, specs, split phase, etc.

TLDR below.

Well, a while back I started this thread: house-battery-and-energy-management as a way to keep track of, and get suggestions on improving my home energy efficiency and adding a battery etc. It's been a while since I've had any interesting progress to note there, but I've been researching and planning a lot.

I live in the US, so split phase 240V at 60 Hz. At the moment (since plans keep changing as I learn more) I'm planning to add a sub-panel next to my main panel as it's running out of spaces for breakers as I upgrade the wiring. I'm not using more power, just splitting that power up into more circuits. Some due to modern codes, and some because a few of my old circuits have way too much stuff on them.

So I figure, why not make that sub panel compatible with a generator? A manual transfer switch is easy to install and would make it legal in my area, and I could use a small-ish generator to run some basic stuff on the sub panel. Fridge, freezer, microwave, some outlets and lights.

Bare with me, I'm getting to the inverter part.

At some point, I'd like to add a battery to run the sub panel so I wouldn't necessarily need to run the generator for the whole blackout. Just to charge the battery if the blackout lasts long enough to drain it. Well, researching generator/sub panel solutions, it seems here in the US, sub panels are almost exclusively split phase 240V. You can get single phase 120V, but they're pretty small panels, and I had hoped to have some future expandability and flexibility. Also, maybe I'll want to add a 240V circuit to the backup someday.

That's all well and good, having a 2-pole MTS and sub panel and a compatible generator. But when I go to add a battery and inverter (even some solar someday, maybe); that's what has me confused. Seems nearly all inverters are single phase. I guess you can double them up to make a split phase 240V, if they have the ability to communicate, to make sure the phases are... phasing at the right time. There are a few split phase inverters out there, but they seem to be inefficient, and the "pure" sine wave doesn't look great to me.

What I mean is that there are Low frequency inverters that can handle huge peak amps and inductive loads. But they are only something like 80% efficient and have a Total Harmonic Distortion of 10-15%. And they call that "pure". They also consume something like 150W of power just sitting there idle.
There's also High frequency inverters that are something like 93% efficient, and have a THD of around 3-6%. I can't remember exact numbers as far as idle power usage, but it's way less than 150W!

Anyway, the only split phase inverters I've seen are Low frequency, and something that bothers me: the neutral cable is the same size as the hot cables. That means if I bought a W split phase inverter, and used it exclusively for 120V circuits, I couldn't use the full 12.5A on each hot (like I could if I were using 240V circuits) I'd have to cut the wattage in half to keep the neutral cable only receiving 12.5A. Unless I got myself confused with the math. W at 240V is 12.5A, but that same amperage is only W at 120V. Anyway, I've seen RV neutral wires melted because of this exact issue.

So at the moment I'm not sure if 2 paired units would be better, or 1 split phase unit. Which leads me to another problem. I can't seem to find an inverter that has a really solid reputation. I keep seeing reviews about companies not honoring warrantees, or having terrible customer tech support. Or the machine itself just doesn't deliver what it promises. Or they don't have a product that will work for me. Or I can't find a place that sells them. Brands I've looked at so far are:
Growatt (really bad tech support according to reviews, but reviews can't always be trusted...)
SunGoldPower (low efficiency, high THD)
MPP Solar (confusing website, hard to find specific models for sale)
Aims (expensive, high power draw, no solar charger that I could find)
WZRELB (no split phase, can't be paired either)
Sigineer (low efficiency, high THD)
PowMR (no split phase, can't be paired either)
Victron (way too expensive)

Maybe I'm just looking in the wrong places. And how important is it for the sine wave to be "pure" anyway? Is 10-15% TDH acceptable for things like refrigerators, microwaves, and electronics? I don't think I have any incandescent lights left in my house. They're all either LED or Fluorescent.

TLDR: Can anyone recommend a brand or unit that will work well with a backup sub panel, generator, battery, and maybe even solar? I just want to toss Deye into the ballpit aswell.

SUN-5/6/7.6/8K-SG01LP1-US | 5-8kW | Single Phase | 2 MPPT | Hybrid Inverter | LV Battery Supported Inverter Company, Supplier | Deye Inverter Technology

NingBo Deye Inverter Technology Co.,Ltd is China SUN-5/6/7.6/8K-SG01LP1-US | 5-8kW | Single Phase | 2 MPPT | Hybrid Inverter | LV Battery Supported inverter company and supplier。 The series, SUN-5/6K-SG01LP1-US SUN-7.6/8K-SG01LP1-US/EU, is a single-phase low voltage (48V) hybrid inverter ...
I have the 5kW EU version and i'm pretty happy with it so far. Bought it for € from China, including shipping and taxes.
Mine has no fans and besides a very quiet whine noise like old CRT TV's, makes 0 noise. For best efficiency, you'd want the solar panels above 350V while in use. All models sip 70-90W with AC on and no loads connected. So its better to get one big one instead of two smaller ones. You can run multiple in parallel if you wish. Just give the Manual a read.

However, the inverter has two shortcomings.
1st - The MPPT tracker, like most budget inverters, has no shadow management for solar panels. If that is a big problem, you might be better off with a premium brand like SMA or Fronius.
2nd - The actual working electronics (mppt, inverter, battery voltage booster) are seperate from the measuring equipment for the enduser. The whole unit works very well. But at least with my unit, if i dial in 230V AC in the settings, i do get spot on 230V AC measured with a oscilloscope and multimeter, but the display and wifi dongle will report 234V AC. Similar story about all other voltages and currents all around the unit and there is no way to calibrate it.

And at last, i want to give MPP Solar a shutout for being a terrible company. I had the MPI 5,5kW unit, which was obnoxiously loud, is more inefficient, the manual shows Windows XP software and my inverter died on me after a short. Got quoted 170€ for the replacement part, got charged nearly 300€ and its still not working. The other parts have a wait time of over 3 months.

So i ditched the now € MPP Solar MPI 5,5kW unit in favour of the in all regards better € Deye SUN-5k-SG03LP1-EU. Here is a great video that will help you understand the neutral wire in a 240 split phase system. View: https://www.youtube.com/watch?v=qM2hJmtq3T4
Electrician U also has lot of great other fundamental electrical knowledge videos including one on 3 phase which has finally helped me figure it out in my head after years of trying.

On a related note it is very easy to wire a 240 designed sub panel with only a 120 input you just wouldn't be able to run anything 240 off that panel. It sounds like you want a 240 option down the road anyways so might as well set it up with the right inverter and generator for 240 split phase anyways. I haven't looked into 240 generators specifically but I imagine it would have to be one specifically designed for 240 split phase where is has the neutral center tap wire rather than some inverters or generators that run without native 240 without a neutral to split the phase.

One piece I am not entirely sure on myself so would love other folks clarifying is how much of a generator or inverters rated load can be used if you are only using one side of the split phase. My current understanding is that you can only use about half of the total rated capacity(or one of the inverters capacity if operating in parallel to make split phase.) My logic is that if a 6KW 240 inverter can output 25 amps across the transformer and I am only using the one half of the transformer by drawing on a neutral and hot wire then I can draw 25A at the 120 which equals about 3KW but not the full 6KW because that would be 50A on half the transformer coil and 0A on the other half and be imbalanced. This is also a case where maybe the transformer is better able to balance an imbalanced load like that than if you were instead using high frequency inverters where drawing 120 power is only connected to one of the inverters so it makes even more sense that you only have the capacity of that one inverter. All this is why even in standard grid power split 240 that most USA houses have you have to balance your loads across both halves of the 240split which is done pretty automatically because of how the main conduit bars are aligned in standard breaker boxes. Every other breaker is drawing 120 off the opposite hot(and so the opposite half of the transformer) and it also is why 240 breakers connect to two hots that are next to each other but not the same hot.

As for specific recommendations. I am currently planning a big 12KW new solar system to add to my off grid home and am currently looking at Victron because they seem like the best ones and there is a great DIY/Hacking community that I can use to trick the system into operating the way I need it to in my unconventional system. I am building this new system on the barn several hundred feet from the main farmhouse(where my parents live), and my house each of which has their own off grid system and the plan is to have the barn system act like the grid as far as the homes are concerned. This way I can minimize wire size for the long runs and maximize peak load capability in each building but it is complicated and needs good software that I can hack if needed. I do want to look into cheaper alternatives that might be good enough and signature solars EG4 is on my list to look into since on paper they seem to have most functions of the victron and are half the price. Thanks folks, I appreciate the input!

I've been thinking along the lines of a hybrid inverter. In my area, I could feed power back to the grid for a credit. My provider is very pro solar. I'm not sure I'll have the area needed for enough solar panels to do that though. But the other advantages to a hybrid inverter would come in handy, I think.

I haven't been able to find any WZRELB inverters that can do spit phase or be linked. I have a small 120V version and I'm impressed with it. It does exactly what it says it will do. I also have a PowMr solar controller. It's cheap, but works well enough for what I paid for. Same problem as WZRELB though. Can't find split phase or pairable units. Maybe they're out there and I just haven't found them yet.

David Poz and Will Prowse sound familiar. I've probably seen some of their videos already, but I'll take a second look. I will also look more closely at EG4, SMA, Schneider, and Deye.

So two paired inverters could potentially use twice the idle power as a single integrated split phase. I hadn't thought of that, but it makes total sense. I'll watch out for it.

I've been looking in more detail about how the split phase inverters work. It seems that some use a single auto-transformer with a center tap for the neutral. So the idea that one could only use W total on the 120V neutral in a W inverter seems to hold true. I've also seen that MPP makes a split phase inverter that uses dual transformers. So each hot line has its own corresponding neutral. That would eliminate the issue altogether. Though I wonder if that kind of inverter wouldn't use more power than a single transformer one. Something to look into.

Interesting that you had a bad experience with MPP. I've only ever heard raves about them. Though I've read some really bad reviews on every unit I've researched so far. They do have a couple inverters that might work for me though. The LV and the LV. Basically the same but the 50 means W and the 60 means W. I saw a review showing the dual transformer setup. Seems the LV can't power up chop saws, but I have no intention of doing that. Finally found a seller and a list of specs for it. There's no mention of THD, just "pure" sine wave. That's a minus. But it apparently uses less than 100W at idle. Probably pretty good for a dual transformer setup.

Anyone hear of Current Connected? They have the LV for sale here.

Maybe I'm over complicating things by insisting on split phase. But single phase 120V has it's own issues. I'd be limited to a 30A breaker from the main panel to feed the sub panel via the grid. Which for now, is my primary source of power.

I did finally get around to adding up all the things I can think of that might potentially be added to the sub panel:
Fridge: 6.5A 780W (required)
Freezer: 3.5A 420W (required)
Microwave (input): W
240V heaters: 750W (x2) W
120V heaters: 750W (x2) W
5,000 BTU A/C: 4A (x4) W
Lights: 10W (x6) 60W
Laptops: 19.5V 3.3A (x2) 128.7W
Cell Phones: 0.5W (x3) 1.5W (required)
Gateway: 18W (required)
Router: 9W (required)
Wifi: 18W (required)
CPAP: 5.5W (required)

Of course, the A/Cs and heaters would be mutually exclusive. And the heaters use more Watts so I'll just count them. Although, they may be excluded too depending on how many Watts I can manage to send to the panel. Anyway, the totals are...

Required: 1,252W
Would be nice: 6,140.7W

This assumes no losses or inefficiencies, and all the devices would be running full-on at the time. Which would not be the case. Like with the fridge. It often doesn't run at all, and when it settles down and the door is closed, it only uses 2.2A while running. Or the microwave, which would be run for 30 seconds to a minute typically. In fact, the only things that would run all the time would be the gateway, router, and wifi. Which use almost nothing. And if the internet is broken too, may as well shut those off.

I have a functional fireplace and a fair amount of firewood stored away. It's only set up to heat one room, but it would eliminate the need for electric heaters.

So if I'm really frugal, I could get away with a 3kW system, or even less. A 6kW system would be really nice though. But I think it will only work if I can get a split phase inverter. That's what I'm hoping to do eventually. Run the sub panel off solar/battery. If I ever have excess power, I'll have to figure out what to do with it. The main function though, is to provide backup power to select circuits during a grid outage.

I made some diagrams (gotta have diagrams!) to help me wrap my brain around this stuff. So here is the first step as I see it:

The grid is the primary source, and the generator is the secondary. Looks like the transfer switch would be wired up like a sub panel or junction box. With the neutral isolated but not switched. Here's what I think is going on inside a transfer switch:

Top lugs are grid, bottom lugs are generator, and the middle lugs go out to the sub panel. Out is connected to either grid or generator via a "knife" switch, having the effect of being an on-off-on double throw.

The sub panel is your basic split phase sub panel. I've installed these before, no problem. The essential circuits will all be moved here. I don't really need a diagram for this, and you guys probably don't either, but I was having fun drawing, so I'll share it anyway.


So the challenging part for me is adding the inverter and battery. Maybe it depends on which inverter I buy, but I think it would hook up something like this:

Maybe the inverter should go between the transfer switch and the sub panel. I don't know. But at this stage the inverter/battery becomes the secondary source of power, and the generator is tertiary. The grid would still be the primary source for the sub panel. In the event of a power outage, the battery would supply the sub panel until it got low, at which point I'd start up the generator to charge it and run the sub panel. I figure a 6kW battery, 6kW inverter, and 6kW generator should go well together. It's very unlikely the sub panel would be using 6kW for most of the time, so the generator should be plenty to charge up the battery while also running the sub panel. And when the battery is full, I'd shut the generator off. During short outages, the generator may not be needed at all, and the battery could be charged by the grid later when power is restored.

During normal happy grid times, the inverter and battery wouldn't be needed at all, and the inverter could be shut off. I suppose a battery maintainer could be used to ensure the battery is topped off and ready to go. Saving much of that 100W idle consumption of the inverter.

The last stage would be adding solar panels.

Doesn't look like much of a difference on the diagram, but installing a solar array would probably be a thing I'd have to hire out. And it will change the whole dynamic of the power system. The grid would still be the primary source of power for the main panel, but the sub panel's primary would be the solar. The inverter will most likely have at least 1 MPPT solar controller built in, so I don't have to worry about that. I did some measurements a while back, and I don't remember details, but I think if I covered all of my potential areas with panels I could get something like 10kWh per day in the summer and 1kWh per day in the winter. Very disappointing results, which prompted me to go this route instead of trying to power my whole house with solar.

Anyway, the battery would be the secondary source for the sub panel, followed by the grid as the tertiary. And the last one (quaternary?) well whatever #4 would be called would be the generator. Though I'm not sure the inverter would know the difference. I guess hybrid inverters can tell if the grid is on or not, and so they know whether to back-feed excess power into the grid or keep it isolated. I'll have to talk to my utility provider about that. And during inadequate sunlight, the inverter may also be able to use some solar and only draw what's needed from the grid.

I'm guessing the generator, inverter, and battery should all match each other as fare as Watts go. So I'm thinking with a 6kW inverter, I should also have a 6kW battery (minimum) and a 6kW generator. I have my eye on a 6kW inverter generator it's got both electric start, and a pull chord. Runs on either gasoline or propane. Outputs split phase 240V.

Just as an aside, I recently got one of those clamp meters that measures AC Amps inductively. I measured my furnace last night. It's a central forced air electric furnace. The heating element and the blower are on different circuits. And I suspect the labels may be swapped. But what I got was something like 42.5A and 20A. So the furnace in total is 15kW. I looked around, and it seems that is a reasonable amount of power for a furnace sized for my house. This year I hope to get bids on some duct improvements and a heat pump. But that's another story for another thread. I just thought it was kind of interesting. I've been thinking along the lines of longer-term power outages past a day or two. And would it really be that difficult to do without 240V devices. So I've revised my list of items, and added new questions.

240V devises I can think of include:
Central air furnace: way too power hungry to ever be considered for off-grid use. Even if I upgraded to a heat pump.
Cloths dryer: convenient, but really unnecessary.
Water heater: I want to get a heat pump water heater. Would use about W, so possible, but expensive to set up for off grid.
Wall heaters: Two Cadet wall heaters for supplemental heating on the second floor. Can do without.
Kitchen range: 40A range could use as much as W. Could "easily" be substituted with the microwave and BBQ.

Our area has a water tower, so we still have tap water available during power outages. But it's filled with an electric pump. So once it's empty, it's empty until power is restored. How long it lasts depends on the frugality of the community.

One item I hadn't thought of before is the cloths washer. Mine takes 9A, and can run on cold water only. Clothes washers can be filled with water manually. We could do without washing cloths for a while, but we'd eventually run out. Probably after the community tower is empty. But if there were some disaster and we had to go weeks or months without power, assuming there were water available somewhere, a load or two of clean laundry would be really nice.

It's hard to predict the scarcity of things like food, water, gasoline, and propane until such a disaster would actually happen.

Anyway, so new list of things I'd "need" to have on backup power, assuming that things like cell towers and ISPs are still working:
Fridge: 6.5A 780W (2.2A 264W)
Freezer: 3.5A 420W
Laptops: 19.5V 3.3A (x2) 128.7W
Cell Phones: 0.5W (x3) 1.5W
Gateway: 18W
Router: 9W
Wifi: 18W
CPAP: 5.3W

If there's no internet or cell towers working, I suppose the various electronics become unnecessary. .5W total.

Microwave (input): W
Cloths washer: 9A W
120V heaters: 750W (x2) W
5,000 BTU A/C: 4A (x4) W
Lights: 10W (x6) 60W

These things would be very nice to have. W total. Though one could lower this by not running the microwave and washing machine at the same time. Or turn of the heaters or some of the A/C units. And we'd certainly not run the A/Cs and heaters at the same time. So more like W.

Let's say it's hot out and we're running all 4 A/C units. Laptops are on, but fully charged so only using half of their total power. Maybe a couple lights are on. And we decide to heat something up in the microwave. Total would be .5W. If the fridge and the freezer happened to be running at the same time, that would be .5W. About 82% of the capacity of a W inverter.

So maybe a 120V inverter will work after all. I looked into those Pro/Tran sub panels, and they might be the way to go in this case. It would solve the single breaker/load balance issue. It would not solve the running out of spaces on the main panel issue. I'm also not seeing how to add a 120V W inverter to all this, and still be able to use power from the grid. 120V breakers and sub panels only go up to 30A from what I can find. Including the Pro/Tran. W at 120V would need 50A. Seems like I either need a split phase inverter anyway if I want W or 2 W inverters, and 2 sub panels? May as well go with the split phase in that case I think. My wife really enjoyed your on-site water treatment system. She's a civil engineer specializing in drinking water. So she deals with community sized versions of this all the time.

Well, I don't know how much more I want to put into the inverter side of things right now, but I've learned quite a lot. I feel like when the time comes to buy one, I'll know much better questions to ask, and what features to look for.

One thing that still concerns me, is that almost none of the inverter companies list their products' Total Harmonic Distortion. The two I was able to find listed theirs at 5-15% or 10% average. This seems really high to me. Shopping around for inverter generators and smaller inverters like the one I bought for my mini fridge and A/C battery, they're almost all listed at 3-5%. I've read that anything higher than 5% starts causing issues with electronics.

Now, I'm no expert so I could be talking nonsense here, but my understanding is that electronics are fed by switch-mode power supplies now a days. Which means the AC is immediately rectified to DC and filtered through a capacitor and maybe even an inductor or two to get a nice flat DC Voltage. Which then goes through a high frequency transformer and more filters. Can a low quality modified square wave really survive all that and still make the whatever device malfunction? Is THD really that critical if you're not using super sensitive equipment in a lab or something?

Anyway, I did see one inverter from SunGoldPower has a THD of 3%. This wasn't in the specs or manual, it was kind of an afterthought in one of their feature paragraphs on the website. I sure hope that 3% is typical of solar inverters. Too bad my multimeter can't measure and verify THD. I guess you need a regular oscilloscope (not my little $20 one) some fancy math, and an understanding of what harmonics actually are in order to measure it.

I made a list of inverters that come somewhere near doing what I want, and compiled a list of features that I could find.


If I were to buy one today, it would probably be the BluePower IP. Who knows what products will be out in a couple years though. I also noted that every single brand I researched had a mixture of very happy customers and ones with horror stories of either the product or its tech support. My only direct experience is with WZRELB. Too bad they don't have pairable or split phase inverters. Maybe someday...

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Why Are Solar Inverters Important?

The solar power process starts with sunshine. Photovoltaic cells in solar panels harness the energy from the sunlight, creating an electrical charge. The charge produced is a direct current or DC energy. However, DC is not suitable for use in your home. A solar inverter converts (or inverts) the DC energy into alternating current (AC), a form of energy that is safe and useable by your home appliances and electronics.

Aside from converting electricity to a practical form, solar inverters also help to flatten abnormal spikes or dips in your current and protect your sensitive appliances from damage. Solar inverters help to maximize the energy produced by your system by determining the ideal voltage for your modules to function at their best. Inverters that record production and consumption are a great way to monitor your power usage as well.

The Main Types of Solar Inverters

There are several different types of solar inverters. Here are the four main types available on Inverter.com.

On-grid inverters or grid-tied inverters are solar inverters that connect directly to the utility grid. They convert DC into AC directly to allow users to power their appliances. Users can also send surplus energy to the grid.

Off-grid inverters or stand-alone inverters are designed to work with batteries. They are capable of powering residences or commercial projects by converting DC from the solar panels into AC in storage batteries.

Micro inverters are small inverters attached to individual solar panels. Instead of having a central inverter on a solar array, the DC to AC energy conversion occurs at the panel level.

Hybrid inverters or multi-mode inverters combine the features of on-grid and off-grid inverters. They can draw and convert energy from both the solar array and the battery system.

How to Choose the Right Inverter

1. Choose Your System

Do you want the independence of an off-grid system or prefer to have the security of an on-grid system? If the power grid in your area is unreliable, a hybrid inverter may be better suited to your needs. The hybrid inverters available on Inverter.com can automatically switch between off-grid and on-grid modes to achieve the best energy outcomes. If you plan to have several modules that experience different levels of shading, micro inverters may be the best option to maximize power output.

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2. Compare the Efficiencies

Conversion efficiency determines how much current is lost when DC is turned into AC. Small inefficiencies can add up over time to cost you a fair sum in electricity loss. Thus, you should aim for an efficiency of 96% or higher. The maximum efficiency of an inverter could be as high as 98.6% in some on-grid models with MPPT efficiency of up to 99.5%. MPPT stands for maximum power point tracking and it is the process of optimizing the match between system components to maximize energy extraction.

3. Check Key Parameters

Many features determine how well your solar inverter works. Some of these critical parameters are rated output voltage, output power, and overload capacity. The single-phase voltage level for most countries is between 220V and 240V. However, in the US, the standard voltage level is 120V for most everyday electronics and 240V for appliances such as washing machines and ovens. Your output voltage should be in the safe operating range for your electronics.

4. Look for Quality Construction

Since solar inverters are often installed outdoors, invest in models made of quality materials that can withstand the elements. For instance, the micro inverters on Inverter.com are designed to be waterproof. They avoid deterioration by preventing rainwater from pooling on the inverter surface. Your inverter should also feature an efficient cooling system to prevent overheating due to continued operation or strong sunlight. Look for units with a good working temperature and humidity range.

5. Consider Additional Features

Solar inverters can come with additional features or accessories that add value to your solar energy system. For example, certain hybrid inverters have built-in timers that can switch your inverters on during the day and off during the night. Inverters can come with digital LCD panels that display detailed operational information or be fitted with Wi-Fi data collector devices that enable you to monitor and track your energy data.

Most solar inverters have a minimum warranty of 12 months. That said, it is best to do your research to find the right system for your needs before purchasing your inverter. Inverter.com specializes in reliable power inverter products with competitive prices. If you need professional recommendations on how to set up your solar energy system, visit Inverter.com for the latest in solar technology and expert advice.

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