Suggestions on choosing an inverter?

[rebelrider.mike]

Well that's an interesting point. When I started this thread, I didn't know enough about inverters to answer most of those questions. I'm a bit further along now, so I can take a crack at it.

In general, my highest priority is to have some power available to key circuits in the event of a grid outage. My area has short outages every year due to wind storms. Every few years we're hit with a big one, and there is so much damage that it can take days to get power back. Weeks in the more remote areas. I'd rather not have to be running into town for gasoline or propane every couple days, and assuming that's what everyone else will be doing too, there may be fuel shortages. So I'd like to employ a generator, battery and solar panels.

My second general priority would be to have a reduced power bill. Since I'll have solar and a battery set up at some point, may as well use the free electricity instead of the stuff I have to pay for. It's too dark in the winter, and I use too much electricity to ever go off grid. But I can certainly collect enough solar power even in winter to cover a significant part of my overall power usage.

One priority I don't have that a lot of other people do, is selling power back to the grid. I really have no interest in that for a couple reasons. Firstly, I don't think I'll be making much excess power most of the time. Maybe a little in the summer, but I don't think it'll be enough to be worth it. Secondly, my PUD and I have a philosophical disagreement about how solar should be used. They'll never approve a grid-tie system as long as the solar continues to power my house during a grid outage. Even if I have a lockout or transfer switch installed. They're fine with generators though. Makes no sense to me.

On to specifics I'm looking for in an inverter. It took a while, but I finally figured out that I definitely want a split phase unit. I see that there are transformers out there to allow 120V inverters to power 240V devices. But as I want my key circuits to be able to use grid, generator, or inverter power, they will need to be compatible. As the grid and generator are both split phase, so must the inverter be.

The next thing I'm looking for is cost. Not just in the short run, but also looking to the future. What I mean is that every inverter will eventually fail. Given the dismal state of tech support now a days, I'm assuming that if my inverter breaks, I'll have to buy a new one. Can't depend on companies to honor their own warrantees. I see that I could buy 5 EG4 inverters for the cost of a single Sol-Ark. Maybe the Sol-Ark is made of sterner stuff and would outlast 5 EG4s. I don't know. From my noob perspective I see people say stuff like that, but I have yet to see proof that less expensive devices are guarantied to be junk.

Another consideration is whether the inverter can provide split phase by itself, or if it needs to be paired to a twin. Having to buy two inverters doubles the cost right from the start. It also doubles the idle power usage, and I'm sure it isn't great for efficiency either. Also, if one fails a few years down the road, will I be able to find a compatible replacement, or will I have to replace both? A single unit that provides split phase on its own makes a lot more sense to me.

Related to single vs. paired units is the power output. I'm looing for about 6kW, but I could get by with a little less. Though a pair would only need to provide 3kW per unit. Not all brands have 6kW units or pairs. I was going back and fourth between the possibility of a pair vs. a unit for a while, so I researched both. Ultimately I decided to go with a single split phase unit.

Inverter efficiency is another one. I decided 90% or higher would be the cutoff for me. This was sometimes a tricky value to find. A lot of inverters are advertised as 99% efficient. But that comes from how well it sends power from the grid to the load. I'm interested in the efficiency from DC to AC. There's also the efficiency from solar DC to battery/inverter DC. Also usually in the high 90s.

Availability was pretty difficult for me at first, having no idea where to shop except maybe Amazon. A lot of brands' websites don't sell directly but have a "where to buy" link. Often the seller's website says "we have that brand, but not the model you're looking for." So for a while, many of these inverters I was interested in, I couldn't find a price or seller. That's mostly cleared up now.

Having at least 1 integrated MPPT solar charge controller in the inverter makes a lot of sense to me. And almost all the inverters I found have at least 1. For the ones that have none... they aren't any cheaper, and in some cases are even more expensive. More than one isn't necessarily better. For example the EG4 only has one but it can handle a fairly large array. Vs. another, I think one of the MPPs that has two independent controllers, but they each can only handle a small array. For me the single larger one fits what I want to do a little better.

Finally there's Total Harmonic Distortion, or THD. This was quite a rabbit hole! For one thing, not all companies are willing to put a number to this specification. Victron and SunGoldPower flat out refused to admit their inverters even had harmonic distortion. That was a deal killer to me. Turns out THD is a difficult number to nail down. In the case of "pure" sine inverters, you can have a different value of THD depending on whether the inverter is under load or not. And how much load. And whether the load is resistive, non-linear or inductive. Conventional generators also have harmonic distortion, though it's generated in a different way. And different kinds of loads can create harmonic distortion that adds to the whole system. A big system like the grid pretty much dilutes harmonic distortions. But a tiny system like an off grid house it can add up quick. So the best answer a company can give is a ballpark figure. From what I've seen most pure sine inverters are rated at <5% THD or better. 0% being an ideal perfect wave. Even the almighty grid has a THD of around 3%.

Well that was a long-winded response, but you ask for it, LOL.

[Ampster]

.....
As you can see, this list is still incomplete, and I've got to go back and take a closer look. I did my best to find at least 1 product from each popular brand that I'm aware of.

What is missing is what feature set is important to you? Since everyone is split phase that is a given and does not need to be listed Do you want back up. peak shaving or both? A lot of those are not UL listed. Is that important? Do you want AC coupling capability, grid interaction or grid selling capability?

[rebelrider.mike]

I don't know if this would be interesting or useful to folks, but its easy to share, so...

InverterSpecsA.png
These are the first of the specs I've compiled for each inverter I've researched. The cells I marked red are the deal-breakers for me. But they may not matter to others.

Anyway, 4 of these didn't get eliminated, and I'm looking into a few more specs to see if I can choose one over the others.
InverterSpecsB.png
As you can see, this list is still incomplete, and I've got to go back and take a closer look. I did my best to find at least 1 product from each popular brand that I'm aware of.

[Ampster]

..........Where did you find it?

It is not on the spec sheet but I thought I saw it on the Signature Solar website but now cannot find the exact reference. One of the EG4 models does show UL1547 listing.

[J.P.M.]

The EG4 has a certification from TUV, whatever that is?

TUV is an inspection association that tests and certifies products, systems and procedures not unlike ISO 9000, etc.
It's German in origin and been around a long time.
Google it for more info.

[rebelrider.mike]

A product certification company that I'm not familiar with. But my local L&I has them listed as an acceptable certification source. I haven't seen it listed anywhere in EG4's documentation. Where did you find it?

[Ampster]

The EG4 has a certification from TUV, whatever that is?

[rebelrider.mike]

I understand, and rest assured, I'm not buying anything today. Sometime this year I'll be contacting a solar contractor to get a home energy/solar audit. They'll no doubt have a lot to say about permits and approved equipment. They'll also make a list of things I can do to make the house more energy efficient, as well as the size and locations of any solar arrays that might fit my house. Maybe they'll have an inverter available that does all the things I want and have an approved listing.

I'm doing all this research ahead of time so I can ask intelligent questions when I go to the PUD, L&I, and the solar contractor. Oh, by the way, I was browsing my local L&I website today, and it turns out they'll happily accept certifications from a number of different laboratories, besides UL. Of course, the EG4 has none of those either, but who know what will happen over the next year or two?

[J.P.M.]

I couldn't find any UL listing either. I'm pretty sure it doesn't have one. For me, that means I can use power from the grid, but I wouldn't be able to sell power back to the grid. That's ok with me. In my area, a grid-tie system must be shut off completely during a power outage. My primary reason to install any of this stuff is to have backup power during power outages. So a UL listing would be nice, but for me, not having it isn't a deal breaker.

It also means the system probably won't get permitted if one is required.

[SunEagle]

I couldn't find any UL listing either. I'm pretty sure it doesn't have one. For me, that means I can use power from the grid, but I wouldn't be able to sell power back to the grid. That's ok with me. In my area, a grid-tie system must be shut off completely during a power outage. My primary reason to install any of this stuff is to have backup power during power outages. So a UL listing would be nice, but for me, not having it isn't a deal breaker.

Remember unless you have batteries any type of inverter will not provide constant power due to shadows (clouds and such) on the panels.

IMO unless you have a grid tied system and selling excess power back to the POCO the best and most reliable emergency back up power source would be a generator of some kind which you will need if you use batteries so you can charge them if the sun isn't shining and the grid is unavailable so why go with a solar/battery system. So look for a UL listed grid tie inverter and go that way.

[rebelrider.mike]

I couldn't find any UL listing either. I'm pretty sure it doesn't have one. For me, that means I can use power from the grid, but I wouldn't be able to sell power back to the grid. That's ok with me. In my area, a grid-tie system must be shut off completely during a power outage. My primary reason to install any of this stuff is to have backup power during power outages. So a UL listing would be nice, but for me, not having it isn't a deal breaker.

[Ampster]

.........

If I were to pick one today, it would be the EG4 6000EX-48HV. It has the most features I'm looking for without having some kind of deal-breaking flaw. I don't need to pick one today, so it will be interesting to see what new products become available in the next year or two.

I could not confirm if the EG4 was UL listed if UL compliance is a deal breaker. The UL spec needed in my jurisdiction is UL1741SA. Typically Tier one inverters which comply with that spec cost several times more than the EG4.

[rebelrider.mike]

Microinverters can be a great solution for some systems. In my case, they would lead to extra conversions, and I'd need additional control devices I think, to make them work during a power outage.

I ended up looking at 17 different inverters, and compared 10 specifications of each that I thought were important. A lot of inverter companies don't publish all their specs, so this was rather difficult at times. I was surprised and frustrated to find how many companies refuse to publish the total harmonic displacement of their products. A couple even refused to acknowledge that their inverters had any.

If I were to pick one today, it would be the EG4 6000EX-48HV. It has the most features I'm looking for without having some kind of deal-breaking flaw. I don't need to pick one today, so it will be interesting to see what new products become available in the next year or two.

[solar pete]

If going micros get some spares right from the get go it will save mucking around later

[GoingElectric]

I appreciate the responses. I have found that most things I buy work fine, but then there's the occasional issue with something. I've also got a long and frustrating history with tech support. They either seem to be polite but clueless, or they assume I'm and idiot or a liar (or both). A few companies have been fantastic. But not many.

So the good news is that I probably won't get around to buying an inverter until 2024 at the earliest. This year I hope to install the sub panel and maybe even the backup generator. I've also got several other projects competing for my time this year. Who knows what new products will be out by then? But in the meantime, I hope to get my brain wrapped around all this inverter stuff so I can make a good decision as to which products to buy. It's been an interesting study so far.

I was thinking of doing one roof (no shadow) with string inverter, but seeing a video listing + and -, going with all micros.