The inverter is always going to be one of the key components in any off-grid or hybrid solar power system, so choosing the right one is an important decision.
Recently, EG4, who are now one of the big boys in the industry, released a new style of inverter called the FlexBOSS 21, which now sits alongside their top-selling 18KPV Hybrid Inverter. A while back, we put out an in-depth review of the 18KPV explaining why it’s such a popular and high-quality option. We also released a first-look review of the new FlexBOSS 21 shortly after it was launched.
Since both of these units have a lot in common, and they both really impressed us, it has caused a bit of confusion amongst those looking to figure out which option is the best fit.
So, to help make an informed decision and you choose the right option, we’re going to break down their features, main differences, potential use cases for each option, and much more in this head-to-head comparison.
Before diving into what sets them apart, let’s talk about the ways the FlexBOSS 21 and 18KPV are similar:
So, given that they share a lot of similarities and the same basic core functionality, where do the two units actually differ? Let’s break it down.
EG4 designed the FlexBOSS 21 to address some of the limitations they found with their extremely popular 18KPV Hybrid Inverter. The result? A bigger, better, and more cost-effective unit. Here’s a quick breakdown of the ways it differs from its older sibling:
As you can probably guess from the names of the two units, the FlexBOSS 21 can handle 21kW of solar input versus the 18KPV’s 18kW solar input. This is great if you’re looking to get the most out of your solar array by selling more power back to the grid or charging your batteries even faster.
With that said, a 21kW solar input is insanely high, so you’re going to have to have a lot of solar panels to get the most out of it. Even an 18kW solar input is extremely high, so most residential buyers aren’t going to get close to maxing out either unit.
Both units can output 12,000W, but the FlexBOSS 21 takes things a little bit higher because it can boost to continuous output of 16,000W when solar is available. Again, for those with huge solar panel arrays, the FlexBOSS 21 can be the ideal unit.
Another issue EG4 seemed to address when they designed the FlexBOSS 21 was increasing the surge capacity. Since it has an extremely high 24kW surge output, it is powerful enough to start appliances that have huge start-up requirements, including incredibly demanding appliances, like a 5-ton air conditioner.
If you’re running your system completely off-grid, the FlexBOSS provides 66 amps of continuous power compared to the 18K’s 50 amps. It also sheds a lot of the components and inputs you need for a grid-tied setup, which is why EG4 is able to offer it at a lower price point.
In fact, the FlexBOSS 21 is typically about $700 cheaper than the 18KPV, largely because it removes the 200A service pass-through, which most off-grid users don’t need.
This was actually the main reason EG4 developed the FlexBOSS 21. Basically, they wanted to be able to offer their off-grid customers a cheaper unit that didn’t come with unnecessary grid-specific features. While they were designing something cheaper for off-grid customers, they must have figured it was worthwhile just upgrading a few of the specs over its predecessor, the 18KPV.
For those who need grid tie-in capabilities, EG4 also recently introduced the GridBOSS MID. If you’re using the FlexBOSS 21 in any sort of grid-tied setup, you’ll need it. Here’s why the GridBOSS is a necessary pairing:
Again, the combination of FlexBOSS 21 and the GridBOSS MID ends up being cheaper, easier to install, and more efficient than having the 18KPV running with traditional transfer switches and wiring. Plus, in our opinion, the two units also offer a much cleaner look.
Before we make a case for the original 18KPV, let’s quickly look at the types of buyers who would benefit from using the FlexBOSS 21 over the older model.
The FlexBOSS 21 was specifically designed for off-grid setups, with better output and no unnecessary pass-through. Since it sheds stuff that you don’t need in order to lower the price, it also prevents you from spending money on features you’ll never use.
If you’re running appliances with high power demands, like large well pumps, air conditioners, or heavy-duty tools, this unit has a higher output with solar, so it can handle more.
If you have a huge solar panel array, the 21kW solar input that you get with the FlexBOSS is going to allow you to actually get the most out of your panels. With its higher inputs and outputs, as well as its scalability, it’s also more practical for commercial applications, like solar farms.
Now, despite all the advantages discussed above, and the fact the EG4 18KPV Hybrid Inverter is starting to look a bit dated, it still has a place, so it could be the right one for you. Let’s look at why someone might still be drawn to EG4’s former best-selling inverter:
Unlike the FlexBOSS, which requires the GridBOSS for full grid integration, the 18KPV has everything built into it right out of the box. Sure, it’s more expensive and you’d still have to add a manual transfer switch to allow it to meet code, but you can put grid power directly into it right away, which could be appealing for certain users.
In our opinion, you could make an argument for this being the best touchscreen on any inverter on the market today. It’s responsive, intuitive, and even includes a built-in FAQ section, so there’s no need to grab the manual if you encounter problems during or following installation.
With that said, you can purchase a separate plug-in screen for the FlexBOSS for about $100, but it sits inside the panel door and doesn’t offer the same level of functionality as the screen you get standard with the 18KPV.
If you’re wondering why EG4 didn’t just add this same touchscreen display to the FlexBOSS, the answer is they wanted to make the unit as affordable as possible, which meant slashing a few frills.
If you’re adding solar to an existing setup, the 18KPV makes integration easier with its gas generator inputs and AC coupling capabilities. Plus, you don’t have to go out and buy or find wall space for the GridBOSS if you’re going with an 18KPV.
While the FlexBOSS 21 is the newer and generally much better option, there are still quite a few use cases for its older brother. So, let’s look at some reasons why certain people would still want to choose the EG4 18KPV:
If you want grid tie-in without having to find space for another large unit, the 18KPV keeps things simple. While the combination of the FlexBOSS and the GridBOSS actually looks pretty sleek, they’re still two fairly large units that you’re going to need to find space for.
Given this, those with small cabins and cottages might not have space for both, or a real need for all of the extra power you get with the FlexBOSS 21 and GridBOSS combination, even if they are technically cheaper than the 18KPV.
Believe it or not, some buyers choose the 18KPV strictly for its built-in touchscreen. Even Signature Solar informed us that they’ve had a few customers mention that they choose it specifically for that display.
While we wouldn’t exactly say that the screen is enough that it would push us to choose an 18KPV over a FlexBOSS 21, we have to admit it is a really impressive and intuitive display.
If you’re replacing an existing inverter, so you already have everything set up for a hybrid inverter, you might not need the benefits the GridBOSS setup provides, making the 18KPV the more convenient, plug-and-play option.
While the FlexBOSS and GridBOSS combination will be much easier to install for most users, that’s only when you’re comparing them against having to go out and purchase additional components to hook the 18KPV up.
If you’re looking for the best performance, highest solar input, and overall best value, the FlexBOSS 21 is the clear winner. Even if you’re building a grid-tied or hybrid setup, when you pair the FlexBOSS 21 with the GridBOSS, it’s also a more cost-effective on-grid solution than purchasing an 18KPV and the additional components that you’ll need to get it up and running.
With that said, the 18KPV is still a really solid inverter that could be a decent option for certain users. If, for example, you want a plug-and-play inverter with built-in grid connectivity, a fantastic touchscreen, and gas generator integration, the 18KPV might be the better choice for you.
At the end of the day, you can’t go wrong with either one, but your specific needs and budget will determine which is the right fit. Still, we’d probably say 99 out of 100 people are going to be better off with the newer FlexBOSS 21 and its GridBOSS companion, but don’t be afraid to call up EG4 or Signature Solar for yourself if you’re still unsure. You can also watch our individual reviews of each piece of equipment to learn more.
Signature Solar: https://signaturesolar.com
Use Code: THESOLARLAB50 for $50 Off Your Order
Shop Solar: https://shopsolarkits.com
Use Code: THESOLARLAB for $101 Off Your Order
Signature Solar: https://signaturesolar.com
Use Code: THESOLARLAB50 for $50 Off Your Order
Shop Solar: https://shopsolarkits.com
Use Code: THESOLARLAB for $101 Off Your Order
We test solar products so you don’t have to. Check out our opinions and which units we think are worth your money and which ones aren't.
More Reviews >
