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No Sales Tax 💵 Beat-Anyone Price Match 💲 Free Parts for Life 🛠️ Free Shipping on Most Items 📦

No Sales Tax 💵 Beat-Anyone Price Match 💲 Free Parts for Life 🛠️ Free Shipping on Most Items 📦

No Sales Tax 💵 Beat-Anyone Price Match 💲 Free Parts for Life 🛠️ Free Shipping on Most Items 📦

No Sales Tax 💵 Beat-Anyone Price Match 💲 Free Parts for Life 🛠️ Free Shipping on Most Items 📦
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Gray battery pack with 'Flexboss 21' branding on a white background

EG4 FlexBOSS21 All-In-One Hybrid Inverter

SKU EG4FLEXBOSS21
Sold out
$4,139.99
$3,599.97
No sales tax: save about $270 vs. the 7.5% U.S. average sales tax rate. Why?
Indiana orders are taxed. DE, MT, NH and OR have no state sales tax.
Availability: Translation missing: en.general.icons.icon_check_circle icon Out of stock

✅ FREE REPLACEMENT PARTS FOR LIFE ⚙️

Find a better price somewhere else?

Well... we will BEAT it. Call us today to get the best price in the market!

Call/Text Us: 1-888-855-7286
Live Chat With an Expert

  • US Based Authorized EG4 Dealer

    Full manufacturer warranty included

  • 4-5 Day Freight Delivery + No Sales Tax

    More savings on every purchase and ships in 4-5 business day

  • 30-Day Returns & Price Beat Guarantee

    Simple returns + best price guaranteed

  • Post-Purchase Customer Support

    Dedicated help whenever you need it


ESTIMATED DELIVERY BETWEEN

Order within to get it by the earliest date.


The EG4 FlexBOSS21 hands you full control of your power, whether you're tied to the grid, backing it up, or living completely off it.

Why You'll Love The EG4 FlexBOSS21

  1. Runs your whole home, even the big loads. With 16kW of continuous output and enough muscle to start a 5-ton air conditioner, you're never stuck choosing between the fridge and the AC when the power drops. Everyone stays comfortable, no compromises.
  2. Three ways to power your life. Run fully off-grid, stay grid-tied with backup, or sell your extra solar back to the utility. You stop renting your power and start owning it.
  3. It grows as you do. Pair up to 16 units for a massive 256kW and pull from three independent MPPTs feeding 21kW of solar. Buy what you need today and expand whenever you're ready.
  4. Peace of mind, built in. Monitor and adjust everything from your phone over Wi-Fi, all housed in a weatherproof NEMA 4X enclosure and backed by a 10-year warranty. You're always in the loop, and always covered.

Your life, with the EG4 FlexBOSS21

Think back to the last time the power went out. The scramble for flashlights. The food slowly warming in the fridge. That nagging worry about how long it'll last.

Now picture the opposite. The grid drops, and inside your home nothing changes. The switchover happens in about 20 milliseconds — faster than you can blink — so the TV keeps playing and the AC keeps humming. You barely notice.

That's daily life with the EG4 FlexBOSS21. On sunny days it turns your roof into a power plant, topping up your batteries and trimming your bill. When utility rates climb, it can sell your surplus back to the grid. When a storm rolls through, it quietly keeps your family safe and comfortable.

Behind that simple experience sits a lot of smart engineering. It talks directly to your batteries through closed-loop communication, so charging stays safe and efficient. It accepts up to 600V of PV input, which means smaller cabling and often no combiner box — a cleaner, simpler install. And it pairs with the EG4 GridBOSS, so you manage your entire energy storage system from one place.

All of this runs at 97% efficiency and under 50dB of fan noise. It makes the most of the power you worked to generate, without the racket. That's what taking control of your energy actually feels like.

 Placeholder Image

The EG4 FlexBOSS21 in a nutshell:

  1. 21kW PV input across three MPPTs — capture more of your sunshine, with the freedom to run panels on different roof faces and angles.
  2. Near-instant backup switching (about 20ms) — outages come and go without your appliances ever skipping a beat.
  3. GridBOSS-ready with closed-loop battery comms — run your whole energy storage system as one smart, coordinated setup.
  4. Rapid shutdown, arc-fault and ground-fault protection — NEC 2020-ready safety that looks after your home and everyone in it.
 Placeholder Image

What's Included

Everything you need is included with your product.
  • EG4 FlexBOSS21 All-in-One Hybrid Solar Inverter
  • 90A Breaker: Compatible only with the EG4 FlexBOSS21
  • Smart Port Breakers: Rated at 30A, 40A, 60A, and 80A.
  • User Manual

Please Note:
  • You must purchase a 70A Breaker separately for use with the EG4 18kPV Hybrid Inverter.
  • You must purchase a 50A Breaker separately for use with the EG4 12kPV Hybrid Inverter.
  • A 125A Breaker (sold separately) can be used with either the Smart Port or Gen Port.

EG4 FlexBOSS21 All-in-One Hybrid Inverter Specifications
Specification Details
Input Voltage Range 120/240VAC; 120/208VAC (Split-phase)
Output Power 16kW continuous when using pv input, with a peak surge capacity of 24kW
Dimensions 29.5 x 20.5 x 11.2 inches
Weight 88 lbs
Warranty 10-year standard warranty, covering all major components

Frequently-Asked Questions

Can the EG4 FlexBOSS21 operate both off-grid and grid-tied?

Yes! The FlexBOSS21 is designed for off-grid energy independence, grid-tied integration, and hybrid operation with battery backup.

What battery types are compatible with this inverter?

This inverter is optimized for 48V LiFePO4 battery banks, ensuring efficient and long-lasting performance.

Can I expand my system with additional inverters?

Yes, the FlexBOSS21 supports parallel operation, allowing multiple units to be stacked for increased energy output.

Does it support remote monitoring?

Yes! The Wi-Fi and RS485 connectivity allow real-time system monitoring and control via the EG4 app.

Let the experts help you find your perfect EG4 FlexBOSS21 setup

Not sure how the EG4 FlexBOSS21 fits your loads, your panels, or your batteries? That's exactly what we're here for. Our team works with systems like this every day, and we'll help you size it right the first time — no guesswork.

Chat via email — support@kratopower.com

Chat on the phone — +1 888-855-7286

EG4 FlexBOSS21 documents and materials

Everything you need to spec, install, and register your EG4 FlexBOSS21:

Manual and Specifications

Shipping is FREE on most items to customers within the 48 Contiguous States and the District of Columbia. We do not ship to Alaska, Hawaii, or any outlying islands and territories.

Heavy items ship by LTL freight with free liftgate service. Freight is FREE to IN, OH, PA, MI, IL, KY, WV, WI, IA, MO, TN, DE, MD, NJ, NY, VA, DC, CT, MA and VT. Everywhere else in the lower 48, freight is FREE on orders of $4,000 or more. Below $4,000, one flat freight rate covers the whole order: $149 when your freight items weigh under 150 lb in total (most inverters and single batteries) or $299 at 150 lb and up (wall-mount batteries, cabinets, refrigerators). Commercial battery systems over 1,000 lb: email support@kratopower.com with your ZIP for a freight price. Your shipping cost always shows at checkout before you pay.

Processing time for orders is 1 business day

Shipping time for orders is 4-5 business days


Want to know more about our Returns Policy? Read more here.

Want to know more about our Shipping Policy? Read more here.

We get it. You've got a lot of choice when it comes to online retailers. Here's why we think you should shop with us at Krato Power.

  • Family Owned & Operated. Ask for Alex (Owner) at any time!
  • 4-5 Day Free Shipping on most items to the 48 Contiguous States and the District of Columbia. Freight items include free liftgate service and ship free to 19 states + DC and on orders of $4,000+; elsewhere freight is a flat $149 or $299, shown at checkout before you pay.
  • NO Sales Tax except for IN
  • Secured Purchase. All Customer data is secured with SSL Encryption
  • 30-Day Returns. Start a return within 30 days of delivery. See our return policy for details.
  • Exceptional Customer Service. Check out our About Us page.
  • Call or Text Us - We are really here! (In the USA). 1-888-855-7286
In Stock and Ready To Ship

All of our items are in stock and ready to ship. All items ship within 1 business day.

Top Customer Service

We have excellent customer service. Questions? Call us at 1-888-855-7286

30-Day Returns

30-Day Easy Return Policy

Price BEAT Guarantee

Found a better price? We will BEAT it!

Schedule a Consultation

  • Still interested but want to talk at a diferent time?
  • Schedule a consultation here for later!
Book a Consultation
Call to Order: +1 888 855 7286
Description

The EG4 FlexBOSS21 hands you full control of your power, whether you're tied to the grid, backing it up, or living completely off it.

Why You'll Love The EG4 FlexBOSS21

  1. Runs your whole home, even the big loads. With 16kW of continuous output and enough muscle to start a 5-ton air conditioner, you're never stuck choosing between the fridge and the AC when the power drops. Everyone stays comfortable, no compromises.
  2. Three ways to power your life. Run fully off-grid, stay grid-tied with backup, or sell your extra solar back to the utility. You stop renting your power and start owning it.
  3. It grows as you do. Pair up to 16 units for a massive 256kW and pull from three independent MPPTs feeding 21kW of solar. Buy what you need today and expand whenever you're ready.
  4. Peace of mind, built in. Monitor and adjust everything from your phone over Wi-Fi, all housed in a weatherproof NEMA 4X enclosure and backed by a 10-year warranty. You're always in the loop, and always covered.

Your life, with the EG4 FlexBOSS21

Think back to the last time the power went out. The scramble for flashlights. The food slowly warming in the fridge. That nagging worry about how long it'll last.

Now picture the opposite. The grid drops, and inside your home nothing changes. The switchover happens in about 20 milliseconds — faster than you can blink — so the TV keeps playing and the AC keeps humming. You barely notice.

That's daily life with the EG4 FlexBOSS21. On sunny days it turns your roof into a power plant, topping up your batteries and trimming your bill. When utility rates climb, it can sell your surplus back to the grid. When a storm rolls through, it quietly keeps your family safe and comfortable.

Behind that simple experience sits a lot of smart engineering. It talks directly to your batteries through closed-loop communication, so charging stays safe and efficient. It accepts up to 600V of PV input, which means smaller cabling and often no combiner box — a cleaner, simpler install. And it pairs with the EG4 GridBOSS, so you manage your entire energy storage system from one place.

All of this runs at 97% efficiency and under 50dB of fan noise. It makes the most of the power you worked to generate, without the racket. That's what taking control of your energy actually feels like.

 Placeholder Image

The EG4 FlexBOSS21 in a nutshell:

  1. 21kW PV input across three MPPTs — capture more of your sunshine, with the freedom to run panels on different roof faces and angles.
  2. Near-instant backup switching (about 20ms) — outages come and go without your appliances ever skipping a beat.
  3. GridBOSS-ready with closed-loop battery comms — run your whole energy storage system as one smart, coordinated setup.
  4. Rapid shutdown, arc-fault and ground-fault protection — NEC 2020-ready safety that looks after your home and everyone in it.
 Placeholder Image

What's Included

Everything you need is included with your product.
  • EG4 FlexBOSS21 All-in-One Hybrid Solar Inverter
  • 90A Breaker: Compatible only with the EG4 FlexBOSS21
  • Smart Port Breakers: Rated at 30A, 40A, 60A, and 80A.
  • User Manual

Please Note:
  • You must purchase a 70A Breaker separately for use with the EG4 18kPV Hybrid Inverter.
  • You must purchase a 50A Breaker separately for use with the EG4 12kPV Hybrid Inverter.
  • A 125A Breaker (sold separately) can be used with either the Smart Port or Gen Port.

EG4 FlexBOSS21 All-in-One Hybrid Inverter Specifications
Specification Details
Input Voltage Range 120/240VAC; 120/208VAC (Split-phase)
Output Power 16kW continuous when using pv input, with a peak surge capacity of 24kW
Dimensions 29.5 x 20.5 x 11.2 inches
Weight 88 lbs
Warranty 10-year standard warranty, covering all major components

Frequently-Asked Questions

Can the EG4 FlexBOSS21 operate both off-grid and grid-tied?

Yes! The FlexBOSS21 is designed for off-grid energy independence, grid-tied integration, and hybrid operation with battery backup.

What battery types are compatible with this inverter?

This inverter is optimized for 48V LiFePO4 battery banks, ensuring efficient and long-lasting performance.

Can I expand my system with additional inverters?

Yes, the FlexBOSS21 supports parallel operation, allowing multiple units to be stacked for increased energy output.

Does it support remote monitoring?

Yes! The Wi-Fi and RS485 connectivity allow real-time system monitoring and control via the EG4 app.

Let the experts help you find your perfect EG4 FlexBOSS21 setup

Not sure how the EG4 FlexBOSS21 fits your loads, your panels, or your batteries? That's exactly what we're here for. Our team works with systems like this every day, and we'll help you size it right the first time — no guesswork.

Chat via email — support@kratopower.com

Chat on the phone — +1 888-855-7286

EG4 FlexBOSS21 documents and materials

Everything you need to spec, install, and register your EG4 FlexBOSS21:

Manual and Specifications
Shipping

Shipping is FREE on most items to customers within the 48 Contiguous States and the District of Columbia. We do not ship to Alaska, Hawaii, or any outlying islands and territories.

Heavy items ship by LTL freight with free liftgate service. Freight is FREE to IN, OH, PA, MI, IL, KY, WV, WI, IA, MO, TN, DE, MD, NJ, NY, VA, DC, CT, MA and VT. Everywhere else in the lower 48, freight is FREE on orders of $4,000 or more. Below $4,000, one flat freight rate covers the whole order: $149 when your freight items weigh under 150 lb in total (most inverters and single batteries) or $299 at 150 lb and up (wall-mount batteries, cabinets, refrigerators). Commercial battery systems over 1,000 lb: email support@kratopower.com with your ZIP for a freight price. Your shipping cost always shows at checkout before you pay.

Processing time for orders is 1 business day

Shipping time for orders is 4-5 business days


Want to know more about our Returns Policy? Read more here.

Want to know more about our Shipping Policy? Read more here.

Why Buy From Us

We get it. You've got a lot of choice when it comes to online retailers. Here's why we think you should shop with us at Krato Power.

  • Family Owned & Operated. Ask for Alex (Owner) at any time!
  • 4-5 Day Free Shipping on most items to the 48 Contiguous States and the District of Columbia. Freight items include free liftgate service and ship free to 19 states + DC and on orders of $4,000+; elsewhere freight is a flat $149 or $299, shown at checkout before you pay.
  • NO Sales Tax except for IN
  • Secured Purchase. All Customer data is secured with SSL Encryption
  • 30-Day Returns. Start a return within 30 days of delivery. See our return policy for details.
  • Exceptional Customer Service. Check out our About Us page.
  • Call or Text Us - We are really here! (In the USA). 1-888-855-7286