Stripping bloated solar inverter technologies back to basic DC to AC energy conversion is seemingly where the Delta Flex range of solar inverters are making their mark. As a proven solar inverter manufacturer, Delta is now supporting an extremely minimalist design in the Flex range over previous models and like for like rival inverter technologies. With such a refined package, why does the Delta Flex fly below the radar of many?


Make and model:  Delta Flex

Variants:  2.5 | 3 | 4 | 5 kW.

  Design, Performance.



First Impressions…the Delta Flex is compact. Second impressions, it’s light. What’s missing? Definitely not a dependable heat sink which is a big positive within any fanless, convection cooled solar inverter design. Therefore, has the Delta Flex compromised in areas where alternative inverter manufacturers of similar technologies are hesitant to?

Comparing the essential criteria of design, features, performance, software, guarantee and affordability against the industries best specifications will assist a greater perspective. 

Which Delta inverter do you require? The Delta Flex is the modern single-phase inverter by Delta for systems rated at 2.5 – 5 kW.

  • Single-phase, 2.5 – 5 kW, Delta Flex Series (You are here)
  • Single-phase Storage, 5kW, Delta Hybrid E5 (Coming Soon) >
  • Three-phase, 6 – 10 kW, Delta RPI (Coming soon) >
How to know if you have a single phase or 3-phase power supply? 


Delta RPI H5A Inverter

Potentially one of the more exciting string inverter technologies made available in recent years. Complimented by a phenomenally large heat-sink for its size, the new-release all-weather IP65, fanless design of the Delta Flex is yet to win any significant industry awards to date but should provide much competition with such an innovative package. As the modern-day interest of many, battery design compatibility is achieved via both AC or DC coupling through select technologies.

Download the Delta Flex datasheet here:

3.9A SUPERIOR design, the Delta Flex solar inverter accrued a Solar Review Inverter Assessment Criteria Design score of 3.9 out of 5.


Delta RPI H5A Inverter

Despite the reduced overall size, the Delta Flex inverter range isn’t short of the prominent features many desire. Dual Multiple Power Point Tracking (MPPT) assists with solar array optimisation. Although, falls short of an advanced shadow management protocol onboard. Aiding fewer points of failure, the multifunction LED only interface supports local App connectivity for detailed inverter production insight eliminating the need for the less dependable LCD interface. Remote data access is achieved either through an inbuilt WiFi module or Ethernet.

Expanded features to further enhance the Delta Flex range for personal suitability exist through the likes of 1st party expanded monitoring capabilities and rapid shutdown options. Manufacturer supplied module-level optimisation options are not available although can be achieved using a 3rd party device such as the Tigo Energy TS4-O. Those seeking a particular installation requirement must note that an inbuilt DC isolator is absent.

3.8A SUPERIOR feature rating, the Delta Flex solar inverter accrued a Solar Review Inverter Assessment Criteria Features score of 3.8 out of 5. 


Delta RPI H5A Inverter

As an excellent performer is where the Delta Flex range makes its mark. Weighted European efficiency is among a superior class with 96.8% efficiency. Further complimenting the respectable efficiency is a wide operating temperature range from -25oC up to +60oC (-13oF to +140oF), while derating occurs beyond +40oC (+104oF). Weight and noise emission criteria are both outstanding. The lightweight 12kg package that is the Delta Flex is barely noticeable sound wise emitting no more than no more 20 db(A). Where won’t the Delta Flex perform?  Installation locations greater than 2000m above sea level or environments likely to exceed 95% humidity.

Average Inverter 95%
Delta Flex (avg) 96.8%

Above: Solar inverter European efficiency.

4.4Considered EXCEPTIONAL, the Delta Flex solar inverter accrued a Solar Review Inverter Assessment Criteria Performance score of 4.4 out of 5.


Delta RPI H5A Inverter

Ranking inline with an average inverter warranty, 5-years, the Delta Flex offers little in the way of excitement from a manufacturer guarantee perspective. Warranty extensions are available to purchase, however, with no manufacturer trained installer network and should the installation fail to  meet manufacturer specifications, the warranty could be as worthless as the paper it’s printed on. Not to be discouraged, the Delta Flex holds a trustworthy warranty against industry alternatives if installed correctly.

Average Inverter (base)
Delta Flex (base)

Above: Base manufacturer warranty on a scale of 12-years. 

2.3AVERAGE, Delta Flex solar inverters accrued a Solar Review Inverter Assessment Criteria Guarantee score of 2.3 out of 5.


Delta RPI H5A Inverter

As with most inverter manufacturers they are Hardware manufacturers first. Software manufacturers second. Although a consistent evolution on the positive side is a progression in the right direction nonetheless. 

View the full Delta Monitoring Portal review here > (Coming Soon).

3.0Considered GOOD, the MyDeltaSolar monitoring software accrued a Solar Review Inverter Assessment Criteria Software score of 3.0 out of 5.

Technology Ranking.

3.5The Delta Flex range is considered a respectable product technology wise ranking VERY GOOD in the Solar Review Inverter Assessment Criteria without affordability points applied. To view the overall product score and entire product summary at the bottom of this post, Keep scrolling!


Delta RPI H5A Inverter

As they say, you get what you pay for. The Delta Flex presents on the more expensive side when compared to alternative like makes from the same manufacturing region, however, delivers a lot more in comparison. Worth paying a little more for.

As a gauge, Delta Flex H5A 5 kW inverters are available online from:

 USD 1000  |  AUD 1400  |  EURO 900 

Excludes taxes, shipping and installation.

Source – Google

3.7Presenting VERY GOOD affordability for the technology, the Delta Flex solar inverter accrued a Solar Review Inverter Assessment Criteria Affordability score of 3.7 out of 5.


3.6Seeking a dependable inverter technology built to perform without having to break the bank? The Delta Flex range may just be the perfect fit. The minimalist and modern design encourages end-user appeal while presenting exceptional performance at a more affordable level. As a global superpower in robotic engineering, Delta has delivered to the international solar market an inspiring inverter technology which most should consider.  

Have a question?

Don’t be shy, leave it below and a Solar Review community member will respond with the insight you need.


How was the score for the Delta Flex calculated? By utilising the Solar Review Inverter Assessment Criteria V2.1 >


Please enter your comment!
Please enter your name here