Renogy E.Flex 21 Review – Portable Solar USB Charger

Renogy E.Flex 21 Review - Featured Image

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Product: Renogy E.Flex 21 Portable Solar Panel USB Charger
Price: $79.99
Dimensions Folded: 11.0 x 7.3 x 1.2 inch/280 x 185 x 30 mm
Dimensions Unfolded: 23.0 x 11.0 x 0.8 inch/585 x 280 x 20 mm
Weight: 28.9 oz / 820 g
Solar Panel: 25-year power output
5 Year 95% efficiency
10 year 90% efficiency
25 year 80% efficiency
5-year workmanship and materials
Accessories: 12 month material

Renogy E.Flex 21 Review

I will be taking a good look at the E.flex 21 watt portable solar charger. Matching it with the Renogy 20000 mAh power bank.  Pitting it against the Anker 21 watt portable solar panel. Looking at the good and not-so-good points. And flicking through other E.Flex products in the range.

A bit about Renogy

Renogy was started by students at Louisiana State University. Renogy LLC was organized in 2010 and in 2013 they launched their online store. By 2013 they incorporated as the RNG Group Inc. In 2016, Renogy won two bronze-level Golden Bridge Awards. One of them for best product of the year with the Lycan solar power station.

Renogy Factory

Today Renogy produces a wide range of solar products and solutions. These include the recreational vehicles, home, truck, marine and commercial sectors. With solar power becoming more popular and more widely used as an alternative source of power generation. Their product range and technological innovations are bound to expand. To meet the challenges of global warming and reducing the world’s carbon footprint.

Renogy products are well-made and respected. The company has a reputation for quality workmanship, reliability, durability, and customer service. E.Flex portable solar power kits are engineered to fit into these high standards. That’s enough about the company, it’s onto the review proper.

What Is The E. Flex 21 Watt  Portable Solar Panel USB Charger?

This is a Renogy promotional video that features the E.Flex portable solar panel. It is showing the E.Flex 30. But the 21 is the same except it has 3 solar panels instead of 4

The E.Flex portable is made from three folded 7-watt solar panels. These are molded together within a nylon carcass, making it a soft fold-up panel. Then wired to a junction box with 2 USB ports. These are housed in a pocket to help protect them from knocks and the elements.

It has 5 cloth hooks so it can be hung using carabiners. And is completed with a kickstand. The portable solar panel folds down to about the size of a quality magazine. The E.Flex is a solar charger and doesn’t store a charge. A power bank is required to be able to do that. 

Solar CellUnknown
Module Type3 x 7 Watt
Efficiency22% to 25%
Dimensions Folded11.0 x 7.3 x 1.2 inch/280 x 185 x 30 mm
Dimensions Unfolded23.0 x 11.0 x 0.8 inch/585 x 280 x 20 mm
Weight28.9 oz / 820 g
USB Output2 x 5V/2.4A max
Optimum Operating Voltage6V
Optimum Operating Current3,5A
Open Circuit Voltage7.2V
Optimum Operating Current3.5A

Unusually Renogy is not saying the type of solar cell that is incorporated into the solar panel. They do however say that the E.Flex 21 has an efficiency rating of up to 22% to 25%. But remember these results will have been achieved in lab conditions. 

Renogy E.Flex 21 Review

I would say that to achieve the best results. Standing the solar panel up on its kickstand will collect the greatest amount of sunlight. If you are going to attach it to your pack using the carabiners. I would make sure the sun was behind you.


The E.Flex 21 has 2 x 5V/2A USB ports housed in a small controller unit. Which incorporates the latest ISolar technology. It has a LED indicator that will flash. If it has been shut off due to overcurrent or short circuit.

ISolar technology
Renogy E.Flex 21 - ISolar Technology

The incorporated ISolar technology is designed to provide;

  • Detection of an attached device to deliver the correct charge for that make/model
  • The fastest possible charging speeds
  • Auto-reconnect if charging is interrupted by cloud or shade
  • Protect your device from overheating
  • Reconnection after charging disruption
  • Over current and short circuit protection

Tip; To achieve the fastest possible charging speeds. Remember to turn off your device’s Bluetooth and wi-fi etc … 

Remember; The ports are standard 5V/2A USB and not fast charging ports. They will charge your device just fine.  But don’t be expecting lightning speeds this is a small 21w solar panel. Not a 100 or 200w panel. And is meant for providing charging back up when off-grid.

Renogy E.Flex 21 - Durable

Because it is constructed of nylon the E.Flex 21 is very durable. Knocks bumps and the odd accidental drop will do little damage to it. It is waterproof but remember the junction box isn’t. This is where the USBs are housed and care needs to be taken around liquids. 

 It will probably survive liquids accidentally spilled on it. But as a precaution, if it starts raining, stow it away. Do not leave it out overnight as it might rain.

Renogy E.Flex 21 - Durable

One of the biggest benefits of the charger is its portability. Because it is so small and light it will comfortably fit into any pack or car. Fantastic for charging devices on a day out at the beach, a lake or in the forest. All you have to do is stand it up and let the sun and solar panel do its work. You can even use it if you travel around a lot for work. No more being caught out with a low battery. When the boss calls to find out how things are going


If you are using it for hiking, cycling or backpacking. You will have few problems fitting it into your pack. Because it folds down to about the size of a magazine. Weight is always a concern but at just  28.9 oz / 820 g. It will not take up too much of your weight allocation making it easy to carry around.

What you really want to know is; Will the solar panel be reliable? It will be as long as you remember its limitations. As a 21w portable solar panel, it is probably best used for topping off devices or power banks. 

I wouldn’t allow my device’s battery to deplete below 70% without topping it off.  If deeper charging is required for example 50%. I would work on 15% + charge per hour in full sunlight. That means 3.5 hours of exposure to bring your device to full charge Cloudy conditions will reduce the percentage per hour.

What can the E.Flex 21 charge?
Renogy E.Flex 21 - Mobile Phone
  • Smartphones
  • Android
  • Apple (original cable required)
  • Cameras
  • Small USB devices like a fan
  • Power Banks

Charging a power bank instead of a device directly. Would enable you to charge a tablet. 

How can I use the E.Flex 21?

The portable solar panel can be used for various outdoor activities such as;

  • Days out
  • Trekking
  • Hiking
  • Camping
  • Picnics
  • Fishing
  • Boating
  • Climbing
  • Backpacking
  • Cycling
What’s in the box
Renogy E.Flex 21 - In The Box

1 x Renogy E.Flex 21 Portable Solar panel USB Charger
1 x 23.6inch/60cm Micro USB Cable
1 x USB-A to USB-C Cable
2 x Carabiners

Power Banks

Most solar chargers have a limitation in the fact that under certain conditions like a cloudy day. If the cloud prevents charging whilst your device (e.g a smartphone). Is connected to the solar charger the battery can discharge back into the panel. 

This means your battery will lose charge. But if you charge a power bank instead of your device, this cannot happen. Because the power bank will prevent this by cutting the connection to the panel until sunlight returns. It will then automatically start charging again. 

The other advantage is that you can top up the power bank all day and charge your device at night. This is great for when you are out hiking or cycling for a couple of days or more. 

What Is The Renogy 20000mAh Power Bank?

200000 mAh Power Bank

This power bank is super light and super small and will charge any USB device. It has an on off switch and LEDs indicating levels of charge. Ideal to match up with the E.Flex 21 portable solar charger.

Capacity20000mAh / 72Wh
Battery ChemistryLithium-Ion
Dimensions2 x 2 x 4.05in / 5.1 x 5.1 x 10.3cm
Weight11.55 oz / 327.5 g
Charge CyclesUp to 1,000 times
Output Ports3 x 5V/2.4A max
Input Port5V / 2.4A max
Warranty12 month material

In case you didn’t know what mAh means;
It is the battery capacity expressed as a milliampere of an ampere-hour.

In case you didn’t know what watt-hour means:
It is the rate of energy the power bank will produce, to charge an electronic device per hour. You can find a technical explanation here (source:, The higher the Wh, the more devices you can charge, (and how quickly)


For such a small power bank the Renogy 20000mAh has a very large capacity. The lithium-ion battery will last up to 1,000 charge cycles. Which I have to say is pretty impressive.

Size and Weight 

The size and weight is ideal for any outdoor activity where space is tight. It will easily fit into a handbag. And you will hardly feel it’s 11.55 oz / 327.5 g in a pack. The combined weight with the E.Flex 21 is 2.53lbs/1.15kg. 

200000 mAh Power Bank - Portable
Output Ports

The three USB output ports can charge 3 electronic devices simultaneously. These include;

  • Smartphones
  • Cameras
  • Tablets
  • USB Enabled Laptops
Safety features
Short Circuit ProtectionCell Overvoltage Protection
Backflow PreventionOutput High-Voltage Protection
Automatic Cut Off ProtectionInput High-Voltage Protection
Input Overcurrent RegulationOutput Overcurrent Regulation
Cell Overcurrent ProtectionAutomatic Current Matching
Anti-Static ProtectionVoltage Boost Technology for Cable Drop Compensation
200000 mAh Power Bank - Capacity
What’s in the box?

1 x Renogy 200000mAh Portable Charger
1 x 23.6in/60cm Micro USB Charging Cable
1 x Travel Pouch
1 x User Manual

What’s Good About The E.Flex21 Portable Solar panel USB Charger?


With an efficiency rating of 22% to 25% and Renogy’s ISolar technology incorporated. You should have little trouble charging your devices or power bank.


The warranty for the E.Flex suggests Renogy is pretty confident about the product’s reliability. As long as you treat it as what it is; A 21w portable solar panel for backup use. I doubt it will disappoint when using it on the go.


Your pack weight and the amount of things you can fit into it is always important. I think you will find that the E.Flex will fit quite snuggly in a pack. Without you having to compromise what you can carry with you.

Renogy E.Flex 21 - BackPack

What’s Not So Good About The E.Flex 21 Portable Solar panel USB Charger?

Not fully waterproof

The E.flex 21 is described as water-resistant, not waterproof. As I mentioned earlier this is because of the USB housing. It is protected and enclosed within a pouch. that is closed using velcro. I think it will be ok in light rain but I would pack it away in heavy weather.

Unknown solar cell

I don’t know why Renogy hasn’t released which kind of solar cell the E.Flex uses. But the literature says the efficiency rating is high. I do not want to speculate with regard to this. So I suppose it needs to be taken at face value. 

Direct sunlight required

All solar panels perform best in direct sunlight. You need to remember this is only a 21w portable solar panel. The convenience of attaching to your pack to collect sunlight is great. But it will not be as efficient as when standing it up in direct sunlight. And if it is cloudy I wouldn’t be expecting miracles.

What Other Products Are There In The E.Flex Range?

Renogy E.Flex 21 - The Range

There are 3 other portable solar panels in the E.Flex range;

SpecsE.Flex 10E.Flex 30E.Flex 50
Power Wattage10w30w50w
Solar CellMonocrystallineUnknownMonocrystalline
EfficiencyHigh EfficiencyUp to 22% – 25%21% – 23%
Dimensions Folded9.5 x 5.9 x 0.26 inch11.8 x  6.3 inch/30 x 16 cm19.9 × 16.1 × 0.8inch/506 × 408 × 20mm
Dimensions Unfolded9.5 x 12.2 x 0.13inch25.4 x 11.8 inch / 64.5 x 30 cm32.5 × 19.9 × 0.2inch/826 × 506 × 5mm
Weight13oz1.6 lbs /716 g5.25lbs/2.38kg
USB Port 1 x 5V/1.92A Peak3 x 5V/2A1 x 5V/3A and 1 x 5V/2.4A
Warranty Panels25 Year Output
5 year Material and Workmanship
Warranty Accessories12 Months12 months12 months

Renogy E.Flex 21 Vs The Anker 21w PowerPort

Renogy E.Flex 21Anker 21w PowerPort
Solar CellUnknownMonocrystalline (SunPower)
Module Type3 x 7 Watt3 x 7 Watt
Efficiency22% to 25%21.5% to 23%
Dimensions Folded11.0 x 7.3 x 1.2 inch/280 x 185 x 30 mm11.1 x 6.3inch
Dimensions Unfolded23.0 x 11.0 x 0.8 inch/585 x 280 x 20 mm26.4 x 11inch
Weight28.9 oz / 820g17.6oz/499g
USB Output2 x 5V/2.4A max2 x 5V/2.4A max
WarrantySolar Panel: 25-year power output5 Year 95% efficiency
10 year 90% efficiency25 year 80% efficiency5 year workmanship and materials
Accessories: 12 month material
18 Months

These are both 21w three-fold 7-watt portable solar panels. The Renogy is claiming a higher efficiency rating than the Anker. 

Size and weight

The PowerPort is significantly lighter than the E.Flex and slightly smaller. However the reduced surface area will affect sunlight collection over the E.Flex.

Renogy E.Flex 21 - Kick Stand

Both have two 5V/2.4A  USB ports built into a protective pouch. And incorporate advanced technologies for charge management. 

Warranty and Price

The Renogy has a far superior warranty but the Anker is $10.00 cheaper. But Renogy has frequent offers on their products.

You can look at a full Anker PowerPort review here

Is The Renogy E.Flex 21 Any Good?

Renogy is well known for producing quality solar products and I can’t see the E.Flex being any different. As a solution for a small lightweight portable solar panel to charge phones. It fits the bill quite nicely to generate electricity out in the wilderness. 

It might also be handy at home if there is a power cut or extended outage. It would be nice to be able to charge your phone. Or a fan or a flashlight under emergency circumstances. It is always best to be prepared 

I hope you enjoyed this review and have found it helpful. If you have any questions about the Renogy E.Flex 21 Portable Solar Panel. Or want to leave your own personal review, please feel free to leave a comment below.

Renogy E.Flex 21 Portable Solar Panel USB Charger


Is It Worth Buying?


Value For Money


Overall Quality





  • Efficiency
  • Reliability
  • Size


  • Not Fully Waterproof
  • Unknown Solar Cell
  • Direct Sunlight Required
Spread The Solar Love

7 Comments on “Renogy E.Flex 21 Review – Portable Solar USB Charger”

  1. Hey Steve,

    Thanks for providing such extensive information about portable solar panels. It’s extremely fascinating and seems to be the way to go these days. I am one who believes in innovations that are environmentally safe and friendly and I know that more and more people are moving towards utilizing solar power.

    The specifics you provide on your site are extremely helpful. Keep up the good work.

    L, Sammy

  2. Hi! Steve, I would say I learned a lot about Solar Panels in your article but still I am confused about The Renogy 20000mAh Power Bank matching up with E.Flex 21 portable solar charger. They should be connected each other when charging the power bank? So, is it required to purchase both of them because they should go together? I hope to learn more about this two because I am one of those type of person who loves to travel and needs portable charger. This Portable Solar Panels will definitely a big advantage for me on my travel adventures. Thank you so much. Best Regards.

    1. Hi Shierly.

      You do not have to buy both the E.Flex 21 and the 200000mAh Power Bank. The E.Flex 21 will charge your smartphone without the Power Bank.

      The Power Bank is a portable rechargeable battery and is a recommendation only. The idea is to charge the power bank rather than directly charge your phone. Because it is safer and more convenient. You would then charge your phone from the power bank. 

      This is handy because you could charge the power bank all day with the E.Flex 21. Detach it from the solar panel in the evening. And charge your phone with the power bank at night while you were asleep.

      I hope that now makes sense. If you have any further questions please do not hesitate to ask



  3. Very nice job on providing accurate and useful technical information Steve.  I am very impressed with the 25% efficiency of the solar cells.  I am guessing here but it may be a market edge with this high efficiency cell for them to not disclose where these excellent cells came from!  I believe that 17% is the industry standard. 

    Nylon is a very expensive material selection for the carcass.  Very durable and strong.  Renogy hasn’t spared any expense in the design of this unique charging station.   Nylon has a glass transition temperature of 70c  (158f)  Quite hot before it begins to soften.    I am very impressed with their material selection.

    Great article, I may buy one.

    Very much appreciated Steve,


    1. Hi Chris 

      Yes the nylon carcass is an interesting choice of material. It does make it more expensive than other 21w solar chargers. But because of Renogy’s warranty I think the material just makes it more appealing. Knowing it isn’t going to fall apart in a couple of months. Gives a certain piece of mind.

      By the way it is on offer right now so it’s worth a peak



  4. Hi Steve
    Thanks for sharing your review on the Portable USB solar charger –Renogy E. Flex-21. I am an avid Traveler and also long distance cyclist. I was searching for a solution for an eco-friendly charger while I am on the road .your information came as a surprise to me and I found it exactly as per my requirement .can you please suggest if I connect two charges in series then will I be able to charge my laptop ?
    Warm Regards
    Gaurav Gaur

    1. Hi Gaurav. 

      I would look at the slightly larger E.Flex 30 as well that I mention in other products in the range. 

      And charge the 20000 mAh or larger power bank with the E.Flex solar charger. 

      It is much safer to charge a laptop from a power bank than directly from the solar charger. This is because under certain conditions. Like very cloudy weather the laptop battery can discharge it’s charge back into the solar charger. 

      This cannot happen when with charging a power bank. Because it will automatically cut the charging connection if there isn’t any charging. (Your laptop does not have a mechanism to do this). Then when the sun comes out again it will automatically start re-charging. 

      I hope that makes sense



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