Power Output
Despite only being a 14w device, the Renogy E-FLEX not only charged devices faster than competitors, but even outperformed competing 20w and 24w panels. In trials with our test smartphone, the Renogy E-FLEX generated an average of 4.04 volts, and charged 1% of our test smartphone every 1 minute and 16 seconds — over 22% faster than the next closest competitor.

Power/Size Ratio
The Renogy 14w E-FLEX sports four 5” x 7” solar panels, for a total of 140 square inches of solar cells. This placed the E-FLEX on the smaller size of solar chargers. Weighing in at only 1.3lbs, the E-FLEX was also one of the lightest devices we tested, and outperformed every competitor in terms of power (charging speed) per square inch with a Gear Institute power/size ratio score of 5.67.

Durability
The panels for the Renogy 14w E-FLEX are built from durable PET polymer substrate, held together by a rugged synthetic canvas. Overall durability is quite good: the canvas case is extremely durable and the panels themselves withstood impact strikes from a hammer of approximately 15 and 30 pounds force with only cosmetic damage, and without serious impairment. The panels can also withstand a considerable amount of torsion, but appear to stress beyond approximately 90 degrees of twisting. Though the E-FLEX’s overall durability is excellent, it is still however only average when compared to competitors. 

Features
Like many of its competitors, the Renogy 14w E-FLEX is a no-frills portable solar charger, offering only two 2.1A USB charging ports, a micro USB charging cable, and an integrated velcro pouch for small storage.

Value
Priced at only $39.99, the Renogy 14w E-FLEX delivered significantly more power per dollar spent, but was also the least expensive portable solar charger tested. The Renogy E-FLEX is an outstanding value.