It has solar-panel charging capability: a built-in solar panel lets it charge (or at least top-up) using sunlight.
Specifications
If you consider buying a DP-7724, you should demand that the seller specify clearly:
• Battery capacity (in mAh and voltage)
• Type of battery (Li-ion / Li-polymer)
• Input specs (solar panel output — voltage/wattage & USB/AC input)
• Output specs (USB-A, USB-C, DC — voltage/current)
• Realistic expected charging cycles (how many phone charges, about how long solar charging takes)
• Whether there’s a charge / discharge / over-current protection circuit
