This is one of the more practical questions from people who want to keep a powerbank topped up from their garden panels or run devices from solar without going through the house circuits. The answer depends on how you connect things.
Via the house socket (standard plug-in solar route)
If your panels feed generation into the house circuits via a microinverter, any device drawing from those circuits during generation hours is indirectly powered by solar. A powerbank plugged into a house socket, a USB charging hub, a phone charger — during the hours your panels are generating, these draw from the same circuit the solar is feeding. The net effect: the powerbank charge costs you little or nothing from the grid while solar is producing above your base load.
This works for any USB-charged device, any powerbank, any portable charger. It is indirect — you are not connecting the panels to the powerbank directly — but the electricity cost is the same: near zero for every unit generated and self-consumed.
Direct panel-to-battery charging
Large portable power stations (EcoFlow DELTA, Jackery Explorer, Bluetti, Goal Zero) have DC solar input ports rated for 12V to 150V. You connect solar panels directly to this input and the power station charges from DC without any AC inverter involved. This is the cleanest off-grid approach and works without any house electrical connection at all.
Standard small powerbanks for phone charging do not have solar input ports. For those, you need an AC inverter — either the house microinverter route, or a small dedicated 12V-to-240V inverter connected to the panel via a charge controller and battery.
The EcoFlow STREAM as a powerbank
The EcoFlow STREAM units are effectively very large capacity power stations with solar input. Panels charge the STREAM’s battery via the MPPT inputs. The STREAM’s own USB ports and AC outlets power anything plugged into them — including charging other powerbanks. No grid connection required. This is the cleanest off-grid solar-plus-storage solution for camping, garden use, or anywhere away from the mains.
For the EcoFlow STREAM’s off-grid capabilities in detail, see the relevant section of our EcoFlow STREAM FAQ.