The solar charging feature is generally seen as a last-resort or emergency option rather than a primary charging method. It can take several days of direct sunlight to fully charge the large capacity battery (e.g., 10 days for a full charge with 10 hours of sun per day). A green indicator shows when it is charging via solar power.
Charging Speed: While some models offer fast charging (PD 15W, QC 3.0), the charging speed can be mixed, with some users reporting that it takes a while to charge via wall outlet as well