The technology relates to managing nighttime power for solar-powered vehicles. A system may include a sunrise estimator for estimating a time until a next sunrise, a battery state estimator for estimating a battery state, a critical battery estimator for determining a battery threshold, below which subsystems may be powered off, and an alert monitor to determine, and communicate to the solar-powered vehicle, a charge threshold and a restart charge threshold. A method may include operating a vehicle in an operational power mode, estimating a time until a next sunrise, estimating a battery state, determining a preservation battery threshold based on the estimated time until the next sunrise and the estimated battery state, determining a minimum charge threshold based on the preservation battery threshold, monitoring a battery charge level of the vehicle throughout the night, and if the battery charge level drops below the minimum charge threshold, implementing a preservation power mode.