  We examine the age of information (AoI) of a status update system that
incorporates energy harvesting and uses the slotted ALOHA protocol. We derive
analytically the average AoI and the probability that the AoI exceeds a given
threshold. Via numerical results, we investigate two strategies to minimize the
age of information (AoI): transmitting a new update whenever possible to
exploit every chance to reduce the AoI, and transmitting only when sufficient
energy is available to increase the chance of successful delivery. The two
strategies are beneficial for low and high update generation rates,
respectively. However, an optimized approach that balances the two strategies
outperforms them significantly in terms of both AoI and throughput.
