  In this paper, we consider an information update system where wireless sensor
sends timely updates to the destination over a random blocking terahertz
channel with the supply of harvested energy and reliable energy backup. The
paper aims to find the optimal information updating policy that minimize the
time-average weighted sum of the Age of information(AoI) and the reliable
energy costs by formulating an infinite state Markov decision process(MDP).
With the derivation of the monotonicity of value function on each component,
the optimal information updating policy is proved to have a threshold
structure. Based on this special structure, an algorithm for efficiently
computing the optimal policy is proposed. Numerical results show that the
optimal updating policy proposed outperforms baseline policies.
