  This paper opts to mitigate the energy-inefficiency of the Blockchain
Proof-of-Work (PoW) consensus algorithm by rationally repurposing the power
spent during the mining process. The original PoW mining scheme is designed to
consider one block at a time and assign a reward to the first place winner of a
computation race. To reduce the mining-related energy consumption, we propose
to compensate the computation effort of the runner(s)-up of a mining round, by
granting them exclusivity of solving the upcoming block in the next round. This
will considerably reduce the number of competing nodes in the next round and
consequently, the consumed energy. Our proposed scheme divides time into
epochs, where each comprises two mining rounds; in the first one, all network
nodes can participate in the mining process, whereas in the second round only
runners-up can take part. Thus, the overall mining energy consumption can be
reduced to nearly $50\%$. To the best of our knowledge, our proposed scheme is
the first to considerably improve the energy consumption of the original PoW
algorithm. Our analysis demonstrates the effectiveness of our scheme in
reducing energy consumption, the probability of fork occurrences, the level of
mining centralization presented in the original PoW algorithm, and the effect
of transaction censorship attack.
