Energy efficiency issues in blockchain technology is a critical research area that addresses the high computational and energy costs associated with maintaining decentralized networks, particularly those using Proof of Work (PoW) consensus mechanisms. Traditional PoW blockchains, such as Bitcoin, consume substantial electricity due to intensive mining operations, raising environmental and operational concerns. Research explores energy-efficient consensus algorithms like Proof of Stake (PoS), Delegated Proof of Stake (DPoS), Proof of Authority (PoA), hybrid consensus models, and adaptive mining strategies to reduce energy consumption while maintaining security and decentralization. Recent studies also investigate layer-2 solutions, off-chain processing, sharding, and blockchain architectures optimized for low-power and sustainable operation. Applications span cryptocurrencies, decentralized finance (DeFi), IoT networks, supply chain management, and smart contracts, where energy efficiency is essential for scalability and sustainability. Current research emphasizes balancing energy consumption with security, performance, and decentralization, establishing energy-efficient blockchain design as a key requirement for environmentally sustainable and practical decentralized systems.