Blockchain users save on transaction fees but the blockchain technology is far from free to install. For example, the "proof of work" system that Bitcoin uses to validate transactions consumes large amounts of computing power. In the real world, the power of millions of computers in the bitcoin network consumes close to what Denmark consumes annually. Assuming electricity costs globally are $ 0.03 ~ $ 0.05 per kilowatt hour, mining costs averaged between $ 5,000 and $ 7,000 per bitcoin, excluding hardware costs. Despite the Bitcoin mining costs, users continue to increase their electricity bills to validate transactions on the blockchain. This is because when miners add a block to the bitcoin blockchain, they are rewarded with enough bitcoin to make their time and energy valuable. In the case of blockchains that do not use cryptocurrencies, the miners will need to be paid or otherwise encouraged to verify transactions. Some solutions have begun to be produced for these problems. For example, bitcoin mining farms are set up to use solar energy, excess natural gas from crushing fields or power from wind farms.