Every transaction requires at least one block (typically several) to be added to the block chain, and the block size limit means that, in fact, energy consumpti

Every transaction requires at least one block (typically several) to be added to the block chain, and the block size limit means that, in fact, energy consumption in Bitcoin is proportional to the number of transactions. Beyond technical details, there is also the economic incentive: miners are paid to include transactions in new blocks, and if there are more transactions (thus higher demand) the fee will rise and miners will consume more power in order to collect the higher fees.