What is TRON energy and why USDT transfers need it
TRON energy is a network resource consumed by smart-contract calls such as USDT TRC-20 transfers; without it, TRX is burned to pay the cost.
TRON does not charge fees in the same way as Ethereum. Instead, it uses two resources. Bandwidth covers the size of a transaction in bytes, and every account gets a small amount for free daily. Energy covers computation by smart contracts. A plain TRX transfer needs only bandwidth, but a USDT TRC-20 transfer is a contract call and needs energy.
There are three ways to cover energy. You can stake TRX (in the current Stake 2.0 model) and receive energy that regenerates over time. You can rent energy from another account that has staked TRX, often through marketplaces. Or you can have none, in which case the network burns TRX from your balance to pay for the energy used. Burning is the simplest option and often the most expensive for regular transfers.
The cost of a transfer is not fixed. A USDT transfer to an address that has never held USDT requires noticeably more energy than a transfer to an address that already has a balance, because the contract must create a new storage entry. The energy price in TRX is also set by network parameters and can change.
For businesses that receive many payments, energy becomes an operational concern when moving funds out of incoming addresses. Each address that received USDT needs energy or TRX to send it onward, so sweeping thousands of addresses without planning can waste a lot of TRX. Common mistakes are keeping USDT on addresses without any TRX and treating the fee seen in one transaction as constant.
Moonvex handles this itself: the service sweeps received funds and provides the resources needed to move them, so merchants do not have to buy, stake or rent energy for each address.