  In this paper, we address the digitization of physical assets using
blockchain technology focusing on energy and peer-to-peer trading on
decentralized energy markets. Because they are forward markets and operate on a
day-ahead timeline, the energy transactions are settled only at the movement of
energy delivery. Having the option of locking the energy tokens by a
third-party escrow becomes a highly desirable feature. Thus, we define a
Lockable ERC20 token that provides the option for an owner to lock some of its
tokens using smart contracts. A time-lock and an escrow party account or smart
contract can be specified allowing the tokens to be unlocked when certain
business conditions are met. For validation purposes, we have considered a
peer-to-peer energy trading scenario in which the Lockable ERC20 token was used
to digitize the surplus of energy of prosumers. In this case, the energy tokens
committed in blockchain transactions are successfully locked up until the
actual delivery of energy, the settlement considering the monitored data of
energy meters.
