TransActive Grid, a startup from Brooklyn (USA), has built a locally generated electricity microgrid, a tiny Internet of Energy (IoE) that allows residents with rooftop solar panels to sell their excess power to their neighbors. Payments are made via PayPal using blockchain technology, the same technology that underlies the virtual bitcoin currency.

A blockchain is a distributed database that maintains a continuously-growing list of data records hardened against tampering and revision. The list is stored on every computer in the system, and is continuously updated as each transaction is completed.

The Brooklyn project, a joint venture between LO3 Energy and Consensys, uses blockchain software from Ethereum to monitor the energy flowing in and out of each network node enabling energy trade in a peer-to-peer fashion. No central authority is in control: the system monitors itself to stop fraud. Instead of paying an energy services company that buys renewable energy credits, the user directly pays the producer of the electricity he/she consumes, effectively cutting out the middle man.