A power distribution control system for control of a plurality of power assets connected to a grid, the system comprising: a server for selecting, from a set of power assets known to the server, a subset of power assets (10, 11, 12) that are to form a string and sending instructions, over a server-client link, to the selected power assets (10, 11, 12) to form a balanced string that is to have no net flow of energy in or out of the grid or is to maintain a steady net flow of energy in or out of the grid, wherein the string comprises at least two different power assets selected from: sources, stores and responsive loads, and a router for controlling each of the power assets (10, 11, 12) in the string and for communicating with controllers of other power assets (10, 11, 12) in the string on a peer-to-peer basis to maintain balance in the string; wherein the server is further operable to communicate with the routers (13, 14, 15) of the power assets (10, 11, 12) in the string and to indicate to each router: (i) what are the other assets (10, 11, 12) of the string so that the routers of the assets (10, 11, 12) can commence communication with each other; and (ii) future collective behaviour of the assets (10, 11, 12) of the string in terms of need to maintain line voltage and/or need to maintain line frequency, which the power assets (10, 11, 12) in the string together should together attempt to fulfil by negotiating times and quantities of power transfer between themselves. a server for selecting, from a set of power assets known to the server, a subset of power assets (10, 11, 12) that are to form a string and sending instructions, over a server-client link, to the selected power assets (10, 11, 12) to form a balanced string that is to have no net flow of energy in or out of the grid or is to maintain a steady net flow of energy in or out of the grid, wherein the string comprises at least two different power assets selected from: sources, stores and responsive loads, and a router for controlling each of the power assets (10, 11, 12) in the string and for communicating with controllers of other power assets (10, 11, 12) in the string on a peer-to-peer basis to maintain balance in the string; wherein the server is further operable to communicate with the routers (13, 14, 15) of the power assets (10, 11, 12) in the string and to indicate to each router: (i) what are the other assets (10, 11, 12) of the string so that the routers of the assets (10, 11, 12) can commence communication with each other; and (ii) future collective behaviour of the assets (10, 11, 12) of the string in terms of need to maintain line voltage and/or need to maintain line frequency, which the power assets (10, 11, 12) in the string together should together attempt to fulfil by negotiating times and quantities of power transfer between themselves. (i) what are the other assets (10, 11, 12) of the string so that the routers of the assets (10, 11, 12) can commence communication with each other; and (ii) future collective behaviour of the assets (10, 11, 12) of the string in terms of need to maintain line voltage and/or need to maintain line frequency, which the power assets (10, 11, 12) in the string together should together attempt to fulfil by negotiating times and quantities of power transfer between themselves.