Berlin and Sydney. Real transactions on the Arbitrum test network, through the Exergy contracts. Each one can be opened and checked.
It tests the central claim of Exergy at the hardest moment: when someone has no energy of his own and no neighbour who can spare any. The note still works. Inside a community it buys energy over the wire. Between communities, where there is no wire, it is sold for money, and the money pays the power bill. The deal pays both sides: the buyer takes a note only when a kilowatt-hour through it costs him less than one from his own socket, and the seller gets money he needs right now. People accept it because behind it stands a share of all the energy stored across the network's batteries. That energy really exists, just not necessarily next door. That is what it means for the note to be backed. And if it works when everyone is empty, the noon surplus the grid pays pennies for finds a buyer all the more.
His battery is empty. His neighbours' batteries are empty too, so nobody here can take his notes for energy. He does hold notes, earned earlier when his battery was charging. He needs money to pay his power bill.
Evening, battery empty, no notes left. His grid sells energy at a high price. His neighbour Bob has energy, and in their community, as across the whole Exergy network, members give each other energy for notes. So Jack needs a note, and one that costs less than a kilowatt-hour from his socket.
Battery full since noon, and nowhere to put the surplus: the grid pays pennies for it. Bob is Jack's neighbour; they are in the same community, joined by its wire. A note suits him better than cash: with it he gets energy himself when he is the empty one, or sells it anywhere in the network.
Prices are illustrative: Jack's grid sells at 35 cents per kWh, Bob's grid buys surplus at 5 cents, and the note changed hands at 25 cents per kWh it holds. The deal is 10 kWh.
Each compared it with his own alternative and came out ahead. When a deal pays for both sides, it happens. When it happens for money, the note has a price.
There is no wire between Berlin and Sydney. Hans is empty, Jack is empty, and value still crossed: Hans's notes became money from Sydney, and Jack got his energy from Bob over his own community's wire. What crossed the border was not energy but its value. That is the hardest case. Bob's noon is the everyday one: a surplus the local grid would pay pennies for found a buyer on the other side of the planet.
Sydney is 9 hours ahead of Berlin: noon in Sydney is 3 a.m. in Berlin, and 7 p.m. in Sydney is 10 a.m. in Berlin.
Hans is in the Berlin community; Jack and Bob are in the Sydney one. Both communities take part in Exergy, and their members settle energy with each other in notes. It pays everyone: a note gets you energy from a neighbour when you have none, and money anywhere in the network when money is what you need. Energy for a note changes hands only inside a community, over its wire. The note itself can go anywhere.
When Hans's battery was charging, the energy was measured and notes were issued against it. His community credited him his share: 12 notes. Later the battery ran down, and the notes stayed.
Bob's battery went from 9.45 to 13.5 kWh: it is full, 4.05 kWh added. The report is signed by the device and by the community's system; the contract checked both signatures and issued notes against the new energy. The network's stock grew, and the number on every note went up.
In Berlin, Hans is empty, his neighbours are empty, and the power bill is due. In Sydney, Jack is empty and out of notes, and Bob has energy. Jack pays Hans money, and Hans sends him notes worth 10 kWh across the border. On the test network, test ether stands in for money; in real life it is euros or dollars.
Hans pays his bill with that money, not out of his own pocket. His problem is solved.
The exchange runs at the protocol rate: exactly as many notes as hold 10 kWh at the moment of the deal, and nobody haggles over it. The energy flows over the community wire. Not one electron crossed a border. Hans sent Jack slightly more, 11.46: the difference covered a small protocol fee, and Jack has 0.04 left.
Jack got energy cheaper than from his grid. Bob sold his surplus for more than the grid would give.
Bob's battery held 13.5 kWh. He gave Jack 10, the battery caught a little sun, and 3.6 kWh is left. Jack used those 10 kWh, and they left the stock of the whole network: it was 125.55 kWh, now 115.69. The number of notes is the same; nobody burns them. So every note in the network got lighter: from 0.8777 kWh per note to 0.8082, minus 0.07 kWh on each one. Consumption shows up in the number.
Along the bottom are the step numbers; up the side, kWh per note (the axis is cropped so the change is visible). The number is below one because part of the energy that notes were once issued against has since been used, while the notes remain. The drop at step 5 is large because the demo network is small: 10 kWh is 8% of its stock. In a large network one such trade barely shows. When batteries charge again, the number goes back up, as in step 2.