Island hands you a cutaway house with a rooftop array, a battery cabinet in the basement, and no grid. The tagline is the scenario: seventy-two hours off grid, in January, with the state of charge falling from the moment the lights come on. Every circuit you leave closed is a promise the battery has to keep, and the game is the arithmetic of which promises you break first. It lives on the Home Energy Lab because it turns that library’s central abstraction — the kilowatt-hour — into something you watch being spent in real time.
How to play
Everything works with a mouse, a fingertip, or the keyboard. You have ten circuits to open and close — refrigerator, chest freezer, well pump, sump pump, heat pump, water heater, lights, router, medical equipment, and worse — and each carries its real running wattage and its real starting surge: the fridge draws 120 watts but asks for 620 on startup, the well pump runs at 1,000 and surges past 3,000. The inverter has a continuous rating and a surge rating, and it enforces both the way real hardware does — peak overload trips it instantly, continuous overload trips it on a delay — so the order you switch things on in matters as much as what you switch on.
There are three scenarios. Winter Storm is the title fight: seventy-two January hours with a weak sun and a house bleeding heat. Summer Heat is forty-eight July hours where the array is generous but the cooling loads are hungry. Rolling Blackouts is the odd one out — thirty-one hours of a heat wave with scheduled cuts, where power is unlimited between the cuts and the whole game is what you do in the ten minutes before each one: charge the battery, pre-cool the house, heat the water tank. A generator and an electric car sit in reserve. The EV pack is four to six times the size of the house battery, which makes it tempting — though the game is quick to remind you that it is an evacuation vehicle first and a battery second.
What the house actually runs on
The energy balance is honest end to end. Solar production is computed from the solar day, the cloud cover, and the array’s derating, with the panels laid on the roof slope they are actually bolted to — and when the battery is full, surplus sunshine is simply lost, which is how you learn what curtailment means. The house itself is a thermal model: it loses about 130 watts for every degree between inside and out, so heating in January is a running tax rather than a toggle. The fridge and freezer drift toward ambient when you shed them, and food starts to go once the fridge sits above 5 °C, which turns “just switch it off for a while” into a bet with a deadline.
At the end of a run the game scores what kind of outage you had: how comfortable the house stayed, whether the food survived, what got damaged, and how much energy you wasted — including the kilowatt-hours of sunshine that went nowhere because you charged the battery at the wrong time. The lesson the scoring keeps teaching is the one the scenarios are built around: preparation is the entire mechanic.
How it was built
Island is hand-written WebGL and JavaScript, no engine. The house is drawn as a cutaway — the front trimmed away so the rooms read like a doll’s house — and the commit history records it becoming a place: first “a kilowatt-hour, spent in real time,” then a sky, a lot, and a sun that actually casts, so the array brightens and shadows move as the solar day the simulation is integrating passes overhead. A later pass put January on the lot, furniture in the rooms, and cable on the wall, and the battery cabinet got its own light that washes the basement wall behind it, so the state of charge is something you can see from across the room.
The last commit before this page went up is the honest kind: a camera lens that fits a phone, and four bugs in the simulation. If the numbers feel unforgiving, they are meant to — the array on the roof makes about 29 kWh on a clear July day, the battery only holds ten, and the game never pretends otherwise.