Ten rooftop-solar homes sit around a shared local market hub, each with its own battery, its own load, and its own noisy little patch of sky. Instead of every household defaulting to the utility as the only buyer and seller, this simulator clears a real uniform-price double auction every simulated half hour: houses with midday surplus sell it to houses with a deficit at a price that lands between the low feed-in tariff and the full retail rate, and only the leftover imbalance crosses the pylon to the outside grid. Flip P2P trading off to see the same neighborhood fall back to grid-only exchange, and watch self-sufficiency and community savings collapse — a small, concrete picture of what "energy choice" and "energy independence" actually buy a community.