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Energy·applied

Battery Storage

Why it matters

Solar generation and a household's life run on different clocks: the array peaks at noon, the home peaks at breakfast and evening, and the heating season peaks exactly when generation bottoms out. The battery is the machine that reconciles those clocks. In Ukraine since 2022 it also decides whether a blackout is an inconvenience or an emergency. Battery prices followed the same collapse as panels, and that quietly rewrote what autonomy costs. Energy independence stopped being a millionaire's statement and became a mid-sized line in a construction budget. Every kilowatt-hour of storage is bought resilience — against the grid, the weather, and the war.

Role in 001's holistic picture

The battery is the short-term memory of the energy organism: the array writes to it by day, Energy Management reads from it by night. It has a cheaper sibling for heat: the buffer tank. Every kilowatt-hour that hot water can hold instead of electrons should go there. Its hardest sizing question comes from winter: the string of dark days sets the size, and the average night is a weak guide. Those stored kilowatt-hours are also the physical core of blackout independence and of the building's autonomy.

In the world

The economics behind home storage are an already measured collapse. Per BloombergNEF's December 2025 survey, lithium-ion pack prices fell another 8% year-on-year, to a record-low global average of $108/kWh. Stationary-storage packs dropped hardest of all: 45% in a single year, to $70/kWh. That made the battery in a basement the cheapest kind of battery on earth for the first time. The engine is manufacturing overcapacity and the shift to lithium-iron-phosphate cells — the same chemistry House 001's pack is built from. Cheap storage has pulled autonomy into ordinary homes at national scale. Per the solar association BSW-Solar, Germany added some 580,000 home battery systems in 2024 alone, and the installed total passed 1.8 million. In barely a decade such systems crossed from enthusiast hardware to a mass-market default.

How 001 engages with it

House 001 runs on 25 kWh of LiFePO4 — 15 kWh self-assembled from EVE 280 Ah cells plus 10 kWh of stock rack modules — against its 6 kW array. That combination holds full autonomy from mid-February to mid-November, season after observed season. That self-assembly rests on a broad practice: a worldwide self-build powerwall community bench-tests these very cells. The independent tester Off-Grid Garage (Andy Schwarz) publishes capacity, internal-resistance, and BMS data on the EVE 280 Ah among many others. That open measurement lets a home-made pack be trusted instead of hoped for. The house's sole AC source is a no-name Chinese 7 kW inverter of sturdy low-frequency design. We genuinely do not know the brand, and in years of service it has never made us need to. The bank also has a biography that says more about storage than any datasheet. For about a year in 2024–2025 it was 45 kWh feeding a two-house microgrid — House 001 and a neighbour's home together — until the split gave the neighbour his 15 kWh DIY pack for his own PV and inverter. Later, during the heavy blackouts, another 5 kWh left with a second no-name inverter to guard the family's city apartment. Storage is resilience you can carry to where it is needed. The topology stays constitutional throughout: the grid cannot power the house directly at all. It may only charge the battery through a small dedicated charger. The grid is a guest that tops up the reserve, never the master of the system.

For Unity Hub, our published winter-PV analysis called the specified 30–40 kWh "a bare minimum" and pointed toward ~60 kWh for comfortable overnight autonomy in multi-day overcast periods. The same text noted a counterweight: a larger array relaxes the battery question. The final storage architecture is active design work, and House 001's DIY battery based on EVE cells stands as the lived precedent for the packs we plan to assemble ourselves. That architecture's story will be published when it settles.

Maturity: applied. Years of measured operation at House 001; Unity Hub sizing under active design with the published analysis as its baseline.

Further reading