The Battery Bank
This pattern is shaped by
Problem
When solar panels generate power only when the sun shines, and the grid delivers power only when it functions, the building exists in a state of double dependency — exporting its surplus at midday for pennies, importing it back at evening peak for dollars, and going dark entirely when ice storms or heat waves bring the grid down. The forces pull apart: self-generation wants to keep what it makes; resilience wants power when all else fails; economics wants to buy low and sell high; but without storage, all three lose.
Evidence and Discussion
The arithmetic of solar without storage is punishing. A typical rooftop system in Edmonton generates 80% of its daily output between 10 AM and 4 PM, yet household consumption peaks between 5 PM and 9 PM — after the sun has weakened or set. Without batteries, surplus generation flows to the grid at wholesale rates (often 3-5 cents/kWh in Alberta), then flows back at retail rates (12-18 cents/kWh) a few hours later. The building generates enough energy to cover its needs but captures only a fraction of the value.
The resilience case is starker. During the February 2021 Texas grid collapse, 4.5 million homes lost power for days in freezing temperatures. Homes with solar panels but no storage went dark alongside everyone else — the panels cannot operate without grid connection unless paired with battery backup. Meanwhile, homes with battery systems maintained critical loads: refrigeration, a few lights, phone charging, medical equipment. The California Public Utilities Commission found that after the 2019 Public Safety Power Shutoffs, battery storage installations in affected areas increased 400% the following year. People remember what it felt like to lose power, and they remember which houses kept their lights on.
The technology has crossed a threshold. Lithium iron phosphate (LFP) batteries now offer 6,000+ cycle lifespans — roughly 15-20 years of daily cycling — at costs that have fallen 90% since 2010. Tesla's Powerwall, Enphase's IQ batteries, and similar residential systems provide 10-15 kWh of usable storage in wall-mounted units roughly the size of a water heater. The U.S. Investment Tax Credit (30% through 2032) and various provincial and utility incentives have made the payback period for storage increasingly reasonable, particularly where time-of-use rates create significant peak/off-peak spreads.
Alexander did not write a storage pattern — batteries were exotic technology in 1977. But his pattern *South Facing Outdoors* (Alexander 105) recognized that buildings must orient themselves to capture what nature provides. The Battery Bank extends this logic: capture what the panels harvest, hold it through the gap between generation and need, and release it when darkness falls or the grid fails.
Therefore
Install battery storage sized to cover critical loads for 24 hours and to shift at least 80% of daily solar generation to evening use. Place the battery bank in a conditioned, accessible space — basement, utility room, or garage — where it can be monitored and maintained without special equipment. Wire critical circuits (refrigerator, a few lights, one outlet per floor, medical equipment if present) through an automatic transfer switch so they remain powered during outages. The system should be testable: once per year, simulate a grid outage and confirm that critical loads operate for at least 12 hours on stored power alone.