Solar + battery backup for a multi-day PSPS in California (2026)

• A standard grid-tied system will not run your home in an outage. Grid-tied inverters must stop energizing your wiring within about 2 seconds of losing the grid (UL 1741 / IEEE 1547), so a normal solar-only home goes dark at noon on a sunny day. The one exception is a purpose-built sunlight-backup configuration, and it only covers small daytime loads — never the night.
• PSPS events are multi-day operations, not flickers. Southern California Edison ran 13 separate PSPS events in 2025; on ten of them, more than 24 hours passed between the first circuit coming back and the last.
• Without solar recharge, one ~13.5 kWh battery runs a critical-loads home for about 1.7 days (fridge, lights, WiFi, furnace fan, a medical device, a pump ≈ 7.2 kWh/day).
• Solar recharge is the biggest lever on this page. On an average December day — the weakest solar month in Los Angeles — a 2.5 kW array already produces more than a 7.2 kWh critical-loads day consumes, so the modelled battery still has charge on day 14. A run of storm or heavy-smoke days produces less than the monthly average, so treat that as a planning result, not a guarantee.
• Whole-home backup is a different animal. Add central AC, an electric water heater and EV charging and the day jumps to ~37 kWh — past what one battery can store and past what one battery can deliver at once.

Sizing arguments usually stall on a vague phrase — “outages can last hours to days.” The number that should drive your battery decision is public. Every California investor-owned utility files a PSPS post-season report with the CPUC, and SCE's 2025 filing lists each de-energization event with the time the first circuit was restored and the time the last circuit was restored.

The six critical rows add up to 7.2 kWh/day. That is the number behind “one battery, about a day and a half” — 12.15 usable kWh after the 10% reserve, divided by 7.2, is 1.7 days with no sun at all. Everything above that comes from the roof.

A battery is only self-sustaining if the roof puts back what the house takes out. In Los Angeles that number swings by about 75% across the year, and — as SCE's 2025 table shows — shutoffs happen at both ends of that swing.

The practical reading is that two conditions have to hold at once, and the second one is the one people miss. The array has to cover the day's energy, and the battery has to be big enough to carry the night on its own. For critical loads both are easy: 1.5–2.5 kW of panels covers an average day in any month, and the night portion is under 4 kWh, well inside one battery. For whole-home loads the second condition bites hard. A 37 kWh day puts roughly 20 kWh into the dark hours — more than one 13.5 kWh battery holds — so in our model one battery runs out on the first night in August whether the array is 7 kW or 16 kW, while two batteries with a 7 kW array still have charge on day 14. More panels cannot fix a bank that cannot survive until sunrise.

Three honest caveats. These are monthly averages that include cloudy days, so any single outage can land well below them — a winter storm, a stretch of marine layer, or heavy wildfire smoke all cut output, and nothing in this model says the sun will cooperate on the days your grid is down. In the other direction, a Santa Ana wind event — the classic PSPS trigger — usually arrives with clear skies, so production during those particular outages tends to run above the table. And in island mode a hybrid system throttles the array once the battery is full and the house is satisfied, so surplus beyond that is not banked anywhere.

The reason the first three exist is the same safety rule: every grid-tied inverter sold in the U.S. must include anti-islanding protection under UL 1741 and IEEE 1547, and stop energizing your wiring within about two seconds of losing the grid, so it cannot electrocute a lineworker repairing a “dead” line. Without a gateway and a backup-capable inverter, that rule takes your panels offline with everything else. The mechanism is covered in do solar panels work in a power outage.

As approximate 2026 California ranges before incentives: one ~13.5 kWh battery with a hybrid inverter runs $13,000–$18,000 installed, a backup gateway adds $2,000–$3,500, a critical-loads subpanel $1,000–$2,500, and whole-home backup with two or more batteries and a possible panel upgrade adds $10,000 and up. Per-kWh pricing, what moves it, and retrofit-versus-new-solar differences are in how much a home battery costs in California.

1. Get your real daily kWh. Take the kWh from your last bill and divide by the days in the billing period — LADWP bills most residential customers every two months, so use the period on the statement, not 30. That is your whole-house day; backup only needs the part you would keep running.
2. List the loads you would not switch off. Medical equipment, refrigeration, a well pump, heat in winter. Everything else is negotiable at hour 40 of an outage.
3. Read the two ratings off the battery datasheet — usable kWh and continuous kW — and check both against the model above, not just the first one.
4. Ask the installer for the island-mode behaviour in writing: what is on the backup panel, what the backup reserve is set to, and whether the array can recharge the battery with the grid down. Not every retrofit can.

Everything above is a model. This is a system we designed, permitted and energized, with the numbers that matter for backup. It is a useful test case because its specification lands exactly on two of the model's inputs: 27 kWh of usable storage (two units' worth) and a 10.12 kW array.

Now put its own numbers into the model above — two batteries, a 10 kW array — and ask what it survives:

A larger example on the same principle: an Altadena home in a Tier 3 fire-threat area, where we paired 26.7 kW of solar with more than 38 kWh of storage. Its owner learned about the next SCE shutoff from a neighbour the following morning.

It does not predict whether your address will be de-energized — that depends on your circuit and the fire-threat map. It does not price a specific proposal, rank battery brands, or model your bill savings. The day-by-day figures assume a healthy battery, a shade-free south-facing array and average weather for the month; a storm week, heavy shading, an ageing pack or a system that cannot recharge in island mode will all come in lower. And the SCE table describes SCE's 2025 season, not a forecast of 2026.

Figures on this page come from the primary sources below and, where noted, from Cali Energy calculations using the stated assumptions. Rates, incentives, and program terms change; each was verified September 4, 2026.

1. SCE — 2025 PSPS Post-Season Report (CPUC R.18-12-005), Table 1: Aggregate Restoration Times for 2025
2. CPUC — Utility PSPS reports (post-event and post-season)
3. PVGIS (European Commission JRC) — PV performance tool, Los Angeles monthly output
4. EIA Residential Energy Consumption Survey
5. California Distributed Generation Statistics — SCE Interconnected Project Sites dataset (Jan 2020 – Mar 2026)
6. Enphase — IQ8 Sunlight Backup (daytime, battery-free backup: scope and requirements)
7. Tesla — Powerwall 3 datasheet (13.5 kWh usable, 11.5 kW continuous at 240 V)
8. IEEE 1547 — Standard for Interconnection and Interoperability of Distributed Energy Resources
9. UL 1741 — Inverters, Converters, Controllers for Distributed Energy Resources
10. IRS — Residential Clean Energy Credit
11. SelfGenCA — SGIP Program Metrics
12. CPUC — Net Billing Tariff (NEM 3.0)