Is Your Home Prepared for Wildfire Season? A Guide to Backup Power in California

Is Your Home Prepared for Wildfire Season?

Red flag warnings are back on the forecast. If you live in California and you've been through even one wildfire season with a Powerwall, you know what that means: your utility might cut your power before the fire ever starts.

That's not a malfunction. It's the plan.

What Are Public Safety Power Shutoffs (PSPS)?

A PSPS is a proactive outage. When conditions get dangerous enough, meaning high winds, low humidity, and dry vegetation, PG&E, SCE, or SDG&E will de-energize specific circuits to keep their equipment from sparking a fire. A downed line or an arcing transformer during a 50 mph wind event in dry brush is how some of the state's worst fires started. Shutting the grid off first is the utilities' answer to that risk.

None of the three utilities publish one hard number that triggers a shutoff, and that's by design. SCE, PG&E, and SDG&E each run a risk model that weighs wind speed, humidity, dry fuel, and real-time field observations against conditions on a specific circuit, not a townwide switch. High wind combined with low humidity and dry vegetation in a high-risk area is generally what puts a circuit on the watch list, but the actual call comes down to what's happening on that stretch of line right then. If you live in a designated Tier 2 or Tier 3 High Fire-Threat District (check your utility's map, not just your city), you're a candidate for shutoffs even if your specific street has never burned.

The frustrating part is the timeline. Utilities try to give 24 to 48 hours notice, but wind events shift fast, and shutoffs can start with only a few hours' warning. Restoration isn't instant either. After the weather clears, crews still have to physically inspect every mile of line before re-energizing, which is why a "one day" PSPS regularly turns into three or four.

The Role of a Powerwall During a PSPS

This is where a Powerwall stops being a nice-to-have and becomes the thing standing between you and a warm refrigerator full of spoiled food.

When the grid goes down, a properly configured Powerwall system islands your home automatically and near-instantly, so you won't even notice the transition unless you're staring at the Tesla app. Your critical loads, whatever you've wired to backup, keep running off battery. For some installs that's most of the panel; for others it's a narrower critical-loads subset, depending on how many Powerwalls you have and how the system was sized.

The obvious wins are the ones you'd expect: lights, the fridge and freezer, your internet router and modem so you're not cut off from information mid-emergency, and outlets to keep phones charged. But the less obvious win is medical equipment. If anyone in your household relies on a CPAP machine, an oxygen concentrator, or refrigerated medication, a PSPS is a real risk. Losing power for even a few hours can mean a trip to the ER or scrambling for a hotel room, and having a Powerwall keep that equipment running is what avoids it.

Tesla's Storm Watch feature matters a lot here. It watches NOAA severe weather alerts, and when one hits your area, it automatically charges your Powerwall to 100%, even if your normal reserve setting is lower to save room for time-of-use arbitrage — which, under NEM 3.0, is where most of a California solar home's value now comes from. High-wind warnings and other severe weather alerts often overlap with PSPS-triggering conditions, but Storm Watch is keyed to NOAA's system, not your utility's fire-risk model, so don't assume it will always catch a shutoff before your utility does. That's exactly why the setting is worth checking before this season gets going: if you've got Storm Watch disabled or your reserve percentage set low for daily bill optimization, you could be sitting at 20% state of charge right when a shutoff hits. A state-of-charge floor that grid-charges you back up when you drop below it is the belt to Storm Watch's suspenders.

How Long Can a Powerwall Last?

This is the question everyone actually wants answered, and the honest response is: it depends, but let's do the math.

A single Powerwall holds 13.5 kWh of usable energy. A typical California home draws somewhere in the ballpark of 1 to 2 kW continuously when you count the fridge cycling, the router, some lighting, and phantom loads from everything else plugged in, though this varies a lot by home size and equipment. At that draw, one Powerwall alone gets you somewhere in the range of 7 to 13 hours before it's empty. That's not a full day, and definitely not enough to ride out a three-day PSPS if you're running the house normally.

There's a second ceiling here that has nothing to do with how much energy is sitting in the battery. Capacity is kWh; output is kW, and they're separate limits. A Powerwall 2 can only push 5 kW continuously, with a short 7 kW burst available for about ten seconds to cover motor startup, while a Powerwall 3 tops out at 11.5 kW. Output is usually the limit you hit first. If the AC compressor kicks on while the fridge, the well pump, and the microwave are already running, a single Powerwall 2 can slam into that 5 kW wall with the battery still at 80% charge. And it doesn't politely trim the extra load. The Powerwall stops backing up the house entirely, clicks audibly while it tries to come back, and restarts about a minute after you've gone and turned things off. Stacking units raises both ceilings together, so two Powerwall 2s buy you 27 kWh and 10 kW. That's the expensive fix, and it's the least interesting one, but it works — and SGIP still covers a meaningful share of a second unit if you're in an eligible category.

Two things change the math without buying more hardware.

Solar is the big one. If you've got panels and the shutoff happens during daylight, your system recharges the battery while it's also covering your load. A decently sized array can fully offset daytime consumption and top the battery back up, which is why most Powerwall-plus-solar households can ride out extended outages indefinitely as long as the sun cooperates and they're managing consumption. Worth knowing what your array actually produces on an average September day rather than what the sales sheet said. A PSPS that starts at 6 p.m. and runs overnight gets none of that benefit until sunrise, so the time of day a shutoff begins matters almost as much as whether you have panels at all.

The other lever is load management, and it's the one people underestimate. An HVAC compressor cycling on a hot September PSPS day can pull roughly 3–4 kW on its own, depending on the unit and the house — it tops the list of appliances that wreck a demand peak for the same reason it drains a battery in an outage. Skip the AC, run ceiling fans instead, and you've cut your draw in half while also buying back most of your output headroom. This is exactly the kind of thing automation should handle for you rather than something you manage manually at 2 a.m. during a windstorm.

Staying Informed and Prepared

A Powerwall keeps the power on. Staying informed is a separate job, and during a PSPS, information is what buys you time to prepare instead of react.

Every California utility runs its own PSPS alert system, and you have to opt in — it's not automatic just because you're a customer. PG&E's sign-up lives in your online account or the PG&E app. SCE handles enrollment through your account preferences, and their site also publishes tier classifications if you want to check where your area falls. SDG&E runs a similar process through their customer portal. None of it takes more than a few minutes, and none of it happens until you go do it.

Beyond utility alerts, watch for National Weather Service Red Flag Warnings for your county. These often precede a PSPS notice by a day or more and give you an earlier signal than waiting for the utility itself to confirm. Keep a battery pack or two charged for phones independent of your home system, know where your circuit breaker panel is and which loads are on backup, and if anyone in the house depends on medical equipment, have a documented backup plan that doesn't solely depend on your Powerwall holding a charge for four straight days.

Where a Powerwall Fits Into Your Wildfire Plan

None of this works if the system is misconfigured going into fire season. A Powerwall set to a low reserve percentage for TOU savings, with Storm Watch off and no one watching for grid conditions, is going to underperform exactly when you need it most. The households that ride out a shutoff smoothly are the ones that sorted this in August, not during the first red flag warning of October.

Raising that reserve has a trap in it, though. Tesla silently rounds any backup reserve you set between 81% and 99% down to 80%, then reports it back as saved, so the 95% you dialed in for fire season is actually 80%. Push it to 100% and you get the opposite problem: the Powerwall force-charges from the grid, which can set an expensive peak on your bill. Grid Getter works around both, snapping those values to the 80% Tesla actually honors and holding a genuinely full battery by switching operating modes instead of pinning a number. You can also schedule a daily action to toggle Storm Watch or set your reserve, and DemandGuard's Weather Guard stops peak shaving from temporarily lowering your reserve whenever Storm Watch is active or severe weather is forecast for your area, which is frequently the same weather that puts your circuit on a shutoff list. Connecting a Powerwall and seeing what it'd do on your rate plan is free.

Automation or not, open your Tesla app right now, go to your Powerwall settings, and confirm Storm Watch is turned on. Takes about ten seconds, and it's the single setting most likely to matter the next time PG&E, SCE, or SDG&E calls a shutoff on short notice.