Does Solar Work When the Power Goes Out? Why Panels Shut Off and What a Battery Changes

It’s the most common surprise for new solar owners in San Diego: the grid goes down on a sunny afternoon, and the house goes dark anyway. Here is why that happens, and what has to be added for solar to keep your home running.

https://www.youtube.com/watch?v=HnQt502CGRA

Key takeaways

• A grid-tied solar system without a battery shuts off during an outage, even on a sunny day. It’s designed and required to, to protect line crews.
• Under IEEE 1547, a grid-tied system has to stop energizing the grid within two seconds of an outage. This is called anti-islanding.
• A battery with a backup switch isolates your home from the grid, so the solar can keep running and recharging the battery.
• A Powerwall 3 stores 13.5 kWh, delivers up to 11.5 kW continuously and accepts up to 20 kW of panels through its built-in solar inverter.
• A battery can usually be added to existing solar, and on normal days it covers SDG&E’s expensive 4 to 9 p.m. hours.

Frequently asked questions

Do solar panels work during a power outage?

Not on their own. A standard grid-tied system shuts down when the grid does. A system with a battery and a backup switch keeps powering the home, and it can keep doing it for days as long as the sun recharges the battery.

Why does my solar shut off when the power goes out?

It’s a safety requirement called anti-islanding. Utility crews expect de-energized lines, so the IEEE 1547 standard requires a grid-tied system to stop energizing the grid within two seconds of an outage, and inverters are tested and certified to that behavior under UL 1741.

Can I add a battery to my existing solar system?

Usually, yes. The design depends on your current inverter and electrical panel, so that’s the first thing an installer should look at.

Will solar recharge my battery during an outage?

Yes, with a battery like the Powerwall 3, which has a built-in solar inverter. Once the backup switch isolates your home, the panels power the house and refill the battery during the day. Tesla says that if the battery runs down below about 10 percent, it goes into standby and tries to restart from solar each hour during the day.

Should I choose whole-home or partial backup?

Whole-home backup keeps every circuit on the battery and is the most seamless. Partial backup moves essential circuits to a backup panel, so the battery lasts longer. The right choice depends on how long outages run in your area and what you can’t do without.

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The panels are on the roof. The sun is out. SDG&E has a Public Safety Power Shutoff in effect, or a transformer blew down the street. And your home, with its solar system producing at full output, has no power.

Nothing is broken. That’s how a standard grid-tied solar system is designed to behave, and it’s required to.

The short answer

A typical solar system without a battery does not power your home during an outage. A solar system with a battery and a backup switch does, and it can keep doing it for days as long as the sun keeps recharging the battery. That pairing is what people mean by solar battery backup, or blackout protection, in San Diego.

Why grid-tied solar shuts off

Most San Diego solar systems are grid-tied: the panels feed an inverter, the inverter feeds your home, and anything extra flows out to SDG&E’s lines. When the grid goes down, that last part becomes a hazard. Utility crews working to restore power expect de-energized lines. A solar system pushing electricity back onto those lines could injure them.

So the industry standards that govern inverters require them to detect an outage and stop exporting quickly. Under IEEE 1547, a grid-tied system has to cease energizing the grid within two seconds of an outage. Inverters are tested and certified to that behavior under UL 1741. This protection is called anti-islanding, and it’s the reason your panels go quiet the moment the grid does, no matter how sunny it is.

What a battery adds

A battery fixes the problem by changing what the system is connected to. With a Tesla Powerwall 3, a Backup Switch installed at the meter disconnects your home from SDG&E’s lines automatically when the grid fails. Once your home is physically isolated, there’s no risk to line crews, and your solar system is allowed to keep running inside that small, self-contained “island.”

From there, the pieces work together:

• The battery runs the house. Each Powerwall 3 stores 13.5 kWh and delivers up to 11.5 kW continuously.
• The panels recharge the battery. The Powerwall 3 has a built-in solar inverter that accepts up to 20 kW of panels, according to Tesla’s datasheet, so daytime production goes into the battery and your home.
• The system manages itself. Tesla says that when the battery is nearly full during an outage, the Powerwall tells the solar inverter to throttle back or shut off, since there’s nowhere for extra power to go. If the battery runs down below about 10 percent, it goes into standby and tries to restart from solar each hour during the day.

The U.S. Department of Energy puts it simply: for solar to keep running in an outage, it needs a properly configured inverter and a storage system. Its solar and resilience basics page explains the concept.

Whole-home backup or partial backup

When you add a battery, you also decide what it powers:

• Whole-home backup keeps every circuit on the battery. It’s the most seamless option, and Tesla says a Powerwall 3 system can provide whole-home backup to most homes. Large loads like central air, pool pumps and EV charging will drain the battery faster.
• Partial backup moves essential circuits (refrigerator, lights, internet, medical devices, a few outlets) to a backup panel. The battery lasts longer because it isn’t feeding everything.

Neither is better in general. The right answer depends on how long outages run in your area and what you can’t do without.

What about the solar you already have?

If you have solar and no battery, you’re not starting over. A battery can usually be added to an existing system, but the design depends on your current inverter and electrical panel, so that’s the first thing an installer should look at. Under SDG&E’s current solar billing rules, a battery also earns its keep on normal days by covering the expensive 4 to 9 p.m. hours, so the added backup comes with bill savings attached.

What a multi-day shutoff looks like with solar and a battery

Here is how a well-designed system behaves through a two-day Public Safety Power Shutoff:

1. Before: Tesla’s Storm Watch sees the red flag warning and charges the battery to full.
2. Shutoff begins: the Backup Switch disconnects the home and the battery takes over automatically.
3. First evening and night: the battery runs the house.
4. Next day: the panels power the home and refill the battery.
5. Restoration: when SDG&E re-energizes the line, the system reconnects to the grid automatically.

SDG&E says shutoffs can last from several hours to multiple days, which is why the daytime recharge matters as much as the battery itself.

Make your solar work when you need it most

If your panels go dark when the grid does, a battery is the missing piece. Stellar Solar can look at your existing system, or design a new one, so your home keeps running through the next outage. Stellar Solar has been San Diego’s trusted solar installer since 1998, A+ rated with the BBB and a repeat winner of San Diego’s Best Solar in the Union-Tribune Readers Poll. Call 866.787.6527 for a free evaluation, or get your free quote here.

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Keeping a CPAP and Other Medical Devices Running When SDG&E Shuts Off Power

If someone in your home depends on a CPAP, an oxygen concentrator or another powered device, a Public Safety Power Shutoff is more than an inconvenience. Here is how SDG&E’s notifications work, how much power common devices actually use, and how to keep them running for a night or for days.

https://www.youtube.com/watch?v=_OrLRiMkaHY

Key takeaways

• SDG&E’s Medical Baseline program may bring extra outreach during a shutoff, including in-person contact attempts. Notification is not backup power.
• A ResMed AirSense 11 CPAP draws about 56 watts, roughly 0.45 to 0.6 kWh over an eight-hour night.
• Oxygen concentrators are a different scale. A Philips EverFlo averages about 350 watts, or roughly 8.4 kWh a day.
• A portable power station can often cover a CPAP for a night or two. A home battery with solar covers the household and recharges every sunny day.
• Put the device on a backed-up circuit, test it before fire season, and ask your doctor and supplier what the device needs.

Frequently asked questions

How long will a CPAP run on a battery during a power outage?

It depends on the battery’s capacity. An AirSense 11 uses roughly 0.45 to 0.6 kWh over an eight-hour night, and most of that goes to heated humidification, so a portable power station can often cover a night or two, especially with the humidifier off if your doctor says that’s acceptable. Compare the station’s watt-hours to your device’s nightly use and leave a margin.

Does SDG&E notify Medical Baseline customers before a power shutoff?

SDG&E says Medical Baseline customers may receive additional support during a PSPS, including in-person contact attempts, on top of the calls, texts and emails every affected customer gets. Enrollment is what triggers the extra outreach, so apply before fire season.

Does SDG&E guarantee power for medical devices?

No. SDG&E’s Medical Baseline materials say the utility cannot guarantee uninterrupted service and that customers on life support should arrange a backup power supply.

Can a home battery run an oxygen concentrator?

Yes, with the right sizing. A home concentrator like the Philips EverFlo averages about 350 watts and often runs around the clock, roughly 8.4 kWh a day. A Tesla Powerwall 3 stores 13.5 kWh, and solar recharging during the day is what makes a multi-day shutoff manageable.

Does SDG&E help pay for backup power for medical devices?

The 2026 Generator Assistance Program offers a $150 rebate toward a portable power station ($200 for CARE and FERA customers) to customers in High Fire Threat District Tier 2 or Tier 3 areas who have experienced a PSPS. SDG&E’s Generator Grant Program also offers a short resiliency assessment by phone for Medical Baseline customers and customers with access and functional needs in those areas who have experienced a PSPS since 2019.

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For most households, a shutoff means warm drinks and a dark living room. For a household with a CPAP machine, an oxygen concentrator, a powered bed or a medication refrigerator, it means planning. The good news is that a Public Safety Power Shutoff is usually announced ahead of time, and the power these devices need is often smaller than people expect.

This article covers the power side of the plan. Talk to your doctor and your equipment supplier about the medical side, including what your device needs and how long it can safely go without power.

How SDG&E notifies Medical Baseline customers

SDG&E’s Medical Baseline program is best known for its billing benefit: extra gas and electricity at the lowest baseline rate, or a discount on untiered time-of-use plans, for households where someone has a qualifying medical need. It’s the program most people mean when they search for an “SDG&E CPAP discount” or a “medical device discount.” It also matters during shutoffs. SDG&E says Medical Baseline customers may receive additional support during a PSPS, including in-person contact attempts, on top of the calls, texts and emails every affected customer gets.

Two things are worth knowing:

• Enrollment is what triggers the extra outreach. If someone in your home uses a powered medical device and you’re not enrolled, apply now rather than at the start of fire season. We explain how the allowance works in our guide to the SDG&E Medical Baseline Allowance.
• Notification is not backup power. SDG&E’s own Medical Baseline materials say the utility cannot guarantee uninterrupted service and that customers on life support should arrange a backup power supply.

How much power a CPAP actually uses

Less than most people think. ResMed’s user guide for the AirSense 11 lists a typical power draw of about 56 watts, with a peak around 73 watts. Over an eight-hour night, that works out to roughly 0.45 to 0.6 kWh.

Most of that comes from the heated humidifier and heated tubing. ResMed’s figures for the earlier AirSense 10 show the machine alone using a small fraction of what it uses with humidification turned on. That’s useful during an outage: if your doctor says it’s acceptable to run without heated humidification for a night or two, your battery or power station will last much longer.

Oxygen concentrators are a different scale

A home oxygen concentrator draws far more than a CPAP and often runs around the clock. Philips lists its EverFlo home concentrator at about 350 watts on average. Run for 24 hours, that’s roughly 8.4 kWh a day, roughly 14 to 19 times what a CPAP uses in a night. Some newer concentrators use less, but the scale is the point. It needs to be in the plan from the start, not added at the last minute.

Option 1: a portable power station

A portable power station is a large rechargeable battery with outlets. For a CPAP, it’s often enough to cover a night or two, especially with the humidifier off.

• Check the capacity. Compare the station’s watt-hours to your device’s nightly use, and leave a margin.
• Check how it recharges. Once it’s empty, it needs a working outlet, a car, or a solar panel.
• Check whether SDG&E helps pay. The 2026 Generator Assistance Program offers a $150 rebate toward a portable power station ($200 for CARE and FERA customers) for customers in High Fire Threat District Tier 2 or Tier 3 areas who have experienced a PSPS.

SDG&E also runs a Generator Grant Program for Medical Baseline customers and customers with access and functional needs in those same areas who have experienced a PSPS since 2019. It offers a short resiliency assessment by phone and information on resources you may be eligible for.

Option 2: a home battery with solar

A power station covers one device. A home battery covers the household. During a shutoff, a Tesla Powerwall 3 disconnects your home from the grid automatically, stores 13.5 kWh and delivers up to 11.5 kW continuously. With solar panels, it recharges during the day, which is what makes a multi-day shutoff manageable for a home running an oxygen concentrator around the clock.

A few setup details make the difference:

• Put the device on a backed-up circuit. If your system uses partial backup, make sure the bedroom outlet for the CPAP or concentrator is on the backup panel. Label it.
• Turn on Storm Watch. Once enabled in the Tesla app, Tesla’s Storm Watch charges the battery to full when alerts such as red flag or high wind warnings are issued for your area.
• Test it. Before fire season, flip the main breaker or run a test with your installer and confirm the device keeps running.

A plan for the next shutoff watch

1. Enroll in Medical Baseline if you qualify, and confirm SDG&E has your current phone numbers.
2. Ask your doctor or equipment supplier how long your device can go without power and what backup they recommend.
3. Know your device’s wattage and estimate its daily energy use.
4. Pick a backup that covers at least the longest shutoff your area has seen, with room to spare.
5. When the watch notice arrives, charge everything to full.

Build backup around the device that matters most

If someone in your home depends on powered medical equipment, Stellar Solar can design solar and battery backup around that device first and the rest of the house second. Stellar Solar has been San Diego’s trusted solar installer since 1998, A+ rated with the BBB and a repeat winner of San Diego’s Best Solar in the Union-Tribune Readers Poll. Call 866.787.6527 for a free evaluation, or get your free quote here.

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