Free tool · Tesla Powershare · November 2026

How long can your Tesla power your Texas home?

Pick your home and your equipment. You get an estimate of how many days and hours Powerwall 3 and your Tesla can carry the house in an outage on a normal Texas day. In a heat wave or a hard freeze your home uses more, so backup will be shorter. Every number we use is listed under “How we estimate this”.

+ Add appliances and AC units

The calculator already counts a typical home: fridge, lights, electronics, cooking basics and one central AC. Add anything big on top of that. Pick it, hit Add, and repeat as often as you need. Remove an item with the ×.

    What to back up iSlide to match how you would live during an outage. The less you run, the longer your backup lasts. Anywhere in between works too, and the numbers update as you slide.

    Bare minimum: fridge and freezer, lights, internet, phone chargers, fans and the gas furnace fan. The AC, oven, dryer, pool pump and other big loads stay off. That is roughly a third of a normal day without the AC.

    Energy smart: the whole house stays backed up and the AC stays on, but you set it a few degrees higher (say 78°F instead of 74°F), run big appliances one at a time and run the pool pump and hot tub about half as much. That is roughly three quarters of a normal day.

    Normal use: life as usual. AC at your normal setting and everything on whenever you want.
    Bare minimumEnergy smartNormal use

    + Use your real usage data (optional, most accurate)

    Have your utility data? Upload it or type in a monthly number for an answer based on your actual home. iWhat we need: your electricity use for the last 12 months, in 15-minute or hourly steps.
    Most of Texas (Oncor, CenterPoint, AEP, TNMP areas): log in at smartmetertexas.com, pick “Energy Data 15 Min Interval”, set the last 12 months and click “Export My Report”.
    Austin Energy, CPS Energy and co-ops: look for “Download my data” or “Green Button” in your online account. CSV or XML both work.
    Privacy: the file is read in your browser and never sent to us.

    Smart Meter Texas or Green Button file. It stays on your device.
    Use a normal month like spring or fall, not a summer peak. This replaces the home size, AC and appliance guesses.

    Equipment

    Solar (optional)

    Sky during the outage

    Estimated backup

    Calculating…

    This is an estimate for a normal day. Real backup time depends on your actual usage: how much the AC runs, whether you have electric heat strips, how energy efficient your home is, and what else is on.

    Powerwall 3
    Car via Powershare

      Get a real plan for your home: send 3 photos

      Quotes from photos, usually the same day. No site visit needed.

      What about heat waves and freezes? These numbers are for a normal Texas day. In a 100°F+ heat wave the AC can run three to four times as long, so backup can be less than half of what you see above. In a hard freeze, electric heat strips can drain it even faster, while a gas furnace barely changes it. See Powershare backup in summer vs winter.
      How we estimate this

      Backup time = energy available ÷ daily use. We keep the model simple on purpose, so you can check every step.

      Daily use

      • Everything but heating and cooling: 10 kWh plus 0.004 kWh per sq ft a day (18.8 kWh for 2,200 sq ft). Energy smart uses 75% of that, Bare minimum 35%.
      • Check: the average Texas home uses about 1,110 kWh a month, roughly 37 kWh a day (EIA, via BKV Energy). Our default home (2,200 sq ft, 3.5-ton AC) on a normal day lands near 29 kWh a day, close to the 30 kWh a day Tesla uses for its own Powershare estimates.
      • Air conditioning on a normal day: 1.0 kW per ton for about 3 full hours a day.
      • Heat waves and freezes: not modeled here. In a heat wave the AC runs much longer, and electric heat can use several times more power in a hard freeze, so backup is shorter. See Powershare backup in summer vs winter.
      • Your bill: monthly kWh ÷ 30. Energy smart uses 75% of that. Bare minimum still uses our model, since it turns most things off.
      • Extras per day (whole home): single-speed pool pump 12.6 kWh, variable-speed 2.2 kWh (NREL); electric water heater 12 kWh (4,000 W for about 3 hours, EnergyBot); hot tub 6 kWh (Jacuzzi real-world median); electric dryer 2.2 kWh, one load a day (DOE test load); electric range and oven 1.5 kWh (3,000 W for about 30 minutes a day); dishwasher 0.8 kWh; aerobic septic system about 2 kWh; medical equipment 7.2 kWh (an oxygen concentrator at about 300 W around the clock). Well pump 1.5 kWh (about an hour a day); second fridge or freezer 1.5 kWh (ENERGY STAR ranges). The dishwasher, septic and medical numbers are typical ratings, not measured data. Septic, medical equipment, the well pump and fridges stay on even on Bare minimum. For the peak check we add the extras’ power: all of them for Normal use, only the biggest for Energy smart and Bare minimum.
      • Energy smart: AC at 70% (thermostat a few degrees easier). Bare minimum: AC off.

      Energy available

      • Powerwall 3: 13.5 kWh each, 11.5 kW continuous, 185 A motor-start rating (Tesla datasheet). We assume it is full when the outage starts.
      • Car: usable pack (start % minus the % it keeps), minus 10% for conversion losses. Car output is 11.52 kW at 240 V.
      • Usable pack sizes we use (estimates; Tesla does not publish usable capacity and it varies by build): Model 3 Standard 60, Long Range 75, Performance 79 kWh. Model Y Standard 69.5, Long Range/Premium 79, Performance 79 kWh. Cybertruck 120 kWh for every trim (its battery label shows 123 kWh total).
      • Solar: kW × 5 sun hours a day, cut to 25% on cloudy days. Counted only with Powerwall 3.

      What we leave out

      • EV charging and big loads that aren’t on the extras list, like a shop or a second AC system. If you have them, your number will be lower.
      • Battery aging, a very cold car battery and how your home is actually insulated. This is an estimate, not a guarantee.

      Sources

      Powershare backup questions

      How many days can a Tesla power a house in Texas?

      It depends mostly on how much you run the AC. On a normal Texas day our model puts a 2,200 sq ft home at about 29 kWh a day. Two Powerwall 3 plus a Model Y Long Range (starting at 90%, keeping 20%) last about 2 days 15 hours on Normal use, about 3 days 14 hours on Energy smart and about 11 days on Bare minimum. With one Powerwall 3 and the same car, it lasts about 2 days 4 hours on Normal use. In a heat wave or a hard freeze your home uses more, so backup is shorter.

      Do I need Powerwall 3 for Powershare?

      Eligible Model 3 and Model Y (ordered in the US after Oct 1, 2026) need Powerwall 3. They can’t use the Powershare Gateway. Cybertruck can work with a Powershare Gateway and a Universal Wall Connector, which usually backs up part of the home (the essential loads), or with Powerwall 3 for whole-home backup. If you already have a Powershare Gateway, it gets swapped for a Gateway 3 when Powerwall 3 goes in.

      What about a heat wave or a freeze?

      This calculator uses a normal day. In a heat wave the AC runs much longer, and if you heat with electric heat strips, a hard freeze can use several times more power than a normal day. Either way backup is shorter, so outage settings and smart use matter more. We cover both in Powershare backup in summer vs winter.

      How much of my car’s battery does Powershare use?

      You choose. You set a limit on how much of the car’s battery Powershare can use, so you keep enough charge to drive. This calculator assumes the car keeps 20% unless you change it.

      Does solar extend Powershare backup?

      Yes. With Powerwall 3, solar recharges the batteries during the day. In our model an 8 kW system makes about 40 kWh on a sunny day, more than the home uses on a normal day, so two Powerwall 3 batteries can keep going as long as the sun keeps coming out. Solar isn’t required for Powershare.