It’s a familiar Scottish scene.
The wind picks up. Rain lashes the windows. The lights flicker once… then everything goes quiet.
Across the street, houses go dark.
But inside your home? The fridge is still running. The Wi-Fi hasn’t dropped. The heating controls are live. You barely notice the outage.
That’s what properly installed battery storage does. It doesn’t just store electricity. It protects your home. It keeps life moving when the grid stops.
At The Edinburgh Boiler Company, we’re seeing more homeowners ask the same question:
“How long will a Tesla Powerwall actually run my house during a power cut?”
Let’s break it down clearly — without the fluff.
Tesla Powerwall Backup Time in Scotland
For the average Scottish household:
Around 34 hours and 30 minutes of whole-home backup.
Here’s how that works:
- Average Scottish electricity use: 3,429 kWh per year
- Roughly 9.4 kWh per day
- Tesla Powerwall 3 usable capacity: 13.5 kWh
Calculation:
(13.5 ÷ 9.4) × 24 = 34.49 hours
So just under a day and a half powering everything as normal.
But here’s the important bit — that’s if you power the whole house.
If you prioritise essential circuits only, you can stretch that to two days or more.
- Energy stored determines duration.
- Load demand determines runtime.
- Smart configuration maximises backup.
Whole-Home Backup vs Essential Loads: What We Recommend
When we install battery storage systems at The Edinburgh Boiler Company, we discuss two setup options.
Whole-Home Backup
Everything stays live.
Simple and seamless — but drains faster.
Essential Circuits Backup
Only priority circuits are protected:
- Fridge/freezer
- Broadband router
- Boiler & heating controls
- Lighting
- Selected sockets
If you reduce daily usage from 9.4 kWh to around 4–5 kWh during an outage, your Powerwall can last well over 60 hours.
The less electricity you’re using during a power cut, the longer your battery will last. Cutting back to just what you genuinely need can add many extra hours — sometimes even an extra day — of backup time.
Focusing on essential circuits like your fridge, broadband and heating controls makes your home far more resilient. You’re protecting the things that matter most, rather than trying to power everything at once.
And the way the system is wired makes a real difference too. By separating essential loads from the rest of the house, a properly designed setup can stretch your backup time significantly and keep your home running smoothly when the grid goes down.
We design systems around how your home actually runs — not generic averages.
What Drains a Powerwall Fast?
Here’s a realistic look at common appliances and how long one fully charged Powerwall (13.5 kWh) would run them individually.
| Appliance | Typical Wattage | kWh Per Hour | How Long 13.5 kWh Would Last |
| Air source heat pump | 3,500 W | 3.5 kWh | 3 hrs 51 mins |
| TV | 100 W | 0.1 kWh | 5 days 15 hrs |
| Refrigerator (average draw) | 167 W | 0.167 kWh | 3 days 9 hrs |
| LED lightbulbs (5) | 50 W | 0.05 kWh | 11 days 6 hrs |
| Phone charger | 5 W | 0.005 kWh | 112 days 12 hrs |
Heating systems are the biggest factor.
If you run a heat pump constantly, you’ll flatten a battery in hours. If your heating is gas-based and only uses electricity for controls, your runtime increases dramatically.
If your home uses electric heating, such as panel heaters your battery will drain much faster during a power cut. Heating simply demands a lot of power.
On the other hand, if you have a gas boiler and only need electricity for the controls and circulation pump, your battery will last significantly longer. With lower electrical demand, your backup time stretches much further.
Tesla Powerwall 2 vs Powerwall 3: What’s the Difference?
Both the Tesla Powerwall 2 and Powerwall 3 store 13.5 kWh of usable energy.
The key difference is output power:
- Powerwall 2: ~5 kW continuous output
- Powerwall 3: Up to 11.5 kW continuous output
That higher output in the Powerwall 3 means you can run more appliances simultaneously without tripping limits.
- Storage capacity determines how long it lasts.
- Output rating determines what runs together.
- Installation design determines performance.
We assess your peak load before installation to ensure your system is correctly sized.
Adding Solar Panels: Extending Your Backup Time
When you combine battery storage with solar panels, everything changes.
During daylight hours:
- Solar panels power your home
- Excess electricity charges the battery
- The battery supplies power overnight
In summer, many homes can operate almost independently from the grid. Even in winter, solar can top up your battery and extend outage runtime significantly.
When your solar panels are generating electricity, they don’t just power what you’re using in the moment — they also top your battery back up. That means the energy you collect during the day is stored and ready to use later.
Even a few decent daylight hours can make a real difference during an outage. Every bit of solar production helps extend how long your home can stay up and running.
Put the two together — solar panels and battery storage — and you’re far less dependent on the grid. You’re producing, storing and using more of your own energy, which gives you greater control and far more peace of mind.
At The Edinburgh Boiler Company, we install complete solar and battery storage systems — designed specifically for Scottish weather conditions and grid infrastructure.
How to Calculate Your Own Powerwall Runtime
Here’s the simple method we use during consultations:
- Find your daily usage (kWh) from your electricity bill
- Divide 13.5 by that number
- Multiply by 24
Example:
If you use 7 kWh per day:
13.5 ÷ 7 = 1.93 days
1.93 × 24 = 46 hours
For essential-only backup, total just those appliance loads and calculate using:
Energy (kWh) = Power (kW) × Hours
We handle these calculations for you during a home survey to ensure your system is properly sized.
Is One Powerwall Enough?
For most Scottish homes:
- One Powerwall = 1–2 days backup
- Two Powerwalls = 2–4 days
- Larger systems = long-duration resilience
Homes with electric heating, EV chargers or high daytime demand may benefit from additional storage.
The more battery capacity you have, the more resilient your home becomes. It’s not just about having power — it’s about how long you can keep things running without compromise.
Ultimately, the right system size depends on how you actually use energy day to day. A small flat and a busy family home have very different demands, so the setup should reflect that.
And just as important as the battery itself is the quality of the installation. When it’s designed and fitted properly, everything works seamlessly and reliably when you need it most.
Battery Storage Installation in Edinburgh & Across Scotland
If you’re considering battery storage installation in Edinburgh, the Lothians or across Scotland, we provide:
- Full home energy assessments
- Essential load circuit design
- Tesla Powerwall installation
- Solar + battery integration
- MCS-compliant installation
- Ongoing support and servicing
At The Edinburgh Boiler Company, we don’t just install batteries. We design systems around how your home actually uses energy — so when the next winter storm hits, you’re protected.
Because backup power isn’t just about savings.
It’s about staying warm.
It’s about staying connected.
It’s about knowing your home keeps running — even when the grid doesn’t.
If you’d like a tailored battery storage quote, we’re happy to run the numbers for your property and show you exactly how long your home would stay powered.
Frequently Asked Questions
Does a Tesla Powerwall automatically turn on during a power cut?
Yes. When professionally installed with backup capability, a Tesla Powerwall automatically detects a grid outage and switches your home to battery power in a fraction of a second.
Most homeowners don’t even notice the transition. The system isolates your property from the grid for safety and continues powering connected circuits.
Can a Tesla Powerwall power an electric shower?
In most cases, no — not for extended periods. Electric showers typically draw 8–10 kW while running. Although the Tesla Powerwall 3 can technically handle high short bursts, running a shower would drain the battery very quickly. For backup resilience, we usually recommend prioritising essential circuits instead.
How Many Panels Does It Take to Refill a Battery Like That?
Runtime is only useful if you can recharge the battery the next day. See how many solar panels to charge a 300Ah battery.
Will my solar panels work during a power cut without a battery?
No. Standard grid-tied solar systems shut down during a power cut for safety reasons. Without battery storage, your panels will not power your home during an outage.
Adding a battery with backup functionality allows solar generation to continue charging the battery and supplying your home when the grid is down.
