How Much Solar Battery Backup Do You Need in Bermuda? A Sizing Guide for Hurricane Season
If you already know you want battery backup for the next hurricane season, the next question is almost always the harder one: how much battery do you actually need? Sizing a home battery well isn't about maximum capacity, it's about matching a battery to the loads that matter most, for as long as an outage is likely to last, without paying for capacity that never gets used. Here's the same general planning approach used across the solar industry, applied to Bermuda's own outage history, so you can walk into a site assessment already asking the right questions.
Why "How Big a Battery Do I Need" Is the Right Next Question
Our earlier article, 5 Ways a Solar Battery Protects Your Home and Office, covers why battery backup matters in Bermuda: three separate storms in a recent four-month stretch left tens of thousands of BELCO customers without power, and a battery paired with Enphase Storm Guard means your system pre-charges itself ahead of a forecast storm rather than waiting for the grid to fail. That article deliberately stopped short of naming a specific backup duration or capacity, because that number depends on your home, not on a general rule.
This article picks up from there. It won't tell you exactly how many kWh your house needs either, but it will walk through how that number actually gets calculated, so the site assessment conversation makes sense before you have it.
Start With Your Essential Loads, Not Your Whole House
The most common mistake in battery sizing is starting with the size of the house instead of the size of the load. A battery backup system does not need to run everything your home normally runs. It needs to run what matters during an outage, for as long as the outage lasts.
Solar educators generally group backup loads into three tiers:
- Life-safety and essential loads: refrigerator and freezer, LED lighting, internet and router equipment, medical devices, and device charging. Combined, these typically draw somewhere in the range of 700 to 1,600 watts for an average home, and they're almost always the first priority in any backup plan.
- Comfort loads: a well pump, a sump pump, or a single mini-split unit for one or two rooms. These add roughly 1,000 to 2,500 watts on top of the essentials, and whether they're worth including depends on your specific circumstances (a well pump, for instance, is essential rather than a comfort item if it's your only water source).
- High-draw loads: central air conditioning, an electric range, a water heater, or EV charging. These are typically excluded from battery backup plans entirely, because backing them up would require a battery system sized (and priced) closer to whole-home capacity.
The point of this tiering isn't to tell you what your home needs. It's to show that "backup power" is a design decision with real tradeoffs, not a single fixed target.
A Simple Formula for a Rough Estimate
Once you know your essential load in watts and how many hours you want to cover, a formula used across the solar industry gives a rough estimate of the battery capacity required:
Battery kWh needed ≈ (critical load watts × backup hours) ÷ 1,000 ÷ efficiency factor
The efficiency factor (typically 0.8 to 0.85) accounts for inverter losses and the portion of a battery's capacity that isn't usable at 100% depth of discharge. This formula is a planning tool, not a quote. It's a useful way to sanity-check a number a site assessment gives you, and to understand roughly why a bigger battery costs what it costs, but it leaves out things a proper assessment accounts for: your home's actual measured usage, your panel and circuit layout, and whether you want partial-home or closer-to-whole-home coverage.
How Long Do Bermuda Outages Actually Last?
The "backup hours" part of that formula is where Bermuda's own outage history is more useful than a generic rule of thumb. Looking at the three storms referenced in our pillar article:
Hurricane Imelda (October 2025) left approximately 18,000 BELCO customers without power at its peak. By the following afternoon, BELCO had restored service to roughly 2,600 customers, with restoration continuing beyond that point; the utility didn't publish a single confirmed end time for full restoration, and its head office reopening the day after suggests the process ran past 24 hours for at least some customers.
Hurricane Melissa (November 2025) affected a similar number, around 19,000 customers, but the timeline looked different: by 11 p.m. the same day, roughly 17,200 of those addresses already had power back, with BELCO's managing director noting most customers were restored soon after crews began work. Five downed utility poles, each taking four to eight hours to repair, were the main reason a smaller number of customers waited longer.
18,000 and 19,000 customers. That's roughly how many BELCO customers lost power in Hurricane Imelda and Hurricane Melissa, two similarly sized 2025 outages with very different endings: Melissa saw most customers restored within about 17 hours, while Imelda's restoration was still ongoing more than a day later. Two storms of comparable size, two very different timelines, which is exactly why planning around a full day of essential-load autonomy is a more realistic baseline than picking one fixed number.
The February 2026 winter storm affected a smaller footprint of around 3,000 customers. Read together, these three events suggest most Bermuda outages resolve within a day, but a meaningful minority run longer, usually where infrastructure damage like downed poles is involved. That's consistent with why many solar educators recommend sizing a home battery for roughly one full day of essential loads as a baseline, rather than for a worst-case multi-day scenario, since a battery large enough for several days of full backup is usually a far more expensive way to cover a rare event than pairing a one-day battery with solar recharge and, where needed, a generator.
One Battery or Several? What Modular Sizing Looks Like
Modern battery systems, including the Enphase batteries used in AES installations, are modular: each unit is a fixed building block, and a system is built by combining however many units the load and budget call for, rather than being custom-manufactured to an exact size. A system built around this kind of unit is sized in whole-battery increments: one unit, two, three, and so on, based on the load calculation above and how many hours of autonomy you're planning for.
5.0 kWh of usable capacity per unit. That's what a single Enphase IQ Battery 5P provides (3.84 kW continuous output, NEMA 3R rated for outdoor installation). Because systems like this are built in whole-unit increments, your final system size becomes a question of how many building blocks your essential loads and budget call for, not a one-off custom build, and it's often expandable later if your needs change.
This is a useful thing to understand going into a site assessment, because it reframes the question from "what's the perfect number" to "how many of these building blocks make sense for my essential loads and my budget."
Common Myths and Mistakes in Battery Sizing
- "Bigger is always better." A larger battery costs more, and if it's sized well beyond your actual essential-load needs, that extra capacity may sit unused for years between storms. Right-sizing to your real loads, with a sensible autonomy target, is usually a better use of budget than maximizing capacity.
- "I need to back up my whole house." Very few Bermuda homes need whole-home backup to get through a typical outage safely and comfortably. Prioritizing essential and comfort loads, rather than everything on the panel, is how most well-designed systems keep both cost and complexity reasonable.
- "Solar will recharge the battery instantly during a storm." Solar recharge depends on daylight and weather. During and immediately after a hurricane, cloud cover and rain limit how much a solar array can contribute, which is exactly why Storm Guard pre-charges the battery from the grid ahead of a forecast storm rather than relying on same-day solar production.
- "The formula above is my actual number." It's a planning estimate using rough, general appliance wattages. Actual appliance draw varies by model and age, and a proper assessment measures your real usage rather than assuming averages.
What Actually Determines Your Number
A site assessment looks at several things a general formula can't: your home's actual historical electricity usage (typically pulled from BELCO billing history rather than estimated), which circuits you want backed up and how your electrical panel is laid out, whether you want partial-home or closer-to-whole-home coverage, and your budget, since battery capacity and system cost scale together. AES sizes each system against this real information during a site visit, rather than quoting a number from a formula alone.
Battery sizing starts with identifying essential loads, not the size of your house. A general industry formula, paired with your own home's numbers, gives a useful planning estimate, and Bermuda's own outage history suggests roughly one day of essential-load autonomy is a reasonable baseline for most homes, with the option to size larger. Modular battery units mean a system is built in whole-unit increments matched to that estimate. The real number for your home comes from a site assessment that accounts for your actual usage, panel layout, and budget, not from a formula alone.
Frequently Asked Questions
How many kWh of battery backup does a typical Bermuda home need?
There's no single answer that applies to every home, but general industry reference ranges put a small home's essential-load backup at roughly 10-14 kWh, a medium home at 13-27 kWh, and a large home or closer-to-whole-home backup at 27 kWh or more. Your actual number depends on your specific loads and usage, which is why AES sizes each system during a site assessment rather than quoting a fixed figure.
What's the difference between "essential load" backup and whole-home backup?
Essential load backup covers a defined set of priority circuits, typically refrigeration, lighting, internet, and similar smaller loads, sized to run efficiently on a smaller battery. Whole-home backup aims to keep everything running, including high-draw items like central air conditioning, which requires a substantially larger and more expensive system.
How long do Bermuda power outages usually last?
Based on the three most recent major events, most Bermuda outages resolve within about a day, though a minority of cases run longer where infrastructure damage such as downed utility poles is involved. This is one reason many homeowners plan around roughly one day of battery autonomy as a starting point.
Can I just add more batteries later if I start small?
Modern modular battery systems, including Enphase batteries, are generally designed to be expandable, since each unit is a discrete building block rather than a custom-built size. Whether expansion is straightforward for your specific system depends on your original installation, so it's worth raising during your initial site assessment if you're considering starting smaller.
Does a bigger battery mean a bigger solar array?
Not necessarily. A battery stores energy regardless of how it was generated, whether from your solar array or, when needed, from the grid ahead of a storm via Storm Guard. That said, a larger battery generally recharges faster and more fully with a larger solar array, which is one of several factors an assessment considers together.
Will my battery recharge during the storm itself?
Solar recharge during an active storm is limited by cloud cover and rain, so it isn't something to rely on for immediate backup. This is exactly why pre-storm charging features like Enphase Storm Guard exist: the battery charges to full from the grid before the storm arrives, based on the forecast, rather than depending on solar production during the event.
What appliances should I prioritize if I can't back up everything?
Refrigeration, lighting, internet and communications equipment, and any medical devices are the most commonly prioritized loads, since these directly affect safety and comfort during an outage. A well pump is often added to this list for homes where it's the primary water source. High-draw items like central air conditioning and electric water heaters are typically left off a backup circuit list because of the battery capacity they'd require.
Is the sizing formula in this article exactly what AES uses?
The formula and appliance wattage ranges here reflect general approaches used across the solar industry, presented so you understand the logic behind sizing before a conversation with AES. Your actual system is sized against your real, measured usage and home configuration during a site assessment, not from a generic formula alone.
How much does a properly sized battery backup system cost in Bermuda?
Cost depends on how many battery units your load calculation and autonomy target require, along with your existing solar setup and any incentives you may qualify for. Our Cost & ROI article and our incentives and rebates guide cover the broader cost and rebate picture; a site assessment is the way to get a specific number for a system sized to your home.
What's the first step if I want to figure out my own number?
Start by listing your essential loads and roughly how many hours you'd want to cover, using the tiers and formula in this article as a starting point. From there, an AES site assessment turns that rough estimate into an actual sized recommendation based on your real usage and panel layout.