How do I calculate what size solar battery system I need?

List every device you plan to power, find its wattage, estimate how many hours per day you will use it, and multiply to get watt-hours per day. Add 15 to 20 percent for conversion losses. That total is your daily energy budget. Choose a power station with at least that much usable capacity, and a solar panel that can refill it during one day of good sun. A typical household running phones, lights, a fan, a laptop, and a small refrigerator needs roughly 500 to 1,500 watt-hours per day.

What size solar panel do I need for a 1000 watt-hour power station?

A 200 watt panel is the sweet spot for a 1,000 watt-hour station. In good sun, it produces roughly 150 to 180 watts of real-world output, which refills the station in about 6 to 8 hours of productive sun. A 100 watt panel works but takes a full day or more of good sun to refill the same station. Check that the panel's wattage and voltage are within your station's solar input specifications.

Can a solar battery system run a refrigerator during a power outage?

Yes. A small energy-efficient refrigerator or mini-fridge draws roughly 50 to 100 watts when the compressor runs, which cycles on and off throughout the day. A typical mini-fridge uses about 300 to 600 watt-hours per day. A 1,000 watt-hour power station with a 200 watt solar panel can sustain this load indefinitely in sunny conditions, recharging during the day what the fridge uses over 24 hours. A full-size refrigerator uses 1,000 to 2,000 watt-hours per day and requires a larger system.

How long will a solar battery system last during cloudy weather?

In sustained heavy overcast, a solar panel produces only 10 to 25 percent of its rated output. A 200 watt panel might deliver 20 to 50 watts, collecting 80 to 300 watt-hours over a day instead of the 700 to 1,000 watt-hours possible in full sun. The system runs from stored energy, and the station drains faster than the panel can refill it. Reduce loads to essentials, stretch what is stored, and catch up when the sun returns. Two to three cloudy days in a row is the stress test for any portable solar system.

What is the difference between a portable solar battery system and a whole-home battery?

A portable system uses a foldable solar panel and a portable power station. It powers individual devices plugged directly into it, stores 500 to 3,000 watt-hours, and can be set up by anyone in minutes. A whole-home battery system, like a Tesla Powerwall or Enphase IQ, is permanently installed, wired into the house electrical panel, stores 10,000 to 40,000 watt-hours, and powers the home's circuits automatically during an outage. The portable system is cheaper and requires no installation. The whole-home system is seamless but costs $10,000 to $20,000 installed.

Should I buy two smaller power stations or one large one?

Two smaller stations give you redundancy, portability, and the ability to power two locations at once. If one fails, the other still works. One large station simplifies the setup, runs higher-wattage devices that smaller stations cannot handle, and avoids the complexity of managing two batteries. For most households, a single station in the 1,000 to 2,000 watt-hour range with one 200 watt panel is the simplest and most effective starting point.

Solar Battery Systems: How to Size and Pair Panels with Power Stations

THE RELATIONSHIP BETWEEN PANEL AND STATION

The panel is the generator. The station is the tank.

A solar battery system has two jobs. During the day, the panel collects energy from sunlight and fills the station. Day and night, the station delivers stored energy to your devices. The system works when the panel can refill the station faster than the station drains. It fails when it cannot.

Every decision in system sizing flows from one question: how much energy do I use in 24 hours, and can the panel replace that amount during the productive solar window?

The solar panel

Converts sunlight to electricity. Works 4 to 6 productive hours per day. Rated in watts.

The energy flow

Panel fills station during daylight. Station powers devices day and night. The cycle repeats.

The power station

Stores energy for use anytime. Delivers USB, DC, and AC power. Rated in watt-hours.

THE SIZING METHOD

Build your energy budget in four steps.

This is the process that decides everything else. Do it before you shop. The numbers are simple arithmetic, and getting them right means the system you buy actually works.

1

List every device you will power

Write down each device, its wattage (check the label or the manual), and how many hours per day you will run it. Multiply watts by hours to get watt-hours per device per day.

2

Add them up

Sum the watt-hours for all devices. This is your raw daily energy need. A typical emergency load (phones, lights, laptop, fan, mini-fridge) runs 500 to 1,500 watt-hours per day.

3

Add 20 percent for losses

Energy is lost to inverter conversion (DC to AC), cable resistance, heat, and charging inefficiency. A 20 percent safety margin covers these losses and gives you headroom for devices you forgot to count. Multiply your raw total by 1.2.

4

Size the station and panel

The station's usable capacity should equal or exceed your adjusted daily total. The panel's daily energy harvest should match it.

Panel harvest formula: Panel real-world wattage (about 75% of rated) multiplied by productive sun hours (4 to 6 in most locations). A 200W panel producing 150W in real sun for 5 hours collects 750 watt-hours. That covers a 600 watt-hour daily budget with margin.

COMMON DEVICE WATTAGES FOR REFERENCE

Device	Watts (typical)	Hours/day	Wh/day
Smartphone charging	10 to 15W	2	20 to 30
LED light (per bulb)	5 to 15W	6	30 to 90
Laptop	30 to 65W	4	120 to 260
USB fan	5 to 10W	8	40 to 80
Mini-fridge (compressor cycles)	50 to 100W	8 effective	400 to 800
Wi-Fi router	6 to 12W	24	144 to 288
CPAP (without humidifier)	30 to 60W	8	240 to 480
CPAP (with heated humidifier)	50 to 100W	8	400 to 800

THREE SYSTEM SIZES

Start where you are. Scale when you need to.

Solar battery systems form a natural ladder. Start with the tier that matches your current needs and budget. Each tier up adds capability and cost. Most households never need the top tier.

1

The phone-and-lights kit

20 to 30W panel + power bank or small station (100 to 300 Wh) · $60 to $150

Charges phones, earbuds, headlamps, and small USB devices. This is a USB solar charger paired with a power bank. It does not run AC devices.

Best for: Apartment dwellers, hikers, cyclists, or anyone who just needs phone power during a short outage.

2

The household essentials system

Sweet spot

200W panel + 500 to 1,500 Wh station · $400 to $1,200

Powers phones, LED lights, a laptop, a fan, Wi-Fi, a CPAP machine, and a mini-fridge. Recharges daily from the panel. Runs indefinitely in sunny weather. This is the system that covers the gap between a power bank and a gas generator for most households.

Best for: Most households preparing for multi-day power outages, car campers, remote workers, and anyone with a powered medical device.

3

The heavy-use or multi-day system

200 to 400W panel (or two panels) + 2,000 to 5,000 Wh station · $1,500 to $4,000

Adds a full-size refrigerator, a microwave (briefly), power tools, or sustained air conditioning from a small window unit. Multiple panels speed recharging and provide redundancy. This tier overlaps with small gas generators in capability but runs silently and without fuel.

Best for: Households with heavy loads, extended off-grid stays, or anyone who wants generator-level capability without the noise, fuel, and maintenance.

THE 24-HOUR CYCLE

How energy flows through a full day.

Understanding the day-night energy cycle changes how you manage the system. Productive sun hours are limited. Everything you consume after sunset comes from what the panel stored during the day.

Daytime (4 to 6 productive hours)

The panel produces power. The station charges. If the station is full and you are running devices, the panel's output goes directly to powering them, preserving the battery.

This is your harvest window. Everything the system does at night depends on how much energy you collected here. Maximize it: deploy the panel early, angle it correctly, keep it in full sun, and minimize unnecessary loads during peak solar hours.

Night (no solar input)

The panel produces nothing. Every watt-hour you use comes from the station's stored energy. Loads that run continuously overnight (a fridge, a CPAP, a fan) are the biggest drain.

The station's capacity must be large enough to cover overnight use plus a margin. If you wake up with the station below 20 percent, the panel may not refill it by the next nightfall, and the system starts falling behind.

THE BALANCE POINT

A system is in balance when the panel replaces in one day what the station uses in 24 hours.

Above balance, the station stays full and you have surplus. Below balance, the station drains day over day until it dies. Cloudy weather pushes the system below balance temporarily. The station's capacity is your buffer for those days. Two to three days of cloudy-weather buffer is adequate for most locations; more if you live in a region with long overcast stretches.

THE STRESS TEST

What happens when the sun does not cooperate.

Sunny-day performance is easy. The stress test for any solar battery system is sustained cloudy weather, which is exactly when power outages tend to happen. Here is how to manage it.

Know your reduced harvest

Heavy overcast cuts solar output to 10 to 25 percent of rated wattage. A 200W panel producing 30 to 50W under thick clouds collects 120 to 300 watt-hours in a day, down from 750 to 1,000 on a sunny day. Light overcast is less severe, cutting output by roughly a third.

Cut loads immediately

When the forecast shows sustained clouds, shift to essentials-only mode before the battery drops. Turn off the fridge and eat perishables first. Reduce screen time. Use headlamps instead of room lights. Every watt-hour you do not spend is a watt-hour you do not have to replace.

Harvest every available watt

Even under clouds, the panel produces some power. Keep it deployed all day. On overcast days, the sun is diffuse rather than directional, so panel angle matters less, but full exposure to the open sky still matters. Do not bring the panel inside because the weather looks bad.

Have a backup charging source

A car with fuel can charge most portable power stations through a 12V DC car charger port. A gas generator is the traditional answer. Even a neighbor with grid power and a long extension cord works. Solar is the primary source, but a resilient system has a secondary option for the days solar cannot keep up.

WHAT GOES WRONG

Six system mistakes to avoid.

Buying a big station with a small panel. A 2,000 watt-hour station paired with a 60 watt panel takes three to four sunny days to recharge from empty. The station's capacity is wasted because the panel cannot keep up. Match the panel to the station: roughly 1 watt of panel per 5 to 7 watt-hours of station capacity.

Not doing the energy budget math. Buying the first station that looks big enough without listing your actual loads leads to either overspending (buying more capacity than you need) or underspending (buying a station that runs dry overnight). The four-step budget takes 15 minutes and prevents both mistakes.

Ignoring the voltage spec. Every power station has a maximum solar input voltage. If the panel's open-circuit voltage (Voc) exceeds it, the charge controller can be damaged. This is the one pairing mistake that can break equipment. Check both spec sheets before connecting.

Leaving the station in direct sun. The panel needs sun. The station does not. Heat degrades lithium battery lifespan and triggers thermal throttling that slows charging on the hottest days. Run the cable to shade and keep the station cool.

No test run before the outage. Deploy the system on a sunny weekend. Run your intended loads for 24 hours. See what the station reads the next morning. That number tells you whether your budget math was right and whether the panel can keep up. One test is worth a hundred estimates.

Treating the system as set-and-forget. Lithium batteries degrade over time and lose capacity. Solar panel output drops slowly with age and faster with damage. Test the system once or twice a year: measure how much the panel collects and how long the station runs your loads. Catch declining performance before the next outage finds it for you.

BEYOND PORTABLE

When the portable system is not enough.

A portable solar battery system covers most short-term and moderate-load scenarios well. But some households outgrow it. Here are the signs, and the next steps.

Signs you have outgrown portable

Your daily energy budget exceeds 3,000 watt-hours
You need to run central HVAC, a well pump, or a sump pump
You want the backup to switch on automatically with no manual setup
You want circuits in your house backed up, not just devices plugged into the station
Outages in your area regularly last a week or more

The next steps up

Expandable portable systems: Some stations (EcoFlow Delta Pro, Bluetti AC500) accept expansion batteries that push capacity to 6,000 to 25,000 watt-hours while remaining portable. This is the bridge between portable and permanent.
Whole-home battery with transfer switch: Tesla Powerwall, Enphase IQ, or similar permanently installed batteries wired into your home panel. Costs $10,000 to $20,000 installed but provides seamless, automatic backup.
Rooftop solar with battery storage: The full solution. Rooftop panels generate power daily, a battery stores it, and a transfer switch keeps the house running during outages. The property-scale solar guide covers this path.

WHERE TO GO NEXT

U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, "Solar Photovoltaic Cell Basics." energy.gov/eere/solar/solar-photovoltaic-cell-basics. Accessed 18 September 2026.
U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, "Solar Energy Basics." energy.gov/eere/solar/solar-energy-basics. Accessed 18 September 2026.
U.S. Energy Information Administration, "How much electricity does an American home use?" eia.gov/tools/faqs. Accessed 18 September 2026.

Solar battery systems: the math that makes it work.