Solar Power Station Sizing: Loads First, Then Panels

Before you buy a solar power station, you need two numbers on paper: how many watt-hours your household uses in a day without the grid, and how many watt-hours your panels can put back in a day where you live. If the second number is smaller than the first, the battery runs down and stays down. The station is the last decision you make, not the first.

What to do first:

1. List the devices you actually need during an outage.
2. Write down each one's watts and hours of use per day.
3. Add up the daily watt-hours.
4. Estimate what your panels can realistically put back where you live.
5. Compare stations against both numbers.

This guide is part of our Off-Grid Blueprint series on power, water and food independence.

Which devices belong on your outage list?

Start with what keeps the house running safely, then stop. Phones, a radio, a few lights and the internet router are usually on the essential line. Refrigeration may be. A room full of appliances is not. Ready.gov's power outage guidance tells you to take an inventory of the items you need that rely on electricity and plan alternate power for them. That inventory is the start of your load list.

Be honest about what you can leave off. Every device you cut makes the battery last longer and makes the solar math easier.

How do you turn watts into a daily energy number?

Watts tell you how fast a device uses power. Watt-hours tell you how much energy it uses over time. For a steady load, the math is simple: operating watts times hours of use per day equals watt-hours per day.

Two cautions. The wattage printed on a label is usually the maximum draw, not what the device pulls all day. And appliances that cycle on and off, like a refrigerator, do not run at their label wattage around the clock. For those, a plug-in electricity meter left on the device for a full 24 hours gives you a much better number than the nameplate.

What does a worked example look like?

Here is a sample outage list. These are example numbers to show the method, not measurements of any particular device. Replace them with numbers from your own labels or a plug-in meter.

Look at what that table tells you. The essentials come to 418 watt-hours a day. Add the refrigerator and the list jumps to 1,318. That one appliance is more than twice everything else combined. If you are planning around keeping food or medicine cold, our review of the EcoFlow GLACIER portable fridge/freezer covers the cooling side of that problem.

These are paper numbers. A station loses some energy converting its battery to household AC power, so the real figure you can use is lower than the battery's rated capacity. Check the manual for your exact model, or measure.

Is capacity enough, or does output matter too?

Both matter, and they are different specs. Capacity, in watt-hours, is how much energy the station holds. Output, in watts, is how much power it can deliver at one moment. A station can have plenty of stored energy and still fail to start a device whose startup draw is higher than the station can deliver. Motors and compressors are the usual suspects.

Check three things against the exact model's documentation before you buy: continuous output, startup or surge capacity, and whether it has the right outlets and ports for your devices.

How much can your solar panels put back each day?

A panel's rated watts are measured under ideal test conditions. On your porch or in your yard you will get less. Sun angle, shade, clouds, dust, heat and wiring all take a cut, and the season changes everything.

For a location-specific estimate, use the free PVWatts calculator from the National Laboratory of the Rockies, a U.S. Department of Energy lab. Its default allowance for system losses is 14 percent, which the PVWatts manual says covers things like soiling, shading, wiring and connections. PVWatts is built for grid-connected installations, so treat its numbers as a starting point for portable panels, not a promise. It also gives you month-by-month estimates. Plan around the weakest month you expect to need the system, not the best one.

Here is the math with example numbers. Say you have 200 watts of panels and your location gets about 4 hours of full-sun equivalent on a typical day in the month you care about. That is 800 watt-hours on paper. Take 14 percent off for losses and you are near 690 watt-hours. In the example above, that covers the 418 watt-hour essentials list with room to spare. It does not cover 1,318 watt-hours with the refrigerator. To close that gap you can cut loads, run the fridge on a schedule, or add panels, up to the limit the station will accept.

That limit matters. Every station has a maximum solar input, and the panels have to match its voltage and current range, not just its plug. Matching connectors alone is not a compatibility check. Read the manual's solar input section before you buy a single panel. Our earlier article on solar generators for off-grid living covers battery chemistry and panel pairing in more detail.

What if someone in the house depends on powered medical equipment?

Then make a phone call before you shop. Ready.gov's guidance is to talk to your medical provider about a power outage plan for medical devices and refrigerated medicines. Work with your equipment supplier and clinician on what that device needs and for how long. A product listing is not evidence that a station will run your particular device for the time you need.

One catalog candidate: EcoFlow DELTA 3 Classic (1024Wh)

The EcoFlow DELTA 3 Classic (1024Wh) is the single shopping candidate in this guide. This is catalog-only coverage: Fortified Living has not tested this unit, measured its runtime or verified its performance with your appliances or panels. No price, recharge-time or appliance-runtime claim is being made here.

Here is what EcoFlow's US product page lists, checked October 8, 2026:

• Rated capacity: 1,024 watt-hours
• Cell chemistry: LFP (lithium iron phosphate)
• AC output: 1,800 watts total
• Maximum solar input: 500 watts

Set those against the example worksheet. The 418 watt-hour essentials list is well under 1,024 on paper. The 1,318 watt-hour list with the refrigerator is not. And the 500-watt solar input caps how many panels you can usefully connect, which caps how much you can put back each day. Run your own numbers before you decide.

It belongs on your comparison list if you are shopping for a portable battery station and are willing to check the exact model against your load worksheet and charging plan. It is wrong for your plan if you need a guaranteed whole-home solution, have not confirmed an essential device works with it, or cannot build a workable solar budget. Panels are not included with the base model. EcoFlow's page also sells bundles that add panels or other gear, so check which version you are ordering.

It may also be more than you need. If your list is phones, a radio and a light, power banks you already own and a hand-crank or solar radio may cover it. We compare two stations of this size side by side, with honest downsides, in our backup power guide.

The link below is a paid link. If you buy through it, Fortified Living may earn a commission at no extra cost to you.

Check the EcoFlow DELTA 3 Classic (1024Wh) listing and exact-model documentation (paid link). Confirm that the listing still identifies DELTA 3 Classic (1024Wh), and check the included components before ordering. Do not substitute specifications from another DELTA model or assume panels are included.

Sources

• Ready.gov: Power Outages
• National Laboratory of the Rockies: PVWatts Calculator
• PVWatts Version 5 Manual (system losses default)
• EcoFlow US: DELTA 3 Classic Portable Power Station (1024Wh) specifications

Last reviewed: October 8, 2026. Product specifications checked against EcoFlow's US product page on October 8, 2026.