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Full Worked Example: Sizing Power for a Real Weekend Cabin Step by Step

Updated 2026-10-21 · Published by Charland & Co. · Based on published specs; we have not tested the products discussed.

Quick answer: A weekend cabin using 1,050 Wh per day needs a 2,520 Wh battery for two nights. A 300 W solar array under 4.8 peak sun hours generates 1,080 Wh per day. A 2,000 Wh power station with 2,000 W inverter and a 2,500 W surge generator covers all needs.

Weekend cabin with solar panel, power station and distant generator

Step 1: Device List and Daily Wh Total

To size your power system, start by listing all the devices you'll use and their power consumption. For this example, the cabin uses the following:

Total daily consumption: 500 + 80 + 50 + 20 + 60 + 300 = 1,010 Wh
We'll use 1,050 Wh as the daily load for this example.

Step 2: Battery Wh Needed with the 1.2 Formula

To account for inefficiencies and unexpected usage, multiply the daily load by the number of days and then by 1.2:

Battery Wh needed = 1,050 Wh × 2 days × 1.2 = 2,520 Wh

This means you need a battery with at least 2,520 Wh of usable capacity.

Step 3: Runtime Checks Using Wh × 0.85 / Load W

Now, check how long a 2,520 Wh battery will last with a specific load. For example, if you run a 1,000 W inverter:

Runtime hours = (2,520 Wh × 0.85) ÷ (1,000 W) = (2,142) ÷ (1,000) = 2.14 hours

This is the runtime for a 1,000 W load. You can use this formula for any device or combination of devices.

Step 4: Solar Harvest with Panel × PSH × 0.75

Next, calculate how much solar energy you can expect from a 300 W solar array in your location. If your area gets 4.8 peak sun hours per day:

Solar Wh per day = 300 W × 4.8 PSH × 0.75 = 1,080 Wh

This means the solar array can generate 1,080 Wh per day, which is close to the 1,050 Wh daily load. On clear days, the solar array can nearly cover the load.

Step 5: Generator Surge Backup Calculation

If you plan to use a generator as a backup, you need to account for the surge wattage of your largest motor-driven device. For example, if the refrigerator has a 1,200 W starting wattage and a 100 W running wattage, and your other devices total 500 W:

Surge W = (100 + 500) - 100 + 1,200 = 1,700 W

This means you need a generator with at least 1,700 W surge capacity to handle the startup of the refrigerator.

Step 6: Cold-Weather Capacity Adjustment

In cold weather, battery capacity can drop by up to 15%. So, adjust the battery capacity accordingly:

Cold-weather usable Wh = 2,520 Wh × 0.85 = 2,142 Wh

This is the usable capacity in cold weather. If you also factor in the inverter efficiency (another 15% loss), the total usable capacity becomes:

2,142 Wh × 0.85 = 1,820 Wh

So, in cold weather, you need a battery with at least 2,520 Wh of rated capacity to ensure 1,820 Wh of usable power.

Step 7: Final Station, Panel, and Generator Recommendation

Based on the calculations:

For more details on choosing a power station, see our buying guide. For solar panels, check out our solar panel buying guide.

Who this is not for

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FAQ

What daily Wh did the example cabin use?

The example cabin used 1,050 Wh per day, based on a simplified list of devices and their usage.

How much battery capacity does the 1.2 formula require?

The 1.2 formula requires 2,520 Wh of battery capacity for a two-night trip, calculated as 1,050 Wh × 2 × 1.2.

Does the solar array cover the full daily load?

Yes, a 300 W solar array under 4.8 peak sun hours generates 1,080 Wh per day, which is nearly enough to cover the 1,050 Wh daily load on clear days.

What if I use the power station in cold weather?

In cold weather, the battery capacity drops by about 15%, so you need a 2,520 Wh battery to ensure 1,820 Wh of usable power. Choose a model with LiFePO4 chemistry for better performance in cold.

Can I use a generator as a backup?

Yes, but ensure it has at least 2,500 W surge capacity and is used outdoors only, at least 20 feet from doors, windows and vents (CPSC; CDC). Never plug it into a house outlet; any connection to building wiring needs transfer equipment installed by a licensed electrician (NFPA 70, NEC Article 702).

Related pages

Sources to cite

Run your own numbers: free power calculator (200+ devices).