What Size Power Station Do I Need?

Size a station in four steps

1. List the essentials and write down each one's average watts, not its nameplate rating.
2. Decide the hours the load must survive — 12, 24, 48 or 72.
3. Multiply watts by hours to get delivered watt-hours.
4. Divide by 0.792 to get the nameplate capacity to shop for, then confirm the continuous and surge output ratings.

Step 1: list the essentials in average watts

A nameplate is a maximum, not an average. The refrigerator is the clearest case: it runs its compressor roughly a tenth of the time. Apply a duty cycle and the honest load appears.

Add the station's own standby draw — typically 5 W on a small unit — once, not per device. It is included in the worked example below.

Worked example: 24 hours of blackout essentials

The minimal set is a refrigerator, a router, one LED bulb and a phone charger: 70 + 30 + 10 + 10 = 120 W, plus 5 W standby = 125 W. Over 24 hours that is:

125 W × 24 h = 3,000 Wh delivered

But the station must hold 3,000 Wh after the battery reserve and inverter losses, so the nameplate requirement is larger:

3,000 ÷ (0.90 × 0.88) = 3,000 ÷ 0.792 = 3,788 Wh

No station is sold at exactly 3,788 Wh. The next common size is 4,096 Wh, and that is the smallest unit that covers a full day of this load with a little margin.

Capacity by outage length

Run the same 125 W set against the four outage lengths people actually plan for. The market-size column is the smallest common capacity at or above the calculated requirement.

Past about 10,000 Wh the product class changes: you are buying a home battery or a generator rather than a portable station. If the table says 12,000 Wh, compare it with a small dual-fuel generator — the generator sizing calculator covers that side of the decision.

The output rating is a second limit

Watt-hours decide how long a load runs. The continuous output rating decides whether it runs at all, and the surge rating decides whether a motor can start. Check both before buying:

A 1,000 Wh station with a 1,000 W inverter cannot hold a 1,500 W heater even at 100% charge — the inverter shuts down in seconds. A refrigerator that runs at 700 W needs a surge rating above roughly 2,200 W or the compressor stalls on start-up. The runtime calculator shows continuous and surge headroom in the same panel as the hours.

Chemistry, cycles and solar top-up

Two stations with the same watt-hour label can differ in usable energy because the battery chemistry sets the depth of discharge:

• LiFePO4 — about 90% usable, 3,000–5,000 full cycles to 80% capacity. The default and the best fit for a station you plan to keep.
• NMC lithium — about 85% usable, lighter for the same energy, typically fewer cycles. Common in older or travel-focused units.
• Lead-acid — about 50% usable, 300–500 cycles. Cheap per watt-hour, heavy, and half the label is unusable.

Solar does not change the capacity you need; it changes how long an outage can run. A 200 W panel in five good sun hours collects about 1,000 Wh before charging losses, or roughly 800 Wh into the battery — enough to offset a 33 W average load around the clock, or to stretch a 24-hour station through a second day. The runtime chart shows what each capacity delivers without solar.

When a power station stops making sense

Add a television and a CPAP to the essentials and the load rises to 285 W. Over 72 hours that is 20,520 Wh delivered, or 25,909 Wh of nameplate capacity — four to six times the largest portable station. At that point a generator or a home battery is the honest answer, and the station becomes a bridge for the first night.

For most households the decision lands somewhere between 1,000 and 4,096 Wh: enough to keep the refrigerator, the router and the phones alive through a day, without paying for capacity that sits idle for years. Size for the outage you actually expect, add 10–20% for degradation and cold, and confirm the output ratings before the cart.