23.5 Independent power for an apartment
In this section (4)
In an apartment, a gasoline generator is almost never a good idea: the exhaust gets into your home and your neighbors', many complexes prohibit them, and gasoline becomes scarce just when you need it (safety rules in chapter 9). The realistic option is a portable battery power station, ideally with LiFePO4 chemistry (more cycles and more stable), charged with portable solar panels and, while there is power, from the wall.
Concepts in two lines
- Watts (W): how much power an appliance uses while running. The station must have an inverter that can handle the sum of what you plug in at the same time, including the startup surge of motors (refrigerator).
- Watt-hours (Wh): total energy. A 50 W fan running for 8 hours uses 400 Wh. The station's capacity is measured in Wh. Calculate with 80–85% of the advertised capacity, because some is lost in conversion.
Approximate consumption table
Typical approximate values; check the label or manual of your appliance. The most accurate figure for the refrigerator is its yellow EnergyGuide label: kWh per year ÷ 365 = kWh per day.
| Appliance | Approx. power when running | Reasonable daily use | Approx. energy per day | Worth it? |
|---|---|---|---|---|
| Modern full-size refrigerator | 100–250 W (startup surge is several times higher) | Cycles on its own, 24 h | 1,000– 2,000 Wh | Only with a large station and a good panel. Better: empty it and use a cooler. |
| 20-inch box fan | 50–100 W | 8–10 h | 400–1,000 Wh | Yes, on low-medium speed. |
| Ceiling fan | 15–90 W | 8 h | 120–700 Wh | Yes, if the station has an output to the building wiring (not common in a rental). |
| USB or rechargeable fan | 3–10 W | 10 h | 30–100 Wh | The most efficient; one per person and per pet. |
| CPAP without humidifier | 30–60 W | 8 h | 240–480 Wh | Medical priority. With a humidifier and heated tubing the consumption can double or more: ask the manufacturer. |
| Oxygen concentrator | Varies a lot by model | As prescribed | Can be very high | Consult the supplier; you need a specific plan and will probably need to leave early. |
| AM/FM/NOAA radio | 1–5 W | 4 h | 5–20 Wh | Yes. Better with AA batteries or a hand crank. |
| Cell phone (full charge) | 5–20 W while charging | 1 charge | 10–20 Wh per phone | Yes: only a few Wh per phone. |
| LED bulb or lamp | 5–10 W | 4–5 h | 20–50 Wh | Yes; headlamps with batteries are better. |
| Laptop | 30–90 W | 2–3 h | 60–270 Wh | For work or documents; in moderation. |
| Internet modem and router | 10–20 W | Only if there is service | 100–300 Wh | Only if your provider is still providing service. |
| Microwave, kettle, electric hot plate | 1,000–1,500 W | Minutes | 50–150 Wh per use | Possible with a large station, in short uses. |
| Small window air conditioner | 400–1,000 W or more | — | Several kWh | Not sustainable with a portable station and balcony panels. |
| Electric heater | ~1,500 W | — | Very high | No. In the cold, bundle up (chapter 14). |
Example: daily energy budget for a household
How to size your system
| Level | Station (capacity) | Solar panel | What it realistically covers |
|---|---|---|---|
| Basic | ~500–1,000 Wh | 100–200 W | Phones, radio, lights, USB fans, 1 CPAP without humidifier. No refrigerator. |
| Intermediate | ~2,000 Wh | 200–400 W | The above + 2 box fans at night + laptop. Refrigerator only for short periods to cool down. |
| Large | ~3,000–4,000 Wh or more | 400–800 W | The above + refrigerator on good sun days. Still does not cover continuous air conditioning. |
Solar production: varies with the season, clouds, angle, and shade. As a rough guide, on a clear day in much of the U.S. a panel produces over the day something like its rated power multiplied by 3 to 5 hours, minus losses; on cloudy days, much less. Measure what your panel actually produces in your yard before counting on it.
