How to size a portable power station
- Running watts (W): add up everything you might run at the same time. The power station's continuous AC output must be higher.
- Surge watts: fridges, freezers and pumps take 2 to 5 times their running watts for a moment when the motor starts. The surge (peak) rating must cover your running load plus the biggest start-up.
- Watt-hours (Wh): watts x hours of use. Add up a day, then multiply by the days you want to cover.
- Usable capacity: the inverter and battery lose some energy, so plan on about 85% of the rated Wh. A 1,000 Wh unit gives roughly 850 Wh at the socket.
Fridges and freezers
A fridge does not run all day. The compressor switches on and off, so a typical UK fridge-freezer uses about 0.5 to 0.8 kWh a day, not its running watts x 24. The figure on its energy label (kWh/annum) divided by 365 is a good daily estimate. Keep doors closed: the Food Standards Agency says a fridge should stay cold for up to 4 hours, and a full freezer should stay frozen for up to 48 hours (24 hours if half full). In a short cut you may not need to power them at all. You can also run a freezer for a few hours, then unplug it.
What a portable unit cannot run
Kettles (up to 3 kW), electric heaters, ovens, hobs, immersion heaters and tumble dryers draw more than most portable power stations can supply, and would empty one in minutes. Use a low-watt travel kettle, fill vacuum flasks before a planned cut, or use a gas hob if it lights safely by hand. Some units have a "power lifting" or "boost" mode that runs heating appliances at reduced power. It does not help with motor start-up.
Safety
- Never run a petrol or diesel generator indoors, in a garage, shed, porch or near open windows. Its exhaust contains carbon monoxide (CO), which you cannot see or smell and which can kill. The NHS says turning on vehicle or lawn mower engines in an enclosed space, such as a garage, can cause a build-up of carbon monoxide.
- Never use a barbecue or camping stove indoors or in a tent. Fit a carbon monoxide alarm in each room with a gas, oil, coal or wood appliance (NHS).
- CO symptoms include headache, dizziness, feeling sick, tiredness and confusion. Get into fresh air and call NHS 111, or 999 if someone collapses or is struggling to breathe (NHS).
- Battery power stations make no fumes and can be used indoors. Keep them dry, ventilated and away from heat. Do not cover them while charging, and stop using a damaged or swollen unit.
- Plug appliances straight into the power station. Never connect it, or a generator, to your house wiring (for example with a plug-to-plug lead). This back-feeds the grid and can kill line workers. Fixed connections such as a boiler changeover switch must be fitted by a qualified electrician.
Medical equipment
If anyone relies on powered medical equipment (CPAP, oxygen concentrator, home dialysis, a stairlift or a powered bed), join the free Priority Services Register through your energy supplier or network operator. Be Ready says that if you rely on your energy supply for medical reasons, your network operator can tell you about planned power cuts. Ask the device maker or your clinical team for the real power draw, battery options and what to do in a cut. Do not rely on these estimates for life-sustaining equipment. Call 105 to report a power cut.