Choosing your backup power type
There are three ways to keep a house with utility service running when the power goes out. They differ enormously in cost, in paperwork, and in whether you are allowed to install them yourself. Working out which one you need comes before choosing equipment.
Read this part first
Anything that connects a power source to your house wiring must physically prevent that source from reaching the utility line. If it does not, you can energize a line that a utility worker believes is dead. This is not a theoretical hazard, and it is the reason these three approaches are kept separate here rather than blended into one article.
Never connect a generator to your house by plugging it into a wall outlet with a double-ended cord. It is sometimes called a suicide cord, and it is called that for a reason. It backfeeds the utility, it leaves the cord's exposed prongs live, and it bypasses every protective device in the building.
Start with two questions
Do you need to power anything that is hardwired? A furnace, a well pump, a sump pump, central air, or hardwired lighting cannot be run from an extension cord. If the answer is no, and you mainly want a fridge, some lights, and your devices, portable is enough and it is the cheapest and simplest answer by a wide margin.
How long and how often do outages last where you live? A few hours once a year is a different problem from three days every winter. Storage is expensive, and the honest answer for long rural outages is often a generator rather than more batteries.
If you need hardwired circuits, you are choosing between a transfer switch and a grid-interactive system, and that decision is mostly budget. A transfer switch is the pragmatic answer. A grid-interactive system costs several times more, needs utility approval, and in exchange gives you automatic operation and everyday solar savings.
The three approaches
Portable power stations
A battery in a box with outlets on the front. You plug appliances into it directly with extension cords. It never touches your house wiring.
- House wiring
- None
- Permits
- None
- Who installs it
- Anyone
- Good for
- Keeping a fridge, lights, phones, internet, and a CPAP running through an outage of a few hours to a couple of days.
- Limits
- Cannot run anything hardwired: no furnace, no well pump, no central air, no hardwired lighting. Extension cords across the floor.
Transfer switch or interlock
A switch that disconnects selected house circuits from the utility and connects them to a generator or battery system instead. Only one source can be connected at a time.
- House wiring
- Yes, isolated from the utility while running
- Permits
- Almost always required
- Who installs it
- Licensed electrician for the panel work in most places
- Good for
- Powering hardwired things: furnace, well pump, sump pump, hardwired lighting. The normal answer for a house that loses power regularly.
- Limits
- Costs more, needs a permit, and the switching is manual unless you pay for automatic.
Grid-interactive system
Solar and batteries that work alongside the utility day to day and carry the house when it fails. The inverter synchronises with the grid and disconnects automatically when the grid goes down.
- House wiring
- Yes, synchronised with the utility
- Permits
- Permit, inspection, and a utility interconnection agreement
- Who installs it
- Licensed installer. Not a DIY project
- Good for
- Whole-house or near-whole-house backup with no manual switching, combined with everyday solar savings.
- Limits
- By far the most expensive, and the longest to arrange. Utility approval can take months.
Why these are kept separate
Much of the backup power writing online blends these three into a single article, which is where people get hurt. The instructions differ, the code differs, and the consequences of applying one set of instructions to another kind of installation are not merely that it works badly.
Every page in this section states at the top which topology it describes, what code applies to it, and who is allowed to do the work. If you find yourself on a page that does not match the system you are building, you are on the wrong page.
Whichever you choose
- Work out what you actually need to run before buying anything. Backup capacity is expensive, and most people need far less than they expect once they separate essentials from conveniences.
- Anything burning fuel goes outside. Portable generators produce carbon monoxide in quantities that kill quickly, and every year people die running them in garages, basements, and doorways. Outdoors, well away from windows and vents, with working CO alarms inside.
- Test it before you need it. A backup system discovered to be faulty during an outage is not a backup system.