Before you spend a dollar on panels or batteries, this electricity usage monitor is one of the best investments you can make in a DIY solar project. Plug any appliance into the Kill A Watt and it tells you exactly how many watts it draws and how many kilowatt-hours it uses over time, replacing guesswork with real numbers.
This matters more than most people expect: nameplate wattage on appliances is often wildly different from real-world draw, and things like fridges and well pumps cycle on and off in ways that are hard to estimate without measuring. We cover why this step comes before sizing anything else in Efficiency First: Cutting Your Solar Needs Before You Buy.
In practice, most people use this electricity usage monitor to audit their biggest power draws — refrigerators, space heaters, water heaters, and anything with a compressor or heating element — before deciding how large a solar and battery system they actually need. Oversizing a system to cover appliances you could swap for efficient versions is one of the most expensive mistakes in DIY solar.
It’s a small, inexpensive tool, but it pays for itself the first time it saves you from buying an extra battery or panel you didn’t actually need.