Lights Out, Part 2: Solar Power When the Grid Goes Down

Start with what you need, not what you buy

In Part 1 we covered water, food, heat and the bug-out bag. This part is about power. Most people shopping for solar start with the panel. Start with a list instead. Write down what you truly need to run when the grid is down, how many watts each thing draws, and how many hours a day you will use it. Multiply, add it up, and you have your daily power budget in watt-hours.

A simple blackout budget might be LED lights, a radio, a few phone charges and a fan, which together come to a few hundred watt-hours a day. The refrigerator is the big one. Typical kitchen fridges use somewhere around 1,000 to 2,000 watt-hours a day, according to power-station makers and testers, because they cycle on and off around the clock. A cheap plug-in energy meter will tell you what yours really uses.

What a panel really makes

A panel's rating is what it makes in perfect sun, and real life is never perfect. Solar installers measure sunlight in peak sun hours, and most of the country gets somewhere around three to six of them a day, less in winter. After losses, a 100-watt panel usually makes roughly 300 to 500 watt-hours on a good day, according to solar suppliers like Renogy. Clouds, shade, dirt and a poor angle all cut that down.

So one 100-watt panel can keep lights, a radio and phones going. Running a fridge takes several panels and a battery big enough to carry it through the night.

Three sizes of setup

The starter setup is a portable power station of about 500 to 1,000 watt-hours with a folding panel. It needs no wiring, fits in a closet and covers lights, phones, a radio and a fan. The middle setup is a larger station or battery bank of two to five kilowatt-hours with several panels, enough to run a fridge part of the day. The big setup is a permanent rooftop array with a home battery, installed by a licensed electrician, that can carry much of a house.

Batteries: lithium versus lead-acid

Lead-acid batteries are cheaper up front, but you should only use about half of their stored power if you want them to last, and they wear out after a few hundred deep cycles. Lithium iron phosphate batteries, often written LiFePO4, cost more but let you use most of their capacity and are commonly rated for thousands of cycles, according to Battle Born Batteries. Over a few years, lithium usually costs less per day of use. One catch: most lithium iron phosphate batteries should not be charged below freezing, so keep them somewhere that stays above 32 degrees.

The mistake that can kill a lineman

Never connect solar or a generator to your house wiring by plugging it into an outlet. Power can flow backward into the lines outside, and a repair crew that thinks the line is dead can be electrocuted. Electric co-ops warn about this backfeed every storm season. If you want power in your walls, hire a licensed electrician to install a proper transfer switch or an inverter built to shut off when the grid goes down.

Afterlight read: start small this month

Do your power budget tonight with a pen and paper. Then buy the smallest setup that covers it, learn how it behaves through a cloudy week, and grow from there. Power you have tested is worth far more than power you plan to buy.