Buying a Giant Battery for the Next Blackout or Off-Grid Adventure
Understanding Watt-Hours (Wh)
Buying a giant battery for the next blackout or off-grid adventure can be daunting, especially when hundreds or even thousands of dollars are on the line. To get it right, you need to become intimate with the watt-hour (Wh). The watt-hour is a measure of capacity, or how much electrical energy a battery stores. If you know how much power — measured in watts — your devices consume, then the Wh rating of a battery lets you quickly calculate how long those devices will run.
Calculating Watt-Hours
For example, a typical LED light bulb requires about 10W to illuminate. So a 1000Wh (1kWh) battery can run that bulb for 100 hours because Wh divided by watts gives you the time. For context, the average US home consumes about 889kWh per month, or about 29.2kWh per day, according to the US Energy Information Administration. During a blackout, you’d need about $15,000 worth of batteries on hand to keep it running for just one day (based on a rough average of 50 cents per Wh of battery capacity). But that’d be silly because you really only need to keep your critical devices running for as long as the power is out.
Wh and Ah: Understanding the Numbers
We capitalize the “W” in Wh and kWh because the watt is named after Scottish inventor and engineer James Watt. Sadly for James, not all batteries or devices sold list the Wh spec; some opt for amp-hour (Ah or mAh) instead, where the capitalized “A” is for French physicist André-Marie Ampère. No offense to André-Marie, but the amp-hour is a dumb spec for consumer devices because it requires knowing the voltage. Nevertheless, amp-hours multiplied by the voltage gives you watt-hours.
Calculating Your Battery Needs
According to the most recent data available, US homes average about five to eight hours of electricity interruptions per year. But natural disasters like hurricanes and wildfires can extend outages over days. Buying a battery is therefore like buying insurance: do you spend more to cover all possible outcomes or just protect yourself against the basics? Either way, you need to calculate the watt-hours.
Common Household Devices and Watt-Hours
There are many publicly available watt-hour calculators available, including this one from EcoFlow and this one from Unbound Solar. What follows is a list of common household devices and a very rough estimate of how much power they could consume over a single day. To determine your battery needs, identify which electrical devices are critical to you and how long they’ll need to run, and then total up the watt-hours. That’s how much battery capacity you’ll need to survive without power.
Bar Chart: Watt-Hours Used by Different Appliances and Gadgets
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Portable Power Stations and Solar Generators
In the real world, the actual watt-hours available to power your devices can be lower than the capacity written on the battery due to factors like age and operating temperature. And batteries aren’t very useful if you can’t easily access that stored energy. That’s why they’re often sold in the form of all-in-one power stations (aka “solar generators,” if equipped with a solar charge controller) with built-in AC and DC outputs for USB devices and household appliances. Just know that they divert some of that battery capacity to convert DC power to AC, to keep Wi-Fi and Bluetooth radios operating, to maximize solar energy collection, and possibly to heat the battery so it can be charged in cold weather.
Conclusion
Regardless of your energy needs, understanding watt-hours is crucial for buying the right battery. By calculating your watt-hour needs, you can determine the right amount of battery capacity to keep your critical devices running during a blackout or off-grid adventure. Remember to hedge a bit and purchase at least 10 percent more capacity than you actually need, and don’t forget to consider the age and operating temperature of your battery to get the most out of your investment.
Frequently Asked Questions (FAQs)
Q: What is a watt-hour (Wh)?
A: A watt-hour (Wh) is a measure of capacity, or how much electrical energy a battery stores.
Q: How do I calculate my battery needs?
A: Identify which electrical devices are critical to you and how long they’ll need to run, and then total up the watt-hours. That’s how much battery capacity you’ll need to survive without power.
Q: What is an amp-hour (Ah)?
A: An amp-hour (Ah) is a measure of capacity that requires knowing the voltage. Amp-hours multiplied by the voltage gives you watt-hours.
Q: How do I choose the right battery for my needs?
A: Calculate your watt-hour needs and consider factors like age and operating temperature to get the most out of your investment.
Q: What is a portable power station?
A: A portable power station is a device that combines a battery with a solar charge controller and other features to provide power on the go.
