Purchasing a large battery for potential blackouts or off-grid use can be an overwhelming task, particularly with substantial investments at stake. A misstep could lead to overpaying for an unnecessary product or falling short on capacity to power essential devices. Familiarity with watt-hours (Wh) is crucial in making the right choice.
Watt-hours indicate the capacity of a battery, representing the amount of electrical energy it can hold. Understanding how much power—measured in watts—your devices require allows you to determine how long those devices can operate using the battery’s Wh rating. For example, a standard LED bulb draws approximately 10 watts. Therefore, a 1000Wh (or 1kWh) battery could power that bulb for 100 hours, calculated by dividing Wh by watt consumption.
To provide some perspective, the average American household uses about 889kWh monthly, translating to roughly 29.2kWh daily, per data from the US Energy Information Administration. In the event of a blackout, one would need a battery system valued around $15,000 to maintain power for just one day (estimated at 50 cents per Wh). However, it is more practical to focus on powering critical devices only for the duration of an outage.
Wh vs. Ah
The “W” in Wh and kWh honors Scottish inventor James Watt. Unfortunately, many batteries and devices display capacity in amp-hours (Ah or mAh), based on French physicist André-Marie Ampère, which can complicate understanding. The amp-hour measurement requires knowledge of voltage; however, multiplying amp-hours by voltage yields watt-hours.
According to the latest statistics, US homes experience an average of five to eight hours of power disruptions annually. However, severe weather events like hurricanes and wildfires can prolong outages for days. Thus, opting for a battery can be seen as a form of insurance: deciding whether to invest more for extensive protection or just for essential coverage. Calculating watt-hours is vital in this decision-making process.
Various watt-hour calculators are freely accessible online, including one from EcoFlow and another from Unbound Solar. Below is a list of common household devices along with approximate power consumption estimates over a single day. Identifying critical devices and their operating time will help you approximate your watt-hour requirements, indicating the needed battery capacity for enduring power outages.
Table above based on a chart originally compiled by EcoFlow, modified with additional appliances and data.
In practice, the usable watt-hours for powering devices can be less than the stated battery capacity due to variables like battery age and temperature. Additionally, accessing this stored energy conveniently can be challenging. Therefore, many batteries come in the form of integrated power stations (often termed “solar generators” when equipped with solar charging capabilities) featuring built-in AC and DC outputs suitable for home appliances and USB devices. Be mindful that some battery capacity is utilized to convert DC power to AC and to operate Wi-Fi or Bluetooth connections, as well as to collect solar energy and maintain battery heat for optimal charging conditions.
It is advisable to purchase at least 10 percent more battery capacity than your calculated needs. Most battery solutions intended for RVs and homes can be expanded as necessary. Typical RV batteries start at around 1kWh and can range up to 15kWh, contingent on spatial and weight limitations. These batteries are also adaptable for home use, allowing for near-limitless scaling.
Those living in vans often have modest energy needs and are attentive to their power consumption. For example, I typically use about 1.6kWh daily while traveling in my modified Sprinter van. My energy usage includes maintaining a Starlink Mini connection, making coffee and tea, cooking using an induction cooktop, and keeping essential 12-volt devices running, such as LED lights, a water pump, and a portable fridge. Additionally, I frequently charge various devices like laptops and phones.
Currently, I am testing an EcoFlow Delta Pro 3 solar generator, which has a total battery capacity of 8kWh, allowing me to live and work off-grid comfortably for at least four days. I utilize a combination of fixed and portable solar panels, along with an alternator charger, to maintain my energy reserves, enabling weeks of off-grid living in sunny locations.
Home charging systems are analogous but larger and costlier. Houses can be outfitted with solar roofs and integrated battery backup systems from various manufacturers such as Tesla, Jackery, EcoFlow, and more. Alternatively, an electric vehicle can power home appliances using its substantial battery, or traditional portable generators can provide power without modern technology.
Ultimately, accurate watt-hour calculations are essential. By mastering this key figure, individuals can take significant strides towards achieving energy independence.
