With electricity costs soaring, home batteries have never looked so attractive. Whether you want to store the excess generated by your solar panels or simply buy electricity at the cheapest possible rate to use later when power is most expensive, a home battery can help. It’s never been easier to get a home battery installed, but this rapidly expanding market can be confusing, and there are several things to consider before you buy.
I’ve spent months researching home batteries, chatting to folks who use them, and then having one installed myself, and I have tips for anyone interested in getting a home battery of their own.
Why Would You Want a Home Battery?
There are several reasons you might want to invest in a home battery, and they are not mutually exclusive:
- You want to store excess power from your solar panels.
- You want to live off-grid.
- You want to guard against power outages.
- You want to buy electricity at a cheap rate and store it for use later.
Home batteries are a win-win, potentially benefiting power companies too, because battery storage is an essential part of grid balancing and can help manage and make the most of the intermittent power generated by renewables (solar, wind, waves).
How Do Home Batteries Work?
Photograph: Simon Hill
A home battery is like a big power bank for your home. But rather than lithium-ion, they tend to be lithium iron phosphate (LFP or LiFePO4), because it is safer, more durable, and less prone to thermal runaway. In other words, less likely to overheat and burst into flames. There are a few manufacturers working with sodium-ion (Na-ion) batteries, which are potentially cheaper, more environmentally friendly (they don’t require lithium), and perform better in the cold, but they are also larger and don’t last as long.
Home battery technology is often the same as you’ll find in electric vehicles. Some folks have even suggested employing EV batteries as home batteries. But there are potential issues with that, not least finding your car battery drained in the morning. EVs are also driving the technology forward toward solid-state batteries, which are smaller for the same capacity, safer as they don’t have liquid electrolytes inside, and longer lasting.
Many home batteries come in modular systems, so you can add the capacity you want, but they require an inverter to convert the DC (direct current) power stored to AC (alternating current) power you can use. Folks with solar panels, or those who plan to add them in the future, should opt for a hybrid inverter, which can also convert the power from the panels for use or storage.
Inverters have different power ratings in kilowatts (kW) that dictate how much power you can draw at any given moment. Households with modest needs may get by with a 3.6-kW inverter, but that limits your continuous draw to 3.6 kW. They usually have a peak load capability that goes higher, enabling you to pull more for a brief period. If you have high-demand appliances like an EV charger or heat pump, you will want at least 5 kW, and folks with larger demands or larger batteries will want to go higher (6 to 10 kW).
What Should I Look For?
There are several things to watch out for when buying a home battery:
- Capacity: Measured in kilowatt-hours (kWh), this tells you how much total energy the battery can hold.
- Power output: Measured in kilowatts (kW), this shows how much energy the battery and inverter can deliver at any moment.
- Depth of discharge: This is how much of the battery’s capacity you can safely use without damaging it.
- Efficiency: This is the percentage of the power you put into the battery that you can actually use, because some energy is always lost in the storage process.
- Warranty: This is a guarantee about the minimum performance you can expect before a battery degrades (they all degrade over time), and it’s often stated in years and charging cycles (whichever comes first). For example, EcoFlow promises at least 70 percent capacity after 15 years or 6,000 charging cycles.
How Much Home Battery Do You Need?
EcoFlow via Simon Hill
It can be tricky to calculate how much battery capacity you need, and it depends on your use case. If you want to guard against outages or live off-grid, you must consider how much power you use over time and also the sum of your maximum power usage at any given moment to ensure your capacity in kWh and output in kW are enough. If the output is not high enough you may not be able to run power-hungry appliances at the same time, so you’ll have to think about how you use your power.
For folks like me, simply looking to buy at a cheaper rate to use when power is more expensive, any capacity will benefit you. But if you have a cheap six-hour rate overnight, for example, then you ideally want it to last for the other 18 hours. It makes sense to get as much as you can up-front because the installation costs are high. Even adding to modular systems later often requires professional installation to avoid voiding your warranty.
Do You Need Upgrades or Permission?
The home battery will connect to your main electrical panel via a cable, and it may require some upgrades. There was no room on my fuse board when I got a home battery installed, so they had to install a second breaker box.
Some inverters may require permission from your electric distribution utility or local distribution company. Here in Scotland, the distribution network operator must approve your inverter, but you can install and then notify up to 3.6 kW, whereas larger inverters require prior approval.