For electricity costs up, home batteries have never looked so attractive. Whether you want to save as much money as your solar panels generate or simply buy electricity at a cheaper rate to use later when energy is more expensive, a home battery can help. Home battery installation has never been easier, but this fast-growing market can be confusing, and there are a few things to consider before you buy.
I’ve spent months researching home batteries, talking to people who use them, and installing one myself, and I have some tips for anyone interested in getting their own home battery.
Why Would You Want a Home Battery?
There are a few reasons you might want to invest in a home battery, and they’re not all equally divided:
- You want to store more energy from your solar panels.
- You want to live off the grid.
- You want to monitor the power outage.
- You want to buy electricity at a cheap rate and store it for later use.
Home batteries are a winner, energy companies can also benefit, because battery storage is an important part of balancing the grid and can help manage and make the most of short-term energy produced by renewables (solar, wind, waves).
How Do Home Batteries Work?
Photo: Simon Hill
A home battery is like a giant power bank for your home. But instead of lithium-ion, they are usually lithium iron phosphate (LFP or LiFePO4), because it is safe, durable, and not prone to thermal runaway. In other words, you are less likely to overheat and burst into flames. There are a few manufacturers that work with sodium-ion (Na-ion) batteries, which are probably cheaper, more environmentally friendly (they don’t need lithium), and perform better in the cold, but they are also larger and don’t last as long.
Home battery technology is often similar to what you’ll find in electric vehicles. Some people even suggest using EV batteries like home batteries. But there are potential problems with that, not least finding your car battery dead in the morning. EVs also advance the technology in solid-state batteries, which are smaller with the same capacity, safer as they do not have liquid electrolytes inside, and last longer.
Most home batteries come in modular systems, so you can add the capacity you want, but they need a converter to convert the stored DC (direct current) energy into AC (alternating current) energy that you can use. People who have solar panels, or those who plan to add them in the future, should choose a hybrid inverter, which can also convert the energy from the panels for use or storage.
Inverters have different power ratings in kilowatts (kW) that indicate how much power they can draw at any given time. Households with modest needs may be able to get by with a 3.6-kW inverter, but that limits your continuous draw to 3.6 kW. They usually have a higher load capacity that goes up, allowing you to pull more for a shorter period of time. If you have high-demand appliances like an EV charger or heat pump, you’ll want at least 5 kW, and people with bigger needs or larger batteries will want higher (6 to 10 kW).
What Should I Look For?
There are a few things to be aware of when buying a home battery:
- Power: Measured in kilowatt-hours (kWh), this tells you how much total power the battery can hold.
- Discharger: Measured in kilowatts (kW), this indicates how much power the battery and inverter can deliver at any given time.
- Depth of discharge: Here’s how much battery capacity you can safely use without damaging it.
- Good performance: This is the percentage of the energy 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 the battery degrades (they all degrade over time), and is usually stated in terms of age and charge 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 by Simon Hill
It can be difficult to calculate how much battery capacity you need, and it depends on your use case. If you want to monitor blackouts or stay off the grid, you must consider how much energy you use over time and the total amount of energy you use at any given time to ensure that your capacity in kWh and output in kW are sufficient. If your output is not high enough you may not be able to run power hungry appliances at the same time, so you will have to think about how you use your power.
For people like me, if you’re just looking to buy at the cheapest price you can use when power is expensive, any capacity will benefit. But if you have a cheap rate of six hours overnight, for example, then you want it to go on for another 18 hours. It makes sense to get as much as possible up front because the installation costs are high. Even adding on modular systems later often requires professional installation to avoid voiding your warranty.
Do You Need an Upgrade or a Permit?
A home battery will connect to your main electrical panel via a cable, and may require some upgrades. There was no room on my fuse board when I installed the home battery, so they had to install a second breaker box.
Some inverters may require approval from your utility or local distribution company. Here in Scotland, the distribution network operator must approve your inverter, but you can install and charge up to 3.6 kW, while larger inverters require prior approval.
