Including electricity costs increasingly, home batteries have never looked so attractive. Whether you want to store the surplus produced by your solar panels or just buy electricity at a cheaper price to use later when energy is more expensive, a home battery can help. Installing a home battery has never been easier, but this rapidly expanding market can be confusing, and there are a number of things to consider before you buy.
I’ve spent months researching home batteries, talking to people who use them, and then have one installed yourselfand I have some tips for anyone who wants to get their own home battery.
Why Would You Want A Home Battery?
There are several reasons you may want to invest in a home battery, and they are not exclusive:
- You want to save a lot of energy from yourself solar panels.
- You want to live off the grid.
- You want to protect against power outages.
- You want to buy cheap electricity and save it for later use.
Home batteries are a win-win, and they can benefit power companies too, because battery storage is an important part of balance the grid and can help manage and make better use of intermittent and renewable energy (solar, wind, tidal).
How Do Home Batteries Work?
Photo: Simon Hill
The home battery is just as big power bank to your house. But instead of lithium-ion, it is lithium iron phosphate (LFP or LiFePO4), because it is safer, more durable, and less susceptible to thermal runaway. In other words, less chance of overheating and bursting 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 work better in winter, 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 have suggested it using EV batteries as home batteries. But there are potential problems with that, not least finding your car battery dead in the morning. EVs are also pushing technology forward solid state batterieswhich are smaller for the same capacity, safer as they have no liquid electrolyte inside, and last longer.
Most home batteries come in modular systems, so you can add the capacity you want, but they require an inverter to convert the stored DC (direct current) power into usable AC (alternating current). People with solar panels, or those planning to add them in the future, should choose a hybrid inverter, which can also convert energy from the panels for use or storage.
Inverters have different power ratings in kilowatts (kW) that determine how much power you can draw at any given time. Households with modest needs can get by with a 3.6-kW inverter, but that limits your continuous draw to 3.6 kW. They usually have a peak bearing capacity that goes higher, allowing you to pull more in less time. If you have high-demand equipment like an EV charger or heat pump, you’ll want at least 5 kW, and people with larger needs or larger batteries will want to go higher (6 to 10 kW).
What? What Should I Look For?
There are several things to consider when buying a home battery:
- Ability: Measured in kilowatt hours (kWh), this tells you how much energy the battery can hold.
- Power output: Measured in kilowatts (kW), this shows how much power the battery and inverter can produce at any given time.
- Depth of discharge: This is how much battery capacity you can safely use without damaging it.
- Efficiency: This is the percentage of the energy you put in the battery that you can use, because some energy is always lost in the storage process.
- Warranty: This is a guarantee of the minimum performance you can expect before the battery degrades (they all degrade over time), and is often specified in years 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 via Simon Hill
It can be difficult to calculate how much battery capacity you need, and it depends on your usage. If you want to protect yourself from blackouts or live off the grid, you must consider how much energy you use at any given time as well as your total maximum energy consumption at any given time to ensure that your capacity in kWh and output in kW are sufficient. If the output is not high enough you may not be able to run hungry devices at the same time, so you will have to think about how you use your power.
For people like me, looking to buy cheap to use when power is more expensive, any power will do. But if you have a cheap midnight overnight rate, for example, then you want it to last another 18 hours. It makes sense to get as much as you can up front because installation costs are high. Even upgrading to standard systems later often requires professional installation to avoid voiding your warranty.
Need Updates or Permissions?
The home battery will be connected to your main electrical panel via a cable, and may require some upgrading. There was no room on my fuse board when I installed the house battery, so they had to install a second breaker box.
Some converters 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 then notify up to 3.6 kW, whereas larger inverters require prior approval.
