Home batteries: how to install them and how much they cost

With electricity costs High-voltage home batteries have never been so attractive. Whether you want to store the surplus generated by your solar panels or simply buy electricity at the cheapest possible price for later use 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 many things to consider before purchasing.

I’ve spent months researching home batteries, chatting to people who use them, then installing one myself, and I have advice for anyone interested in getting their own home battery.

Why do you want a home battery?

There are several reasons why you might want to invest in a home battery, and they are not exhaustive:

• You want to store excess energy from your solar panels.
• You want to live off the grid.
• You want protection from power outages.
• You want to buy electricity cheaply and store it for later use.

Home batteries are a win-win, and potentially benefit energy companies too, because battery storage is a key part of grid balancing and can help manage and make the most of intermittent power generated from renewable energy sources (solar, wind, wave).

How do household batteries work?

Photo: Simon Hill

A home battery is like a big power bank for your home. But instead of lithium ion, it tends to be lithium iron phosphate (LFP or LiFePO).₄), because it is safer, more durable and less susceptible to thermal runaway. In other words, less likely to overheat and ignite. There are a few manufacturers that work with sodium-ion (Na-ion) batteries, which are likely to be cheaper and more environmentally friendly (doesn’t require lithium), perform better in the cold, but are also larger and don’t last as long.

Home battery technology is often the same as you’ll find in electric cars. Some people have even suggested using electric car batteries as household batteries. But there are potential problems with that, not least if your car battery dies in the morning. EVs are also pushing technology forward toward solid-state batteries, which are smaller for the same capacity, safer because they don’t have liquid electrolytes inside, and last longer.

Many household batteries come in modular systems, so you can add whatever capacity you want, but they require an inverter to convert stored DC (direct current) power into AC (alternating current) power that you can use. People with solar panels, or those who plan 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) which determine how much power you can draw at any given moment. Households with modest needs can get a 3.6 kilowatt inverter, but this limits the continuous draw to 3.6 kilowatts. They usually have a higher maximum load capacity, allowing you to tow more for a shorter period. If you have high-demand devices like an electric car charger or heat pump, you’ll need at least 5 kilowatts, and people with larger demands or larger batteries will want higher power (6 to 10 kilowatts).

What should I look for?

There are several things you should pay attention to when purchasing a home battery:

• capacity: Measured in kilowatt-hours (kWh), this tells you how much total power the battery can hold.
• Power output: Measured in kilowatts (kW), it shows how much power the battery and inverter can provide at any given moment.
• Discharge depth: This is the amount of battery capacity you can safely use without damaging it.
• efficiency: This is the percentage of energy you put into the battery that you can actually use, because some energy is always lost in the storage process.
• a guarantee: This is a guarantee about the minimum performance you can expect before the battery degrades (they all degrade over time), and this is often stated in years and charge cycles (whichever comes first). For example, EcoFlow technology 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 use case. If you want to protect against power outages or live off the grid, you should consider how much energy you use over time and also the sum of your maximum energy use at any given moment to ensure that your capacity in kilowatt hours and output in kilowatts is adequate. If the output isn’t high enough, you may not be able to power power-hungry devices at the same time, so you’ll have to think about how you’re using your power.

For people like me, who are simply looking to buy at a cheaper price to use when power is more expensive, any capacity will benefit you. But if you have a cheap rate for six hours for one night, for example, you’re better off going for another 18 hours. It makes sense to get as much as possible upfront because 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 house battery will be connected to the main electrical panel via cable, and may require some upgrades. There was no room on my fuse panel when I installed a home battery, so they had to install a second breaker box.

Some transformers may require permission from your electrical distribution utility or local distribution company. Here in Scotland, your inverter must be approved by the distribution network operator, but you can install up to 3.6kW and then notify it, while larger inverters require prior approval.