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Types of batteries
There are two important factors to consider when comparing battery types: chemistry and coupling.
Chemistry
Different types of battery chemistries vary primarily in their power density, i.e., how much electricity they store in a certain amount of space. The main chemistries you'll see in home batteries are:
- Lead-acid batteries
- Lithium-ion batteries
- Flow batteries
Lithium-ion batteries are the most popular type used in residential and commercial energy storage systems, while lead-acid batteries are the oldest–and often the cheapest–technology. Flow batteries, the newest to the market, are not very common, but can store more energy relative to other battery chemistries.
AC vs. DC coupled batteries
Solar panels produce direct current (DC) electricity, and batteries store DC electricity. However, we use alternating current (AC) electricity to run our homes and businesses. This means that in order for you to use either the electricity from your solar panels or battery, it will have to be inverted from DC electricity to AC electricity.
Batteries can either be AC coupled or DC coupled. An AC coupled battery takes AC electricity, inverts it to DC electricity, stores it, and then inverts it back to AC electricity to use in your home or business. This is the most common setup for a solar-plus-storage system, and is almost certainly what you’ll get if you already have a solar panel system installed and are adding storage later. Importantly, while it’s the most common setup, there are downsides from an efficiency standpoint: you lose electricity every time you invert electricity from DC to AC or back again. And with any AC coupled system, your electricity will be inverted many times.
On the other hand, a DC coupled solar-plus-storage system charges your battery straight from your solar panels, without first inverting it to AC electricity or back again. To do this, a DC coupled storage system requires a hybrid inverter that acts as both a solar and storage inverter.
