Battery Storage - How does it work?

Battery Storage

Solar systems generate electricity to power your home during daylight hours and the more sun there is the more they will generate. Any power produced that is not used within your home will be exported to the grid. If you need to use electricity during the hours in which your solar is not producing any power, you will have to purchase the electricity from the national grid.

With our solar battery chargers you will be able to store any electricity produced by your solar panels that has not been used, to use at any time, completely free of charge!

The battery storage systems work similar to a regular battery that you would find in standard home items like a torch or a TV remote; the electricity generated by the solar panels that is not being used anywhere else in your home is used to charge your battery. Then, later in the day, even when the sun has gone down, the solar battery storage can be used to power your home, completely independent from the grid.

AC Coupled

Solar panels generate Direct Current (DC) and batteries also store DC, however the grid along with household appliances use Alternating Current (AC). In order for your battery storage system to work there needs to be an inverter to change the currents. There are two types of set-up, either AC Coupled or DC Coupled.

In an AC Coupled set up there are two inverters. The first is what would be installed with your standard solar system which converts the DC to AC. The second inverter converts the current from AC back to the DC that is needed to charge the battery.

This set-up is generally used for a storage system being retrofitted to an existing solar array.

DC Coupled

Solar panels generate Direct Current (DC) and batteries also store DC, however the grid along with household appliances use Alternating Current (AC). In order for your battery storage system to work there needs to be an inverter to change the currents. There are two types of set-up, either AC Coupled or DC Coupled.

This type of set up only needs one inverter for both the solar panels and the battery. The electricity generated from the solar panel flows into the inverter as a Direct Current (DC), this ‘hybrid inverter’ then either converts it into Alternating Current (AC) to be sent to the house or the grid, or the inverter keeps the current as DC to be sent to the battery in order to charge it.

This type of set-up can only be used for a new solar system being simultaneously fitted with a storage system, and cannot be used on a retrofit.

Battery Types: Lithium-ion batteries

Lithium-ion batteries are very popular with domestic solar storage systems.

  • More efficient
  • Faster charging
  • More capacity
  • More expensive
  • Smaller and lighter
  • Lifespan of 10+ years

Most batteries are equipped with a ‘mains charging’ feature to top up the batteries when they cannot reach full charge from the solar alone – this is common in winter, this is because incomplete charging can have an effect on the lifespan of your battery.

Battery types: Lead-acid batteries

Lead-acid batteries are often used for energy independent properties, who live entirely off the grid, where more storage is needed.

  • Considerably cheaper
  • Less efficient
  • Shorter lifespan (up to 7 years)
  • Bigger and heavier
  • More maintenance

The average solar PV system can last 25+ years, unfortunately, there aren’t any battery systems with that length of lifespan, so your battery system will need to be replaced within the lifetime of your solar system.

Battery Capacity

The average three bedroom household will require a battery between 3kWh and 6kWh, whereas, if you are looking to go completely off-grid, you would need a battery around 10kWh.

Batteries tend to lose some energy during charging and discharging, meaning that a battery’s actual usable capacity will be less than the battery’s stated capacity – this will vary due to the ‘depth of discharge’.

The two types of battery provide different depths of discharge:

A 6kWh lithium-ion battery with a 75% ‘depth of discharge’ will provide 3kWh.
A 6kWh lead-acid battery with a 50% ‘depth of discharge’ will provide 4.5kWh.