In a conventional solar pv system the house will use all the electricity produced from the panels before it imports electricity from the gird. If the panels produce more electricity than the house is using at that point in time it will export it to the grid to be taken up by other users.

In a battery storage solar pv system, this extra power will be diverted to the battery bank in your house and stored to use later when your house requires more energy than the array can provide and at night when the solar pv is not generating.

The wiring of the system is such that the house will use the battery power preferentially ahead of the grid (like conventional solar), thus saving you money as you no longer need to buy as much expensive electricity from the grid. You can use your free electricity that you have already generated instead!

If the battery bank is full, and your house demand is being met by the solar, any excess generation will still be exported to the grid, as usual, so other users can benefit.

There are two types of battery storage solutions for solar pv arrays, DC-Coupled and AC-Coupled. All solar pv panels produce DC current and this is then changed to AC current by the inverter so the power can be used by the appliances in the house. As a result, there is a DC side and an AC side to a solar pv system. Whether a storage solution is DC-Coupled or AC-Coupled refers to which side of the inverter the battery bank is.

In a DC-Coupled system the solar pv panels and the batteries are before the inverter and therefore the batteries can be charged directly from the panels at high efficiency as there are minimal losses. When power is required from the batteries the stored electricity then passes through the inverter to be used by the house just like normal power would from the panels.

In an AC-Coupled system the DC current from the panels is changed to AC current by the inverter, this is then changed back to DC by a second inverter to charge the batteries. When power is required from the batteries the stored power is then passed back through the second inverter to become usable AC current again.

The main advantages of an AC-Coupled system are that it is easily retrofit-able to any solar pv system and simple to install and does not require altering the solar pv system already installed.

With a DC-Coupled system there may be a need for an inverter change to make sure it is compatible with the new battery system but having one inverter increases the efficiency of the whole system and saves space which is useful in many domestic situations. This is also a great option for a new solar pv installation.

There are two main types of batteries sold to work with solar pv systems. These are Lead-Acid batteries and Lithium-ion batteries. These two types of batteries work very differently and both have merits depending on the conditions and location of the solar system. For domestic on-grid systems Li-ion batteries represent the best solution:

• High Energy Density (more energy per unit area)


• High depth of discharge (DOD)


• Higher continuous power output


• Long battery life / high number of charge cycles


• High efficiency between charging and discharging