A solar system that is attached to the grid but also has a battery is commonly referred to as a Hybrid Solar power system. There is a wide range of Hybrid solar systems available and they all operate in slightly different ways so there are a lot of pros and cons to weight up when choosing a Hybrid system. Fundamentally they all operate by using an energy meter which detects power flows at you meter box. When the energy meter detects excess solar power heading out to the grid, the battery starts to charge to stop the power leaving. When the energy meter detects power coming into the site, the battery starts discharging to stop you buying power from the grid. 

People generally install hybrid systems for two reasons. The first is they want to use as much of the power they are generating as possible. These systems are set up to maximize self consumption. For these systems the battery needs to have a very good cycle life and be able to discharge to a low level. For efficiency, the system should be able to charge the battery directly with the DC solar power. Battery charging with AC power is less efficient. Our self consumption hybrid systems are built around the Sonnen Hybrid all in one Energy Storage system. The Sonnen has a built in inverter, and has DC charging of the battery. The batteries have the best warranty we have come across at 10,000 cycles, and they can be discharged to 90% DOD (depth of discharge). They tick all the boxes and they are a very tidy unit as well. As a bonus, Sonnen, a German company now produce the Sonnen in the old Holden factory in Australia. 

The other reason that people want a battery is to provide some power in the event of a power outage. If you have solar panels and a battery, it makes sense to at least be able to use the system in a power outage. While most Hybrid systems are able to provide back up power, the level of power available varies greatly. The Sonnen mentioned above doe have a backup capacity but it is limited to 10 amp supply. This is enough to run a fridge and freezer and charge a phone, but it can not start a water pump. The Sonnen also has the ability to keep the solar going in a power outage. Some systems give you power from the battery, but once the battery is flat, the solar cant recharge it until the grid comes back on.

With systems installed with a back up function, your also have to reserve a certain amount of battery capacity in case the power fails. The larger the capacity you reserve, the less is available for self consumption cycling during the time the grid is up. This affect's the economics of installing the battery.

For any customer that wants a bit more power during a power outage and a bit more of a robust system, we use Victron equipment in a more off grid style architecture. The system is still attached to the grid and can send power to the grid when the batteries are full, but it can also operate off the grid indefinitely and provide power to large loads in needed. 

At todays rates of power, and solar feed in tariff (what the power companies pay you for the power), its not economical to install a battery to save money. Installing a hybrid system currently is more of a self consumption motivator and an environmental motivator as using your own solar power at night is better for the environment than using national grid power in the peak period as it has a large coal and gas component. 

This will change in the near future as every power company have said they are moving to a time of use pricing model to better manage demand. When this happens, the price of power will be high during the peak times, so when this happens the battery system will come into its own as long as it can be set up in time of use mode. In this mode, you program the time slots when it expensive power, and that when the battery discharges.