Choosing Between a Solar Array Expansion and Adding Batteries

26th Nov 18

Written by James Doyle

Homeowners and businesses who already use a solar power system are often interested in enhancing their installation, especially if they were previously paying high electricity bills. However, there are many ways in which a photovoltaic array can be upgraded. A common option is simply adding more solar panels to produce more electricity, but battery systems have also become a viable addition.

When choosing between a solar array expansion and adding batteries, no option can be considered better than other for all cases. The best option can only be determined by analysing the electricity consumption of a building and how it is distributed throughout the day. Of course, there are cases where both options are beneficial, assuming the budget is available.

Expanding a Solar Photovoltaic System

The main benefit of making a solar array larger is getting a higher electricity output, which leads to further reduction of your power bills. However, keep in mind that this does not change how solar generation is distributed during a day:

  • Most of the electricity is generated in the hours around noon.
  • Generation is reduced early in the morning and late in the afternoon.
  • There is zero electricity output at night.

A solar array expansion is recommended if your daytime energy use is high enough to consume the additional electricity being generated. On the other hand, if you already have surplus energy production around noon, the business case for a solar array expansion is not so attractive:

  • You get a higher kilowatt-hour production, but cannot use a significant portion of the additional output. Most of the new production will end up being exported to the power network, and you only  get a reduced feed-in tariff.
  • For example, if you are paying more than 30 cents/kWh, getting only 10 cents/kWh for surplus production is not very attractive.

Commercial buildings with plenty of daytime activity can normally benefit the most from a solar array expansion. If electricity consumption is high during the day, and especially in the hours around noon, the building can probably fill its entire rooftop with solar panels without reaching surplus production. In this case, the full value of each kilowatt-hour is being saved, and not a reduced feed-in tariff.

Adding Batteries to an Existing Solar Power System

When a building has a solar power system already operating at surplus production, there is little benefit from making the array larger. In this case, you would simply be delivering more cheap electricity to your power retailer, and batteries can be a viable option.

The simplest way to use batteries is balancing generation and consumption: the battery system is configured to absorb any surplus generation from your solar array, and to provide energy when building consumption is higher.

Batteries can also make building energy consumption smoother, trimming sudden peaks in demand. Many commercial and industrial electricity users in Australia are subject to capacity charges, which are calculated based on the highest demand peak for a 12-month period. Since batteries have a fast response, they can trim these peaks and lower your capacity charges.


A solar array expansion and a battery system can be complementary upgrades, since the extra output from more solar panels can be used to charge batteries. However, you can only determine the best combination of solar generation and battery storage with a professional assessment of your building’s power consumption.


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