What size solar battery do I need?

Fast read

The excess solar energy that would generally be exported to the grid is stored using solar batteries. The amount of power consumed by the home, the size of the solar panel system, and the percentage of electricity utilised during the day vs the night all affect the size of the required solar battery.

The typical 6.6 kW solar panel system generates roughly 25 kWh annually. Depending on the location, the typical family residence uses about 20 kWh of electricity daily for the average home. Therefore, the size of a solar battery should be between 10.4 and 14.4 kWh. This will cover any nighttime electricity usage that exceeds needs.

However, the battery size might need to be increased if the house contains an electric car to meet its charging requirements.

Solar battery sizing explained to you

Solar batteries allow a residential property or business to store excess solar energy. Rather than letting that energy be exported to the grid. Those electricity exports to the grid are usually rewarded via a low payment of 5 to 10 cents per kW/h. As a result, solar batteries and their size equip owners to power their residences at night with renewable energy.

Here is a rough calculation of solar battery size

The sizing of a home solar battery depends on various factors. However, one could expect very roughly that a 10-13kWh solar battery could be enough to power an average family home at night (assuming the solar system is big enough and the panels produce enough spare electricity during the day).

We come to this initial conclusion because the average home consumes about 20 kW/h per day in electricity. Therefore if we count roughly 50% consumption during the daylight hours and 50% at night, a solar battery this size will cover the needs of most homes.

Now to get into more specific individual calculations. But, first, one must examine their electricity bill and determine their average daily consumption over the past 12 months.

If your home consumes 30kW/h per day, then in a rough calculation, you would need approximately 15 kW/h of solar battery storage to be relatively self-sufficient.

Of course, your solar system must also be big enough to generate sufficient excess electricity to fill the battery. So the sizing of the solar system, the household’s consumption pattern, and the solar battery’s size need to be finely aligned and tuned.

This is where an expert is needed to check consumption patterns. As well as the available roof space for solar and battery needs.

A detailed example for you

Daylight hours, when the sun is shining on solar cells, can account for around 30% to 60% of an average household’s electricity usage. Whereas nighttime accounts for the rest.

Naturally, the specific details depend on how much time people spend in the home during the day.

Retirees will have a high percentage of daytime in comparison to a family. When everyone is out of the house during the day, cooking, TV watching, and washing occur at night.

The average family home uses around 20 kWh of electricity throughout the day. The average 6.6kw solar panel system produces an average of 22 kWh of electricity annually in Hobart, 24 kWh in Melbourne, and 29.5 kWh in Brisbane.

In our specific example, only 40% of the household’s electricity is used when the sun is shining and the solar panels are operating.

If this household were in Melbourne, only 9.6 kWh of electricity produced by solar panels would contribute to the household’s daily electricity consumption. The rest being 14.4 kW/h on average per day, will be exported back to the grid.

animated battery image which has been sized correctly
Solar batteries allow the storage of energy produced during the day for later use.

What does this mean

This means that 10.4kWh, of the 20 kWh average electricity use per day will need to be purchased from the energy grid to cover the nighttime use. So the solar system generates enough electricity daily to supply the family’s needs. It does not produce it at the right time.

This is where a solar battery system is essential to make our “homegrown” renewable electricity available 24/7 when we need it.

In our sample above, we import 10.4 kWh at night and export 14.4 kWh during the day. So we have 14.4kWh available to fill a battery. So, in conclusion, the best solar battery size for your home ideally sits somewhere between 10.4 and 14.4 kWh.

As you can see, many calculations and considerations are involved. This is why we recommend high-quality, focused experts to assist.

BUT THERE IS MORE…

There is now one new factor to consider. This might double or even triple the solar battery size required.

This factor is the electric car. Many homes have two or even three vehicles, and most cars travel at least 50 km daily in major cities. Therefore, one would need to cater to these future EV cars’ charging needs via the solar battery.

With a need to use 12 to 18kWh to travel 100 km. A 20 to 30kWh solar battery size could supply the house at night and help charge the EVs daily.

To get all this consumption covered by the rooftop solar system. One would have to have a solar system that generates at least the daily household and EV charging consumption of about 40 kW/h.

So because of the EV – we have just doubled the PV system and solar battery size needs of a standard home.

You can use our output calculator here to determine your personal needs or how big a solar system one would need to create this much solar each day, for most days of the year.

Average daily generation

Suppose we use the average daily generation of 40 kW/h as our yardstick. Then in Darwin, we would need a 7.73 kW system. In Perth an 8.55 kW, in Brisbane 8.95 kW, in Adelaide 9.45 kW, in Sydney a 10.02 kW, Melbourne 10.95 kW, and in Hobart, one would need at least a 12kW solar system.

You can see by the numbers above that different parts of Australia will generate additional kWh of electricity for each kW of the system. So it clearly shows that the amount of sunshine and sun intensity is directly linked with the overall output of the solar system.

Interestingly, we would need a 50% bigger solar system in Hobart. But, compared with Darwin, it generates the same amount of electricity.

So what’s the best solar battery size for me?

Your solar battery’s size has to cover at least your nighttime consumption. Ideally, even a little more to take care of those rainy periods when solar production is reduced.

So one has to break down one total 24-hour electricity consumption into the daytime and nighttime parts. These numbers will allow your solar installer to give you the correct solar battery size.

All these numbers will be unique to each household. So feel free to check out our solar and battery calculators to understand better what suits you.

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