Should I Add a Battery to my Existing 3kW Solar System?

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A few things to consider when adding a battery to your existing 3kW solar system.

To begin, determine whether your current system is large enough and has the technology to charge a battery. In general, a 3 kW system will not be large enough and we recommend a minimum PV system size of 6.6 kW before a battery should be considered.

So if your system does not generate enough excess solar power each day to charge a battery, you may need to upgrade or add more solar capacity. Consider what you hope to accomplish by installing the battery and how you intend to use the stored electricity.

An experienced solar designer and installer can help design a complete upgraded solar and battery solution that suits your home and family's needs.

Should I add a battery to my existing small solar system?

It’s great that you are interested in adding a battery to your existing solar system. In theory, this will allow you to better use your own solar electricity. A few things that you will need to consider for this include the size of your current solar system, to make sure the investment is worth it.

Can the existing system charge the battery?

Firstly, you need to explore whether the existing 3kw solar system has the capacity to charge a battery. A 3 kW solar PV system or actually anything below 5 kW is nowadays considered a small solar system.

Therefore the exported electricity of such a system will not be that much. So have a look at the monitoring data. This will indicate the amount of electricity from your solar power system being used and the amount exported back to the grid.

Old panels installed on home
Relative small solar systems installed 10, 8 or even as recent as 5 years ago are often not large enough in capacity to marry up well with a home storage battery

To add a battery and make it economical, you would need to have enough excess solar energy generated daily (that is being exported!) to be able to charge the battery that you would like to install. A perfectly north-facing 3kw solar system will, on average, produce 13kWh of electricity per day (more in summer and less in winter).

After daylight self-consumption for many homes, which could actually be more than 13 kWh, on many days there would be minimal PV electricity available to enter the battery.

So, if you still would like to have a battery, it must be a relatively small battery of 2-4kWh. Such small units, would then only last 2 to 3 hours in a blackout if the homeowners are extremely frugal. You will need to look at and consider what value such a small battery will actually add to your home.

Do I need to upgrade my renewable energy system?

The second option is to look at upgrading or adding further solar capacity. If your system is 3kW with a 3kW solar inverter, then adding more panels to the existing solar system is not an option. As solar installation rules change regularly, in most likelihood your 5-plus-year-old system is not compatible with current rules.

While the technical regulations allow you to continue operating your old system, any upgrades or additions to this system will have to see the latest rules applied, which makes the upgrade not economical.

For this reason, people either leave existing solar systems unchanged and add a completely new system, or they remove the existing solar system and install a newer PV array. One of the reasons is that 2 different systems with different-looking panels can look quite ugly on a well-presented home.

A brand new system, will enable the home to have increased generating capacity and then add a larger 6kWh, 10kWh or even 15kWh battery. Despite the environmental drawback of uninstalling a perfectly working 3 kW system, this, for most households would be worth it, and the recommended solution.

the Tesla battery is worth it
The cost of home batteries has been decreasing slowly over the years, making them more accessible to homeowners

Save excess solar power

The key reason to install a battery is to save your excess solar power generated during the day. You can then utilise this power during the evening peak and overnight. So it is worth considering how much electricity you use during the evening and overnight. For the average household, this would be 8-12 kWh

Risk of blackout

Additionally, the risk of blackouts may be an issue and can get worse with more EVs accessing the grid and large-scale solar power-generating plants existing in the system.

So to work out your needs during a blackout consider what electrical devices you would want to be working on during this period, (such as a fridge, some lights, a fan, maybe a modem, laptop etc.). To make the battery last as long as possible, it is better to limit the equipment powered during a blackout to essentials.

A blackout is not the right time to prepare a grilled chicken in the electric oven or to bake a cake. Otherwise, it can get extremely expensive to have an exceedingly large battery capacity to entertain such activities.

It may also be worth considering new and developing uses for your electricity from your battery, including Virtual Powerplants. VPPs can earn some additional income from selling power from the battery during peak grid events, back to the grid operators to help stabilise the grid.

Is a 3kW solar system large enough to be effective nowadays?

By current standards, a 3kw capacity solar system is on the smaller side, with the average system size installed across Australia being 8kW plus and getting bigger.

Our recommendation would be to have an experienced solar designer and salesperson review the energy usage of your home and the state of the current system. Did that older system use quality components or are panels and inverter on their way out?

Then ask them to design a complete upgraded solar and battery solution that is going to suit your home and family’s needs for now and the future.

This should include reviewing both your electricity usage patterns within the home, the potential for this to change in the future (such as charging an EV, increasing family size etc.) and the ability to add solar panels to the roof in the future. For most households, opting for a much larger system than your current 3kW solar system would be more beneficial.

So in summary

A 3kW existing solar system is often not large enough to support the average household’s energy needs, let alone charge a battery. Therefore, it is in most cases not worth it to add a battery to a 3 kW solar system.

Nowadays, you would need a minimum size of 6.6 kW PV array to make adding a battery worth it. Even then, it is recommended to have a higher number, such as an 8kW or 10kW array, to support both a solar battery and the home’s energy consumption.

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