Is it worth adding a battery to a small solar system?

I would like to install a battery to my 3kW PV system so I can keep all my solar electricity. Where do I start?

What to consider before buying a battery?

It’s great that you are interested in adding a battery to your solar system. In theory, this will allow you to better use your own solar electricity. There are a few things that you will need to consider for this, including 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 system has the capacity to charge a battery. A 3 kW 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 system being used and the amount exported back to the grid.

To add a battery and make it economical, you would need to have enough excess solar power 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 very little PV electricity available to go into the battery.

So, if you still would like to have a battery, it would then have to be a relatively small battery of 2-4kWh. Such small units, would then only last 2 to 3h in a blackout, if the homeowners are very 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 inverter, then adding more panels to the existing system is not an option. As 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 systems unchanged and add a completely new system, or they remove the existing 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 this would be worth it, and the recommended solution.

Why install a battery in the 1st place?

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 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 very expensive to have a very 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 big enough to do much at all 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 to 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. This will, for most households, show that it would be more beneficial to go for a  much larger system than your current 3kW solar system.

So in summary

A 3kW PV 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.