Solar Batteries – Are They Worth It?

Many of us in the solar industry, along with many solar PV system owners have been long awaiting the day when solar home battery prices will drop sufficiently for them to offer a reasonable financial return.

Solar Choice regularly updates this article to provide a scientific view of “are we there yet?”. Since our first analysis back in February 2017, we have modified our calculators, assumptions and methodology to reflect the changes in the solar battery storage market.

This article is important to us, so if you have any feedback on our methodology or results, we’d love to hear it – send us an email. Also – see our more detailed analysis with 24 case examples here.

How do solar batteries work?

Before we begin our analysis, lets recap on how a solar battery works. Solar panels generate power during the day when the sun is shining. This power is used first to supply energy to the any needs of the home and surplus energy is then typically exported back into the grid. Some energy retailers offer a ‘feed in tariff’ to buy energy back off the customer.

As an alternative to exported energy back into the grid, the surplus power can be used to charge a battery. The home battery storage system can then be discharged in the evening to reduce the amount of power the homeowner needs to buy from the grid.

Solar power batteries store energy in DC. Batteries can be connected in via DC cables to a hybrid solar inverter. Some batteries come with their own inverter built in (e.g. the Tesla Powerwall) and can therefore simply be connected to the main switchboard like any other AC appliance. Read more on AC and DC connections for solar battery storage.

How do you benefit from a solar battery?

There are several ways in which a homeowner can benefit from connecting a solar battery to their solar panel system.

Saving on energy bills by reducing amount of power you buy from the grid

The obvious one is the financial benefit of reducing the amount of power that you need to buy off the grid. A typical residential solar system without a battery will cover about 30%-50% of household power consumption. With a solar battery, this can be increased to 80%, 90% or potentially even 100% of household power consumption.

When calculating your benefits, bear in mind that to charge a battery you have to forgo some solar feed in tariff revenue. For example if you charge a 10kWh battery during the day, that’s 10kWh less feed-in tariff that you will see on your bill. There will still be a benefit as you always pay a much higher rate to buy power than the rate that retailers are willing to buy it back off you.

Keep the lights on during a blackout

Blackouts can be highly frustrating and in some cases a risk to health. Different areas of the electrical network are more prone to receiving blackouts that others. Most solar batteries on the market are now capable of keeping the lights on during a power outage. With some battery models additional hardware is required to enable the battery to continue providing power during a blackout.

With the energy market closing due to soaring energy prices in mid 2022, for some Australians, we see a desire to increase their independence from the power network. Solar and batteries effectively takes the majority of requirements and costs into your own hands.

Reduce your carbon footprint

Although we’ve made huge progress on the rollout of renewable energy infrastructure in Australia, the majority of the power generated on the grid is still from carbon intensive, fossil fuel sources. Installing solar panels is a great start to reducing your carbon footprint, but adding a solar battery will often more than double the reduction in your carbon footprint.

Solar Battery Virtual Power Plant (VPP)

In recent years we’ve seen the emergence of many different Virtual Power Plant schemes in Australia. For a participating homeowner, their solar battery may be discharged or charged by the VPP operator at times when they can make money on the wholesale or ancillary markets.

In exchange for this usage (which is often only a couple of times a year) the VPP operator will offer a benefit to the homeowner which might take the form of one of the below:

1. Bonus feed-in tariff (very high rate for power that is used)
2. Annual fixed fee for participating
3. A discount on the installation of the battery

How much do solar batteries cost?

Solar Choice has been tracking the average cost of residential batteries in Australia across our database of over 200 solar installers in our Battery Price Index since 2017. Residential solar batteries usually cost between $1,000 to $1,300 per kWh of capacity installed depending on brand, size and location.

The below table shows our current price index which excludes all of the state-based rebates:

State rebates for solar batteries

While there is no federal rebate for solar batteries like the STC rebate for solar panels, some of the state governments have introduced rebate programs aimed at accelerating the uptake of residential batteries.

Victoria

A rebate of up to $2,950 is available for Victorian homeowners who have already installed at least 5kW of solar panels, not already received a Solar Victoria solar and have a household income under $180,000 per year.

ACT

In the ACT you can get an interest free loan up to $15,000 to cover the cost of solar and battery systems. The eligibility criteria is quite broad and supports the uptake of a range of climate friendly products.

Solar battery ROI, savings and payback period

To demonstrate the potential returns of a solar battery we’ve put together a common scenario for a homeowner in Australia. We’ve used up to date prices for electricity and solar feed in tariffs and used our proprietary model which simulates the outcome of the project on an hourly basis for the next 2 decades.

If this scenario does not match your circumstances, then you can enter your details into our advanced solar and battery calculator.

Energy Usage Scenario

We have taken a typical scenario with peak energy usage in morning and evening with a total energy usage per day of 30kWh. Energy rates were assumed to be a flat rate of 30 cents per kWh and a feed-in tariff of 5 cents per kWh.

Solar and Battery Solution

We have analysed the impact of a 6.6kW solar system with a 10kWh solar battery on a household with 30kWh of daily usage following the profile in the above graph. Together the solar and battery system would cover 66% of the energy requirements of the house (increasing from 39% from 6.6kW of solar panels only).

The battery is recharged completely on 98.5% of the days. Given the high cost of batteries we recommend including enough solar panels to reach at least an 80% battery utilisation.

Financial return

See the below table which summarises the outcome of the above scenario. The key takeaway is that the payback period for the solar battery is 13 years. Most solar batteries on the market are only warrantied for 5 to 10 years, so in this scenario it is likely that the solar battery will not be able to pay for itself during its lifetime.

Assumptions:

• Flat electricity rate of 30 cents per kWh and feed in tariff of 5 cents per kWh
• Solar and battery pricing from Solar Choice Price Index and Battery Price Index
• Electricity usage of 30kWh a day with load profile as described above
• Energy price inflation at 3% and future cash flow discount rate of 5%

This scenarios does not match up? Put your own details into our Advanced Solar and Batteries calculator and determine the ROI for your own circumstances.

Solar Battery Storage Payback Results by Australian city

In our detailed solar battery study we assessed 24 scenarios including examining the different outcomes in each of Australia’s states and territories. As described in the graph below, solar batteries are most attractive in Canberra, Perth and Sydney when comparing the payback periods.

Important Note: These figures include the ACT battery rebate and the Solar Victoria Rebate and is based on the time of use rates.

Conclusion: Solar Batteries Financially Challenged

Based on our numerous analyses of scenarios over the years, we are yet to see a case to install a residential battery with an attractive financial return. The payback period for a solar battery is usually longer than the warrantied life of the battery, even after factoring in additional discounts from the Solar Victoria rebate or Virtual Power Plants. So installing a solar battery is generally only worth it if homeowners place some value on blackout protection and reducing carbon emissions.

Previously Solar Choice has estimated that residential solar battery prices would need to fall to $200-$300 per kWh of battery capacity installed to provide an attractive return, while the current market price is closer to $1,000 per kWh. We have seen the case for batteries become financially attractive in commercial applications and off-grid scenarios where the revenue calculations are a little different.

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