Explained: The Tesla Powerwall and what it means for Australia's energy market

Updated

The Powerwall, a lithium-ion battery system designed to store electricity generated from rooftop solar panels, is widely considered to be a game-changer for the electricity industry. 7.30 has asked consumer group Choice to crunch the numbers. Here's what they found.

What is the Tesla Powerwall?

While the concept of a home battery storage system is not new to Australians, the Tesla Powerwall unit has been highly anticipated.

The Powerwall is a 7 kilowatt hour (kWh) lithium-ion-battery system that stores electricity generated from rooftop solar panels (or PV panels) during the day so that electricity can be used at night during the peak-usage times.

The system has attracted a cult-like following in recent months after the announcement that Australia would be one of the first countries to have access to it.

The first installations of the Tesla Powerwall are now underway and have a 10-year warranty period.

How does it work?

The battery has a daily cycle, meaning it is designed to charge and discharge each day.

The efficiency of the battery is 92 per cent, so although it has a 7kWh capacity, the Powerwall's working capacity is more like 6.4kWh.

Tesla also has a 10kWh weekly cycle version intended for back-up applications, but it is the 7kWh version you will see in most home installations.

People who already have solar panels will be able to use their own power rather than exporting it to "the grid" — the energy distribution network that carries electricity from power stations to homes and businesses.

One of the Australian providers of the Powerwall, Natural Solar, says that there are only two inverters currently on the market which are compatible with the Powerwall, so most existing solar panel owners will need to obtain a new inverter.

If you do not already have solar panels, the Powerwall can be purchased as part of a complete system that includes solar panels and an inverter.

You will need a solar array large enough to power both your home and charge the Powerwall — for most homes that would mean at least a 4kWh array.

How much does it cost?

If you already have solar panels, the Powerwall and a compatible inverter will cost you between $12,000 and $12,500 depending on which inverter you choose.

Energy companies are selling Powerwall packages for between $13,990 and $16,500 (GST inclusive) and with consideration to rebates for small-scale technology certificates (STCs).

Is the Powerwall big enough to take my house off the grid?

It depends on your energy needs and the number of people in living in your household, but a 7kWh battery is not going to be enough to make most households independent of the electricity grid.

It is possible to install two or more battery units to increase your storage capacity.

So what does this mean for the grid?

The cost of energy has consistently rated as the top concern for Australian consumers according to leading consumer advocacy group Choice.

The latest report shows that almost two-thirds of Australians want to be self-sufficient in meeting their energy needs and while battery systems will not give complete independence for most consumers, it does offer a bit more control.

Costs of battery storage systems have been falling at a rapid rate and forecasts are for this trend to continue as more and more households adopt them. It is expected that prices will halve again within the next five years.

Solar panels have also gotten cheaper, with the Climate Council reporting a 75 per cent drop in price over the past five years.

With the global market for solar panels and battery storage expected to grow tenfold by 2020, the demand for battery systems like the Powerwall should have flow-on effects on prices as economies of scale kick in.

Even if consumers were able to make themselves independent of the electricity grid, they may benefit from selling their electricity back to it rather than storing it.

Companies such as Reposit, an ACT-based start-up, are using the grid's infrastructure to allow people to trade their energy directly on the wholesale market, effectively acting like a mini power station in everybody's backyard.

If there was a wholesale defection by consumers it could create what is known as a 'death spiral' in which a smaller and smaller amount of consumers are left on the grid, leaving only those on lower incomes or those unable to afford a Powerwall to carry the cost of running the grid.

What is the payback time for the Powerwall?

The payback time will be different for every household but in some instances it seems the payback time may well exceed the warranty period for the Powerwall.

There are many factors that need to be taken into account when calculating payback times, but you can get a rough estimate if you know your daily energy usage and what percentage of this energy you use during peak and off-peak pricing periods — this information should be available on your energy bill.

It is also worthwhile checking if there are any state or even local government rebates available for purchasing solar panels or a battery storage system.

The payback time would be less if you already owned a solar panel system, particularly if you are tapping into your own solar power as much as possible, rather than feeding it back into the grid. This would depend on how your feed-in tariff compares to your electricity price.

There are a range of factors that can influence the outcome, including increases in electricity retail prices and ongoing maintenance costs, which you might want to factor into your own calculations, but this case study by 7.30 and Choice might help you get a rough idea:

Andrew has signed up for an installation of a solar array combined with a Powerwall with Origin. He has a freestanding house in a Western Sydney suburb, where he lives with his wife and two children, aged eight and 10.

Andrew's household roughly uses around 38.4kWh of energy per day at a price of 21.81 cents per kWh. Andrew and his wife both work from home part-time, which makes their energy use higher than most households. It also gives them more potential to tap into their own solar energy rather than feeding it to the grid.

If Andrew was to install a 4kWh solar array on his roof, he could expect to generate around 15.6 kWh of electricity per day, on average. About 7.5 kWh of this would be required to charge the Powerwall due to inefficiencies with the battery and inverter, which could then be used to offset 6.4 kWh of his energy use during the night when his solar panels are not producing electricity. This would save him $1.40 per day (6.4 kWh x 21.81c).

If we assume Andrew did not use the remaining 8.1 kWh of solar energy after charging the Powerwall and fed it back into the grid, this would earn him $0.49 per day with a feed-in tariff of 6 cents per kWh. Together with the savings from using the Powerwall to store electricity for later use, this will give a total saving of $1.88 per day, or around $687 per year. With Origin's total system cost of $16,500, Andrew has a payback time of just over 24 years, or 2.4 times the warranty period.

But since Andrew and his wife work from home part-time, this allows them to make the most of their solar panels. If we assume Andrew could use half of his solar electricity remaining after charging his Powerwall every day, then he would lose $0.24 per day in feed-in tariffs but would save an additional $0.88 per day in electricity costs (4.05kWh x 21.81c). This would save him $2.52 per day or close to $921 per year. This equals a payback time of 18 years.

Obviously the more solar energy Andrew can use to power his house the better the payback time will be through lower electricity bills. Assuming he managed to tap into all of his solar power by increasing his daytime energy use and charging his Powerwall, Andrew would be saving $3.16 per day (14.5kWh x 21.81c). This would give an annual saving of $1,154 and a payback time of just over 14 years, which is still four years past the Powerwall warranty period.

In the case of Andrew, we estimate the $1.88 he would save per day by charging his Powerwall and sending the rest of his solar energy to the grid would give a payback time of close to 17 years, based on Natural Solar's price of $12,000 for the Powerwall and a compatible inverter. If he used half of his solar power he could expect a payback time of around 13 years. Only if he used all of his solar power could he expect a payback time that falls within the Powerwall's warranty period — coming in at 9.7 yearFs.

For more consumer information on the Tesla Powerwall, check out the Choice website.

Topics: electricity-energy-and-utilities, alternative-energy, solar-energy, energy, consumer-protection, australia, quakers-hill-2763

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