Home battery storage
Introduction
More than 1.4 million or about 15% of Australian homes are already using solar energy to control their electricity bills and support sustainable power. If that sounds impressive, consider this - ten years ago, this number was limited to just 1500. This is a clear indication of the fact that Australians are ready for a renewables-revolution.
To add to this move towards a solar switch, home battery storage technology is promising practical and cheaper energy solutions for the future. With high electricity costs, climate change weighing heavy on people’s conscience and the country’s vast renewable sources, Australia is expected to be one of the largest markets for battery storage. Here’s a guide into what battery storage means for your home, your energy bill and the environment.
What is home battery storage?
Let’s start with the basics. Just like you use small-to-medium sized batteries in appliances like watches, phones and laptops to store energy so they can be used later, home batteries store the sun’s energy in the day so it can be converted into electricity and used at night.
In a traditional residential solar power system, rooftop solar photovoltaic (PV) panels generate electricity using the sun’s rays in the day. Since this electricity can only be used as long as the solar panels can access sunlight, homes that use the majority of their electricity at night can only use a small part of the total energy generated.
With a solar only system, the ‘excess’ energy generated by the panels is sent back to the local grid and the household earns a fee for this electricity, which is called a feed-in tariff. Consumers then use energy from the grid at night and pay for this separately. To enable households to use all the solar power generated at their home, battery storage technology comes into play.
What does home battery storage consist of?
Solar panels
Installed in an array on the rooftop, solar panels convert sunlight into electricity. According to Energy Australia, an average two-person home needs a 2.8kW to 4kW sized solar power system (with 11 to 16 solar panels) while a three-person home requires a system size of 4.1kW or more (17+ panels).
Home battery
The home battery stores excess electricity generated from solar panels during the day so it can be used at night. The battery can also connect to the utility grid and store surplus energy from the grid during off peak hours to use when the rates are higher.
Inverters
The electricity generated by the solar panels is direct current (DC), while the appliances at our homes use alternating current (AC) electricity. That is why, solar panels and home batteries are connected to the mains power supply through an inverter, which converts the DC power into AC so we can use it at home.
How does home battery storage work?
During the day when the solar panels are generating energy using the sun’s rays, the solar inverter supplies the house with electricity from the panels. This solar energy is also used to charge the home storage battery. In the evening, the inverter supplies the home with the power stored in the batteries. If the battery is discharged below a certain level, the inverter connects to the grid to power the home. If not enough energy is stored via solar, the battery can also be charged using energy from the utility grid.
What are the benefits of home battery storage?
Together with rooftop solar system, battery storage presents a huge opportunity for Australian homes to use a larger percentage of the solar power they generate at home and minimise the need to purchase expensive electricity from the grid. Advantages of home battery storage include:
Lower bills: Since many homes use the bulk of their energy at night, a battery storage system will power the house after the sun goes down reducing your dependency on the electricity from the local grid, therefore lowering your bills.
Green power: Apart from saving you money, battery storage is also good for the environment because it uses solar energy. Also, with the upfront cost for solar systems dipping over time, more people will be encouraged to adopt sustainable energy solutions.
Blackout support: A battery storage system should be able to keep some of your home’s appliances running for a number of hours even when the power is out.
Battery sizes and specifications
When choosing a home battery, there are a number of things to get your head around. While it may seem that the size or total capacity of the battery is the most important feature, a number of other interdependent factors determine how much power can actually be used at a given time and how your battery will perform in the long run. Some of the important aspects to consider include:
Capacity
A battery’s capacity is how much electricity can be produced over a period of time - usually measured in kilowatt hours (kWh). The capacity of your battery should relate to the capacity of your solar system and the amount of excess energy you are able to send back to the grid. For example, say your solar export is between 6 kWh and 9kWh in a day, you can consider a battery with a 7 kWh capacity and if your solar export is between 9 kWh and 15 kWh in a day, you can consider a battery with a capacity of about 11 kWh.
Depth of Discharge (DoD)
This is an important feature of a home battery. DoD is what tells us what percentage of the battery capacity has been used up. For instance, if a 10kWh nominal capacity battery has only 2kWh stored in it, then its current DoD is 80%. While a battery bank may have a capacity of 10kWh, that doesn’t necessarily mean it can store a useable 10kWh of energy. DoD limitations could mean it may only be possible to access 5kWh or 50% DoD.
The higher the DoD, the more battery capacity you can use before recharging is required. While you can use up all the energy stored in the battery, discharging batteries too deeply can significantly reduce the value that they provide over their lifetime.
Cycle life of a battery
The cycle life of a battery is the number of complete charge/discharge cycles that the battery is able to support. Each battery manufacturer will class its batteries as having a set cycle life at a specified average depth of discharge (DoD): for example, 3,000 cycles at 40% DoD.
Round trip efficiency
When you store energy in a battery, some of it is lost due to heat or other inefficiencies. Round-trip efficiency can be defined as how much energy is lost in a “round trip” between the time the energy storage system is charged and then discharged. Say, if 1kWh of electricity is fed into a battery and the amount of energy which can be extracted from that input is only 800Wh then the efficiency of the battery is 80%.
What these features mean for your usage
Now to put things into perspective, let’s take an example of a battery with a total capacity of 7.2kWh. Suppose this has a 90% DoD, you can actually use about 6.5kWh of energy before you need to charge the battery again. The amount of time it will take to use this stored energy depends on your usage. Say for instance, if your demand is 3kW, you will use it over two hours and if your demand is 1kW, your battery will last for six hours.
Who offers battery storage in Australia?
Battery storage is still a relatively new concept here in Australia (and around the world) but it is expected to grow in the coming years which is why a number of energy retailers and independent companies are investing in battery storage solutions. Here’s a quick look at what some of the bigger brands in the market are doing right now :
Tesla Powerwall
Tesla, which made its name in electric cars has launched Tesla Energy here in Australia. Powerwall is a wall mounted, rechargeable lithium ion battery with liquid thermal control and comes in 10 kWh and 7 kWh models. It comes with a 92% round-trip DC efficiency and is expected to cost around $3800 for 7 kWh and $4435 for 10 kWh. The Powerwall is expected to start shipping in late 2015. The system can be reserved via the Tesla website and must be installed by a trained technician.
AGL Power Advantage
AGL was the first major energy retailer to announce it was launching a battery storage device for the Australian market. AGL’s Power Advantage lets you choose from three different battery sizes (7.2kWh, 11.6 kWh and 19.4kWh) to fit with your existing solar system, or with a new installation. The Power Advantage range comes with an inverter and all installation costs included. It is compatible with solar PV systems from 3kW to more than 5kW in size. The three sizes are priced at $9,990, $14,990 and $19,990 respectively and come with a 10-year warranty. While the DoD for the 7.2kWh battery is 90% for the other two it is 80%. If you are interested in AGL’s solution you can register for further updates.
Origin Batteries
Origin Energy is also looking at launching battery storage products with a capacity of 3.6kWh and upwards. The energy provider is yet to announce the other specifications including cost and warranty for the battery. To find out more information you can register your interest on its website.
Enphase
Enphase, a global energy technology innovator, will launch its battery storage solution in Australia and New Zealand in winter 2016. The Enphase AC battery will have the capacity of 1.2kWh and a 95%DoD. It is expected to cost around $1150 but this is yet to be confirmed. You can opt for monthly updates on the system and launch dates for their website.
Battery Storage payback period
According to a Climate Council report, in Australia, most solar PV systems ‘pay for themselves’ in less than a decade. Other studies (Commonwealth of Australia 2014; ESAA 2015) have estimated solar PV systems pay for themselves between 4 to 12 years, with the shortest payback periods in the Northern Territory or South Australia.
Initially when feed-in tariffs were quite generous, Australian households with solar PV had greater incentive to feed as much electricity into the grid as possible. But as these feed-in tariff schemes have been scaled back or stopped in recent years, the incentive is also steadily dropping.
For instance, a typical house in Victoria earns 6.2c/kWh for solar power fed into the grid, (dropping to 5c/kWh in 2016), but are paying a much higher price to buy electricity from the grid (typically around 33c/kWh) when the sun is not supplying the solar panels with any energy.
As feed-in tariffs are phased out and electricity prices increase (particularly at peak times), solar PV systems with added battery storage will become the most economical solution to meet household electricity needs.
The current payback period for battery systems and solar PV according to the Climate Council is estimated between 6 and 12 years in NSW. A 5 to 8 kWh battery system would pay for itself in less than 12 years if electricity prices stay at current levels. If battery system prices continue to fall as expected, the payback is expected to drop to 8 years in 2020 and 6 years in 2030.
The end of power bills?
According to the government website Energy Made Easy, a typical 3-person household in Sydney uses 17.3 kWh a day in summer and 22.8 kWh a day in winter. Depending on how much of this energy is used in the day and at night, a home battery can take a considerable load off the amount of electricity you need to buy from the grid.
However, with the current storage solutions, it will be difficult for a battery to completely power an average home so that it can go entirely off the grid. While storage solutions at the moment may not mark the end of power bills, they can lower your energy spending and decrease the dependency on electricity from the grid.
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