Energy storage update
Domestic energy storage systems are becoming more popular as their prices come down and electricity prices go up. Lance Turner updates what’s happening in the market and what to look for.
The number of domestic renewable energy systems being installed with energy storage batteries has increased dramatically in the last couple of years. Figures from the Clean Energy Regulator show that there have been nearly 10,000 domestic solar systems installed with storage included at the time of installation, including over 2000 from the first half of 2018 (see Table 1). This does not include batteries added to existing PV systems where installation numbers have skyrocketed: in total over 20,000 battery systems were added in 2017, a huge jump on the 6750 systems added in 2016 (see the Climate Council’s report ‘Fully Charged: Renewables And Storage Powering Australia’). Also note that the Clean Energy Regulator’s numbers do not include those systems which have not yet had STCs claimed for them—the regulator allows up to a year for certificates to be claimed.
What’s changing in the market
The range of domestic-sized storage systems continues to change, with new systems appearing and some older systems becoming unavailable. There are systems ranging from a couple of kilowatt-hours, capable of running a few appliances for an hour or two, right up to systems with dozens of kilowatt-hours in capacity, capable of providing a full day of energy backup for the average suburban home.
As systems evolve, new features are added, with more advanced monitoring and connectivity, and even the capability to update system firmware ‘over the air’. A good example of this is the recent update to Tesla Powerwalls, which enabled these systems to check weather reports and fully charge the battery if there is a pending storm, so that maximum backup capacity is available in case of a blackout. We expect to see other manufacturers adding such capabilities to their systems in the near future.
Most systems are now designed to be ‘off-grid capable’: they can not only be used in off-grid systems, but are also capable of blackout backup for grid-connected homes in a suitably designed and configured system.
Buying a battery system
The first step to buying a battery system is to see if it is actually worth buying one. Renew’s ‘Household Storage Analysis’ report found that, given the average expected 10-year lifespan of a typical battery system, the economic value of batteries will still be unattractive for many households for the next few years, but this should turn around by 2020 if the projected falls in battery costs do occur. Of course, this depends on how much energy you use, when you use it, your location, as well as the size of your home’s PV system. Renew has also developed a simulation tool called Sunulator to help homeowners determine the economic value of installing solar PV and battery systems. Find the report at renew.org.au/HBA-report and Sunulator at renew.org.au/sunulator.
There are some cases where the economics may stack up or where there are other benefits. Those involved in a virtual power plant (see later in article) may get batteries at a lower cost, plus the coordination of their systems should provide grid benefits. Other potential cases range from needing backup in the case of power outages, to avoiding wasted generation from an export-limited or oversized PV system, to avoiding exacerbating voltage rise issues in the powerlines on your street. Early adopters installing batteries also help technology development. For more on these sorts of pros and cons, see Energy Flows: How green is my solar in Renew 135.
If you have decided that you want a battery system, then you should have some idea of your budget, the size of the system that fits into that budget (don’t forget the not-insignificant installation costs) and the features you would like; for example, do you need backup in the case of a blackout; what monitoring and control options do you want. If you have an existing solar PV system and want the battery to integrate with that, you may be limited to a storage system that is compatible with your existing inverter or other equipment. You may also want to consider whether the battery has capabilities to interface with third-party services like Reposit.
Another thing to consider is the location of the system. Some lithium battery systems will need to be located in a fire-proofed area, most likely outside or in the garage, and lead-acid systems will need to be ventilated to the outdoors. There will be some installation requirements that apply regardless of the system type, including having adequate space for the installation.
The buyers guide in Renew 141 gives you more information about what to look for, and the Clean Energy Council has put together an excellent set of guidelines, along with a downloadable guide; see www.bit.ly/CECSBSF. A good place to start looking at storage systems currently available is the Solar Quotes battery storage comparison table. This lets you compare systems based on price, size and shape, chemistry, rated capacity, compatibility, warranty, lifespan and other specifications. The Australian Renewable Energy Agency (ARENA) has been performing ongoing testing of numerous battery systems of various chemistries, with interesting results (www.batterytestcentre.com.au).
Battery chemistry options
So what makes one battery type better than another for a particular use, and which technology should you be looking at for your energy storage system needs? Let’s look at the current battery chemistry/design options in a bit more detail.
What about supercapacitors?
There’s been a lot of talk lately about supercapacitors (or more accurately, ultracapacitors) that can take the place of batteries in energy storage systems. Capacitive storage has a much lower ability to store electrical energy than chemical batteries, as it relies purely on storing electrical charge as an electric potential rather than using chemical reactions. This means that for a given amount of stored energy, capacitors are considerably larger and more expensive than a battery of equivalent capacity.
The main attraction of supercapacitors is their ability to charge and discharge at very high rates, as well as being able to undergo many thousands (even millions) of charge-discharge cycles with minimal loss in capacity.
There have been a few ‘supercapacitor’ systems in recent years that have claimed to have specific energy (energy stored per unit of mass) ratings similar to lead-acid and even lithium batteries. Lead-acid batteries have specific energies of 30 to 40 Wh/kg, with lithium batteries ranging up to around 200 Wh/kg, depending on chemistry. Supercapacitors come in under 10 Wh/kg, with most being around half that.
However, a device called a lithium ion hybrid capacitor (also called a carbon-enhanced battery) combines the features of a battery and a capacitor together. These can have specific energies up to 40 Wh/kg (such as for the Yunasko lithium ion capacitor) while being capable of the high charge and discharge rates typical of capacitors. It should be noted that these are effectively still batteries as the bulk of the energy storage is done chemically, and calling them capacitors is not strictly accurate.
True capacitor-only based energy storage systems do not currently have the energy storage capacity per unit volume or mass of any modern chemical batteries, and are considerably more expensive per unit of energy stored. No true capacitor currently manufactured has capacities capable of replacing a battery-based energy storage system of comparative size, weight or price.
Current claims of capacitors with similar specific energies to chemical batteries could be misleading and further scrutiny is advised—these systems could be mislabelled lithium battery systems using lithium titanate cells (for systems rated above around 40 Wh/kg) or lithium enhanced capacitors (hybrid capacitors).
While a battery allows you to store your solar energy for use at a later time, if you can shift heavier loads to the middle of the day you can make much better use of the energy you generate without the need for a battery.
A good example of this is to use a heat pump hot water system (or even a resistive element hot water system, if you have a lot of excess solar), and use a timer to run it in the middle of the day. This allows the hot water system to store the excess solar energy in the form of hot water—effectively making your water heater a form of battery.
The same applies to other loads, such as a hydronic heating system, which can store solar heat in a large water tank for use in the evening when you get home from work, or you can simply shift other loads such as washing machine and dishwasher use to the middle of the day. While the latter isn’t a form of energy storage, it does make effective use of solar electricity at the time of generation, reducing the need for storage. The availability of in-built timers in many appliances makes shifting runtimes easy nowadays, without the need for additional timers.
It’s not just about domestic-scale systems; there’s been a lot happening in the large-scale storage sector. Much more is needed before we get to 100% renewables, but the direction is positive.
Storing large quantities of electrical energy for the grid has traditionally been done using systems such as pumped hydro, where water is pumped to a high reservoir using excess grid power, allowing it to flow back to a lower reservoir via a hydro turbine at times of greater demand. Such systems are well understood and there are numerous pumped hydro systems around the world, with several new proposals for Australia being tabled in recent months. These include Snowy Hydro 2, which involves linking the two existing Snowy scheme reservoirs through underground tunnels and an underground power station with pumping capabilities (www.bit.ly/2KARDX6), and up to 14 potential sites in Tasmania (www.bit.ly/2KCgFFk).
ANU’s Atlas of pumped hydro energy storage identified around 22,000 potential pumped hydro sites in Australia. Although their report noted that the commercial feasibility of developing them is unknown, it also estimated that the best 20 sites could provide all the grid storage Australia needs to move to 100 % renewable energy.
The most well-known of the ‘big batteries’ is the 100 MW Tesla lithium ion storage system installed in South Australia and known as the Hornsdale Power Reserve. It can charge at 80 MW and discharge at 100 MW, and has a capacity of 129 MWh, so it can provide full output for more than an hour. It has already proven its ability to respond to grid demand far faster than any other generation source; when almost 700 MW of generation tripped out last summer, the Tesla battery started feeding the grid to help make up the difference in just a few milliseconds. The grid operators were not aware of the loss of capacity for some time, such was the reaction speed of the battery.
Other large batteries are planned or being constructed, including two in Victoria: a 25 MW/50 MWh battery to be built by Tesla at the 60 MW Gannawarra solar farm near Kerang and a 30 MW/30 MWh battery to be built by Fluence at Ballarat (see www.bit.ly/2MsMnGN).
Virtual power plants
Large-scale storage doesn’t have to be centralised into one location. Decentralised (distributed) generation can be as or more effective in controlling grid voltages, and the distributed aspect of such systems means less strain on single areas of the grid. The most promising form of distributed generation is what’s known as a virtual power plant, or VPP, which involves combining many small solar/battery systems into a single large power source.
With the advent of smart, remotely controlled domestic-scale batteries, it has become possible for energy companies to remotely sync up hundreds or even thousands of their customers’ batteries to provide power to the grid when demand is highest and absorb grid energy when there is excess. This sort of large-scale system can provide grid stability, in both voltage and frequency, by balancing loads and generation, even from variable generation from commercial solar and wind farms.
The biggest virtual power plant in the world was planned for South Australia, with the ultimate goal of installing domestic batteries in 50,000 Housing SA and low-income households. Each battery was designed to produce up to 5 kW, resulting in a VPP able to provide up to 250 MW when required. A change of state government has seen that plan evolve. So far a much smaller VPP has been installed, consisting of 100 Tesla Powerwall 2s in public housing, with the plan to increase that by another 1000 units (www.bit.ly/2KDuFyF). The new government instead planned to give grants for battery storage to around 40,000 homes, but it’s now looking possible that both projects may go ahead, resulting in around 90,000 homes receiving energy storage and PV systems. If this happens, it will form the largest VPP in the world by far (www.bit.ly/2OQd3Tj). Interestingly, AGL has also announced their own separate VPP program for Adelaide households.
Another VPP involves a collaboration between energy retailer Powershop and Reposit, whereby anyone with a Reposit-equipped battery storage system living in NSW, Victoria or Queensland can sign up for the Grid Impact program to become part of a distributed virtual power plant and get paid accordingly (www.bit.ly/2M4iyQB).
In a different type of VPP, Energy Queensland has partnered with GreenSync to create Australia’s largest virtual power plant using GreenSync’s peak response units at large energy users and industrial sites. While not actual energy storage, they can have the same effect of stabilising the grid by controlling when large energy consuming systems such as HVAC units can operate (www.bit.ly/2P20pAS).
Batteries in housing developments
It’s not just home owners who are looking at domestic energy storage—a number of housing estate developers have been installing solar and storage systems on their new housing estates, adding value to the homes by promising lower energy bills.
A 460-home project at Lyndhurst, Victoria, by Villawood Properties, in conjunction with South East Water, offers buyers of the ‘Aquarevo’ homes the option of 5 kW of rooftop solar, plus battery storage provided by Sonnen (www.bit.ly/2vTnVr2).
White Gum Valley, near Fremantle, WA, is an eight-dwelling residential complex that includes units and townhouses that are part of a microgrid. Solar PV panels on rooftops provide electricity to households, with excess solar stored in the strata-owned battery. When the sun isn’t shining, the households source their power from the battery, with the grid acting as a backup when that is depleted (www.bit.ly/2nnYxWe).
The Huntlee Housing Development is a planned off-grid development in the Hunter Valley, NSW. An assessment found that it would be cheaper to build an independent microgrid for the 7500 home development rather than connecting it to the main grid. The development will include 40 MW of PV generation, 30 MW of cogeneration and 40 MWh of energy storage. Construction has already started on the new township, which will be completed in four stages, to be finished by 2045 (www.bit.ly/2MbylfP).
Home builder Metricon, in partnership with solar installer CSR Bradford, is offering NSW and Queensland customers who choose its ‘Designer by Metricon’ range to also have the option to include a Solar ChargePack, which includes 5.4 kW of rooftop solar and the 13.5 kWh Tesla Powerwall 2.
These are just a few examples where solar PV and battery storage are being offered as standard or as an option with new homes, with dozens of home builders around the country adding renewable energy system options to their home designs.