By Susan Neill, Global Sustainable Energy Solutions (GSES) director
As renewable energy competes successfully with the wholesale fossil fuel energy market, investors, manufacturers, governments and the power industry increasingly look for ways to capitalise on the technology and its extensions.
To date, international power markets have seen extensive grid-connected solar deployed successfully. Historically, the more successful and less obvious use of renewables throughout the decades has been for the off-grid power market – supplying reliable power for telecommunications, remote communities, the mining industry, rural properties and so on.
It might be assumed combining the use of grid-connected solar with energy storage would be relatively easy given the technical and market success of these two separate system types. However, grid-connected solar with storage comes with significant challenges.
Grid-connected solar with storage encompasses different product technology options as well as different system configurations. Importantly, the system application chosen will determine which possible grid-connected solar plus storage configurations can be used.
The interest generated by the prospect of energy storage on-grid is international. However, in Australia, more than 1.25 million households have installed grid-connected solar and these households could be the early adopters for adding energy storage systems (according to the Clean Energy Council). Networks are also very interested in investigating and managing the introduction of storage onto their grids. For example, Ergon Energy in Queensland has just announced it will provide grid-based battery storage, without renewables, to provide grid support on its sprawling network.
But what are the reasons individuals and companies would purchase energy storage for a power system with or without a grid-connected solar system?
• Reliability of supply: the system provides an alternate supply for critical or sensitive loads during abnormal grid conditions, e.g. blackout.
• Offsetting peak load: using onsite generation to power peak loads that operate during times of high electricity grid costs to reduce electricity bills; for residential customers, these pricing peaks typically occur in the evenings. Look at figure 1a: it shows a sample grid-connected solar system without energy storage. A large proportion of the daytime solar power is exported. Figure 1b shows the same system with energy storage. In this example, the solar power has been stored for use in the evening, at a time when power purchased from the grid can be more expensive.
• To minimise electricity imported from the grid and to minimise the export of PV generated power – reasons for this could be financial, environmental, etc.
Some technical aspects of these systems are made more difficult because the current Australian standards relating to these systems have not kept pace with the technology, applications and the market. This rapidly developing market needs revision of the current standards to address the technical and risk aspects of these systems.
A discussion currently in the marketplace surrounds how grid-connected solar systems with energy storage will integrate into the current electricity market. The three possibilities are:
1. Private ownership: a privately-owned system could disconnect from the grid and theoretically provide all of the owners’ energy needs (see figure 2). This model requires high upfront investment and the system owner carries the ongoing responsibility for the maintenance and equipment.
2. Utility ownership: energy storage could be provided and operated by the utilities at either a street or a community level, or even in the customer’s home (see figure 3). The grid would still be required as the back-up power source and to charge batteries for systems without a solar system. This setup is often referred to as “in front of the meter”.
3. Gentailer ownership: when a retailer acquires a new customer, they could have the option to install a storage system, with or without solar, instead of having to ensure they have enough generation provision to meet this new demand (see figure 4). This setup is often referred to as “behind the meter”.
Energy storage is a constantly evolving market: watch this space.
