The future is always a fascinating topic. When it comes to digital technology, both crystal balls and ouija boards struggle to keep up with 

the latest technological advancements.

It turns out that for some small parts of the grid, predictions tend to lag behind the evolution that actually happened.

There are many examples like this. However, there is one grid element that has gained a lot of attention as an essential component of the 

next-generation grid, and that is energy storage.

More specifically, it's a battery energy storage system (BESS), which has a rather unique place in the grid. It can be used in transmission 

system, distribution system, and even user side. It's also a key factor in making wind and solar more grid-friendly. Battery energy storage 

is already considered a renewable resource. As a result, the industry has many assumptions about what to expect from next-generation 

battery storage.

Without describing too many techniques, we just need to know one thing in common. That is: these renewable resources generate direct 

current, which needs to be converted to alternating current for use in the power grid. That said, renewable resources are all inverter-based 

resources, and as the number of these devices in the grid increases, it has become a major issue for the next-generation grid.

These inverter-based devices are largely replacing large rotating machines such as generators, steam or gas turbines. The grid used to rely 

on the inertia generated by these rotating equipment to remain stable. Inertia is the kinetic energy storage from these large synchronous 

machines (i.e. the rotation of the shaft matched to the grid frequency). Kinetic energy storage provides dynamic balance between power 

and load.

Before we start the discussion, let’s take a closer look at a brief history of energy storage.

                                                        Dalrymple substation and battery energy storage system in South Australia. Photo credit: Hitachi Energy

01

Transformation experience

In 2009, T&D World published its first supplement on energy storage. The technology at the time was mostly pumped hydro and

lead-acid batteries, and the supplement had a lot of discussion around renewable energy.

Another decade later, when a second supplement on energy storage came out, the changes were staggering. As energy storage

has become part of a more complex application of the grid, the focus has completely shifted. Battery energy storage as part of

distributed energy is the new game-changer and hints at the coming changes.

By using battery energy storage technology on both the grid and the user side, energy storage equipment has entered the field

of grid stability services. "Resilience" is starting to become a buzzword in the grid, opening up new opportunities for battery

storage technology. It has transformed from a previously obscure player to a major force in the grid.

Interestingly, the 2009 supplement cited a research firm’s forecast that the global energy storage market would grow from

$329 million in 2008 to over $4.1 billion in 2018.

Indeed it is! But the final figure was much higher than predicted. According to a recent Fortune business report, the actual figure

for the energy storage market in 2018 has reached about $145 billion. The report also expects global energy storage market

spending to reach $211 billion by the end of 2026.

Battery energy storage applications are definitely a fast-growing technology. It will continue to build on the drive to decarbonize

renewable resources.

Now, let's go back to the discussion of the problems posed by power electronics-based, inverter-based renewable energy. With

the advancement of technology, some new inverter control technologies can solve these problems.

02

"Grid-following" and "grid-building" inverters

The National Renewable Energy Laboratory (NREL) recently published a technical report stating that "today's power system is

rapidly transitioning to more and more non-traditional energy generation, such as wind and solar, and energy storage devices."

These resources Connection to the grid via a "grid-following" inverter. This is another clue as to where the next generation of 

energy storage is headed alongside renewables like wind and solar.

We need to focus on inverter technology. "Grid-following" inverters track the voltage and phase of the grid to control its output. 

These "grid-following" inverters rely on the fact that the voltage and frequency of the grid are stabilized by inertial sources (ie 

rotating masses). The battery energy storage of "grid-following" inverters cannot cope with grid disturbances. When a system 

disturbance occurs, these inverters typically shut down the output until the disturbance passes, and after a major power outage, 

the system needs to be established before restarting the inverter output.

As more and more large fossil fuel plants are decommissioned and replaced by renewable energy sources, the grid needs an 

inertial energy source that can maintain its stability. This is where the "networking" technique comes into play. "Grid-type" 

inverters can build grids or enhance the operation of existing grids. It has an independent internal frequency reference and allows 

"grid-type" inverter island operation.

When "grid-type" technology is combined with advanced automation and control, there is a "virtual synchronization machine".

"Virtual Synchronizers" are able to provide the services needed to operate large amounts of renewable energy for large grids. That's

 why a technological innovation like "grid-connected" inverters is starting to gain interest and lead to next-generation grid dominance.

John Glassmire, Senior Grid Edge Solutions Consultant at Hitachi Energy (formerly ABB Power Grids), provides some practical experience

with 'Grid-Type' technologies, including the use of Virtual Synchronizers on Australia's transmission grid.

Glassmire reports, “Most battery storage deployed globally provides only partial grid stabilization, but the next generation of battery 

storage—especially using 'grid-type' energy storage with virtual synchronizer technology—is critical for enabling It is crucial that renewable

energy completely replace fossil energy based on synchronous technology.”

“For example, 24% of Australia’s electricity comes from renewable energy sources, which is a huge achievement for a country of this size. 

Australia is continuously moving towards net zero emissions, but the output of these renewable energy sources is variable As wind and solar 

capacity grows, new integration technologies are needed. As part of its commitment to advancing renewable energy development in Australia, 

Hitachi Energy is involved in the Energy Storage Integrated 'Commercial Renewable Energy' South Australia Project (ESCRI-SA) , providing the 

project with a large-scale grid edge solution utilizing microgrid technology.”

Figure 1. ESCRI-SA project business model. Among them, ARENA is the Australian Renewable Energy Authority; ElectraNet is the South Australian transmission

grid operator; AGL is the South Australian distribution network operator. Image source: arena.gov.au

According to Glassmire, “Hitachi Energy provided 30MW of battery energy storage on a long radial feeder at the lower end

of York Peninsula in 2018. The ESCRI-SA battery energy storage system is a 'construction' built on the Hitachi Virtual Synchronous 

Generator Platform. Grid-type' system that strengthens the grid by providing inertia, high fault currents, fast power injection, 

and competitive market service. The system also enables a seamless transition to islanded operation when upstream feeders fail. 

Power from the isolated grid Supply comes from the nearby 91 MW Wattle Point wind farm and distributed solar.”

Before the ESCRI-SA project was fully delivered, Glassmire noted: "The virtual synchronous machine provides an extremely valuable 

service to the grid. It mimics the behavior of older technologies such as synchronous motors and synchronous modulators, but is 

entirely enabled by power electronics. .They can even simulate more complex and newer devices, such as STATCOM for stabilizing 

the grid, while providing energy and ancillary services. 'Grid-type' battery energy storage with virtual synchronous machine function 

is similar to the general 'grid-type' battery storage Battery energy storage for inverter systems is different. Automation and control 

therein are key elements for the use of 'grid-type' inverters in large utility grids."

               Figure 3. Dalrymple energy storage power station wiring diagram. Image source: arena.gov.au

03

"Networking" technology that has become a hot spot

Late last year, Australia announced another “grid-connected” energy storage project. Utility AGL began construction 

of a 250MW/250MWh "grid-connected" battery storage project on Torrance Island in November 2021. Batteries will be 

supplied by Wärtsilä, and more than 100 “grid-connected” inverters will be supplied by SMA. The project is expected 

to be fully operational in early 2023. AGL says battery storage will increase to 1,000 MWh in the future. They hope the 

project can participate in Australia's national electricity market.

As interest in “grid-connected” technologies continues to expand, the U.S. Department of Energy (DOE) has announced 

$25 million in funding to the Universal “Grid-On” Inverter Alliance (UNIFI), a government-private partnership. "The 

consortium brings together leading researchers, industry stakeholders, utilities and system operators to advance 'grid-type' 

technologies," the U.S. Department of Energy said. The consortium will be led by the National Renewable Energy Laboratory 

(NREL) , the Electric Power Research Institute (EPRI) and the University of Washington.

One of the consortium's main tasks is to develop interoperability standards for the hardware required for inverter-based 

next-generation grids. Interoperability is a key issue for any emerging technology. We have noted that if new technologies 

are to be accepted by the power system, they must meet interoperability. This is why many manufacturers such as Danfoss, 

Eaton, General Electric, Hitachi Energy, Schneider Electric, Siemens Energy, SMA and many others are interested in the GM 

"Grid" inverter consortium project.

In conclusion, the next generation grid requires inverter-based battery energy storage. The penetration of wind, solar and 

battery energy storage resources is increasing, raising concerns about grid stability. When these three resources exceed 60% 

or more, grid operators get nervous. Older inverter-based technology cannot provide inertia and load stability similar to that 

of large rotating electrical machines.

However, "grid-type" inverters can be used to address these issues, which are more likely to occur than expected.

The "grid" is meant to increase virtual inertia as clean energy replaces large, rotating machines fueled by fossil fuels. Based on 

this, the "grid-type" battery energy storage of the next-generation power grid will play a key role!