Inverter Based Resources in a Rapidly Changing Utility Energy Landscape

Eric Toff Bergman, Strategic Markets Sales Manager, SMA America

The modern utility grid is transforming and evolving. New generation sources, like inverter-based resources (IBRs), can present complex challenges for original equipment manufacturers (OEMs), and grid and utility operators. IBRs and utilities require collaboration to ensure that, even in a dynamic and changing grid, utilities continue to deliver clean, reliable, cost-effective energy for years to come.

An Evolving US Solar Grid

The modern US electricity grid started with a single power plant, the Pearl Street Station generating plant. Located in Manhattan, designed and developed by Thomas Edison, this coal-fired power plant began producing power in 1882 with an initial nameplate of 100kW. This was enough power to light approximately 1,200 lamps (Scientific American). Throughout the past 140 years, the electric grid continued to expand in size, scope, complexity, and generation mix. Today, the US electricity grid, also known as the Bulk Power System (BPS), is the largest and most reliable modern grid in the world. By the end of 2021, the US had 1,143,757 MW of total utility-scale electricity generating capacity and about 32,972 MW of small-scale (distributed) solar photovoltaic electricity generating capacity (EIA). Most of the capacity which has been added since 1882 is based on the same generation model as Pearl Street Station – a spinning synchronous generator fueled by a non-renewable resource. This is changing quickly, as the US continues to see more renewable energy-based generation added into the BPS.

Solar Leading the Charge

While solar makes up only 3 per cent of the overall energy generation capacity of our US grid today, it is the fastest growing generation type on the grid, in part because prices for solar projects have dropped nearly 70 per cent since 2014 (energy.gov). Today, solar energy plants are the most cost-effective energy to build, own, and operate from a levelized cost of energy perspective. Solar energy accounted for 46 per cent of all new electricity-generating capacity added in the US in 2021. This represents the third year straight that solar has comprised the largest share of new generating capacity in the US (SEIA). A recent study run by the US Department of Energy states by 2035, solar energy has the potential to power 40 per cent of the nation’s electricity and employ as many as 1.5 million people. In fact, it is now more cost effective to build new renewable energy plants, than to continue running existing fossil fuel based plants (Bloomberg).

Renewable Energy IBRs and our Grid

While large synchronous generators will likely never completely vanish from the BPS (as they are integral in supplying baseload power for the grid), our energy mix has shifted to a more diversified production pool that includes solar, wind and energy storage generation.

"As a main source of current and future generation, IBRs are poised to support utilities as the nation continues its energy transition"

Solar and storage IBRs, create energy via asynchronous generators while our grid, was originally designed for synchronous generators. The transition to renewable energy generation and IBRs can create challenges for utilities and grid operators (specifically, electrical protection settings, ride through capabilities, voltage control and the possibility to have portions of the network working in “island” conditions.)

Utility Challenges with IBRs

One such example, is a recent grid event which led to an instantaneous reduction of more than 1,100MW of solar generation. The event, known as the “Odessa disturbance,” was initiated by a single-line-to-ground fault on generator step-up transformer at a combined-cycle power plant near Odessa, Texas. More than 30 individual solar facilities dropped offline simultaneously time because the IBRs were programmed to trip when the grid showed a fault. While this is anticipated operation of IBRs on a distribution system, the Odessa IBRs should have been configured to ride through these conditions on the transmission system (BPS) to stay online.

Odessa shows that IBR vendors must work in sync with utilities and grid operators and the event demonstrates why utilities need deeper technical relationships with IBR vendors. In hindsight, these IBRs should have been configured to ride through these conditions on the transmission system. Additionally, the IBRs needed operational standards compliance that would have forced these resources to stay online during the fault condition up the line.

How IBRs can help Utilities and our Grid

How do operators mitigate scenarios like the Odessa disturbance in the future? IBR manufacturers, must work with utilities to develop and support the hardware, software, and solution functionality to integrate into our future grid. As a main source of current and future generation, IBRs are poised to support utilities as the nation continues its energy transition.

How can IBRs help?

1. Before a renewable energy generator is installed and commissioned, IBR vendors should supply and support advanced, equipment models for utilities. These models, such as PSSE RMS models and PSCAD EMT models, help utility designers and operators model system performance across the full spectrum of grid condition scenarios on the BPS.

2. IBR vendors need a deep US-based and US-experienced modeling expertise to support utility grid modeling efforts done in the design phase.

3. IBR vendors should work with the developers and IPPs who build, own, and operate solar and storage power plants to ensure utility settings and configurations are set on the IBRs per the utility requirements (which are based off the modeling done in design phase.)

As utilities continue to add IBRs to the generation mix, experienced, and technically capable IBR vendors a with strategic focus on the future grid, are best poised to support customers through the energy transition.

Reliable Utility Operation Through Industry Standards.

The power industry is also reviewing standards for these IBRs which would mitigate events like the Odessa disturbance. IEEE is in the design phase of IEEE 2800, a standard that addresses the specific requirements around IBR modeling and operation on a synchronous grid. IEEE 2800 will develop technical minimum capability and performance requirements for IBRs connecting to the transmission and sub-transmission networks. These include IBRs’ ride-through capability, ride-through performance, reactive power (voltage) control, active power (frequency) control, power quality, protection, modeling data, measurement data and test and verification (IEEE). This standard will enable highly reliable grids as IBRs continue to add to our generation mix.

IBRs transform energy in a technically different way compared to legacy fossil fuel-based generators. If left unchecked, these IBRs could affect the grid in a negative way. IBR vendors need a deep understanding of these grid conditions and utility scenarios and need the capability to speak to the grid reliability technical specifications of their solution.

IBR vendors should support utilities through advanced modeling and operational configurations of the hardware in both the design and operational phase. Additionally, IBRs should ensure that the generator is designed, configured, and operated as the utility requires and should provide support for the full design life of the plant. Our grid is evolving and it’s the responsibility of generators and utility operators to ensure the grid continues to provide reliable, safe, cost-effective energy – this can only be done if generators and utilities work together in a collaborative effort.

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