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Mobile Energy Storage Systems – Use Cases and Technology Challenges

Presented By:
Farid Katiraei
Innoversa Mobile Solutions
Shadi Chuangpishit
Quanta Technology
TechCon 2024

Abstract

This paper introduces the emerging applications for mobile energy storage systems (MESS) as a clean alternative for replacing diesel generators in all applications that traditionally emergency gen-sets have been utilized. Although small-size “portable” energy storage systems have been around for several years, the technology advancement have enabled utilization of large grid-scale battery technologies in mobile applications at the scale that can supply multiple customers (significant loads) for an extend time, and in various locations. The business case for MESS is also comparable to equivalent diesel genset solutions when incorporating stacking of applications and a multitude of environmental and societal soft benefits such as significant emission and noise reduction. The paper provides MESS definition and key functional requirements along with examples from real-world deployment and use cases.

Introduction

Increase in the number and frequency of widespread outages in recent years has been directly linked to drastic climate change necessitating better preparedness for outage mitigation. Severe weather conditions are experienced more frequently and on larger scales, challenging system operation and recovery time after an outage. The impact is more evident and concerning than before, considering the increased dependency on electricity in all aspects of our lives.

While enhancing reliability and resilience of the power system has been underway, one challenging aspect is to ensure the transformation is well aligned with use of cleaner and sustainable energy resources. The enhancement also requires a paradigm shift from the traditional ways of managing system outages to advanced methods, such as self-healing technologies (to automatically reconfigure the energy flow path through alternative distribution lines for re-energizing load centers after damage to a part of the power system) and mobile energy storage system (MESS). This article addresses deployment and utilization of advanced MESS to support increase in use of clean energy resources with focus on reliability and resilience of energy supply.

Fossil fuel based portable emergency generators (diesel or gas) have traditionally been used during system outages to restore service to a segment of power distribution systems. Being part of a mobile fleet, these generators provide flexibility in managing restoration of impacted sites and for supplying single or groups of customers to temporarily deliver power to critical loads before the system is back to a normal operating condition.

The restoration time could last several hours or—in more severe conditions—several days, exposing impacted customers to significant pollution from the noise and emission of diesel/gas generators. The need for clean electricity and regulatory limitations on operating time of diesel generators suggests finding alternative approach for meeting electricity needs during the outage recovery time.

A mobile energy storage system (MESS) as a clean replacement for diesel/gas generators has mostly been available in very small sizes (a few hundred watts or kilowatts); which is not adequate to supply all critical loads of an industrial or a commercial customer or multiple customers—in a safe and scalable way—through existing (unimpacted) distribution system assets (such as service transformers or lines connecting neighbor customers in a segment).

Two challenges normally affect the use of small portable battery-powered backup power supplies for utility customers:

  • a significant effort may be needed to reconfigure customer connections by separating and isolating supply paths to dedicate the portable backup unit to given loads, and
  • an increase in the size and number of household devices or business usage that would be considered part of the critical load groups.

The preference is to maintain the normal power delivery path from the utility to the end-critical customers as much as possible, rather than re-configuring the connection. Using a properly sized MESS that has microgrid capability for both grid connected and islanded operation, the only required change is to swap the input with a mobile clean energy source. This approach also reduces the effort for restoring customer connection, when the grid is back, by seamless transfer to a healthy grid. Figure 1 shows a MESS unit (white trailer) located side by side with an emergency genset (gray container) of similar size (500 kW) at a rural location for supporting the grid during seasonal high peak load condition. The MESS was used to replace genset to examine capabilities, reliability, and dependability of the technology, while maintaining the genset as a back unit to cover shortcoming in the MESS operation. The use case was successfully concluded. The expectation is that MESS would fully eliminate the need for diesel usage or having a standby diesel in the next high load season.

Figure 1 MESS and a Diesel Genset located side by side at a rural site for a seasonal peak load image

Figure 1. MESS and a Diesel Genset located side by side at a rural site for a seasonal peak load management application.

With increasing adaption of large grid-scale batteries, the capabilities of MESS technologies have grown rapidly in both system sizes and maturity of products. However, additional effort is needed to make the technology scalable for supplying larger systems and be on par or superior to the capabilities of typical portable/emergency diesel generators in ease of interconnection and control capabilities for acceptance and adoption by utilities and fleet managers as promising alternatives for outage management and reliability/resilience services. The fundamental features expected from a MESS are:

  1. Reliable and dependable technology that is immediately available to supply electrical loads.
  2. Mobility and the ability to be relocated from one site to another frequently to cover widespread outage areas with non-coincidental outage patterns.
  3. Plug-and-play standard connection to a site to minimize preparation time needed to quickly re-energize service supplies to customers.
  4. An easy to use and reliable automated control and monitoring platform for streamlining the process of start/stop or changing control modes. This process reduces the burden on an operator especially during stressful outage recovery time.

As the technology is becoming commercially available at the utility scale, utility and fleet owners need to integrate MESS into their asset portfolio properly, including defining a new planning process for scheduling and tracking utilization of the new assets for outage recovery and grid preparedness – as the primary use case. The business justification for the total cost of ownership requires an understanding of all feasible secondary use cases to increase the utilization factor in normal business days (also referred to as business case for blue sky conditions).

Several use cases for outage recovery and emergency response are presented in this article. A benchmark system is used to describe the functionality of the mobile energy storage system for each specific use case and how the technology will impact overall grid preparedness for weather-driven outages.

Mobile Energy Storage System

Per IEEE Std 2030.2.11, a mobile energy storage system is “a kind of energy storage system which has flexible connection points as required and is generally installed on mobile transportation vehicles, such as vehicle-mounted container ESS. Figure 2 shows a schematic of a containerized MESS on a trailer. The key components of the MESS are the energy storage source – either a battery system or other DC sources (such as fuel cell), along with a power conversion system (an inverter) and isolation transformer. To present the concept the figure also shows the semi tow-truck for transporting the unit; however, after relocation to a target site, the tow truck will be removed from the MESS.

Figure 2. Simplified schematic of a containerized MESS with a tow truck2

Two main modes of operation are generally defined for a MESS, namely a) the grid connected mode, and b) stand-alone mode. The system topology and external connection for each mode is shown in Figure 3. By combining the two modes, a new operating condition for seamlessly supplying the load upon loss or interruption to the grid – commonly known as uninterruptible power supply (UPS) mode can also be defined to support power quality required by certain critical load that are sensitive to any momentary interruption or poor quality.

Figure 3. Two essential modes of operation for MESS diagram

Figure 3. Two essential modes of operation for MESS

The MESS unit should be self-sufficient to maintain best operating condition for the operation and to provide the startup (auxiliary) power for black staring the unit. The MESS unit should be designed in a way that mobilization/demobilization can be done quickly to prepare for relocating from one site to another site frequently in support of various applications.

Paradigm Shift

After a long history of relying upon diesel generators for energy supply during outages or at remote customer locations, the time has come to re-think the alternatives. While the alternative technology should have similar or superior technical capabilities to portable diesel generators (e.g., mobility, blackstart function, long supply duration), it must be more environmentally friendly and economically justifiable.

Table 1 presents a high-level comparison between a portable diesel generator versus a MESS from technical and environmental perspectives. Advanced control functions and automation capabilities embedded in a MESS will facilitate utilization for a wider spectrum of grid-connected and outage applications, enabling the stacking of applications and increased value-proposition of the unit. Incorporating multiple use cases by staking applications is critical for building a stronger business case for MESS and its financial justification.

Table 1. MESS Versus Portable Diesel Generators

MESS Use Cases and Examples

While portable diesel generators are mainly limited to an emergency backup power supply for a permitted duration, a MESS can operate and serve customers and the distribution grid for different use cases indefinitely (while the energy supply lasts). MESS use cases and stacking them for seasonal and locational applications is the key in revealing the true values of MESS technology.

Outage Management (Planned or Unplanned)

The primary use case for MESS is supplying customers during system planned/unplanned outages. The importance of outage preparedness and management is significantly growing due to the increased frequency of weather-related outage occurrences globally and across North America. Examples of natural disasters causing grid outages are:

  • Wildfires affecting power lines and substations or high-speed winds causing towers/poles and lines to go down, forcing a power shutdown
  • Flooding that impacts substations resulting in outages for safety
  • Hurricanes bringing down poles and power lines
  • Storms, especially ice storms in cold climates, increasing line/tower loading and causing breakage
  • Drought and heatwave increasing electrical loading resulting in protection system tripping due to overloads.

Public Safety Power Shutoff (PSPS) has been practiced for several years in California-USA to avoid catastrophic wildfires due to extreme weather conditions (e.g., high winds in the dry season). To protect high-risk communities’ safety, the utility de-energizes high-voltage linesin certain areas before weather events occur. This, in turn, exposes several customers to outages for a few hours up to multiple days.

During the last few years, California utilities have initiated research on non-diesel alternatives to address reliability concerns due to PSPS outages. Mobile energy storage systems have been a promising alternative – a technology recently explored by California utilities by engaging in pilot programs, implementing, and verifying the technology in the field.

PSPS outages are planned outages initiated by utilities for specific areas in the system. Utilities power up community centers (acting as shelters or community resilience hubs) to provide electricity and basic needs during the blackout to support communities.

Figure 4 shows an example of a PSPS outage management use case, with a host site (utility fleet) distanced properly from different community centers where the MESS can be recharged from clean energy resources or the utility grid. During PSPS, MESS fleet is dispatched to provide clean and quiet backup power for up to 72 hours in worst cases. Outside of fire season, MESS can be utilized for peak shaving or renewable smoothing while connected to the grid or for scheduled maintenance outages at different system locations.

As part of a demonstration project in southern California, it was shown that a typical 1 MWh unit (packaged in a 20-foot container) was able to supply three community centers for multiple days, depending on the loading of the centers. Utilizing a fleet of MESS, the unit needs to be dispatched back to the host site for recharge and get ready for serving the next event. Key element of the MESS technology is the mobility aspect to provide ability of frequent relocation through backcountry roads with no permit requirement – by having roadworthiness consideration built into the design of the unit that properly meet the department of transportation (DOT) and regional bylaws (typically imposing certain weight and dimension restrictions). Roadworthy design is essential for enabling stacked applications for becoming parts of outage mitigation, scheduled maintenance support of asset upgrade projects and any other seasonal use cases. Figure 5 and Figure 6 show pictures of a MESS during transportation and while parked on customer premises, respectively.

Figure 4. Dispatching MESS for PSPS Outage Management

Figure 4. Dispatching MESS for PSPS Outage Management

Figure 5. Picture of a MESS during Relocation on the Road

Figure 5. Picture of a MESS during Relocation on the Road

Figure 6. Picture of a MESS Parked at Customer Location

Figure 6. Picture of a MESS Parked at Customer Location

Scheduled Outage for Maintenance

Another key use case for MESS is supplying customers during an outage caused by scheduled maintenance of the electric system. Utilities frequently conduct maintenance outages on their system to improve asset health such as replacement of old/stressed cables and services transformers to ensure the reliable and safe delivery of energy to customers. The frequency and location of maintenance outages depend on the infrastructure age, planned upgrade programs, and operation and maintenance guidelines for each utility.

For instance, Southern California Electric utility conducts more than 30,000 maintenance outages across the service territory per year- many of which expose local customers to one or two hours scheduled outage (in best cases). Portable diesel or gas generators are used in certain scheduled outages when a given maintenance program requires more than couple of hours outage or certain critical customers are involved. MESS can be a viable replacement of diesel or gas generators for such scheduled outages.

Routine maintenance and/or system infrastructure upgrade causes customer electricity service interruptions. These outages are normally scheduled in advance and might impact one or several customers depending on maintenance/upgrades as summarized in Table 2.

Table 2. Maintenance Categories and Impact on Customers

Based on the outage schedule, a MESS can be dispatched to the location to either connect to the service transformer (three-phase connection) to serve multiple customers impacted downstream of the transformer or at a single customer site (single-phase connection). Depending on the size of impacted customers, one or more MESS – connected in parallel can supply customers up to their full energy capacity for the duration of the outage.

Additional Use Cases

Energy supply for remote or abandoned load is another use case for MESS. This is typically a non-utility use case dealing with loads that need temporary backup power for a specific event or project that requires power supply only for a short duration in locations or areas with no or limited electric service infrastructure. Possible examples are:

  • Temporary projects or job sites with no access to adequate utility service, mainly for construction projects (at the beginning), oil and gas sites, and mining industries
  • Public events at remote locations.
  • Roadside assistance for electric vehicles (EVs) requiring battery charging on the road/highways

These use cases support the needs of commercial and industrial sectors, for which portable diesel generators have been widely and traditionally utilized. Use of MESS for street events and festivals, or concerts and sports games at arenas offers emergency backup power in cleaner and less noisy ways – which is a key advantage considering public exposure during these events.

Minimizing noise levels, eliminating harmful GHG emissions, additional control and interconnection flexibility, and safety/security considerations facilitated through MESS technology are essential benefits associated with this use case (Figure 7).

Figure 7. MESS for C&I Customers (Supplying a Street Festival) image

Figure 7. MESS for C&I Customers (Supplying a Street Festival)

Benefits of Stacking Use Cases – Business Case Example

For MESS, stacking of the use cases for various seasons and operating conditions is the key to build an attractive business case. Stacking use cases is more critical for the MESS vs. Stationary ESS, because of the higher capital cost associated with mobile technology and limitation of scales and dimension.

An example for a typical 1 MWh MESS unit addressing seasonal needs of a typical utility operation and maintenance program is shown in Figure 8. This program was deployed and demonstrated for a Southern California utility. Each use case is season dependent and provides specific services while managing weather-related outages or implementing routine asset maintenance and upgrade. In the high load seasons, when the MESS is not required for any scheduled or unplanned outage mitigations, typical load management (peak shaving) programs are incorporated to reduce stress on assets such as service transformers and lines. Detailed description of various seasonal MESS uses case with the associated assumptions to achieve operational benefits is summarized in Table 3.

Figure 8. Seasonal Use Cases pie chart

Figure 8. Seasonal Use Cases

Table 3. MESS Use Cases Description

The operational cost of MESS programs is estimated by extrapolating data obtained from seasonal utilization of MESS and incorporating assumptions related to annual frequency and duration of operation for each use case (outage durations or peak demand hours). A cost-benefit analysis is then performed to determine overall cash flow generated over the lifetime of MESS (assuming 10 years) and the Internal Rate of Return (IRR) as an indicator of investment profitability.

In the case described above, based on associated cost components (upfront and annual O&M cost) and total expected savings (from quantifiable benefits such as demand charge reduction, avoided cost of outage, carbon credit), the MESS deployment could be profitable with 30% IRR throughout lifetime of the project. It should also be noted that adding the non-quantified portion related to soft benefits would provide an even higher value proposition.

Key Design Features of a Large-Scale MESS

MESS technology alters the traditional methods of service restorations during outages for emergency and critical customers. It is expected that MESS can easily capture a significant portion of existing markets for portable diesel generators while deployed for emergency purposes and where the regulation for 100% clean and renewable energies are mandated. There are several key features that should be incorporated into design of MESS technology including:

  • 100% self-sustained design with blackstart capability to ramp up the generation and quickly restore power supply to the load.
  • Road worthiness achieved by adhering to the DOT requirements and any other state or regional regulations – so it can be easily transported through highways and country roads.
  • Automatic MESS operation with minimal intervention from the operator.
  • Reliability and dependability as its primary use case is to respond to customer needs during emergency times. This is achieved by extended (continuous) operation for multiple days, while minimizing maintenance downtime through intelligent monitoring and preventative maintenance schemes. MESS features advanced data collection, condition monitoring, and extensive data analytics for incipient fault detection and preventive maintenance.
  • Meeting and exceeding safety and fire protection standards and regulatory compliance requirements.
  • Incorporating automated condition inspection and health assessment schemes to expedite pre-start checks and alarm reporting.

Additional design features of an advanced MESS are presented in Figure 9.

Figure 9. Key Design Features of MESS diagram

Figure 9. Key Design Features of MESS

Conclusions

In line with climate change programs, aiming for a more sustainable and renewable-based energy transition of the power and utility industry, MESS is envisioned to be a key technology offering clean alternative solutions for emergency outage management. To be viable and successful MESS must incorporate flexibility for interconnection and usage, scalability and modularity in energy delivery, and fast response for supply recovery during widespread outages. Furthermore, to become an integral part of utilities fleets and asset portfolio, MESS has to offer: 1) standardization of interconnection process, 2) streamlined operation and maintenance, 3) highly safe, reliable, and dependable solution, and 4) justifiable business case built upon staking of application for both normal and emergency conditions. Increase in the utilization factor of MESS is the number one challenge for achieving an affordable clean solution.

Use cases of MESS and its operational strategies are highly dependent on the geography, jurisdiction, and distribution system characteristics. It is an important step for utilities to evaluate MESS technology based on their own requirements and identify the merits of technology together with its financial justification. Meanwhile, a great effort towards standardization of technology and its integration to customer facilities and utility fleets is required to ensure a smooth transition to a more promising energy supply for emergency response in future.

References

2030.2.1-2019—IEEE Guide for Design, Operation, and Maintenance of Battery Energy Storage Systems, Both Stationary and Mobile, and Applications Integrated with Electric Power Systems.

https://standards.ieee.org/industry-connections/mobile-and-transportable-energy-storage-systems-technology-readiness-safety-and-operation/


1 https://standards.ieee.org/ieee/2030.2.1/5832/

2 Picture courtesy of:
https://www.sciencedirect.com/science/article/abs/pii/S2352152X21007763?via%3Dihub

3 This could be for a planned outage for which MESS is located and connected before the outage or an unplanned outage for which MESS is connected to provide grid support prior to an outage.

4 The time from the moment the generation source is on site to the time that all connections are completed, and system is ready to energize.

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