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How does energy storage influence the distribution system?

JESSICAHARRISONThis author no longer works for DNV GL.

Energy storage has the potential to serve multiple applications on the distribution system, helping to integrate renewables, improve reliability, or temporarily relieve loading to defer or avoid equipment upgrades.

DNV GL is currently simulating the effects of energy storage on the distribution grid with time series power flow analysis. Simulations allow for a bottom-up evaluation of the impacts of storage and provide a way to account for nonlinear circuit outcomes.[1]

Based on these initial studies, DNV GL has observed the potential success of storage to serve these applications, concurrently, or individually. We’ve also discovered indirect benefits, including:

  • Reduced system losses,
  • Enhanced power quality, and
  • Reduce wear and tear of equipment, including voltage maintenance equipment  (such as regulators, load tap changers)  or transformers (due to reduced loading)

The figure below illustrates some sample outputs realized to date.

chart

For these two cases—of different storage sizes—storage reduced peak real  power demand, reduced losses , reduced tap changes and mitigated over- and under-voltage events.

Through the process of simulation we’ve also come to appreciate the host of questions a potential installer faces, including questions like:

  • What types of storage work for applications?
  • Where should storage units be located?
  • What capacities are right to install?
  • How many units are needed?
  • How do benefits and costs change with different configurations?

By simulating batches of scenarios, we’ve started to explore how system design affects outcomes.  For example, locating a single unit at the substation versus multiple units at the edge of the grid can result in different benefits and costs.  The use of multiple, modular units reduces annual investments to smaller incremental amounts and allows for targeted deployment on the circuit as problems arise (such as the growth of PV on a system).  This type of system also provides greater reach into the network, facilitating problems closer to the customer (providing greater coverage for reliability issues, for example).  However, investing in a single central unit can reduce the complexity of installation and controls and can be used to target larger-scale needs (such as integration of utility-scale PV systems).

We’ve also come to appreciate the role that storage controls can play towards maximizing storage value and improving cost-effectiveness.  In particular, bundling applications allows you to achieve the maximum benefit for an investment, and controls are key to efficient bundling.[2]  Yet, controls must be robust.  Ideally control schemes would maximize storage value but be ‘simple’ enough for real-world implementation.  They should be designed to:

  • Coordinate applications to prioritize valued functions
  • Ensure enough energy to serve applications when they’re needed
  • Provide local protections for fail-safe operation

Storage controls must also accurately reflect local market rules and conditions to maximize value.  In turn, optimal applications and controls can vary regionally.  Also, value streams can be highly dependent on policy and may evolve as policies change.

Overall, we’ve found that energy storage can offer the provision of multiple services for a single investment and, in some cases, provide enhanced performance over traditional technologies.  However, a slew of factors should be considered to design and operate cost-effective storage solutions.

DNV GL is currently exploring storage cost-effectiveness as part of a rulemaking by the California Public Utilities Commission (R.10-12-007), and using some of our distribution simulation tools to do so. Initial modeling results are available here.  The engineering, ground-up approach to cost-effectiveness evaluation has helped us identify unique challenges to designing and investing in cost-effective storage solutions, and provided us with a means for comprehensive analysis that accounts for indirect effects and localized conditions.

Jessica Harrison is a principal consultant with DNV GL. She has an interdisciplinary background in the electric power industry, including work in engineering analysis, market assessments and public policy. She has focused on the integration of novel technologies with electricity markets and power systems. She leads the Energy Storage and Electric Vehicles Practice Area in the Americas region of DNV GL. Read her full bio on our contributors page.

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We will continue to explore the possibilities of energy storage on the distribution system, learning through simulation while incorporating lessons learned through real-world experience. If you’re interested in seeing some more detail on the modeling tools or use case results, or would like to share practical insights or field experience with us, please contact Jessica Harrison on our energy storage team.

 

[1] See prior blog post discussing the use of time sequence power flow for assessing PV impacts, PV effects on distribution systems

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