Study: Rail-Based Mobile Battery Storage Can Be Tapped for Backup Power
A Lawrence Berkeley National Laboratory study finds that the U.S. rail network can accommodate mobile battery storage systems to offer flexible backup power during extreme weather events at a lower cost than new infrastructure investments.
A Lawrence Berkeley National Laboratory study identifies batteries aboard freight trains as a flexible and low-cost avenue of backup power during extreme weather events that place extra strain on the power grid, such as heatwaves.
Railway system. Image used courtesy of Pixabay
The researchers explored the potential of using the U.S. railway system as a nationwide backup transmission grid where multiple regions share containerized batteries to address supply/demand gaps and transmission congestion. They found rail-based mobile energy storage (RMES) systems can provide reliable power during low-frequency, high-impact events and at a lower cost than comparable transmission infrastructure investments. Installing RMES systems on trains instead of building new infrastructure and stationary capacity would save the power industry $300 per kilowatt-year (kWy) and $85 per kWy, respectively.
This concept would be useful to boost the power grid’s resilience during heat waves and other extreme weather events, as batteries provide extra flexibility for peak demand. It would also add stability to offset intermittent electricity generation from a growing share of renewables connected to the grid.
The size of this untapped resource is significant, as the U.S. hosts the world’s largest rail network, running nearly 140,000 miles, according to the U.S. Department of Transportation. The Berkeley Lab researchers analyzed freight rail flows, scheduling constraints, and the costs of summoning rail-based batteries during grid disruption. Since operators usually know about these events a few days beforehand, mobile energy storage could travel along existing railways to the relevant region/state within that time frame.
Natalie Popovich, a study co-author and a research scientist in Berkeley Lab’s Energy Analysis and Environmental Impacts unit, said the team wanted to explore technologies complementary to long-distance transmission lines and stationary battery banks. Existing knowledge lacks a cohesive understanding of ways to couple the electric grid with trains capable of carrying one gigawatt-hour (GW) of battery storage, Popovich added.
Estimated freight rail availability nationwide: “a” shows the average number of freight trains traveling daily between states to each independent system operator (ISO); “b” shows the average time to move trains between regions, with the red lines mapping ISO boundaries and blue indicating estimated travel times. Image used courtesy of Berkeley Lab (Creative Commons license)
Rail-based Mobile Energy Storage Benefits
The study was published this month in Nature Energy. Berkeley Lab’s researchers found notable cost benefits in sharing multi-purpose RMES assets across sectors and regions to boost grid reliability. Transporting RMES systems over short distances of 248.5 miles could be more cost-effective than investing in stationary capacity for low-frequency events (2% annually per region). For rare occasions (0.1% a year), RMES beats stationary capacity investments at all distances. And even though RMES is less economical than short-distance transmission, it’s still cheap for low-frequency events with more space between regions.
The researchers noted that RMES lacks the same reserve capability of fast-response stationary assets to manage sudden frequency drops. Still, it can address high-impact events forecasted days in advance.
The study also identified a broader benefit in RMES systems’ ability to replace stationary investments in other areas. In stationary storage, the cost of the battery can cover around 72% of the fixed investment cost ($89 per kWy of $122 per kWy). And when replacing stationary storage, the system saves the full battery cost, exceeding the higher limits of ancillary service revenues (around $70 per kWy) earned by batteries. Additionally, replacing or offsetting transmission investments with RMES could save the $100 kWy cost of an additional 500-mile transmission line.
RMES costs compared to transmission and stationary capacity investments: “a” shows annual event frequency (AEF) and costs for each resource when regions are separated by 2,400 kilometers (1,491 miles); “b” shows how the distance impacts costs for each resource with a 1% AEF per region. Image used courtesy of Berkeley Lab (Creative Commons)
The study found that while no known technical barriers would exclude RMES from grid participation, deploying at scale would require addressing interconnection logistics and costs. Furthermore, state and federal regulations must be modified to include RMES assets in reliability markets and planning.
New York State as an Example
The study demonstrated the value of applying RMES in New York, where the technology can help offset the state’s investment in underutilized resources (such as peaker plants) while also overcoming transmission constraints. With the state’s high freight capacity, RMES only needs one to two days of notice to be sent to a region during high-impact events.
Earlier this year, the New York State Public Service Commission authorized $4.4 billion in transmission upgrades across 62 projects to help integrate the growing share of large-scale renewable energy connected to the grid. The Berkeley Lab researchers found RMES offers a cheaper alternative that could save a portion of that investment.
In the study’s discussion, the researchers wrote that RMES-sharing could be advantageous outside the power sector. Many freights are already adopting battery-electric locomotives, and other transportation modes like container ships can be powered by containerized battery systems charging every 932 miles—unlocking a new business opportunity and an estimated 220 GWh of mobile energy storage to assist the sector in emergencies.
They also noted that some locations are well-positioned to demonstrate this concept. California’s Low Carbon Fuel Standard incentivizes electricity production to substitute diesel fuel, opening an option for RMES owners to use those credits to cover part of the up-front cost of batteries and charging infrastructure.