Battery energy storage systems are more complex than they sound on paper.
Optimec has sponsored this post.
Battery energy storage systems, or BESS, are making waves in the green energy industry. A common complaint about renewable energy is that it’s highly weather dependent: if the sun doesn’t shine and the wind doesn’t blow, then solar panels and windmills sit idle. BESS technology aims to address this challenge by storing clean energy chemically during peak production so it can be used during suboptimal weather conditions.
“It’s a damper or buffer for energy. It facilitates and encourages wind and solar by managing the unsteady power flow,” says Benjamin Beckelynck, Senior Engineering Simulation specialist at Optimec. “When there is no sun and wind, what do we do? We take from the battery. And when we have a lot of sun and wind, we charge the battery.” He adds that the popularity of BESS technology has grown as batteries are becoming smaller, lighter and more energy efficient. Another benefit is that they can be deployed in remote locations, limiting the need for diesel generators and enabling green energy globally.
On paper, BESS technology is straightforward: big containers full of battery modules. But, explains Beckelynck, when you put dozens, perhaps hundreds, of batteries in an enclosure, that system becomes complex very quickly and simulation is the best tool to address the challenges that arise.
Thermal management challenges of BESS design
Perhaps the most intuitive challenge of BESS is temperature management. Batteries tend to have tight operational temperatures. If they get too hot, they can drain quickly and degrade. If they get too cold, they will be inefficient. As a result, BESS deployed in cold climates need heating systems, while those in warm climates need cooling systems. Batteries also produce a lot of heat, so many BESS need cooling systems regardless of their operating environments.
“Some battery modules have internal fans,” says Beckelynck. “But when stacking 100 of them, you might need more fans to cool the BESS. And if it’s in a superhot place, you need a cooling HVAC system. How the HVAC and fans work with the batteries is a challenge as it’s not linear; you need Computational Fluid Dynamic (CFD) analysis.”
CFD helps Beckelynck model the air flow and heat transfer in the BESS to size-appropriate duct, ventilation and HVAC systems that maintain cool temperatures in the enclosure. Then Beckelynck runs optimization simulations to ensure that the air is distributed evenly among the batteries.
“How to distribute the air and optimize the design of the ducts is challenging,” he adds. “Simulation through CFD is the best tool to tackle this challenge and optimize these systems … We use parametric optimization in CATIA. We change the parameters and update the CAD automatically by using the 3DEXPERIENCE. This way all the CAD, CFD and meshing is in one UI, and we can use algorithms to run hundreds of iterations and measure the flows.”
If batteries ever do get too hot, however, they will leak toxic fumes. As a result, enclosures also need to be designed with fail-safes that blow the fumes out through a ventilation system. Beckelynck explains that “these are all problems that CFD can solve.”
Structural challenges of BESS design
In extreme conditions, the batteries can get so hot that they can have explosive, catastrophic failures. In these conditions, the enclosures must be designed to survive the blast and keep everything contained.
“If there is a critical rise of temperature and a blast inside the enclosure, then it should be able to keep it inside,” confirms Beckelynck. “So, we simulate the pressure change and assess if the structures, like the doors and hinges, can contain it.” To make this assessment, Beckelynck uses the explicit solver from Abaqus as explosions are highly kinetic and non-static events.
But these are not the only structural simulations needed to design a successful BESS. An obvious assessment is the strength of the racks and scaffolding holding the battery modules in place. These systems need to have the ability to carry the batteries safely without yielding or deteriorating over the lifecycle of the BESS.
“The enclosure has to be stiff enough to be able to sustain this loading,” says Beckelynck. “So, we check the structural integrity on every part to see if there are stresses and check every bolt rivet and anchor to make sure it maintains structural integrity and isn’t overloaded … We use Abaqus implicit solver in the 3DEXPERIENCE for most simulations.”
A less obvious but equally important structural assessment engineers need to perform ensures that the BESS can survive a seismic event. “Usually, the battery racks are very heavy and tall. So, the center of mass is high. That can be a challenge if there is a seismic event.”
“IEEE standards have us run hundreds of scenarios and to check every rivet and bolt for a safety factor,” says Beckelynck. “We wrote a Python script. There are lots of automations done at Optimec, to make this process more efficient.”
He adds that BESS are rarely produced where they are used. As a result, they need to be transported to their final operating location. The vibrations the BESS experiences during this transportation can damage its structures. Structural simulations can also help address this challenge. To do this, an engineer needs to ensure that the vibrations experienced during transport do not exceed the structure’s eigenfrequencies.
A big tip when designing BESS: use simulation-driven design
Beckelynck explains that the key to BESS design success is to bring simulation front and center. “In simulation-driven design, the numerical results from simulations guide your design process,” he says. “So, when you proceed and finalize [the BESS performance] it’s already included in the design.”
In other words, by addressing the design challenges of the BESS early in development, via simulation, late-stage product redesigns are less likely to occur. This not only saves time, but also money as design corrections late in development are typically more expensive.
“The time it takes to properly do simulation is often underestimated,” says Beckelynck. “But if you do it early in design, overall, you will save time. But you have to do it early.” He explains that many BESS product designers will size and fit the batteries into an enclosure based on physical size requirements and quickly settle on a design. But by doing so they, for example, may not account for the space needed to manage the heat of the system.
“Then major changes might be needed. Like the HVAC system chosen isn’t good enough and it must be resized,” he explains. “But that would require moving the geometry — which changes everything.” If, however, these changes are discovered early in development, via simulation, then it isn’t a big problem. Update the CAD geometry and move on. However, when this issue is discovered on the production floor, after everything is finalized, it could delay production by months and cost millions of dollars.
Instead Beckelynck recommends BESS developers use simulation-driven design to avoid late development changes. He says, “at Optimec we encourage customers to use simulation themselves and we can teach and support these changes in the organization. You don’t need to be an expert analyst. You can extract the eigenfrequencies or CFD flows early to see if the design is going down the right path. It’s all about simulation for designers.”
To learn more about simulation for designers, get in touch with the experts at Optimec.