Photo Credit: Kevin L.J. Hawxhurst
The IMPREL microgrid project uses various forms of energy storage to store energy in the form it will be needed in, and a unique multi-physics approach to optimize the use of onsite sources of renewable energy. CALMAC’s ice-based energy storage provided the microgrid with a durable and smart technology for flexible use of solar and wind to store cooling.
“Ice-based energy storage is the low-hanging fruit of the industry,” said Mark MacCracken, CEO of CALMAC. “The biggest advantage that fossil fuels have over renewable energy resources is that a barrel of oil or lump of coal is a form of stored energy that can be released at any time. Sun and wind are forms of pure energy that, without being paired with energy storage, are either used or wasted. Luckily, energy storage can easily be integrated into our buildings and power grid.”
Energy storage is an integral technology for microgrids, which can act as a single entity that can connect to the power grid or work independently from the grid in what is called “island-mode.” The multi-physics approach used by the IMPREL matches demand to the supply of electricity created by onsite photovoltaic panels and wind turbines. To achieve independence from the rest of the grid, energy is either used as it is generated or stored for later use when output dips. This differs from the traditional approach of our power grid where supply is dictated by demand. In fact, the traditional approach does not account well for the intermittence of renewable energy output, often leading to times when end-user demand surpasses renewable output and vice versa.
“Applying the multi-physics approach to our microgrid project, over the traditional microgrid approach, allowed for the use of fewer renewable energy sources to meet demand, reducing size, costs and the amount of unused energy,” said Dr. Anthony Gannon, Assistant Professor, Mechanical and Aerospace Engineering Department, Naval Postgraduate School. “Using thermal energy storage allowed for the project to greatly reduce its costs and improve efficiency by storing the energy in the form that it would be ultimately used in. Based on the project’s operation, we feel like this design could easily be scaled-up for larger applications.”
There were also operational benefits to using ice-based energy storage. By relying on the phase change of water between solid and liquid, CALMAC’s technology is not susceptible to the negative effects of cycling and can completely discharge. Given this, the lifespan of the ice-based energy storage tanks has been known to exceed 25 years and are 99 percent reusable or recyclable. In addition, controls prioritize loads based on thermal storage percent of completion, constantly matching chiller plant and heat loads in response (limited to 20 seconds) to changes in renewable power, without requiring additional power from batteries. Controls can be monitored remotely via a computer.