Island Base

Microgrid at Navy School Takes Cost-Effective Approach


So much of today’s discussions around microgrids have made the concept seem complex, expensive, and infeasible without generous government support. But in truth, microgrids-defined here as island-able loads connected to onsite power resources-have existed long before the term itself gained traction in the late 1990s.

Across the globe, there are countless facilities-often manufacturing plants, data centers, or temperature-controlled warehouses with no tolerance for downtime-that have had enough generation to separate themselves from the grid for long stretches of time. Typically, these sites’ resiliency has come from diesel or natural gas generators, so neither the facilities managers nor the energy community at large considers these to be cutting-edge examples of “true microgrids.”

But the benefits of resiliency and islanding capability far exceeds their cost: in short, these microgrids work. Even as we look at contemporary, renewable-powered microgrids, we find many examples of inexpensive and effectively islanded power networks.

One example of this is the modest microgrid at IMPEL, the Integrated Multi-Physics Energy Laboratory at the Naval Postgraduate School (NPS) in Monterey, CA. The designers of the IMPEL microgrid, Anthony Gannon and Anthony Pollman, both associate professors at NPS, took a smart approach. Rather than beginning with a wish list of hot technologies, the developers started by looking at the site’s energy demand profile, and then designed a system to meet the site’s specific needs. Gannon and Pollman outlined the microgrid’s characteristics in a paper titled “Multi-Physics Energy Approach & Demonstration Facility” at the 2015 Power and Energy

IMPEL’s developers began by defining the types of energy required-both electric and thermal-and looking first at reducing energy demand through efficiency measures. At that point, they looked at the renewable sources they would need to power the Lab, and the technologies that would most cost-effectively store those intermittent resources.

To meet electric load, IMPEL installed 6.4 kW of rooftop photovoltaics, and 6.4 kW of vertical axis wind turbines. To store the wind and solar power, IMPREL used a mix of electrical and thermal storage: roughly 50 kW of valve regulated lead acid batteries, 48 ton-hours of CALMAC IceBank ice-based cold thermal storage powered by a 9-ton chiller, and a ceramic brick heater and hot thermal storage unit. The energy is transported across the microgrid using six inverters, to create a three-phase system operating at 208 V.

As is often the case, controlling the system was among the most difficult tasks that the microgrid developers faced. Some components ran on the BACnet protocol, others on MODBUS and others still on a serial port-based communications interface.

Ensign Kevin Hawxhurst, then a graduate student at NPS, took on the challenge of integrating these various protocols. Impressively, he created the site’s original microgrid controller using MATLAB, a numerical computing programming language used to develop algorithms. Ensign Hawxhurst built an automation strategy centered around a control loop that polls for data, determine available power and storage levels, then adjust load power, log the data, and re-polls every 20 seconds. After a successful evaluation period, IMPEL decided to replace the MATLAB controls with Programmable Logic Controllers (PLCs) to manage the microgrid, as PLCs are more robust and more standard in such applications.

IMPEL’s highly successful project demonstrates some key takeaways in regards to designing microgrids:

“- Start with the goal in mind. There are a lot of excellent and sophisticated technologies that one can use as building blocks when designing a microgrid. Just because they exist doesn’t mean they need to be deployed. Rather, determine your project objectives first and foremost: if uptime is the goal, perhaps some fossil fuel generators will help you meet your goal with an efficient design envelope and orientation, whereas a sustainable design goal might allow fossil fuels to be eliminated so PV and wind are the way to go. In either case multiple forms of energy storage will surely be a component of the design. This bottom-up determination should inform what equipment you use to build your microgrid.

“- Evaluate efficiency first. Before you size your generation and storage equipment, look to reduce and flatten your energy loads.

“- After an efficient building envelope is designed and renewable generation assets are optimized and installed, don’t let building energy demand limit renewable energy production. Use or store all renewable energy generated. If there is excess electricity production, store the excess in thermal or battery storage.

“- Rather than spending on a cutting-edge battery system, IMPEL chose the same kind of lead acid batteries that are widely used in the telecom sector. These less expensive batteries are all that the system required. Similarly, IMPEL used cold and hot thermal storage in conjunction with electrical storage, rather than add more lead acid cells. Thermal storage is far less expensive than current batteries; ice storage, for example, is typically less than 10 percent the cost of lithium-ion batteries on a per-kWh basis. Why use lithium to power a compressor when you can store cooling at a fraction of the cost? For its next microgrid, IMPEL is using supercapacitors rather than batteries, as IMPEL has found this technology to fit its needs better.

Despite their reputation as novel, expensive, and complex systems, microgrids have been managed effectively-and cost-effectively-for a long time. The introduction of sustainable power sources such as wind and PV should not dramatically alter the equation: with smart systems design, microgrids should remain a valuable and sustainable approach for a wide variety of customers that need them.

Evan Berger is director of energy solutions at Calmac Corp., the world leader in the product design and manufacturing of thermal energy storage technology. His role is to help position the IceBank-Calmac’s flagship product with over 4,000 installations and 500 MW installed in 50 countries-as a key component of the smart grid. Prior to Calmac, Berger worked at various energy and education technology companies in finance and sales. He has also served stints as an investment banker, specializing in private placements and venture capital raises, and as a public interest energy analyst/lobbyist for energy and water issues in Washington, DC.

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