Nestled in a wooded community is a microgrid that defies the usual value propositions. It’s an outlier of a project because microgrids are normally built for different reasons, such as to bring power in developing countries to people who depend on unreliable or non-existent grid infrastructure, or to save on delivering expensive diesel fuel to islands or other remote locations, or to save on corporate energy costs – to mention a few.
So why is this microgrid here? It represents an interesting choice in the diverse and growing portfolio of energy options by its owner. He wanted to substantially upgrade his electric service, but he also wanted to reduce his carbon emissions. This microgrid project represented a unique solution to reduce levelized cost of energy based on the various capital and expense requirements. This microgrid represents a private investment by someone who is attracted to energy innovation and the desire to explore the boundaries of affordable and proven contemporary technology.
In order to create the ultimate personal microgrid, you could start – as this microgrid investor did – with land, multiple buildings, a significant power demand and energy consumption, and a need for charging electric vehicles.
This is exactly the setup that we encountered when approached by the Owner’s Agent for the property owner. This was an unusual request but a great challenge and a very interesting project. We are used to designing solar-storage microgrids for privately owned islands in the Caribbean, but we welcomed the challenge of the different climate, soil conditions, load profile, and solar resource.
We modeled the microgrid system and performance characteristics using HOMER Pro from HOMER Energy. That made it easy to analyze and communicate the performance of the project, clearly portray some of its complex engineering features and benefits to the client, while selling the merits of our approach.
Engineering started in the spring of 2017, construction began in October of 2017, and this microgrid became fully operational in the summer of 2018. It includes a new 4,160 VAC distribution system on the property (the original distribution system was a split-phase 120/240 VAC grid more typical for residential neighborhoods).
The new private medium-voltage grid was engineered to reduce losses resulting from distributing high power levels across the large site. We elected to do it at medium voltage to reduce the line losses, and also in this case to reduce the construction costs. The medium voltage allowed us to use the existing conduit and avoid any more excavation in the rocky ground that would have been necessary for lower voltage runs with bigger cables. This is a common technique we use for private Caribbean island projects. Typically the construction cost is a bit higher, but the energy savings over time make it a significant net-positive outcome.
The project includes a 300 kW fixed-tilt PV array, 650 kWh of lithium-ion batteries, two banks of bi-directional converters (BDC’s) in a DC-coupled architecture, and two engine-generator sets (gensets) that are sized to run 30% of the time. The sizing and configuration of these energy resources were based on the HOMER Pro modeling, which calculates the annual and lifetime Levelized Cost of Energy (or LCOE), based on asset capital cost and ongoing operating expenses. The HOMER model creates an hour-by-hour simulation model of the project, based on the expected load profile, local climate data, and incorporating variability in these system drivers to simulate real-world conditions.