Fort Wayne's Journey Towards Resilience and Clean Energy - Implementation of a Microgrid Program and RNG Injection

In the era of climate change and extreme weather events, utility resilience has become increasingly important. Water facilities face multiple energy-related challenges as they strive to avoid power outages and decarbonize their operations. As a result, many are exploring microgrids for diversified on-site energy management. Microgrids are beneficial for reducing a facility's carbon footprint, improving resiliency of energy availability, minimizing disruption due to a utility outage, and reducing electric utility costs. Currently, microgrids provide less than 0.3 % of U.S. electricity, but their capacity has grown by almost 11% in the past four years, highlighting the growing interest and demand in this area.

Fort Wayne City Utilities (FWCU) provides water, wastewater, and stormwater services for approximately 300,000 people in city and surrounding areas. Over the past 20 years, FWCU has invested in energy resiliency by installing emergency power at its 72-mgd drinking water facility and a biogas-fueled combined heat and power (CHP) system at its 100-mgd wastewater treatment facility. Recently, FWCU has implemented a $24M Microgrid Program at its facilities for sustainable and renewable energy generation, to improve resiliency of energy use, and to move towards the circular water economy. In parallel, a biogas to renewable natural gas (RNG) project is in development at FWCU's wastewater facility. This presentation will encompass both the Microgrid Program and the RNG project, where drivers, successes, and lessons learned will be described. Combined, these two projects will allow FWCU to generate over 11.5 MW of renewable energy from solar and biogas, enough to power nearly 5,000 homes.

Microgrid Program
The Microgrid Program encompasses three of Fort Wayne's water facilities — the wastewater plant, the drinking water plant, and a wet weather retention facility. These three facilities are interconnected electrically to function as a single utility. The Microgrid Program includes solar, a backup battery system, biogas & natural gas-fueled generators as energy sources, and emergency backup generators. The 6.5 MW floating solar array is installed on an existing stormwater retention pond (Figure 1) and is coupled to a 1 MWh battery energy storage system to enhance operational flexibility. The master Microgrid Controller manages the system based on actual consumption from the three facilities and power generation from the energy sources. Renewable sources, such as the solar and biogas powered systems, are preferentially used to limit operational costs and greenhouse gas emissions. A single electric utility connection at one of the facilities is maintained for continuous use.

Energy generation capabilities of the microgrid were balanced against environmental and operational considerations. FWCU prioritized leveraging existing assets and adaptability during the planning stages of the program. Figure 2 shows an example energy demand and supply curve based on a 24-hour period. Solar energy is generated during daylight hours, peaking in the early afternoon, and is supplemented by biogas CHP. During the night, standby generators are used to minimize electric utility consumption.

Based on our results, operation of the Microgrid Program reduces the overall electric utility consumption by 80%, resulting in annual power savings of over $1.5M. Currently, the Microgrid Program is being commissioned, with generating assets being brought online sequentially. The presentation will include operational data and lessons learned from the Microgrid Program.

RNG Project
Fort Wayne operates a successful hauled waste program for co-digestion of outside organic waste, resulting in significantly more biogas than would be generated from the wastewater residuals alone. Biogas produced by the anaerobic digesters at the wastewater plant can be beneficially used continuously in the CHP system as part of the Microgrid Program. If additional digester heating is needed, it can be supplied by biogas-fueled boilers, otherwise excess biogas is flared.

A Bioenergy Model (Figure 3) was developed to evaluate the economics of expansion of the CHP system compared to producing renewable natural gas (RNG). The model accounted for organic waste loading to the digesters, operations and maintenance (O&M) costs, potential RNG value through the sale of Renewable Identification Number (RIN) credits, and the overall heat balance of the digesters. Sensitivity analyses were performed with varying amounts of outside organic waste and economic factors (such as RIN value) to further evaluate the biogas utilization scenarios. Results showed that upgrading most or all of the biogas to RNG was found to be most economically favorable due to the sale of RIN credits.

A biogas upgrading system is currently in design for production of pipeline-quality RNG for injection into the local natural gas distribution system. The RNG equipment consists of a 450-standard cubic feet per minute (scfm) three-stage membrane scrubbing system with hydrogen sulfide (H2S) and siloxane pre-treatment. To minimize construction schedule delays due to long equipment lead times, the equipment was pre-purchased at the 30% design stage. Lessons learned from the project will be described, including the importance of sensitivity analysis to the financial model, allowing for flexibility in biogas utilization operations, and planning for future growth.