Integrating Solar Energy Into Florida’s Power System: A Strategic Solar Energy Implementation Plan at Orange County Utilities

Megan L. Nelson, P.E., is senior engineer; Mark Ikeler, P.E., is chief engineer; and Andres Salcedo, P.E., is deputy director at Orange County Utilities in Orlando. Jennifer Ribotti, P.E., is project manager and Daniel Allen, P.E., is senior project manager at Tetra Tech in Orlando.

Florida, also known as the Sunshine State, has a readily available, abundant resource for energy providers and users across the state. As one of the largest utility providers in central Florida, Orange County Utilities (OCU) is researching best practices to utilize solar energy and reduce energy costs to maximize its operating budget and support the 2030 Sustainable Operations and Resilience Action Plan from Jerry Demings, the mayor of Orange County.

One identified strategy in the plan is installing solar power at a high-energy consumption wastewater treatment facility. Because of the amount of available land, OCU’s Northwest Water Reclamation Facility (NWRF) was selected as the preferred location for a pilot project. At OCU, electricity costs account for approximately 15 percent of the annual operating budget for both the water and water reclamation divisions.

When identifying potential solar projects within OCU, several factors were considered that would provide the best return on this investment:

S Available land space

S Proximity to high power use processes

S Existing regulatory constraints

The OCU owns and operates the NWRF, and power to the facility is currently provided by Duke Energy (Duke). The proposed NWRF solar plant is to have a capacity of 2 megawatts (MW), which will reduce electricity consumption at the facility by approximately 33 percent and up to 60 percent, depending on weather, ambient temperature, available daily irradiance, panel tilt angle versus time of year, and system losses.

This project will be eligible for net metering, meaning that excess electricity generated onsite that’s not consumed will be sent back to the power grid and credited later against consumption during the same time-of-use period. Construction on this project is currently underway and expected to be complete by summer 2023.

The OCU is concurrently assessing sites with open water space for locating floating solar panels. One floating solar panel project that is currently underway and under construction is at OCU’s Southern Regional Water Supply Facility (SRWSF), and it’s also expected to be complete by summer 2023. More solar panel installations will be performed by OCU at its facilities throughout Orange County.

This article focuses on OCU’s solar energy journey to date, including the design, anticipated timeline and energy savings of the proposed solar plant at NWRF, and future considerations for solar energy at Orange County.

Northwest Water Reclamation Facility

The NWRF is owned and operated by OCU and is located at 701 West McCormick Road in Apopka. This facility is currently provided power by Duke and has a typical peak daily power usage of 1.3 MW.

To offset plant power costs and create a moresustainable facility through net energy metering, OCU is currently constructing a solar plant with a peak capacity of 2 MW of peak alternating current (AC [MWAC]), the maximum allowable generation capacity for interconnection and net metering of customer-owned renewable generation per the Florida Administrative Code (F.A.C.), 25-6.065(3).

An array of 2-MWAC panels was estimated to produce up to 60 percent of NWRF’s power and potentially save $430,000 per year in operating costs.

A preliminary technical and feasibility review was prepared for OCU in 2019 (WSP Global, 2019). The review considered two proposed site locations at the NWRF, as well as several site panel layouts, electrical interconnect, yield analysis, basic design considerations, system-installed cost, and preliminary equipment recommendations. It was estimated that a 25-year life cycle of the system with 2 MW could be paid in full within 10 years.

The OCU eventually selected the site shown in Figure 1 as the preferred location for the solar panel plant. Existing site improvements were necessary for the proposed solar plant and generally included new concrete pads, electrical conduit, and minimal equipment to operate the solar panel plant.

The primary reasons for selecting the proposed location for the solar plant were the close proximity to the existing electrical building, the availability of ample undeveloped land that was not otherwise reserved for future plant expansions,

Continued on page 32 and the ability to maintain the natural drainage in the area.

Duke Energy

As mentioned previously, the NWRF is primarily metered through an existing contract with Duke, which will replace OCU’s current meter during the project with a bidirectional meter capable of recording excess energy generation for calculating net metering credits. This site is defined by state law as a Tier 3 generating facility, 100 kilowatt (kW) to 2,000 kW (2 MWAC) in size. Excess energy generation at the end of the billing month is credited to the energy consumption for the next billing cycle. At the end of each calendar year, Duke credits the customer for any unused net metering credits at an annual rate based on the cogeneration (COG)-1 tariff. The rate for COG-1 back in 2020 when the project was initiated was 6.310 cents/kilowatt-hour (kWh), meaning that the customer receives 6.310 cents for each credit not used to offset energy usage during the calendar year. The design of the system included an OCU-owned revenue-quality net meter that will track usage to confirm Duke’s recorded net usage.

Basis of Design

The basis of the solar plant design at the NWRF includes 2-MWAC photovoltaic (PV) panels, arranged as shown in Figure 2. The panels will be distributed on approximately 10 acres of land and include ground-mounted, fixed-position panels approximately18 in. above grade. The panels will have 1000 volt (V)-direct current (DC), 480 V-AC, and three-phase conversion, along with structural supports, inverters, cabling, DC optimizers, AC distribution, grounding, system communications, a medium voltage transformer, and medium voltage switchgear.

Photovoltaic Panels

The system was designed to be fixed-tilt with a 20-degree tilt angle facing due south (not magnetic south) and required that the panels be mounted with a 5-degree west azimuth (panels turned slightly west). A conversion ratio of 1.3 DC/ AC was assumed to account for system losses for the difference in power ratings of factory standard test conditions (STC) versus actual field rating nominal operating cell temperature (NOCT).

A number of panel manufacturers that could be used for the project were selected from a list of Tier 1 providers. Tier 1 solar panels are made by manufacturers that have been rated as such by a reputable, independent PV industry analyst and provide a higher-quality manufacturing process, resulting in products with fewer deficiencies, better warranties, and better panel performance. These are financially stable manufacturers with a greater ability to honor their warranties over the life of the system.

There are a variety of PV module sizes available, and standard cells in the United States include 60 cell, 72 cell, 96 cell, and various versions of half-cell technologies, such as 2x72 (144) halfcell designs. The 60 cell panels are normally used in residential systems with limited roof space and were not considered for this project.

Typical applications for commercial systems are 72 cell panels, and 96 cell panels are generally reserved for large-scale utility systems. The 72 cell and versions of the 144 half-cell designs were used as the basis of design for this project based on cost and weight considerations. Most 72/144 cell units weigh approximately 50 pounds, which is the Occupational Safety and Health Administration (OSHA) limit for one-person manual lifting, making this weight limit a critical factor for installation cost and maintenance.

Direct Current Optimizers

The DC optimizers, with a rapid shutdown feature, were designed to be added to each panel to:

S Maintain maximum efficiency by operating panels as close to maximum power point tracking (MPPT) as practical.

S Mitigate module mismatch loss due to manufacturing tolerance, partial shading, and aging.

S Provide the safety of a rapid shutdown feature.

S Track panel health and status for panel-level maintenance.

Ground-Mounted Structural Systems

Ground-mounted structural systems represent a substantial cost of the PV field installation. This is typically performance-based criteria in bid documents that allow the contractor an opportunity to minimize costs based on system and installation methods. The selected contractor will not be required to use concrete in this design, although they may elect to do so to reduce pile depths.

Inverters

Inverter options include large central inverters with DC string combiners and smallercapacity string inverters with AC outputs that are combined in standard switchboards and gear. The recommended option will be based on equipment costs, installation costs, initial system capacity and expansion considerations, and maintenance costs.

Over the life of the PV system, power electronics are most susceptible to failure; therefore, inverters require careful maintenance, repairs, servicing, and/or replacement throughout the life of the system. Small string inverters are easier to maintain and can be serviced or replaced by most operator technicians. Due to the increased complexity of central inverters, increased service and repairs would be required by manufacturer technicians, and therefore, were not considered for this project.

Small string inverters can be located on the north side of panel strings, benefiting from reduced heat through shade from the PV panels. Depending on structural design, string inverters can be mounted to the panel supports, further reducing installation cost.

Northwest Water Reclamation Facility Solar Plant Timeline

The final design for the NWRF solar plant was completed in fall 2020. The project was bid and awarded to Ecolectrics in fall 2021 for an estimated construction cost of $3,788,000. The Duke Tier 3 interconnection agreement application was approved in spring 2021. Construction is currently underway and is expected to be complete in summer 2023.

The Future of Solar in Orange County

The OCU plans to implement solar power energy solutions, in addition to the NWRF solar plant. Future projects will be strategically prioritized based on potential energy savings for the connected facility, compatibility of site configurations, and existing conditions, as well as other factors, such as shifting economics of products in the marketplace and impacts from associated regulations.

A contract was recently awarded by OCU in the amount of $2,017,000 to D3 Energy for the turnkey installation of a fully operational 1.04-MWAC floating PV system at the SRWSF. It’s anticipated that the proposed system at this facility will achieve an annual energy savings of 20 percent, or $175,000 per year. This investment represents an approximately 11-year return on investment.

While both projects reflect comparable capital investments, maintenance costs are expected to be lower for the floating PV system. Further, consideration of both types of mounting options allows greater flexibility for OCU, as each facility’s unique property layout is assessed for future projects. As the current projects move through the construction phase and into operations, actual energy production rates and maintenance costs will be monitored and assessed.

The OCU is committed to sustainability, resilience, and innovation. With this in mind, it seeks to continue expanding the use of PV systems in an effort to address the sustainability initiative component of this mission, offset energy demands, and reduce greenhouse gas emissions. S