ICARUS RT
Loma Verde Community Center, Chula Vista
Site Assessment Memo
B&V PROJECT NO. 415373
Icarus RT
14 AUGUST 2023
©Black & Veatch Holding Company 2013. All rights reserved.
Icarus RT | LOMA VERDE COMMUNITY CENTER, CHULA VISTA
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Table of Contents
1. Introduction ............................................................................................................................................... 1
2. Electrical and Mechanical Assessment ............................................................................................. 1
3. Electrical Assessment ............................................................................................................................. 1
3.1 Proposed PV Array Layout ............................................................................................................................... 2
3.2 Existing Main Switchboard .............................................................................................................................. 2
3.3 PV Inverter Interconnection: Switchboard Feeder Breaker .............................................................. 3
3.4 PV Inverter Interconnection: Ahead of Switchboard Main ................................................................. 4
4. Mechanical Assessment .......................................................................................................................... 6
4.1 Scope of Mechanical Work................................................................................................................................ 6
4.2 Site Arrangement ................................................................................................................................................. 7
4.3 Piping Schematics ................................................................................................................................................ 8
LIST OF FIGURES
Figure 1 – Aerial View of Proposed PV Array at Loma Verde Community Center ........................................ 1 Figure 2 – PV Array Oriented Due South (Azimuth Angle = 0 degrees)............................................................. 2 Figure 3 – Single Line Diagram, Existing Switchboard MSB and 3 Existing PV Arrays ............................... 3 Figure 4 – Single Line Diagram, New 280 kW Inverter(s) Interconnected Ahead of MSB Main ................................................................................................................................................................ 5 Figure 5 – New Site Layout Showing Solar PV Array and Proposed Piping Route ........................................ 7 Figure 6 – Arrangement of Piping for System and Pool Piping Interconnect .................................................. 8 Figure 7 – Solar Array Piping Schematic ...................................................................................................................... 10
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1. Introduction
To support the advancement of a proprietary photovoltaic-thermal (PVT) energy storage and cogeneration system developed by Icarus RT, Inc., Black & Veatch (BV) has prepared this site assessment memorandum for the Loma Verde Community Center, located at 1420 Loma Lane, Chula Vista, California, 91911. This initial site assessment will then be used as input to detailed design as part of an Engineering-Procurement-Construction (EPC) effort, also by BV.
2. Electrical and Mechanical Assessment
This memo includes a preliminary site assessment of both the electrical and mechanical systems for the Icarus RT PVT system at the Loma Verde Community Center.
3. Electrical Assessment
The electrical assessment involves primarily the development of a 280 kWdc solar photovoltaic (PV) array, modified by the Icarus RT PVT system for thermal energy storage. The solar PV system is planned to include PV modules secured to ground-mounted fixed racks in an open field located immediately adjacent to the north of the Loma Verde Community Center. See Figure 3-1.
Figure 1 – Aerial View of Proposed PV Array at Loma Verde Community Center
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3.1 Proposed PV Array Layout
While production of thermal energy to heat the pool is one of the goals of this project, it is considered to be secondary. The primary goal is actually the production of electrical energy from the solar PV array because the inherent value in offsetting the purchase of energy from the electric utility has a higher intrinsic value than offsetting thermal energy from natural gas-fired water heaters. As such, the solar PV array should be oriented due south for an azimuth angle of 0 degrees, as shown in Figure 3-2.
Figure 2 – PV Array Oriented Due South (Azimuth Angle = 0 degrees) The final design will take into account both electrical energy production and thermal energy, but favor electrical energy. The available land for the solar PV array does not lend itself towards a symmetrical layout, but the solar PV array will be arranged as efficiently as possible while avoiding the right-of-way for what appears to be existing SDG&E 115 kV transmission lines to the north.
3.2 Existing Main Switchboard
Although new construction for two new swimming pools is ongoing at the Loma Verde Community Center by contractor Counsilman-Hunsaker, discussions with Counsilman-Hunsaker reveal that their work does not include replacement or upgrade to the main switchboard (MSB) bus for the facility. The current construction drawing, Sheet E.02, Single Line Diagram, shows that existing Switchboard MSB is rated at 1200 A, 208Y/120 V, 3-phase, 4-wire, with a 1200 A main breaker. Also shown are three existing PV arrays interconnected to the 208Y/120 V distribution system, only one of which has a known size of 50 kW. See Figure 3-3.
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Figure 3 – Single Line Diagram, Existing Switchboard MSB and 3 Existing PV Arrays
3.3 PV Inverter Interconnection: Switchboard Feeder Breaker While the preferred PV interconnection is via a feeder breaker in the existing Switchboard MSB, preliminary calculations in accordance with National Electrical Code (NEC) 705.12(B)(2)(3)(b), show that this is not possible as detailed below.
Switchboard MSB Voltage = 208 V, 3-phase
Switchboard MSB Bus Rating = 1200 A
Switchboard MSB Main Breaker = 1200 A
120% of Switchboard MSB Bus = 1.2 x 1200 A = 1440 A
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Solar PV Array kW Size = 280 kWdc
Solar Inverter kW Size = 280 kWac (assume Inverter Loading Ratio of 1.0, or kWdc = kWac) (Note: Smaller string inverters can be used, but the composite NEC calculations are the same.) Solar Inverter Full-Load Current = 280 kW/1.732/208 V = 777 A Solar Inverter Breaker Size = 1.25 x 777 A = 972 A (or size up to standard 1000 A breaker) NEC 705.12(B)(2)(3)(b) requires that the trip rating of all “source” breakers cannot exceed 120% of the bus current rating. In this case, the two source breakers are the 1200 A main breaker (from SDG&E) and the 1000 A feeder breaker (from the 280 kW inverter).
Switchboard MSB Main Breaker + Solar Inverter Breaker = 1200 A + 1000 A = 2200 A 120% of Switchboard MSB Bus = 1.2 x 1200 A = 1440 A
Conclusion: 2200 A is not less than 1440 A, and this method is not compliant with the NEC.
3.4 PV Inverter Interconnection: Ahead of Switchboard Main As an alternate, interconnection of the solar inverter ahead of the existing switchboard main breaker is permissible, per NEC 705.12(A). This interconnection is shown in Figure 3-4, with a 280 kW solar inverter, or composite collection of smaller string inverters totaling 280 kW.
The one caveat to interconnecting 280 kW of solar inverter(s) is that coordination is required with SDG&E during final design to determine the power capacity of the incoming SDG&E service conductors.
The requirements of NEC 705.12(A) clearly states that “the sum of the ratings of all overcurrent protective devices connected to power production sources shall not exceed the rating of the service.” It is fairly obvious why the NEC has this restriction: The worst case would be when all solar inverters are producing maximum power at the same time the facility load is at a minimum, or zero, which means all solar power is being exported back to SDG&E; thus, the SDG&E service conductors cannot be subject to overloaded conditions.
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Figure 4 – Single Line Diagram, New 280 kW Inverter(s) Interconnected Ahead of MSB Main
However, definitively determining the ratings of the three existing AC disconnecting devices for the existing three solar inverters to determine compliance with NEC 705.12(A) is not possible at this time given the lack of information on the single line diagram.
It should be noted that interconnecting a solar inverter ahead of the MSB main breaker has one disadvantage. While the AC disconnecting device (i.e., molded case circuit breaker or disconnect switch) does indeed disconnect the solar inverter from the incoming SDG&E circuit, performing maintenance or servicing the AC disconnecting device is not possible since the line-side terminations of the AC disconnecting device are energized and exposed to anyone opening the door to the breaker or switch.
The only way to safely service the AC disconnecting device is to schedule SDG&E crews to disconnect the upstream SDG&E transformer, thereby de-energizing the entire facility. Then, to re-energize the facility, SDG&E crews would have to be scheduled to return. In addition to accidentally touching energized surfaces inside the AC disconnecting device, there is always the danger from an arc flash blast hazard.
Such hazards must be calculated and signage applied in accordance with NFPA 70E, Standard for Electrical Safety in the Workplace.
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4. Mechanical Assessment
The mechanical scope includes absorbing heat from the PV panel array and discharging that heat to the competition swimming pool. The PV panels will experience higher efficiencies when cooler, and the extracted heat captured from the solar panels will supplement the existing pool heating system. The result will be more electricity generated by the PV panels with less thermal energy available for heating the swimming pool, however, as stated earlier in the report, electrical power is the primary goal of the project.
4.1 Scope of Mechanical Work
Icarus is providing all the mechanical materials including:
PV panel Heat Exchangers (HX), PV circulation pump, PV to thermal storage tank HX, thermal storage tank, mechanical module (sensor and pump control cabinets), and PV fluid. Piping interconnect from the pump skid to the competition pool heating loop will need to be field verified.
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4.2 Site Arrangement
Figure 5 – New Site Layout Showing Solar PV Array and Proposed Piping Route
The new mechanical room is located east of the competition pool and houses filtration, heating and other systems for the two pools and sprayground. Coordination with the Icarus installation will be required to determine if the solar array thermal recovery equipment will fit withing the existing pool equipment spaces or if a new, exterior building will be required. If a new equipment room or shed is preferred, the room should be placed between the mechanical space and the solar array.
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4.3 Piping Schematics
Figure 6 – Arrangement of Piping for System and Pool Piping Interconnect
The solar heating equipment provided by Icarus will be located within the existing mechanical room or an adjacent shed as required. Coordination with existing equipment will be necessary to determine if space within the existing mechanical room exists for the solar heating equipment. The tie-in for the solar
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heating loop at the competitive pool will be provided by the pool equipment supplier including the recirculating pump. The pool equipment provider will run a 6” PVC supply and return to the mechanical building exterior wall (or other coordinated point of connection) to be continued by the solar heating mechanical contractor. The solar heating mechanical contractor shall receive and set the Icarus equipment and control components and provide all final piping, power, and control systems. Icarus solar heating system piping and components are shown in blue on the attached schematic diagrams. The diagrams and scope outline are to be used for pricing only and do not convey all necessary devices and accessories needed for a complete system installation.
Manual drains shall be located at system low points to facilitate draining. Manual vents shall be provided at high points to allow air extraction when filling.
Provide isolation valves to pool piping connections, heat exchangers and tanks for use during system servicing.
Provide an automatic Glycol fill system with pressure activated injection pump.
Provide an expansion tank sized to accept Glycol system expansion with the storage tank pump not enabled (no heat rejection from Glycol loop).
Provide basket strainers before and check valves after each pump. Provide mechanical pipe unions or flanges to facilitate equipment servicing as required.
Install a current sensor on the existing pool heating pump. Sensor to engage contactor within Icarus control panel to operate the thermal loops between the Icarus heat exchanger, the water storage tank and the solar panel array. The Icarus pumped loops will activate only when existing pool heating pump is active, and the water storage tank temperature is warmer than water feeding pool heaters.
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Figure 7 – Solar Array Piping Schematic
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Each PV panel heat exchanger is connected to a row pipe branch with 1” schedule 80 PVC or CPVC.
These connect to a row branch sized based on the number of panels in the row. The row branch is piped in a reverse return configuration so that the system self-balances flow for each panel heat exchanger. At the top of each panel there is a manual and automatic air vent. Each row supply main will have its own isolation ball valve with an isolation ball valve and balancing valve provided on the return branch.
Provide a pressure and temperature test port integral to the isolation valve for each row’s supply and return. There are also pressure/temperature test ports at each connection to the PV heat exchanger.
These test ports allow temporary installation of temperature and pressure indicators. Temperature and pressure gauges shall be installed at each inlet and outlet heat exchangers and the water storage tank.
Refer to the schematic diagrams above for pipeline sizes. Sizes are provided for pricing only and will require final review by equipment manufacture. Piping from the Icarus mechanical equipment space to the solar panel branch lines should be an engineered, pre-insulated, below-ground piping system such as Perma-Pipe’s PVC-Therm. The above-ground branch piping at each solar panel row to be insulated PVC or CPVC with PVC jacket.