Attachment_11_-_RFIs_1-3_0002.pdf

RFIs 1-3

Question 1: Can the PV system be connected on the utility side of the generator transfer switch? The E-1 drawing shows the solar connected to the load side of the generator transfer switch. Typically, the PV would need to be offline when the generator was the power source for the site. SolarEdge does offer a "Home Backup Interface" that can work with a generator. This seems to be a complication that would have more potential downside than upside and be costly to integrate.

Response 1: The PV system is shown connected on the load side of the Automatic Transfer Switch (ATS), and the NPS intends for this connection detail to be maintained. The designed location was selected for several important reasons:

1. Many utility interconnection agreements do not permit connections on the line side of the ATS. Utilities may require anti-islanding contact from the solar inverter or allow loss-of-power shutdown at the inverter as the sole means to prevent islanding.

2. A line-side connection could risk back feed to the existing laundry facility, which is served via the 208-volt lugs of the pad-mounted transformer, creating potential safety and operational hazards.

Maintaining the PV connection on the load side of the ATS ensures compliance with utility requirements, prevents unsafe backfeed conditions, and preserves reliable operation of both the PV system and existing facility loads.

Question 2: Can a basic NEC compliant string inverter be used? Rapid shutdown isn't required on ground mounts. And optimization isn't of much value either. Eliminating these two complications will enhance reliability and reduce cost. Aside, SolarEdge would not be recommended by the group here due to poor reliability and support.

Response 2: NPS requires the PV system to comply with NEC 2023, Massachusetts State Electrical Code (527 CMR 12.00), and Eversource interconnection standards. For ground-mounted systems, NEC rapid shutdown is not strictly required; however, the system must include appropriate disconnects and safety measures to meet NEC and Eversource requirements. On a small PV system at a single-meter site, Eversource may still require rapid shutdown, depending on their interconnection review.

Optimization features (module-level power electronics) are optional. If the contractor can demonstrate equivalent system performance and receives Eversource approval, basic string inverters are acceptable.

Any substitution must maintain compliance with UL 2703, code-mandated grounding, and interconnection requirements, and be approved in final shop drawings

Question 3: Can we substitute our own engineered driven foot ground mount & framing? Made using 50-year Telespar.

Response 3: The contract documents clearly show concrete footings for the PV system support structures, which must be used as designed.

NPS will not automatically approve alternate engineered footing systems.

Any proposed substitution (e.g., engineered foot or alternative racking) would be considered a value engineering proposal. It must:

a. Demonstrate compliance with all structural, seismic, and wind load requirements per ASCE 7-16 and IBC;

b. Ensure corrosion resistance and durability for a 25-year minimum design life;

c. Include engineer-sealed calculations and drawings for NPS and Eversource review ;

d. Not interfere with module layout, tilt, azimuth, or utility interconnection requirements.

Approval is at the sole discretion of NPS and may require additional review time. Concrete footings remain the default and contractually required solution.