B-2 Solar Array Specifications 6222021.pdf

Requirements and Specifications: Building 101 Replacement Solar Array

1. Product Description

1.1 Summary

A grid-tied, rack-mounted solar photovoltaic (PV) array shall be designed, installed, and commissioned. A package of meteorological instruments outlined in Section 6 of this document shall also be installed and commissioned in conjunction with the aforementioned array.

Some components for this PV system have already been procured and partially installed. Those components are listed under Section 2.2 of this document and shall be used for this requirement; those components listed under Section 2.3 of this document are available for use but using them is not mandatory.

The solar array field must use a single model of bifacial solar module meeting the specifications listed under Section 3 of this document. The total direct current (DC) capacity of the grid-tied solar array, based on Standard Test Conditions (STC) and the power output of only the front side of the module, shall be at least 26 kilowatts (kW) and no more than 34 kW. The roof racking system shall meet the specifications listed under Section 4 of this document. Miscellaneous specifications are listed under Section 5 of this document.

2. Design Constraints

2.1 The solar racking and modules shall be installed on the B Wing roof the Administration Building (Building 101) on the Gaithersburg campus of the National Institute of Standards and Technology. In late 2019, this roof was refinished and converted from a flat built-up roof with gravel top layer to a flat roof with tapered insulation and granular surfaced (cap sheet) top layer.

The array field shall fit within a designated roof area that is 60 feet (East-West) by 90 feet (North-South). Drawings and pictures of the available roof area, before and after the reroofing project, are depicted in Attachments #1 and #2. Please note in reviewing the attachments that two horizontal solar arrays were installed in this same general roof area prior to the reroofing project. The combined footprint of the two earlier arrays was approximately 73 feet (East-West) by 74 feet (North-South), including a 15 foot wide aisle between the two arrays. The offeror is not required to maintain this aisle in the new array design.

2.2 Currently Installed Components That Shall Be Used in the Replacement Solar PV System:

2.2.1 Two SMA Sunny Tripower grid tied inverters

2.2.1.1 Part No. STP15000TL-US-10

2.2.1.2 Rated capacity: 15 kW per inverter

2.2.1.3 Grid connection: 277/480 VAC, 3 phase

2.2.1.4 Includes two independent Max Power Point (MPP) trackers

2.2.1.5 Up to 1000 V DC input voltage range

2.2.1.6 Purchased in 2018; physically mounted in mechanical mezzanine and AC wiring connections completed in 2019; See attachment #3

2.2.2 Two SMA DC Connection Units, one for each inverter

2.2.2.1 Part No. CU1000-US-10

2.2.2.2 Accepts up to 8 string inputs (maximum 4 per MPP Tracking channel) per connection unit

2.2.2.3 UL listed to 1000 V DC

2.2.2.4 Purchased in 2018; physically mounted in mechanical mezzanine in

2019; See Attachment #3.

2.3 Currently Installed Components That Are Available to be Used in the Replacement Solar PV System, but are not Required to be Used.

2.3.1 Partial length, metal conduits that were used with the previously installed horizontal solar array. See Attachment #3.

2.3.1.1 A total of five partial conduits, ranging in nominal sizes from 0.75 inches to 1.25 inches, are available.

2.3.1.2 All partial conduits are located inside the building, on the mechanical mezzanine level.

3 Solar Array and Module Required Specifications

3.1 Bifacial module using silicon crystalline (mono or poly/multi) cells and glass-glass construction

3.1.1 The module may use full size or half-size cells

3.2 The module model may be framed or frameless

3.3 The module shall be compatible with the roof racking system specified in Section

4 of this document.

3.4 Required module dimensions

3.4.1 Length between 65 and 84 inches

3.4.2 Width between 36 and 44 inches

3.5 The module’s integral electrical cables shall allow landscape installation such that a patch cable is not required:

3.5.1 to allow connection to the physically adjacent (i.e., same rack row) modules that are part of a series string (Note: patch cables are allowed to connect consecutive modules of a series string that are mounted in different rack rows)

3.5.2 to connect in the module-level rapid shutdown device (see Section 5 of this document).

3.6 The manufacturer must warranty the electrical performance of the model of module to remain at or above 80 percent of its original rated value for at least 25 years. The warranty shall be in effect from date of commissioning or six months after date of manufacture, whichever is earlier.

3.7 The manufacturer must warranty the mechanical workmanship of the module for at least 10 years. The warranty shall be in effect from date of commissioning or six months after date of manufacture, whichever is earlier.

3.8 The rated performance based on just the front side illumination of the module at standard test conditions shall be:

3.8.1 Rated Power: 350 W or higher

3.8.2 Rated efficiency: 18.5% or higher

3.8.3 Rated Open Circuit Voltage: between 45 and 55 volts

3.8.4 Rated Short Circuit Current: shall not exceed 13 A

3.9 The module shall be capable of being integrated with the existing inverters described in Section 2.2.1 of this document and the existing combiner boxes (connection units) described in Section 2.2.2.

3.10 The manufacturer shall have completed International Electrotechnical Commission (IEC) Standard 61215 certification testing for modules constructed in the same manner as the specific model selected based on the above criteria.

3.11 The manufacturer of the solar module must have been selling modules commercially for at least 5 years and their annual production in at least one of the last 3 years must have exceeded 25 megawatts (MW).

4 Rooftop Solar Racking System Specifications

4.1 The rooftop racking system shall be designed for:

4.1.1 flat roof installations with valley and peaks from tapered insulation.

4.1.2 mounting bifacial solar modules

4.1.2.1 modules shall be mounted to the roof rack at the edges of the module

4.1.2.2 open back racking; no wind deflectors

4.2 The racking system shall permit the maximum tilt angle possible while meeting all other requirements of this procurement. The minimum acceptable tilt angle is 15 degrees.

4.3 The racking system shall elevate the front edge of each module within the array no more than 17 inches off the roof deck, although a lower height is preferred (e.g., 10 inches or lower above the roof deck).

4.4 For research purposes, the racking system shall offer the flexibility for the following two future changes while only requiring changes to either the front or rear uprights, but not both.

4.4.1 adjust the interrow spacings between consecutive module rows, while still having the overall system fit within the area specified in Section 2.1 of this document.

4.4.2 lowering the tilt angle of one or more module rows

4.5 The racking system shall be constructed from aluminum and/or stainless steel components

4.6 The rooftop racking system shall be designed to overcome the wind loads on the finished solar array.

4.6.1 An all-ballast anchoring design is required. No roof penetrations will be allowed.

4.6.2 Ballast requirements

4.6.2.1 The ballast shall not create point loads that exceed the loading limits of the roof .

4.6.2.2 The ballast must not extend more than 6 inches beyond the edge of the array’s rectangular perimeter, as created by either the outer edge of the racking system or, in the case of partially cantilvered modules, by the edge of first and last modules in a row. .

4.6.2.3 The ballast must not detract from the overall appearance of the array when viewed from the elevator lobbies on the uppermost floors of the building tower that is located just north of the eventual array field.

This viewing point is noted in the first figure of attachment #2.

4.6.2.4 The ballast shall otherwise be located to allow the installed 100% ballasted system to best approach the energy generation performance of a hypothetical 100% mechanically anchored system.

4.6.3 The wind loading shall be evaluated based on the following parameters:

4.6.3.1 Design wind speed = 120 miles per hour (mph)

4.6.3.2 Risk Category III

4.6.3.3 Exposure Category C

4.7 The solar array racking and modules shall fit within a roof area depicted in

Attachments #1b and #2 (where two horizontal solar PV arrays were once installed but recently removed). The maximum size of the available area is stated in Section 2.1 of this document. Additionally:

4.7.1 The west edge of the PV array field shall be located 12 (±0.25) feet from the west roof edge.

4.7.2 No elements of the racking system shall come within 26 feet of the east roof edge.

4.7.3 The array layout shall be designed and positioned within the footprint area stated in Section 2.1 and the boundary locations described in Sections

4.7.1 and 4.7.2 of this document to maximize the distance between the east roof edge and the PV array.

4.8 All modules shall be rack mounted in a landscape orientation.

4.8.1 The fully installed solar PV array shall not exceed a design Live Load limit of 30 pounds per square foot (psf).

4.9 No actions shall be taken that cause the roof’s warranty to become null and void.

To achieve this, two specific requirements shall be met:

4.9.1 A protective layer shall be installed such that no element of the new PV array, especially parts of the roof racking system and its ballast, directly contacts the roof’s surface. This protective layer shall meet or exceed the following specifications:

4.9.1.1 Acceptable for use over the granule surfaced modified bitumen membrane cap sheet (Tremco POWERply 300 FR) that is installed on the NIST roof.

4.9.1.2 ½” minimum thickness

4.9.1.3 can be easily cut in the field to the desired size

4.9.1.4 can be installed with gaps between adjacent pieces or having underside grooves to promote water drainage

4.9.1.5 can be used in a stacked or step-stone fashion

4.9.2 A NIST representative having knowledge of the existing roof’s construction and the details of the roofing warranty shall meet with the contractor’s on-site supervisor (1) prior to the initiation of outdoor assembly work to review that the roof protective measures agreed to in the procurement are ready for implementation and (2) at a minimum, after all work on the Building 101 roof is completed to confirm that roof protective measures have been implemented.

4.10 The installation shall not adversely restrict water from draining to the existing roof drains (see Attachments #1 and #2)

4.11 The installation shall not require modifications to the existing roof drains, plumbing vents, exhaust hoods, conduit runs, HVAC equipment, and electrical conduits that service an existing solar array located further south on the same roof (see Attachment #2).

4.12 The racking system when evaluated with the same fire classification Type of module used in the system design must result in a System Fire Class rating of C or better (i.e., A, B or C) fire rating as determined using UL Standard 1703/2703 (or the IEC equivalent standard)

5 Miscellaneous Specifications

5.1 The installation shall occur without any welding or burning unless the contractor is granted a permit by NIST. Should welding or burning be required, the Contractor shall notify NIST and NIST will provide guidance for the permitting process. The Contractor will be responsible for requesting the permit but the permit itself does not have any fee associated with it.

5.1.1 The PV system installation must comply with the 2020 version of the National Electric Code (NEC), including the items detailed below. NEC Clause 690.9 Overcurrent Protection

5.1.2 NEC Clause 690.12 Rapid Shutdown of PV System on Buildings

5.1.2.1 Two Emergency Power Off (EPO) switches with a clearly marked

“OFF” state shall be installed, commissioned and tested under the supervision of NIST electrical engineering and safety officials.

5.1.2.1.1 The first EPO shall be physically installed within 6 ft. of one of the Section 2.2.1 inverters. Design options for this installation shall be provided for review by NIST electrical engineering officials.

5.1.2.1.2 The second EPO shall be located on the exterior of the building in a clearly visible and accessible location near the array being installed. Design options for this installation shall be provided for review by NIST emergency response personnel.

5.2 Fall protection best practices shall be implemented while any work on the roof is underway. The roof edge for the area of interest is protected by a ballasted guardrail system – see the second to last picture in attachment #2. This guardrail will be dismantled and relocated after this PV installation is completed and the system has been commissioned.

5.3 Any electrical connections made within the combiner boxes or at the inverters shall be conducted by a licensed electrician provided by the Contractor.

6 Meteorological (MET) station

6.1 A weather monitoring station co-located with the array shall be installed and commissioned. The weather station shall include the following sensors:

6.1.1 a wind speed and direction sensor

6.1.2 an ambient temperature sensor

6.2 Irradiance measurement capability shall be co-located with the array and provide the following measurements:

6.2.1 Global horizontal irradiance

6.2.2 Plane of Array irradiance on the PV module front surface

6.2.3 Plane of Array irradiance on the back surface of a representative PV module

6.3 PV module performance monitoring of a single module within the PV array

6.3.1 Back of module temperature

6.3.2 Front of module temperature

6.4 Meteorological station communications

6.4.1 All sensors shall communicate measurements to a NIST provided data acquisition system over a sensor bus.

6.4.2 Protocols such as Modbus TCP, Modbus RTU, CANbus, or comparable wireless protocols are acceptable for use with NIST’s data acquisition system.

6.4.3 Third party monitoring of the above MET station instruments is not required or desired; the creation of a web-accessible dashboard is also not required or desired.

6.4.4 Commissioning of the metrology system shall include demonstration of the data pipeline with a NIST-provided data acquisition system.