Freedom Solar Power: East Austin Alley Flat

In early 2016, David Brearley and his wife Molly O’Halloran contracted Austin, Texas–based Freedom Solar Power to permit and install a SunPower PV system for a new alley flat. The downstairs provides a small home office for Brearley, SolarPro’s senior technical editor. The upstairs is a licensed short-term rental unit that doubles as a guest suite. The roof hosts a 4.1 kW PV system that offsets all of the back house electrical loads and a majority of those for the entire property.

The couple developed the architectural plans for the alley flat with solar in mind, calling for a true standing-seam metal roof early in the design process. The plans also specified that all mechanical and plumbing vents had to exit the building via the north roof, ensuring that as much south-facing area as possible was available for solar. Together with their architect, the couple homed in on a hybrid hip-and-gable roof profile that both fits the neighborhood’s historic character and justifies the array to the east to avoid afternoon shading from tall trees.

Because of shading issues and the small roof area, the application favored high-efficiency PV modules and module-level power electronics (MLPE). For optimal array capacity, the architect designed the length of the roof with SunPower modules in mind. In addition to mitigating shading, MLPE also meet Austin Energy’s rapid-shutdown requirements. Brearley purchased SolaTrim protective barrier to proactively address potential issues associated with nesting pigeons, squirrels and leaf litter, and acquired specialty standing-seam roof anchors from Fall Protection Distributors to provide permanent anchors for installers and future service technicians.

Freedom Solar Power was ideally suited to complete the installation. As SunPower’s only master dealer in Texas, the company was able to offer 18-month same-as-cash financing. To stretch their budget, Brearley and O’Halloran acted as their own general contractor and did a lot of work themselves. By financing the PV system, which was the most expensive part of the new build, the couple was able to complete the construction project and start generating rental income before the solar bill came due. After reviewing two proposals, Brearley selected SolarEdge power electronics over ACPV modules. He also decided to oversize the inverter capacity to allow for future expansion, either to incorporate energy storage or to add a similarly sized array on the front house.

Installation logistics were somewhat complicated due to the dictates of new construction. Before the insulation contractor arrived on-site, Freedom Solar sent out a master electrician to hang the inverter, utility disconnect and meter base, and to complete all of the conduit runs, which are entirely hidden inside the exterior framing. The installation crew arrived a few days later to install the mounting system, optimizers, modules and protective barrier. To allow for a rebate inspection, Freedom Solar commissioned the system using temporary power in May 2016. Commercial operations did not commence until April 2017, after the city had closed all of the project permits.

“Freedom Solar Power came highly recommended and did not disappoint. Its team exceeded my expectations at every step.”

David Brearley, SolarPro

Overview

DESIGNER: Josh Meade, lead designer, Freedom Solar Power, freedomsolarpower.com

LEAD INSTALLER: Mark Bedell, master electrician, Freedom Solar Power; Ryan Albert, project manager, Freedom Solar Power

DATE COMMISSIONED: April 2017

INSTALLATION TIME FRAME: 2 days

LOCATION: Austin, TX, 30.3° N

SOLAR RESOURCE: 5.4 kWh/m2/day

ASHRAE DESIGN TEMP: 99°F 2% average high, 23°F extreme minimum

ARRAY CAPACITY: 4.1 kWdc

ANNUAL AC PRODUCTION: 5.5 MWh

Equipment Specifications

MODULES: 12 SunPower SPR-X21-345, 345 W STC, rated power tolerance +5/-0%, 6.02 Imp, 57.3 Vmp, 6.39 Isc, 68.2 Voc

INVERTER: Single-phase, 120/240 Vac service; one SolarEdge SE7600A-US, 7.6 kWac 240 Vac output, 500 Vdc maximum input voltage, 350 Vdc nominal input voltage

POWER OPTIMIZERS: 12 SolarEdge P400 power optimizers (one per module), 400 W rated input, 8 Vdc–80 Vdc MPPT operating range, 80 Vdc maximum input voltage, 5,250 W maximum per dc source circuit for single-phase applications

ARRAY: One 12-module source circuit with a 350 Vdc nominal output voltage as controlled by the inverter and dc optimizers

ARRAY INSTALLATION: Standing-seam metal roof–mounted array, SunPower InvisiMount rail-based mounting system, S-5! mini-clamp attachments, SolaTrim protective barrier, array azimuth 205°, array tilt angle 27°

SYSTEM MONITORING: Inverter-direct SolarEdge module-level monitoring; CURB circuit-level monitoring in back and front house subpanels

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