Mass Renewables: Bailey Residence

In August 2016, Mass Renewables of Bellingham, Massachusetts, became the first company in the state certified to install the Tesla Powerwall lithium-ion residential energy storage system. One of its early deployments of the Tesla product is in the Bailey residence, located in Holliston, Massachusetts. The system dc-couples two Tesla 3.3 kW, 6.4 kWh Powerwalls with SolarEdge’s 7.6 kWac StorEdge power conversion system.

Mass Renewables designed the 9.975 kWdc system to offset 100% of the customer’s average annual electricity use. Local utility Eversource permits net energy metering for PV systems in its territory. During the project design phase, Mass Renewables used a Solmetric Suneye to develop a shade analysis for the site. A hipped section of the home’s south-facing roof as well as several plumbing vents complicated the array layout. The installers took the extra time to hide rooftop junction boxes and conduits from view, resulting in a visually clean array installation.

The Mass Renewables installation team mounted the inverter and batteries in the home’s basement. The two Tesla Powerwalls react to commands from the SolarEdge inverter. For the Bailey installation, Mass Renewables programmed the system to maximize self-consumption and to utilize 80% of the battery capacity (20% battery reserve capacity). In the event of a utility power loss, the inverter automatically islands PV generation and energy storage from the grid and provides energy to select household loads, including the client’s refrigerator, gas furnace blower and controls, bathroom lighting, kitchen lighting and outlets, and wireless router via a new backup-loads panel.

Users can manage several system and battery settings remotely from the SolarEdge monitoring portal. For example, Mass Renewables can remotely change the battery reserve capacity and discharge time of day. During the winter months when storms are frequent, users can program the system to retain 100% battery capacity in preparation for anticipated power outages. During extended utility outages, the PV array continues to charge the system’s energy storage and provides a weather-dependent source of critical backup power. 

“Mass Renewables is proud to be an early adopter of both the Tesla Powerwall and SolarEdge’s StorEdge inverter system. Our New England service territory can experience power outages due to winter snow and ice storms. PV arrays coupled with modern lithium-ion energy storage systems present a significant added value for many of our residential customers. We currently have two of Tesla’s new Powerwall 2.0 energy storage systems presold and look forward to installing this new 7 kW, 14 kWh product in Q2 2017.”

Mike Kelley, Mass Renewables


DESIGNER: Mike Kelley, co-owner, Mass Renewables,

LEAD INSTALLER: Jeff Herman, co-owner, Mass Renewables



LOCATION: Holliston, MA, 42.2°N

SOLAR RESOURCE: 4.5 kWh/m2/day

ASHRAE DESIGN TEMPS: 89°F 2% average high, 1°F extreme minimum



Equipment Specifications

MODULES: 35 Suniva Optimus Series OPT285-60-4-100, 285 W STC, +4.99/-0 W, 8.82 Imp, 32.3 Vmp, 9.59 Isc, 39.4 Voc

INVERTER: Single-phase 120/240 Vac service, one SolarEdge StorEdge SE7600A-USS inverter, 7.6 kWac 120/240 Vac output, 500 Vdc maximum input voltage (PV and battery), 400 Vdc nominal input voltage (PV and battery), 5.0 kWac rated output from battery in backup mode with 7.6 kWac 10-second surge capacity; SolarEdge SE-MTR240-2-200-S1 Electricity Meter

POWER OPTIMIZERS: 35 SolarEdge P300 Power Optimizers (one per module), 300 W rated input, 8 Vdc– 48 Vdc MPPT operating range, 48 Vdc maximum input voltage, 5,250 W maximum power per dc source circuit for single-phase applications

ENERGY STORAGE: Two Tesla Powerwalls (3.3 kW, 6.4 kWh each) configured in parallel (3.3 kW, 12.8 kWh total), 350 Vdc–450 Vdc operating range, 100% depth of discharge allowed

ARRAY: One 17-module source circuit (4,845 W) and one 18-module source circuit (5,130 W), 9.975 kWdc array total at 400 Vdc nominal (module-level current controlled by power optimizers)

ARRAY INSTALLATION: Roof mount, asphalt shingle roofing, EcoFasten Solar GreenFasten GF2 mounting and flashing, Ironridge XR100 rails with integrated grounding, 178° azimuth, 31° tilt

SYSTEM MONITORING: SolarEdge module-level and energy storage monitoring

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