Home, Business & Grid Resiliency: Page 2 of 4


Inside this Article

Residential System: The Rectors’ passive-solar, energy-efficient home, with a 6.48 kW PV system and battery backup, weathers power outages with grace and comfort.
Residential System: A Conext XW6048 inverter and eight Rolls Surrette S-550 flooded lead-acid batteries provide more than 10 kWh of backup at 50% depth of discharge.
Residential System: The recently added 3.3 kW of PV capacity help charge the Rectors’ Chevy Volt for more sustainable transportation.
Commercial System: The Same Sun storefront with a 4.1 kW PV array awning.
Commercial System: The Pika X11400 Islanding Inverter with Pika/Panasonic Harbor Smart “Flex” lithium-ion batteries provide 11.4 kWh of usable backup.
Commercial System: The custom PV awning serves two functions: providing shade for the lower windows and generating energy.
Commercial System: The Pika Energy inverter display showing backup power being used during a grid outage.
Utility System: Aerial view of entire array.
Utility System: Here, 3.9 MWh of lithium-ion batteries provide load balancing and emergency backup for municipal services.
Utility System: The storage system is housed in a climate-controlled shipping container at the Chocksett Road substation.
Utility System: Critical services, like the police station and emergency dispatch, are backed up by the system, which can detach from the greater utility grid during outages.

PV System with Batteries Provides Backup

By Sarah Lozanova

In January 2018, Maine homeowners Eric and Alison Rector learned that a “bomb cyclone” was pummeling much of New England. The couple was on vacation in Mexico, and they soon discovered that many people in their home region were without power. Yet Eric and Alison took comfort that their high-performance house in Monroe, Maine, was protected from freezing pipes and would continue to have running water for the pet sitter. Their home features a dynamic combination of energy efficiency and a grid-tied 6.5 kW PV system with 20.5 kWh of battery backup.

The Rectors’ PV system also provided the support they needed during a six-day power outage last October. “Our 48-volt battery bank gives us running [well] water, space heating, ventilation, lights, and electricity for some appliances,” says Eric. “If our PV system didn’t have batteries, we would be stuck with no power during grid outages.”

Weathering the Storms with PV Power

Sundog Solar of Searsport, Maine, designed the PV system in 2014 to work both on and off the grid. Twelve Canadian Solar PV modules wired to a Schneider Electric charge controller charges a Surrette battery bank and the Conext XW 6048 inverter/charger sends surplus electricity to the grid. “I call the Conext XW 6048 ‘the magic box’ because it seamlessly transitions between being on- and off-grid,” says Eric. “The ‘magic box’ keeps the battery bank full at all times when there is grid power. During outages, there is no need to switch anything manually. All of our critical loads stay powered and, during a sunlit day, the PV system charges the batteries until the grid power returns.”

When a second array of 12 Canadian Solar PV modules was added to the array last year, the system started generating enough electricity to power the home throughout the year and charge their 2017 Chevy Volt plug-in hybrid-electric vehicle (PHEV). Eric and Alison can drive the car about 50 miles on a solar charge before it has to utilize the gasoline engine.

On sunny days, the PV array produces more than enough electricity for Eric and Alison to use in their home. On cloudy days and at night, during an outage, they are conservative and limit their consumption to about 8 kWh from the batteries to keep the batteries well above a 50% depth of discharge.

Efficient Design Saves Energy

The Rectors’ home was designed and constructed by GO Logic and is built to the Passive House standard, a stringent German certification for energy efficiency. Passive House homes typically use 90% less energy for heating and cooling than a conventionally built home.

The 1,100-square-foot home is heated by a combination of electric baseboard heaters and one through-the-wall propane heater, an Empire direct-vent, 20,000 Btu-per-hour model. That heater is connected to a Nest thermostat that tracks its use. Despite living in a cold climate, the couple used fewer than 1,000 kWh and about 35 gallons of propane to heat their home last year. An on-demand propane water heater is used for heating domestic water.

The house features passive solar orientation and south-facing glazing to maximize heating through solar gain. There are generous amounts of insulation in the slab, walls, and ceiling. Triple-pane windows and doors and meticulous air-sealing minimize air exchange between the interior and exterior of the home, eliminating drafts and wasted heating and cooling energy. Because the home is nearly airtight (a requirement of the Passive House standard), a Zehnder heat recovery ventilation system supplies fresh, filtered air to the living room, office, and bedroom.

An Unstable Power Grid

Maine ranks a dismal 49th in power grid reliability, according to the U.S. Department of Energy. As long-term residents of rural Maine, the Rectors are no strangers to power outages, even multiday ones. “The power goes off monthly, perhaps for just an hour or so,” says Eric. In the 1998 ice storm, when the Rectors lived in a neighboring house, the power went out for 11 days.

With a home office, even a short power outage can be highly disruptive. And when the grid is down, Eric and Alison still have to forgo a few luxuries, such as use of the wall oven, stovetop induction range, ice-making half fridge, and washing machine. But in a pinch, they know they can hand-wash and line-dry clothes, and use the patio grill or a portable gas burner for cooking meals. Outside of those constraints, the home and office are unaffected by outages—the priorities are space heating, lights, hot and cold running water, and air circulation. If the couple is away from home, a Nest thermostat alerts them of power outages and monitors indoor temperatures and will turn on the electric baseboard heat that can be powered from the batteries for greater peace of mind.

Comments (2)

solarKings's picture

What about Enphase Energy's upcoming IQ8 Ensemble? Microgrid with no batteries necessary. It will be revolutionary.

Greg Smith_0_0's picture

It's nice to see other companies take SMA's product ideas and implement them for disaster resiliency. The SMA Secure Power Supply was balked at by a few companies, but like every great idea, the scoffers come around.

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