Energy Storage Algorithm Controls Electric Use Spikes in Solar House

The road to all-electric housing starts with realistic solar and battery storage sizing.

When you live in a rugged place like Arizona, available energy at certain times of the year can be at a premium. That’s why when building its homes, Mandalay Homes of Prescott capitalizes on one of the state’s most notable and always-available natural resources: the sun.

Mandalay Homes has been offering solar panels on its homes since 2013, when the production homebuilder first committed to constructing all of its homes to the U.S. Department of Energy’s Zero Energy Ready Home (ZERH) standard. 

Project Info

Project name: Discovery Home, Prescott, Arizona

Builder: Mandalay Homes, Prescott, Ariz.,

Completed: May 2022

Mandalay Discovery HERS Index FULLSeveral recent advances in its product offerings helped the builder garner a Special Grand Award for Innovation in Advanced Home Concepts in DOE’s 2022 Housing Innovation Awards competition, which recognizes exceptional builders in the ZERH Program.

“This year’s ‘Discovery Home’ is the first to test a new energy storage algorithm we’re developing in partnership with Sonnen and Mosaic Building group,” says Mandalay Homes’ president and founder Dave Everson.

Mandalay Homes offers 10-kilowatt (kW) batteries on many of its homes. “We’re taking a different approach to managing the battery charge and discharge throughout the day to make use of cheaper grid power when needed to ensure sufficient energy to get through the evening,” Everson says. 

The new software is also designed to help prevent demand charges by mitigating electricity usage spikes during peak periods. “Our modeling has shown a 60 percent reduction in energy bills with the new algorithm, without excess photovoltaic energy sold back to the utility,” says Everson.

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Mandalay Homes’ all-electric Discovery Home is built around existing and optional sustainable products, such as a roof sized for solar panels, a nominal battery storage system, and an electric heat pump.

A Powerful Package

In 2022, Mandalay began offering all-electric homes at the Jasper clean energy community development in Prescott. Solar PV panels are a standard part of Mandalay’s iONPlus Solar home package, which is available on 65 percent of the models sold by Mandalay. Mandalay offers an energy storage battery package on all of its solar panel-equipped homes. 

Although Mandalay has been offering solar and batteries for several years, this year’s Discovery Home is an all-electric model with both solar panels and the battery designed to manage the time-of-use (TOU) rate plans. With the battery storage, the home avoids the use of higher amounts of fossil fuel-driven power per kWh during peak periods. “We avoid dirty power and reduce the carbon footprint,” says Everson.

This home has 3.74 kW of photovoltaic panels on the roof as well as a 10-kWh, 4.8-Watt nominal battery storage system. Mandalay is taking its commitment to solar one step further by preparing its homes at Jasper to serve as a community energy source. The installation of utilities at Jasper included a dedicated network of conduit for a “virtual power plant.” 

This installed conduit will allow for future aggregation of power from individual homes to a central meter exiting the community. “The expectation is that one day the Jasper community will provide stored clean peak power to the aging housing stock in the area,” says Everson.

Mandalay’s commitment to build to DOE ZERH standards has had an influence beyond the approximately 400 homes it builds. Although Mandalay is not the only builder at Jasper, the developer has mandated that all builders at Jasper construct their homes to meet the DOE Zero Energy Ready criteria.

“The success of the DOE Program and Mandalay was instrumental in this decision,” says Everson. 

No More Natural Gas

Also, based on Mandalay’s commitment to an all-electric home, the newest phase of Jasper was built with no gas installed. Lot plans were oriented predominantly north-south for the benefit of solar panel installation. 

Architectural guidelines for the development specified lower roof slopes, which optimizes the angle for solar production. Mandalay also ensures adequate roof area for solar panels by eliminating penetrations through the roof with the use of side venting and air admittance valves.

A key component of the all-electric home is the mechanical system. Mandalay switched from dual-fuel equipment to an electric heat pump. The heat pump’s variable speed and pressure inverter technology helped the builder maintain high efficiency values during cold weather without the need for gas or heat strips. The cost of this new equipment was offset by eliminating the installation of gas.

Mandalay uses a building information modeling software tool to draft all of its plans and options. As each home’s options are selected, the turning on and off of layers assists the builder in creating a lot-specific plan even though it is operating in a production housing environment.

“Our intention is to continue to monitor the home once it is sold to collect data on the performance, systems, and customer experience. That information will be used to shape future innovation,” Everson says. “Our goal is to continue to improve production efficiency, decrease build times, and dramatically reduce materials waste through advanced construction management technologies.”

Mandalay already employs several quality assurance steps. Every home design goes through an extensive review and departmental checks before being released for construction. 

During construction, weekly meetings are held with the superintendents, customer care staff, and the sales team. In these meetings, the progress of the home and the satisfaction level of the customers are discussed. The sales team also takes weekly photos of the home throughout the build. 

The photos are used to keep the homeowner updated on progress and as an additional layer of quality control. Mandalay Homes employs a comprehensive in-house quality assurance program with inspections that are performed at pre-slab, pre-drywall, post insulation, upon completion, and in the warranty process. Mandalay also uses a web-based collaborative construction management system.

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Mandalay Homes use a slab edge covered with closed-cell spray foam that adheres to the slab edge and the bottom edge of the overhanging bottom plate to form an airtight and watertight seal.

Efficiency is Everything

This home has a Home Energy Rating System (HERS) score of 44, when the PV is not considered, or a HERS of 14 when the 3.74 kW of PV is included. The energy efficiency measures plus the solar system should save homeowners at least $2,000 a year in energy costs compared to a home built to code. Savings are likely greater when the battery and the impact of the utility time-of-use rates are taken into account.

The 10-kW battery size is large enough to get most of Mandalay’s homeowners through the daily late afternoon energy demand peak. Mandalay has found, for most homeowners, the battery covers about 8 hours of the homes’ power needs each day. Some homeowners are able to run on their own stored power all night until the sun comes up the next day and the battery starts recharging.

The unvented attics and vaulted ceilings are insulated on the underside of the plywood roof deck, with 8 to 10 inches of open-cell spray foam for an insulation value of R-33. The roof is topped with ENERGY STAR Cool Roof certified asphalt shingles.

The exterior walls consist of 2-by-6 laminated strand lumber studs spaced 16 inches on center. The stud walls incorporate advanced framing techniques, such as three-stud insulated corners, open and insulated headers, and ladder blocking at interior wall intersections to increase the amount of space in the walls for insulation. 

The wall cavities are filled with open-cell spray foam in the cavities, then wrapped with taped house wrap and covered with a continuous 0.5-inch-thick layer of rigid XPS foam for an R-25 total wall insulation value. The walls are covered with stucco cladding.

While the spray foam insulation in the attic and walls helps to air seal the building envelope, Mandalay takes the additional step of using a whole-house aerosolized sealant process to ensure even the smallest cracks are closed off, resulting in near Passive House airtightness levels. 

This home had air leakage of only 0.66 air changes per hour at 50 Pascals. An energy recovery ventilator (ERV) and timer- and moisture-controlled exhaust fans help remove contaminants from the tight home.

For heating and cooling, the home is equipped with a properly sized, two-stage, 18.2 SEER, 12.38 HSPF heat pump with a fully variable ECM motor and smart home connected user controls. The system uses 4-inch ducts installed in the sealed, conditioned attic.

A 95 percent efficient electric tankless water heater supplies hot water to the home. The water distribution system employs a central manifold with PEX piping, and distant hot water faucets use a smart programmable recirculating pump to reduce wasted water. 

The piping includes an in-line water monitoring and leak detection system with automatic shutoff. All plumbing fixtures are EPA WaterSense labeled for energy and water savings. Outside the home, the builder implemented WaterSense guidelines for drought-resistant landscaping, drip irrigation, and smart irrigation.

Mandalay’s home designs feature large windows and sliding doors. To keep them efficient, Mandalay uses ENERGY STAR rated, double-pane, vinyl-framed, argon filled windows with low-emissivity coatings and an insulation value of U-0.29 (R-3.45) and a solar heat gain coefficient of 0.23.


Key Home Features

Air sealing: 0.66 ACH 50. Open-cell spray foam in walls and attic. Whole-house sealed with aerosolized acrylic air sealant.

Appliances: ENERGY STAR refrigerator,
dishwasher, ceiling fan, exhaust fans (5).

Attic: Unvented attic, vaulted ceilings, 10-inch R-33 open-cell spray foam on the underside of roof deck.

Energy management system: Smart water usage, leak detection, IAQ and RH monitors.

Foundation: Slab on grade, insulated slab.

Hot water: Electric tankless water heater; smart recirculating pump.

HVAC: Central air-source heat pump, 12 HSPF,
18 SEER, 4-inch high-flow flex ducts.

Lighting: 100 percent LED, motion sensors, timers, lighting controls.

Roof: Truss shed roof: OSB, underlayment, asphalt shingles; 4.625-inch raised heel energy trusses.

Solar: 3.74-kW rooftop panels, 10-kWh
battery storage. Solar production tracking.

Ventilation: ERV to central air handler; IAQ monitors in light switches in great room, kitchen, den, bedroom, and owner’s suite. Humidity
sensors in light switches for exhaust fans in baths and laundry.

Walls: 2-by-6, 16-inch o.c., R-25 total: R-25 spray foam; OSB house wrap; stucco.

Water conservation: Low-flow fixtures, PEX piping, drip irrigation.

Windows: Double-pane, argon-filled, low-e, vinyl-framed, single-hung, U=0.29, SHGC=0.23.

Other: Low- or No-VOC products; air purification system; energy usage monitoring; EV charging station.