A new study suggests that solar-powered homes could waste less electricity by changing how power moves between panels, batteries, and heat pumps. In year-long simulations, a direct-current nanogrid cut its total energy use by as much as 9.2 percent and lowered the modeled electric bill by 16.7 percent.
The catch matters. The ideal system was estimated to save only about 61 dollars a year in the Indiana test house, making a costly retrofit difficult to justify. The stronger opportunity may be in new homes and larger buildings designed around local solar power from the start.
How solar electricity takes the long way
Most power grids deliver alternating current, or AC, because it works well for long-distance transmission and changing voltage. Solar panels produce direct current, or DC, while batteries store DC and many household electronics use it internally.
As a result, clean electricity may change form several times before it reaches the device doing the work. Each inverter or rectifier is efficient, but none is perfect, so a little energy leaves as heat during every conversion. It is a small toll charged again and again.
A nanogrid offers a shorter route. This small network links generation, storage, and major equipment inside one building, allowing devices that already make, store, or use DC to exchange power more directly while the home remains connected to ordinary AC service.
Why the heat pump mattered
Why focus on a heat pump? It is often one of the largest electrical loads in an all-electric home, moving heat indoors in winter and outdoors during that sticky summer heat we all know. In the test house, it accounted for more than two-thirds of annual energy use.
The work was led by Aaron H.P. Farha with Jonathan P. Ore, Elias N. Pergantis, Davide Ziviani, Eckhard A. Groll, and Kevin J. Kircher. Their affiliations included Purdue University, Emerson Automation Solutions, and Trane Technologies.
The team adapted a standard four-ton air-source heat pump so its outdoor unit could draw power from a 350-volt DC bus. The paper describes the retrofit as requiring “few hardware modifications and little change in performance,” although the indoor unit remained on AC for safety.
From lab chambers to a lived-in house
The researchers first tested the heat pump for heating and cooling in controlled environmental chambers. A unit of the same model then went into a 1920s, roughly 2,240-square-foot house in West Lafayette, Indiana, occupied by three graduate students.
The home had a 14.3-kilowatt solar array, a 20-kilowatt-hour battery, all-electric appliances, and both AC and DC wiring. Field testing ran from December 18, 2024, through January 16, 2025, with the thermostat near 69 degrees Fahrenheit and outdoor temperatures dropping to about 17 degrees.
The heat pump alone did not show a statistically clear efficiency advantage on DC. Laboratory and field results found broadly similar performance on both power types. The bigger gains appeared only when solar, battery storage, converters, and heating were modeled as one system.
Where the energy savings appeared
The year-long model used measured heat-pump and household loads, matching solar conditions, and battery controls that used local solar first. It compared a standard AC network, a DC network with the retrofitted heat pump, and an ideal version with a factory-designed DC heat pump.
The retrofit configuration used 8 percent less gross nanogrid energy. The ideal version used 9.2 percent less. In simple terms, fewer conversions meant less electricity was lost before it could do useful work.
The modeled annual bill fell by 12.5 percent with the retrofit and 16.7 percent with the purpose-built design. The DC layouts also improved the battery’s round-trip efficiency, meaning more of the electricity placed into storage came back out for use later.
Why a home retrofit may not pay
For the roughly 2,240-square-foot test house, the ideal setup cut the estimated annual bill from about 367 dollars to 306 dollars. That is a savings of 61 dollars. The study calculated that a ten-year payback would support only about 612 dollars in added installation cost.
The estimate assumed electricity bought from or sold to the utility was worth 14 cents per kilowatt-hour. Actual savings would likely depend on local rates, solar credits, climate, equipment size, and household behavior. That electric bill can change the answer quickly.
The model also left out voltage fluctuations, grid interactions, fault protection, long-term reliability, and several other real-world effects. For the most part, this is evidence of technical potential rather than a ready-made plan for homeowners to follow.
A hybrid home may be the realistic future
Equipment remains a major obstacle. Residential heat pumps built for direct DC connections are difficult to find, and DC breakers, connectors, voltage levels, and safety systems still need broader standardization. Direct-current circuits can also be harder to disconnect safely, so this is not a do-it-yourself rewiring project.
Earlier research supports targeted use rather than a complete takeover. A 2022 review of DC power in buildings highlighted promising applications, while a 2023 residential study found that solar panels and batteries were central to reducing conversion losses. The new work adds field data from a major appliance in an occupied house.
The International Energy Agency calls heat pumps a central technology for cleaner heating, and electric vehicles could add another large DC battery to the home. A future building may keep AC for grid service and conventional outlets, with a separate DC backbone for solar panels, storage, vehicle charging, lighting, and heating. Not every home will be rewired, but new solar-heavy buildings could turn a hidden trickle of wasted electricity into a steady, measurable gain.
The full study was published in Applied Energy.
