The DC Nanogrid House: Converting a Residential Building from AC to DC Power to Improve Energy Efficiency
The modern U.S. power grid is susceptible to a variety of vulnerabilities, ranging from aging infrastructure, increasing demand, and unprecedented interactions (e.g., distributed energy resources (DERs) generating energy back to the grid, etc.). In addition, the rapid growth of new technologies such as the Internet of Things (IoT) affords promising new capabilities, but also accompanies a simultaneous risk of cybersecurity deficiencies. Coupled with an electrical network referred to as one of the most complex systems of all time, and an overall D+ rating from the American Society of Civil Engineers (ASCE), these caveats necessitate revaluation of the electrical grid for future sustainability. Several solutions have been proposed, which can operate in varying levels of coordination. A microgrid topology provides a means of enhancing the power grid, but does not fundamentally solve a critical issue surrounding energy consumption at the endpoint of use. This results from the necessary conversion of Alternating Current (AC) power to Direct Current (DC) power in the vast majority of devices and appliances, which leads to a loss in usable energy. This situation is further exacerbated when considering energy production from renewable resources, which naturally output DC power. To transport this energy to the point of application, an initial conversion from DC to AC is necessary (resulting in loss), followed by another conversion back to DC from AC (resulting in loss).
Tackling these losses requires a much finer level of resolution, namely that at the component level. If the network one level below the microgrid, i.e. the nanogrid, operated completely on DC power, these losses could be significantly reduced or nearly eliminated altogether. This network can be composed of appliances and equipment within a single building, coupled with an energy storage device and localized DERs to produce power when feasible. In addition, a grid-tie to the outside AC network can be utilized when necessary to power devices, or satisfy storage needs.
This research demonstrates the novel implementation of a DC nanogrid within a residential setting known as The DC Nanogrid House, encompassing a complete household conversion from AC to DC power. The DC House functions as a veritable living laboratory, housing three graduate students living and working normally in the home. Within the house, a nanogrid design is developed in partnership with renewable energy generation, and controlled through an Energy Management System (EMS). The EMS developed in this project manages energy distribution throughout the house and the bi-directional inverter tied to the outside power grid. Alongside the nanogrid, household appliances possessing a significant yearly energy consumption are retrofitted to accept DC inputs. These modified appliances are tested in a laboratory setting under baseline conditions, and compared against AC equivalent original equipment manufacturer (OEM) models for power and performance analysis. Finally, the retrofitted devices are then installed in the DC Nanogrid House and operated under normal living conditions for continued evaluation.
To complement the DC nanogrid, a comprehensive sensing network of IoT devices are deployed to provide room-by-room fidelity of building metrics, including proximity, air quality, temperature and humidity, illuminance, and many others. The IoT system employs Power over Ethernet (PoE) technology operating directly on DC voltages, enabling simultaneous communication and energy supply within the nanogrid. Using the aggregation of data collected from this network, machine learning models are constructed to identify additional energy saving opportunities, enhance overall building comfort, and support the safety of all occupants.