The zero energy home is an initiative of the U.S. Department of Energy, first developed by its National Renewable Energy Laboratory (NREL) and made commercially viable. A Zero energy home or ZEH is built using state-of-the-art technology and equipment to minimize energy consumption. Though it draws from the power grid, the ZEH also produces energy. On an annual basis, the ZEH produces around the same amount of energy it takes from the power grid – resulting in a net or zero annual energy bill.
When designing and constructing a ZEH, the first step is to focus on reducing the overall energy use of the house. This can be achieved by combining advanced construction practices to enhance the efficiency of the energy saving features of the home. Using these energy-saving building methods, the electricity consumption of the house can be reduced to half that of the average home. This is done by using a small photovoltaic or PV solar system with a capacity of 2.4 kilowatts, for example. Though there are not sufficient ZEH homes built to determine or estimate these costs, research has shown that these features and systems may add about 25 percent or more to construction costs.
Zero energy homes also focus on preventing energy loss from the house. In an average house, 20 to 30 percent of energy may be lost due to duct leakage. In a ZEH, this is prevented by sealing and superinsulating ducts in the house. In addition, improving ceiling and wall insulation, replacing regular window glass with low-E coating window glass, using energy-efficient appliances, and installing a fluorescent lighting system also reduce energy consumption. All of these features are noted and utilized when designing and building the ZEH.
Once the energy efficient design is complete, the PV solar system is installed to provide energy. An array of PV modules is attached to the roof of the house. The PV solar system absorbs sunlight and converts it into a direct electric current (DC). The system makes use of an inverter to convert the direct current into alternating current (AC), for use in the house. To give the house a more aesthetic look, the photovoltaic system is built into the roof, which is known as a building-integrated photovoltaic system (BPIV). The BPIV also minimizes roof penetrations, i.e., reduces the complexity of the roof design and keeps the PV system protected from the elements.
Zero Energy Homes have a number of advantages:
Improved comfort: ZEH homes reduce temperature fluctuations due to erratic energy supply, creating an energy-efficient building envelope.
Reliability: The PV solar system stores excess energy. Thus, a ZEH can continue to function and provide energy even during blackouts.
Financial Security: ZEHs function independent of electricity companies. The ZEH protects its owner from fluctuations in energy prices, thereby providing financial security.
Environmental sustainability: a ZEH is designed to save energy. Since it obtains energy from natural resources like sunlight, a ZEH also reduces pollution.