![]() Renewable resources, such as solar and energy storage elements like batteries, are also inherently DC systems. In such systems, the rectifier in the first stage is followed by a DC-to-AC inverter that drives the motor. However, in a conventional house, native AC motor-driven loads also exist. Some high-end power supplies classified by the EPA as “80 Plus” may offer efficiencies greater than 80%, although legacy systems offer much lower efficiency, especially at lower loads. The average efficiency of all power supplies, as estimated by Lawrence Berkeley National Lab (LBNL), is around 68%. ![]() The efficiency of the majority of these power supplies usually varies between 70% and 75%. Each of these conversions wastes electricity in the form of heat. Usually, this is followed by a second DC-to-DC converter stage that converts the rectified DC voltage into a lower regulated voltage as required by the end load (e.g., 12VDC or 5VDC in personal computers). These and other appliances are fed from multistage power-conversion equipment that first rectifies the incoming AC into DC. However, at the same time, many appliances and lighting technologies, such as televisions, computers, and LED light fixtures, are native DC loads, as are electric vehicles, batteries, fuel cells, and renewable sources. ![]() Modern conventional houses are fed from alternating current (AC). Through the use of high-efficiency electronics and bus architecture, a DC distribution system reduces the amount of consumed energy and, subsequently, the amount of on-site renewable generation required, improving the cost-effectiveness of a ZNE residence. One ZNE-enabling technology is direct current (DC) residential distribution. When energy consumption is reduced, a smaller portion of distributed generation and electrical wiring is needed, which directly translates into reduced building costs and a shorter payback period for the owner. The key to realizing a cost-effective ZNE building is to reduce the net energy consumed by the house’s loads. While conceptually simple, the goal of achieving a ZNE building with a reasonable payback period is challenging due to a myriad of active and passive technologies involved, including: the selection of electrical technologies that consume less energy (high-efficiency appliances, HVAC, and lighting) efficient distribution architecture to cut power losses portable energy storage for energy buffering and the integration of renewables, such as solar, wind, and geothermal energy. Recent mandates from the state of California that require all new residential constructions be “zero net energy” by 2020 - and all new commercial buildings by 2030 - have added further urgency to the drive for energy self-sufficient buildings. Considering the fact that today’s houses and buildings consume 40% of all conventional fossil-based energy generated in the continental United States and Europe, a concept that’s been gaining popularity in recent years is the zero net energy (ZNE) building.Ī ZNE building could significantly cut dependence on fossil-based energy and supply the required energy through on-site distributed generation, such as solar, wind, fuel cells, or microturbines. Increases in global energy costs, coupled with a need to reduce harmful fossil-based emissions, are energizing a worldwide call for clean and efficient energy sources and architectures.
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