The last major technological leap forward in electricity distribution occurred more than 100 years ago. Inefficient, inflexible, and increasingly fragile, our system of alternating current (AC) power distribution is now showing its age. Last century’s AC infrastructure was designed at a time when today’s diverse energy demands could not have been imagined. In an era before distributed energy generation, the ability to transmit AC over hundreds of miles from central plants to individual outlets made it king. Today, however, the homogeneous centralized generation model is giving way to distributed generation, and an alternative method of delivering electricity within homes and buildings is emerging.
Direct current (DC) is the power of our sustainable energy future. It is produced by solar panels, stored in batteries, and consumed by the lights and appliances that we have in our homes and offices today. More than five thousand solar energy systems are installed on US rooftops every week, challenging traditional electric utility service models. Soon many buildings will also be outfitted with batteries for on-site energy storage. Our electronics, modern LED and fluorescent lighting, and many of today’s appliances – which account for more than a third of household electricity consumption – require DC to function. The portion of native DC loads will only continue to grow with the proliferation of efficient lights, consumer electronics, advanced motor-driven appliances, and eventually electric vehicles.
As technology propels us toward a DC-powered future, legacy AC infrastructure anchors us to the past, hindering our ability to realize the full potential of ultra-efficient appliances and distributed energy. Modern distributed energy systems produce DC that must be converted to AC to supply the existing electric grid. This wasteful process is compounded when millions of lights, electronics, and appliances must each convert AC back to DC in order to operate. Up to 30 percent of site-produced DC power may be lost during these redundant conversions as it is transferred from PV panels and batteries through multiple layers of power conversion (see the Appendix “Following the Losses”).
We envision a future where AC and DC power distribution co-exist within buildings, each serving the needs to which they are best suited. In this scenario more DC power is put to use where it is produced and stored, rather than converted, exported to the grid, and converted again. With DC power we can unlock remarkable benefits for consumers, product manufacturers, and the environment. For example:
- Consumers could lower their energy bills and improve the resiliency of their homes during grid outages;
- Appliance and lighting manufacturers could produce more efficient, more reliable, and higher-performance products, while simultaneously reducing material and shipping costs;
- Solar and energy storage companies could offer greater value to their customers and explore new business models through an ecosystem of DC-ready systems and products;
- Electric utilities could experience better load control and minimize exposure to intermittent distributed generation sources behind the meter; and
- The environment would be subject to reduced emissions from central generation plants due to lower total demand and reduced transmission and distribution losses.
Achieving this vision requires cooperation, open dialogue, and a shared commitment among those who have a stake in generating, storing, distributing, and consuming DC power. There are three parts to the DC equation: supply (generation), distribution, and demand (consumption). The first two elements are already progressing. On the supply side, renewable energy companies and battery storage and electric vehicle manufacturers continue to grow their markets and increase the presence of DC power in homes. In terms of infrastructure, coalitions of businesses, nonprofits, and government organizations are busy developing standards and components necessary for reliable DC power distribution in buildings.
But there is still one critical missing piece of the equation: we lack a coordinated effort to promote the demand for DC through manufacture of DC-ready lighting and appliances, and to build public awareness of the benefits achievable through direct use of DC in buildings. Appliances and lighting are the most important interface between people and energy in the home, and their manufacturers and users are an untapped and powerful force to propel market transformation.
In this paper we provide a glimpse into a more energy efficient, reliable, and secure energy future, one in which generation, storage, distribution, and consumption of electricity in the home is increasingly – though by no means entirely – based in DC. We illustrate how in the years to come consumers will radically change the way they access energy services, and examine how market and technological forces are already driving the transition. We explore adoption paths to demonstrate how DC distribution can be introduced into existing buildings in a meaningful way. Lastly, we demonstrate why action is needed in the next one to three years to spur market transformation through DC-ready appliances and lighting, and identify opportunities where greater coordination can maximize the benefits that can be realized in the transition.