Carnegie Mellon University
October 28, 2016

AC/DC: The Push for Better Home Energy Efficiency

Most household appliances and consumer electronics—cellphones, laptops, microwaves, light bulbs, you name it—use direct current (DC) electricity. But back when home outlets were first being invented, the decision was made to use alternating current (AC). In order to use the power generated from the outlets in your home, each of today's devices contains a converter that takes outlets’ AC power and converts it to DC.

The same is true for solar panels—solar panels generate DC. So if you have a solar panel on your roof, it’s generating DC, converting its DC power to AC, sending it to your home, and then converting it back to DC.

Seem inefficient? That’s because it is.

“There’s a whole history of why we use AC instead of DC,” says Engineering and Public Policy (EPP) Ph.D. student Brock Glasgo. “The original decision to use AC was based on the fact that we didn’t have a functioning DC transformer back in the late 1800s. The decision was basically made for us, but they weren’t making the decision based on what our electricity use looks like now. So now, most devices that use electricity are direct current—anything with a circuit board, any consumer electronics, most appliances, and most lighting either runs internally on DC or has DCBrock Glasgo somewhere in its power supply. And our outlets still supply AC. So you’re losing something in the neighborhood of 10-20% of your energy in each of those conversions.”

It’s not difficult to see why this fundamental home energy inefficiency is a problem, which is why Glasgo studies the potential viability of taking the existing power infrastructure in homes and switching it from AC to DC. Using detailed device-level energy consumption data, Glasgo is able to simulate how much energy those same appliances would consume if they were operating on direct current circuits.

Glasgo recently published a paper in Applied Energy with co-authors Inês Azevedo, associate professor of EPP, and Chris Hendrickson, professor of EPP and civil and environmental engineering. The paper is the first in a projected three-part dissertation in which Glasgo hopes to use actual energy consumption data to recommend to policymakers that the reconfiguring of home electricity infrastructure be a valid consideration.  

This first paper specifically looks at whether converting homes from alternating current to direct current makes sense from an energy efficiency and cost perspective. The researchers’ preliminary results suggest that not only is DC a viable solution for home energy efficiency, but AC to DC pilot programs can and should start to be deployed.

The remainder of Glasgo’s dissertation will look at the non-technical barriers to broader adoption of DC, as well as other applications where device-level energy use data can be used to make better investment, policy, and regulatory decisions regarding energy efficiency in the future.

Glasgo, Azevedo, and Hendrickson's paper is entitled: “How much electricity can we save by using direct current circuits in homes? Understanding the potential for electricity savings and assessing feasibility of a transition towards DC powered buildings.”

This piece was originally published by Carnegie Mellon's College of Engineering.