The Renaissance in direct current (DC) took another step forward today as ABB, the Swiss-Swedish electrical equipment conglomerate, announced it will collaborate with Myklebusthaug Management to build a ship powered by a DC grid.
The ship’s grid will essentially transfer electrical power between the thrusters, propulsion drives, battery packs and other appliances on the ship in DC instead of with AC circuits.
Why use a DC grid to link all of these things together? A vast number of appliances and electronic devices—computers, motors, sensors--actually natively run on DC. Solar modules and fuel cells also generate DC power too.
Most power grids and wiring systems, however, are made to transmit alternating current (AC). As a result of the mismatch, power often has to be converted from AC to DC and vice versa several times before it gets used. In a data center, for instance, power often get converted or “stepped down” in voltage five times or more. Each conversion leads to power losses. The heat coming off your notebook brick? It’s waste heat from an AC-DC conversion.
Swapping out a conventional AC grid on a ship with a DC grid can cut power consumption by up to 20 percent, according to ABB. Equip it with solar arrays and the solar module could send power straight to appliances without sending it through a pesky inverter (which converts DC to AC) and another converter to get it back to DC.
The 93-meter, 5,000 ton ship--which will haul equipment and construction supplies for oil companies to offshore platforms among other tasks—will hit the seas in the first quarter of 2013. ABB came up with the idea in 2011 but this will be the first ship with its DC grid.
Most people tend to think of DC as something that went out of fashion along with phrenology and striped, one-piece bathing suits for men in the late 1800s. There is some validity to that point of view. In 1893, AC won the so-called “War of the Currents” when the Niagara Falls Power Company chose AC over DC as its transmission standard.
Thomas Edison continued to wage a campaign for DC and against AC. Technicians under his direction invented the electric chair, and electrocuted a circus elephant named Topsy to dramatize the danger of AC. The campaign flopped. AC won—the technology for AC transmission simply was more economical and feasible.
DC transmission, however, didn’t go completely away. The old, reliable phone system is powered by DC. In the past few years, researchers have started to tease out the benefits of DC. ABB is one of the chief manufacturers of High Voltage DC power lines, which can carry power from solar or wind farms for thousands of kilometers with very low losses.
SAP and others have retrofitted datacenters to cut power. (DC also cuts the amount of equipment and real estate required in a datacenter, says Validus DC Systems, an equipment maker partly owned by ABB.)
General Electric, meanwhile, bought Lineage Power, which produces DC equipment, and has talked about using DC to power mining shovels and other equipment.
Nextek Power Systems and the Emerge Alliance are also promoting DC as a way to cut power in buildings.
It’s old. It sounds crazy. But it will likely play a bigger role in the energy efficient future than you think.
