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Written by Suzanne Foster Porter | Ecova
Back in the 1880s, power distribution technology was a hotly contested topic. The “War of the Currents” featured Thomas Edison (advocating direct current or DC) and Nicolai Tesla/George Westinghouse (advocating alternating current or AC). The public debate became personal and nasty. Edison’s employees resorted to demonstrating electrocution to instill fear about AC power.
Here at Ecova we have no intention of re-opening that debate for the utility-scale power grid. But a century has passed―maybe it’s time to look at the implications of the AC distribution standard on our energy usage. We promise not to be sensational.
Commercial office buildings consume more than 30 percent of all electricity used in the United States. A team from Ecova joined with partners and our client Pacific Gas and Electric to investigate whether DC power distribution within commercial buildings could save energy and costs. Given the size of the opportunity, relatively small incremental savings can have a large impact.
We presented our findings at the 2014 ACEEE Summer Study on Energy Efficiency in Buildings. Here’s a summary of what we found.
POWER CONVERSION LOSSES ARE GROWING
The world is a different place now than it was in the late 19 th century. Commercial buildings are filled with equipment that Westinghouse and Edison could only have dreamed of. Much of it already operates on DC, including:
Today, the AC electricity from the grid is converted to DC power at different points in the building, using individual power converters. Between building-level power distribution and conversion, about 13 percent of the electrical power is lost between the meter and the end device:
Different devices have different voltage requirements, which make a simple, centralized DC conversion solution elusive.
ZERO NET ENERGY BUILDINGS
A growing number of commercial buildings are producing their own energy through solar or other sources, with an objective of realizing Zero Net Energy (ZNE) use. Solar panels (photovoltaic cells) generate DC power. In commercial buildings, this power is then converted to AC for distribution throughout the building, then back to DC for the devices that need it. Clearly, this isn’t the most efficient way to distribute electrical power.
A ROLE FOR DC POWER DISTRIBUTION WITHIN BUILDINGS
The team developed a power flow model and analyzed both energy efficiency and cost effectiveness of implementing DC power distribution systems in buildings. We applied the model both to commercial buildings running on electricity exclusively from the grid and those ZNE buildings generating electricity locally.
For existing buildings drawing power from the grid, any energy conversion savings are offset by losses elsewhere. Staying the present course makes sense – Westinghouse wins this round.
For the growing number of Zero Net Energy buildings generating their own power, however, conversion losses are greater:
Switching to DC power distribution saves about 8 percent of total energy use in ZNE buildings. This is a promising and technically viable avenue for energy and cost reductions in ZNE buildings, but a number of market steps are needed to realize the energy savings opportunity, such as industry-accepted DC distribution standards to guide product developers, building designers, and contractors.
In the future, if DC distribution gains traction, everyone might benefit. As lighting, HVAC and other equipment migrate to DC power loads, the cost benefits of building-wide DC distribution may shift.
Thomas Edison fans can rejoice that within ZNE commercial buildings, DC power distribution may eventually be the winner.