A Broad Canopy

The PV array generates as much electricity as the Bullitt Center uses in a year.

  • The photovoltaic array spreads out like the canopy of a tree to capture solar power for the building.
  • 230,000 kilowatt hours per year is the expected total energy generation by on-site photovoltaic array.
  • There are 575 solar panels in the Bullitt’s array.

A Living Building must generate as much electricity as it uses on site. In Seattle, this problem is a two-sided equation in which production must be maximized and usage must be minimized, so that production equals consumption over the course of a year.

In thinking about the way the site was once energized by the solar power when it was a Douglas fir forest, the designers placed a large canopy of solar panels on top of the building. The 14,000 square foot array, comprised of 575 individual panels, is fastened to a steel substructure that parallels the western slope of the site.

Normally panels are set to face south, at the angle of the latitude so that they can collect sun in the winter. However, the designers realized that in Seattle, most of the sun is received in the summer, and the shallow-angled winter sun would not provide much benefit behind the blanket of clouds that shrouds our fair city during winter. The decision was made to optimize for summer, using the electrical grid as a battery to store power in the summer, and draw power from in the winter. The Bullitt Center energy budget shows how the summer surplus can offset a winter deficit.

The second part of the equation is the energy consumption of the building. A typical office building operates at 92 EUI (Energy Use Index is comparable to miles per gallon in a car). If the Bullitt Center had an EUI of 92, it would have needed an 82,000-square foot solar array on the roof to generate all its energy from the sun. Instead, with the integration of energy saving systems, such as passive ventilation, ground source heating, and natural daylighting, along with the help of tenant energy budgets, the Bullitt Center will be able to operate at an EUI of 16. With such a small EUI, the 14,000 square foot rooftop array is able to provide for all the electrical needs of the building.

Next Building Feature: A Future So Bright – We Need Windows With Shades