The Fraunhofer Center for Sustainable Energy Systems, working with elevator manufacturer thyssenkrupp, prepared a report detailing how they achieved a net-zero solar energy elevator system in a Boston office building. thyssenkrupp published the report last week. (Download Report)

Elevators consume 5 billion kWh of electricity per year in the U.S., costing about $500 million. Since elevators represent up to 80% of all vertical transportation energy, reducing and offsetting their energy use could have a major impact.

To demonstrate the viability of the thyssenkrupp net-zero elevator concept, Fraunhofer CSE performed a field validation in their six-story Boston, MA office building. A net-zero elevator system produces at least as much energy as it consumes over the span of a year. The goal was to achieve net-zero using a solar array that fits within the elevator footprint.

Getting to Net-Zero

It starts with an efficient elevator.

The elevator used in the demonstration (thyssenkrupp Synergy elevator) is equipped with state-of-the-art energy saving features, including a regenerative drive and LED cab lighting. Additional efficiency upgrades were installed during the demonstration, including a more efficient controller capable of a deep-sleep standby mode and an auto-power-down feature that shuts off the cab lights and fan when the elevator is not in use. Together, these upgrades reduced total standby power draw by about 75% and brought the net-zero concept within reach.

To offset the elevator’s energy consumption, the project team installed a rooftop solar photovoltaic (PV) array on Fraunhofer CSE’s Boston office building above the elevator hoistway. The 3.75 kW solar PV system, designed to produce about 4,000 kWh per year in Boston, slightly exceeded its annual production goal in its first year of operation.

To validate the net-zero concept, Fraunhofer CSE continuously monitored the elevator power draw during normal operation over several years, spanning several hardware and software configurations. The resulting measurements were then used to calculate annual energy consumption under different usage and efficiency scenarios.

With the auto-power-down features enabled, and with a low-to-medium activity profile (up to two hours’ travel time per day), Fraunhofer CSE found that the elevator consumed about 8 kWh per day. The solar array generated on average more than 11 kWh day, leading to an annual energy surplus. Considering a hypothetical higher usage scenario, where the number of elevator trips doubles on business days, Fraunhofer CSE projects that net-zero energy is still attainable with the same size solar array.