Wireless lighting control systems allow users to avoid the cost and complexity of installing new iring, but how well do they work? The GSA’s Green Proving Ground program test- ed advanced lighting controls with wireless networking in two California office buildings and discovered energy savings of 54% when pairing the controls with fluorescent lamps that
have dimmable ballasts and 78% when the controls were matched
with LED fixtures.
The John E. Moss Federal Building in Sacramento and the
Appraisers Building in San Francisco served as the test sites for the
control retrofits. All of the fixtures in both sites were programmed
into zones, each of which received at least one occupancy sensor.
Photosensors were added to zones along the perimeter to enable
daylight harvesting. The controls utilized an open standards ZigBee
mesh network and a web-based interface, and both also integrated
with the automation systems at both buildings.
Savings were heavily dependent on the baseline conditions,
GSA found. However, the Appraisers Building, which had a baseline
EUI of 2.3 k Wh per square foot, noted a savings of 39% in lighting
energy with the wireless controls compared to an automatic scheduling baseline. Roughly 22% of that was from the occupancy sensors, 10% from institutional tuning and 7% from daylight harvesting.
Buildings with the GSA’s average EUI of 3. 25 k Wh per square foot,
however, would see a total savings of 54% with fluorescents or 78%
if an LED retrofit was conducted with the control installation.
The incremental cost of adding wireless advanced controls
worked out to roughly $1 per square foot for a payback of three to
six years; adding LEDs to that retrofit would add up to about $3
per square foot, meaning a 10-year payback if the electricity rate
is 12 cents per k Wh. This long payback may deter some potential
investors, GSA notes.
Research Teams Seek
Increased Efficiency of
Perovskite Solar Cells
SOLAR STUDIES YIELD MIXED RESULTS
How Wireless Lighting
Controls Slash Spending
CUT ENERGY USE IN HALF WITH ADVANCED
STRATEGIES
Developing efficient perovskite solar material has been a task that has flummoxed research teams around the world. Two teams of researchers have uncovered new developments in the technology, but their findings range from promising to challenging.
First, the good news. Researchers from Stanford and Oxford
Universities have created a new solar cell that combines two
perovskite solar materials to increase efficiency and lower a building’s carbon footprint.
“When used together with another perovskite semiconductor that
specializes in harvesting visible photons, we are able to convert solar
energy into electricity with 20% efficiency,” says Tomas Leijtens, co-lead author of the study. “We think we will be able to increase the
efficiency to 30%, which would revolutionize the solar industry.”
How It Works
The devices consist of two
perovskite solar cells (PSCs)
stacked together. Each cell is
printed on glass, but the technology could also be applied to
plastic.
Previous studies from Stanford
and Oxford showed that adding
a perovskite layer can improve
the energy efficiency of silicon solar cells, which has been an impediment to solar technology. However, a device consisting of two all-perovskite cells would be cheaper and less energy-intensive to build.
On a less optimistic note, researchers of the Energy Materials
and Surface Sciences Unit at the Okinawa Institute of Science and
Technology Graduate University have been studying the short lifespan of methylammonium lead iodide perovskite (MAPbI3), a common type of perovskite material.
Dr. Shenghao Wang, first author of the study, suggests that fixing the degradation of MAPbI3 perovskites might not be possible.
After removing factors that have been cited as possible degraders of
MAPbI3 perovskites (moisture, atmospheric oxygen and heat), Wang’s
team found that their solar cells continued to degrade anyway.
“We found that these PSCs are self-exposed to iodine vapor at the
onset of degradation, which led to accelerated decomposition of the
perovskite material into lead iodide,” Wang explains. “Because of the
relatively high vapor pressure of iodine, it can quickly permeate the
rest of the perovskite material, causing damage of the whole PSC.”
This does not mean perovskite materials won’t work in solar cells.
In fact, Professor Yabing Qi, another author of the study, explains
that their “experimental results strongly suggest that it is necessary
to develop new materials with a reduced concentration of iodine or
a reinforced structure that can suppress iodine-induced degradation,
