Every little helps
Techno Talk
Mark Nelson
If we’re to eliminate fossil fuels from energy generation, we’ll need to exploit a huge range of nondepletable sources of energy. Techniques involving wind, water and solar power are becoming mature
sciences, but new ‘green’ procedures continue to emerge. Read here about electronic house bricks,
solar panels that are radically cheaper and devices that relish shadows as much as they enjoy sunlight.
D
o you remember the first
Motorola ‘Brick’ mobile phone?
It was the ultimate status symbol
back in 1985, when cellphones were
launched in the UK by BT Cellnet and
Racal Vodafone. Its price tag in those
days was around £1,000 (£3,000 in today’s money) and its ‘Brick’ nickname
came from its size and weight (28oz,
0.8kg), which meant you needed a briefcase to lug it around.
The battery inside the Brick phone
was a NiCad device that allowed just
30 minutes of talk time, which compares rather poorly with a new-style
brick ‘battery’ developed at Washington
University in St Louis, USA by assistant professor of chemistry Julio D’Arcy.
Actually, his development is not a battery but rather a supercapacitor that is
also a brick – a real brick.
Conductive fibres
Supercapacitors, you will recall, are
electrical energy storage devices that
can charge and discharge large amounts
of power rapidly. Their form factors
vary widely, with large, boxy ones used
industrially and small, circular ones
appearing in consumer electronics.
Washington University chose a radically different approach and made their
supercaps in the form of red bricks.
‘Our method works with regular
brick or recycled bricks, and we make
our own bricks as well,’ says Julio
D’Arcy. ‘As a matter of fact, the work
that we have published in Nature
Communications stems from bricks
that we bought at Home Depot right
here in Brentwood (Missouri); each
brick cost 65 cents.’
The bricks must be red, he continues,
because the red pigment in them (iron
oxide) is essential for triggering the polymerisation reaction that takes place
in conductive nanofibers that penetrate
the inner porous network of specially
modified bricks. ‘The polymer coating
remains trapped in the brick and serves
as an ion sponge that stores and conducts electricity,’ he explains. The team’s
calculations suggest that walls made of
10
these energy-storing bricks could hold
a substantial amount of energy.
‘Our coated bricks are ideal building blocks that can provide power to
emergency lighting,’ explains D’Arcy.
‘We envision that this could be a reality when you connect our bricks with
solar cells and place 50 bricks in close
proximity to the load. These 50 bricks
could power emergency LED lighting
for five hours. Advantageously, a brick
wall serving as a supercapacitor can be
recharged withinin an hour, hundreds
of thousands of times.’ Also, with an
eye on the smart, connected future of
buildings he notes that, ‘Using a couple of bricks, microelectronics sensors
would be easily powered.’
Cheaper, greener solar panels
Meanwhile, over at Cornell University
in New York, imaginative thinking has
come up with a new type of solar panel
that offers an energy payback on investment in just four months. This is a
four-times improvement on the silicon
solar cells currently in production. The
new technique uses calcium titanium
oxide, better known as ‘perovskite’,
which results in a less energy-intensive
manufacturing process and is responsible for a much smaller carbon footprint.
Fenqi You, professor in energy systems engineering at Cornell, sums up:
‘Perovskite cells are promising, with a
great potential to become cheaper, more
energy-efficient, scalable and longer
lasting. Solar energy’s future needs to
be sustainable.’
Shadow cells generate power too
You don’t need a brain the size of a planet to figure out that solar cells work best
in bright daylight, which is bad news
for urban areas and other locations that
are not bathed in lovely sunlight. Now,
researchers from the National University
of Singapore have created a clever device
called a shadow-effect energy generator (SEG), which generates electricity
by making use of the contrast in illumination between lit and shadowed areas.
The university asserts that this novel
concept opens up new approaches in
generating green energy under indoor
lighting conditions to power electronics.
Says research team leader, assistant
professor Tan Swee Ching, ‘This novel concept of harvesting energy in the
presence of shadows is unprecedented.
In conventional photovoltaic or optoelectronic applications where a steady
source of light is used to power devices,
the presence of shadows is undesirable,
since it degrades the performance of
devices. Our work capitalises on the
illumination contrast caused by shadows, which induces a voltage difference
between the shadow and illuminated
sections, resulting in an electric current.
The ideal environment for use would
be cities, with constantly shifting levels of light and shade throughout the
day from clusters of tall buildings and
the sun’s changing position in the sky.’
Lower cost
The team hopes that its shadow generator can be fabricated at a lower cost
compared to commercial silicon solar
cells. It comprises a set of SEG cells
arranged on a flexible and transparent
plastic film, with each SEG cell formed
of a thin film of gold deposited on a silicon wafer. This sounds fine, but how
does it work?
Team co-leader professor Andrew Wee
explains, ‘When the whole SEG cell is
under illumination or in shadow, the
amount of electricity generated is very
low or none at all. When a part of the
SEG cell is illuminated, a significant
electrical output is detected. We also
found that the optimum surface area
for electricity generation is when half
of the SEG cell is illuminated and the
other half is in shadow, as this gives
enough area for charge generation and
collection respectively.’
In indoor lighting conditions with
shifting shadows, the harvested energy
is sufficient to power a digital watch
(1.2V). In the next phase of research,
the team will experiment with materials other than gold, to reduce the cost
of the SEG.
Practical Electronics | November | 2020
