A visitor to Victorian London who found themselves in its many narrow alleys would have seen large numbers of wooden shutters reflecting sunlight into the offices. These weren’t just wooden shutters though, but Chappuis’ Patent Daylight Reflectors, invented by a French photographer based on Fleet Street in 1850, and there was a whole range of them to improve lighting inside buildings before widespread electric lighting.

Read more: The forgotten era of Light Reflectors in London’s alleys, Ian Visits.

Night-time power generation analogous to photovoltaics would be an enabling capability for applications such as lighting and wireless sensors. We demonstrate a low-cost power generation device based on thermoelectric generators where the cold side radiates heat to the cold of space by facing the night sky. The power generated is sufficient to maintain a LED at night, enabling battery-free off-grid lighting.

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A large fraction of the world’s population still lacks access to electricity, particularly at night when photovoltaic systems no longer operate. Lighting solutions for resource-constrained, off-grid communities have drawn much global interest with a range of approaches implemented. Solar lights have made progress at this task but, as lighting demand peaks at night, require the coupling of photovoltaic modules to a battery, driving up costs. A modular way to generate electricity at night without the need for storage would thus have direct and significant implications for lighting applications.

A significant fraction of thermal radiation from a sky-facing surface can pass through the atmosphere and reach outer space, enabling passive radiative cooling of the surface to well below the ambient air temperature. We demonstrate a low-cost strategy to harness the cold of space through radiative cooling to generate electricity with an off-the-shelf thermoelectric generator. Unlike traditional thermoelectric generators, which convert waste heat into electricity, our device couples the cold side of the thermoelectric module to a sky-facing surface that radiates heat to the cold of space and has its warm side heated by the surrounding air, enabling electricity generation at night.

The Device

The device consists of a polystyrene enclosure covered in aluminized mylar to minimize thermal radiation from the enclosure and an infrared-transparent wind cover made from 12.5 mm-thick low-density polyethylene previously used in radiative cooling implementations. The thermal emitter consists of 200 mm aluminum disk painted with a commercial black paint. The disk is adhered with heat transfer paste to the cold side of a commercial thermoelectric module. The hot side of the module is coupled to a small aluminum block adhered to a 200 mm aluminum disk with multiple fins outside the enclosure. The entire device sat on a table approximately 1 meter above roof level.

We tested performance outdoors on a rooftop in Stanford, CA, USA in late December 2017 under clear-sky conditions with a dew point temperature between 1 and 3 degrees C during the hours of testing. The device was taken outside shortly after 18:00 h, when the sky was dark. A temperature difference between the two sides of up to 2 degrees C is observed during testing. At the maximum power point, nearly 0.8 mW of power is generated by the thermoelectric module. Normalizing to the area of the radiative cooler this corresponds to 25 mW/m 2 of power generation capacity.

While the power generated from this demonstration may seem, at first glance, modest, we highlight one application here: lighting. We show that the device can directly power a light emitting diode, thereby generating light from the darkness of space itself. We estimate that the LED was operating at approximately 10% of its maximum brightness. In favorable conditions, where the ambient air temperature is warm and the dew point low (summer conditions in a Mediterranean or desert climate), we calculated that power generation of 0.5 W/m 2 may be achievable.

Modular

We emphasize that this result does not represent the ultimate limit of performance for night-time power generation using thermoelectric modules, but is instead intended to point to the practical performance capability of a system similar to the one used here. In principle, the inherent modularity of this approach allows us to scale the system’s size depending on energy needs in a manner similar to photovoltaic systems. Our system uses low-cost, off-the-shelf, commodity components (less than $30 USD for our initial proof of concept demonstration).

Another avenue for improved performance is to optimize the area of the radiator relative to the area of the thermoelectric module, as has been done in solar thermoelectric generators. Related to this, we note that the radiative cooling surface used here is black over solar wavelengths, and thus the device tested could function as a solar thermoelectric generator during the day-time.

Quoted from: Raman, Aaswath P., Wei Li, and Shanhui Fan. “Generating Light from Darkness.” Joule 3.11 (2019): 2679-2686.

“Even the oil lamp began in simplicity and evolved into a machine with multiple wicks, clockwork oil pumps, specialized chimneys, hydraulic, pneumatic, and other variants. This story will take you through the history of illumination methods in lighthouses.”

Read more: Lighthouse lamps through time, Thomas Tag.

“Combining wireless communication, intelligent controls and light emitting diodes (LEDs), smart lamps offer end-users features like colour tuning, dimming, changing lighting scenes, remote control, motion sensing control, daylight control and other features. But these features require energy even when the lamps are not providing light, but are instead waiting for a wireless instruction from a smartphone or remote control unit. Tests conducted on a limited number of smart wireless LED lamps reveal that these products can have substantial standby power use – which, depending on hours of use, can even be higher than the energy consumed when the light is switched on.”

“Domestic light sources… typically operate 1-2 hours per day. The smart lamps producing 200 to 1000 lumens of light tested in this project had an average standby energy consumption representing 51 % of the total daily energy consumption when these lamps are operated one hour per day. That corresponds to an overall efficacy of 9 to 51 lumens per watt, meaning some smart lamps had the equivalent performance of incandescent lamps [16 lumens per watt]. If the lamps are switched on for two hours per day, standby energy represented 35 % and the efficacy is approximately 16 to 64 lumens per watt, much lower than the non-smart LED lamps already on the market today.”

Read more: “Solid State Lighting Annex: Task 7: Smart Lighting — New Features Impacting Energy Consumption” (PDF). Summary. Picture: Lucid. Thanks to Noel Cass.

Under good climatic conditions and using specific technology, the full moon can be a powerful source of light.

Using technology inspired by solar energy concentrators, the “Full Moon Theatre” lights its performances using only moonlight. Moonbeams are collected, concentrated, and focused on stage.

The original Full Moon Theatre was built in Southern France and their plan is to create twelve Full Moon Theatres worldwide.

The Full Moon Project is the brainchild of French opera director Humbert Camerlo. Camerlo got the idea in 1987 and initially tested it by assembling a group of shaving mirrors that focused the light of the moon onto a small sculpture in his garden in Southern France (picture below). Four years later, in 1991, the construction of a full-size theatre began, in collaboration with Irish engineer Peter Rice. Rice would be involved in the project until his death in 1992, after which his disciple, Nicolas Prouvé, took over the collaborative role.

Like most good inventions, the Full Moon Theatre was born out of necessity. Camerlo was setting up an interdisciplinary theatre lab, but had no money to pay for a professional lighting installation.

The original moonlight theatre, 1987. Picture: The Full Moon Theatre.

Performances lit by moonlight are, of course, limited to certain nights when there is both a full moon and a clear sky. When these opportunities occur, however, we have at our disposal a lighting source that is potentially better than artificial light. Moonlight has a similar quality as sunlight.

“We can see at night during the full moon phase reflecting sunlight but we do not have a strong visual accuracy. Under good climatic conditions, the light power of the Moon is 1 on 100 000 to the sun light power. In the same time moon light has practically the same colour temperature to the sunlight. The challenge was to find optical systems to multiply the power of the Moon in order to light a performance and to reveal costumes colours.”

Reflectors

The development of the reflectors has been an on-going process. Three types were made: “Keplers” and “Archimedes” designed by Rice’s teams in London and Paris, and “Copernics” designed by Camerlo. The reflectors track the moonbeams, amplify them and reflect them onto the stage. Some of the reflectors also track the actors on stage.

   Moonlight collectors. Image: The Full Moon Theatre.

Beyond the symbolic or metaphoric use of the moon to light a performance, the Full Moon Theatre laboratory has prompted ideas for experimental work in architecture or even in town planning. The project wants to promote the development of technology for the use of natural light in the visible fringe of the solar spectrum. Underground areas such as subway stations, for instance, could easily be lit by sunlight during the day. The Full Moon Theatre also promotes actions dedicated to reduce light pollution in the world, as moonlight cannot be used when light pollution is high.

Moonlit stage. Picture: The Full Moon Theatre.

For most of its lifespan, the theatre has been a research project. This will soon change. The first public performance in the theatre, in the summer of 2010, had spectators also carrying mirrors to aid the lighting. The ultimate aim of the project, which brings together artists, engineers and scientists, is to set up a planetary network of “Full Moon Theatres”. The plan is to equip twelve open air theatres with full moon technology by 2014 or 2015, using new types of reflectors. We’ll keep you updated.

The Full Moon Theatre.

Thanks to Emmanuel Grimaud.

Edited by Deva Lee.

Related articles: 

• An engineering exploration of Stonehenge
• The bright future of solar thermal powered factories
• Moonlight towers: light pollution in the eighteenth century

The GravityLight uses a sack of sand or stones to gradually pull a piece of rope through a dynamo mechanism which generates electricity to power an LED. It is a cheaper and more sustainable option than a solar powered light, which requires not only a solar panel but also a battery. The product is aimed at the developing world and its makers raised 400,000 dollars at indiegogo.

The technology could be further improved by including pulley mechanisms that were used to operate human powered cranes and lifting devices in pre-industrial times. This would allow a person to lift heavier weights and thus power more powerful lights.

To be precise, the light is not powered by gravity. It is muscle-powered, while gravity stores the energy and fulfills the role of a battery. Hat tip to Bernd Vleugels.

Light-emitting diodes (LEDs) are advertised as environmentally friendly because they are energy efficient and mercury free. However, the material content of the LEDs, which generally include group III-V semiconductors, presents its own set of potential environmental impacts. The rapid growth in the LED industry implies that, ultimately, LEDs will contribute to the solid waste stream, and could impact resource availability, human health, and ecosystems in much the same way as generic electronic waste (e-waste) from computers and cell phones has generated concern in recent years.

Potential Environmental Impacts of Light-Emitting Diodes (LEDs): Metallic Resources, Toxicity, and Hazardous Waste Classification (pdf).

“The digital billboards use more efficient LED (Light Emitting Diode) lighting than traditional signs, but deploy so many of the LED bulbs on each billboard that energy use is high; traditional billboards use just one or two large bulbs to illuminate signs. In addition, digital billboards are illuminated day and night, and require cooling systems that use more energy.”

Source: Yale Environment 360.

Previously: Viva Las Vegas – LEDs and the energy efficiency paradox.