The cells work at night

A new technological development seeks to solve one of the main problems of solar energy production: what do you do when the sun has already set?

Ran Ben Michael, Angle - Science and Environment News Agency

The main criticism leveled at a widespread shift to the production of renewable energy from sunlight (solar) is the lack of continuity in production which is not active at all during the hours of darkness and also changes throughout the daylight hours according to the intensity of the sun (e.g. sunrise and sunset compared to noon) and cloud cover. This is of course a significant limiting factor in relying on sunlight as a main energy source. However, Prof. Jeremy Mundy, a researcher at the University of Davis in California, believes he has found a solution.

Although the price of producing energy from renewable sources has dropped dramatically in recent years and their cost is often lower than that of conventional sources (especially when it comes to large solar fields and land-based wind turbines), photovoltaic cells have three limitations in widespread application. The first is the storage problem, which is also typical of the energy produced from wind or waves, is the storage problem: production is continuous but with peaks, when the energy source is available (wind, sun, waves, etc.), but it is not currently possible to store significant amounts of energy that would be enough for a large modern city or for a small country and provide the energy when the ratio of production and demand reverses. The second problem is that the energy efficiency of the panels is low and that they use less than 30 percent on average of the solar energy that reaches them (in addition, over time the efficiency of the installed panels decreases). The third problem is manifested during cloud cover, shading, and of course, during the hours of darkness. In all these conditions, the cells operate at extremely low utilization or do not produce energy at all.

The first two problems can be overcome with technological developments or optimization of the applications in the field. For example, in early March, researchers from the University of Colorado and other institutions published in Science magazine, about a significant breakthrough in improving the efficiency of the panels by coupling the common silicon cells to layers of a mixture of halogen elements containing iodine, chlorine and bromine, which is cheap and easy to manufacture. On the other hand, the third problem is more difficult to solve.

Prof. Jeremy Mundy, an expert in electrical and computer engineering at the University of Davis, recently proposed a new concept published in the scientific journal "Photonics" of the American Chemical Society, which may make it possible to produce renewable energy even at night.

A normal solar cell consists of materials that absorb the light energy (photons) and turn it into an electric current in a photovoltaic process. Instead, Mundy suggests reversing the mechanism and utilizing the radiation emitted during the hours of darkness from the hot body (the Earth) to the cold body (the night sky) to generate energy.

The new type of cell (thermo-radiative cell, i.e. based on heat radiation) will in this case face the surface of the earth and receive infrared radiation that will turn into the electric current.

Antisolar

Meanwhile, these panels - called "anti-solar" - are only in the stage of building the initial model (prototype). So far, researchers have been able to extract a relatively low amount of energy from them - about 50 watts per square meter under ideal conditions, about a quarter of that of ordinary photovoltaic cells - this is because the energy potential of infrared radiation is lower.

However, it is important to remember that the low output is a relatively small problem. The very ability to add and produce electricity at night - along with efficiency improvements that can be expected here as well - should - if the technology successfully goes through Gimlon processes and shows good performance even outside the laboratory - be the significant change compared to the inability to produce electricity in the dark using light waves today. In addition, if they become an available and efficient technology, anti-solar cells have a certain potential to reduce the need to invest in energy storage solutions, because it will be possible to switch to energy production throughout the day (even if at a lower power).

Mundi's team is not alone in solar innovation. Thus, for example, in November 2019, an international team of researchers published a quite similar idea: in this case, too, the panel (thermoelectric cell) utilizes the temperature difference (heat drop) between the Earth and the night sky to generate electrical energy. Even in this application, the scope of the theoretical production was limited to only 4 W/m2 (significantly smaller even than that of the second anti-solar cell) and provided energy only for a modest LED bulb.

Utilizing the heat differences at night in different ways to expand the energy range of solar panels is not the only direction. About two years ago, a Chinese team developed an initial model of a solar cell coated with a double layer of transparent polymer; When water droplets roll on the polymer, the friction creates an electric current in the cell. The laboratory's development, published in the scientific journal "Nano", is based on the hybrid cell approach - in this case, the ability to convert motion energy when it is cloudy and raining alongside the production of solar energy when the sun is shining.

The goal: continuous supply

If and when such developments leave the laboratory and function successfully and on a large scale in the real world as well, so that solar panels operate continuously, while converting several forms of energy into electricity, renewable sources may take the last technological step they need to reach their goal: a continuous supply of renewable energy. What will probably remain is to overcome the human limitation: in the USA, for example, the opposition to the implementation of renewable energy projects on the part of private landowners is growing, and despite the public ambition to reduce air pollution and slow down the pace of the climate crisis, they remain a failure in the expansion of renewable production.

"The ideas underlying these proposals are very interesting and can push forward research and development in the field of solar energy utilization," says Dr. Sharon Soroker, a consultant and lecturer in the field of renewable energy, "However, these inventions face the test of economic feasibility: there are issues of the cost of materials and the production of the panels and achieving good efficiency. The new ideas do not address other shortcomings of conventional solar, such as cloud cover. Such ideas compete especially with other developments of energy storage, which has other advantages such as stabilizing the electricity grid, responding to peak demand hours or emergencies. At most it appears that anti-solar solutions will be able to reduce the need for storage for the night hours. It is definitely a desirable thing, but only as part of a wider mix of solutions."

for the scientific article

More of the topic in Hayadan:

• There is something new under the sun
• A first of its kind system for splitting water into hydrogen and oxygen with the help of solar energy - at two separate sites
• Another essential part of the photosynthesis process has been revealed