Solar energy is a huge, inexhaustible, and clean resource

Solar power generation is a clean alternative to electricity from produced fuel, without air and water pollution, the absence of global environmental pollution, and no threats to our public health. The energy received from just 18 sunny days on Earth equals the total energy stored in all global reserves of coal, oil, and natural gas.. Outside the atmosphere, solar energy contains about 1300 watts per square meter. After it reaches the atmosphere, about one-third of this light is reflected into space, while the rest continues to follow to the surface of the Earth.

Averaged over the entire surface of the planet, a square meter collects 4.2 kilowatt-hours of energy each day or an approximate energy equivalent of almost a barrel of oil per year. Deserts with very dry air and little cloudiness can get over 6 kilowatt-hours per day per square meter on average throughout the year.

Conversion of solar energy into electricity

Photovoltaic (PV) panels and concentrated solar energy (CSE) systems capture sunlight and convert it into useful electricity. Roof PV panels make solar energy viable in virtually every part of the United States. In sunny locations such as Los Angeles or Phoenix, a 5-kilowatt system produces an average of 7,000 to 8,000 kilowatt-hours per year, which is roughly equivalent to using electricity from a typical US household.

Back in 2015, almost 800,000 photovoltaic systems were installed on rooftops across the United States. Large-scale PV projects use photovoltaic panels to convert sunlight into electricity. These projects often have outputs in the range of hundreds of megawatts, and there are millions of solar panels installed on a large area of ​​land.

How do solar panels work?

Solar photovoltaic (PV) panels are based on high, but surprisingly simple technology that transforms sunlight directly into electricity.

In 1839, the French scientist Edmond Becquerel discovered that some materials would emit sparks of electricity when struck with sunlight. The researchers found that soon this property, called the photoelectric effect, could be used; The first photovoltaic (PV) cell was made from selenium in the late 1800s. In 1950, scientists at Bell Labs redefined technology and, using silicon produced in photovoltaic cells, were able to convert the energy of sunlight directly into electricity.

PV cell components

The most important components of a PV cell are two layers of semiconductor material, usually consisting of silicon crystals. The crystallizing silicon itself is not a particularly good conductor of electricity, therefore impurities are intentionally added to it — a process called the doping stage.

The bottom layer of photocells usually consists of doped boron, which in combination with silicon creates a positive charge (p), while the top layer doped with phosphorus, interacting with silicon, is a negative charge (n).

The extra electrons from the n-type can leave their atoms, while the p-type captures these electrons. Rays of light “knock out” electrons from the atoms of the n-type, after which they fly into the p-type to occupy empty spaces. In this way, the electrons run in a circle, leaving the p-type, passing through the load, and returning to the n-type.

Each cell generates truly little energy (a few watts), so they are grouped in the form of modules or panels. Panels are then either used as separate units or grouped into larger arrays. The transition to an electrical system with a lot of solar energy offers many advantages.

The cost of solar batteries is rapidly decreasing (in 1970, -1kWh of electricity generated from them cost $60, in 1980 — $1, now -20–30%). Due to this, the demand for solar panels is growing by 25% per year, and the annual volume of sold batteries exceeds (in terms of power) 40 MW. The efficiency of solar cells, which reached 18% in laboratory conditions in the mid-1970s, is currently 28.5% for elements of crystalline silicon and 35% for two-layer plates of gallium arsenide and gallium antimonide. Promising elements of thin-film (1–2 µm thick) semiconductor materials have been developed: although their efficiency is low (no higher than 16%), the cost is extremely low (no more than 10% of the cost of modern solar cells). Soon, scientists assume that the cost of 1 kW/h will be equal to 10 cents, which will put solar energy in first place in the energy independence of many countries.

A method of saving solar energy for 18 years has been developed

Solar energy is, without a doubt, a very promising technology, and environmentally friendly. But there is one problem: energy storage. If it is not used immediately, the losses will be incredibly significant. Of course, you can use lithium-ion batteries or more interesting developments, but it would be better to create such a technology that would save the sun’s energy for a long time. And a group of researchers from Sweden succeeded. According to experts, thanks to the new development, energy can be saved for up to 18 years!

Responsible for the development of scientists from the Technical University of Chalmers. A year ago, they were able to create a molecule based on carbon, hydrogen, and nitrogen. When exposed to sunlight, the molecule changes the spatial arrangement of atoms. That is, while maintaining the molecular structure, it changes to another form, called the isomer. The most interesting thing is that during this process the molecule becomes a “carrier” of energy and if it is returned to its original state, the energy will be released. It remains to find the use of this technology and the search for a solution took 1 year. As a result, we have the project Molecular Solar Thermal Energy Storage (MOST).

The energy system MOST works circularly — completely free of emissions, and without damaging the molecules carrying the energy. Illustration: Yen Strandqvist

“The energy in this isomer can now be stored for up to 18 years. And when we want to extract energy and use it, we get more heat than expected,” said the professor of the Department of Chemistry and Chemical Engineering at Chalmers Technical University, head of the research group, Kasper Moth-Poulsen.

To collect energy, a special reflector with a pipe in the center is used. It tracks the movement of the Sun across the sky and works like a satellite dish, following the star. Once collected, the molecules dissolve in the liquid substance and are stored in this state until it is necessary to release the energy back. In order to get energy from an isomer molecule, it must pass through a catalyst in liquid form. As a result, after changing the spatial structure, the temperature of the liquid rises by 63 degrees Celsius. Scientists believe that the MOST can be installed on the roofs of houses in order to absorb the sunlight during the warm period, and the resulting energy can be used to heat the dwelling in the cold.

It is worth noting that the efficiency of using one or another alternative energy source directly depends on the region in which the installation is necessary. But even with the arrangement of such sources, one may encounter several problems that lead to their own kind of difficulties. For example, you may face the problem of the geographical distribution of energy resources. In the north, the days are shorter so the solar batteries will work less than in the south. The second problem of alternative energy is instability. Solar power plants do not work well in cloudy weather and do not work at night at all. Because of these and many other difficulties, the development of alternative energy in the world is slowing down. Burning fossil fuels is still easier and cheaper. But, if on the scale of the world economy, alternative sources of energy do not provide many benefits, then within the framework of a separate house they can be greatly beneficial.