MIT engineers have developed a new project that can store renewable energy sources such as solar or wind power. Such a system will help to provide uninterrupted power supply to even a small city, regardless of the presence of sunlight or wind. This report was published in the journal “Energy and Ecology”.
The concept is that in this case, solar and wind energy is stored in special large tanks of molten silicon in the form of heat, and on demand it is converted back to electricity.
According to the assessment, such a system will be significantly more affordable than lithium-ion batteries, which today store energy from inexhaustible sources.
Basic principles of work
The new storage method was originally associated with a project whose main goal was to find a way to increase the efficiency of one form of renewable energy – concentrated solar energy. Conventional solar plants use photovoltaic panels to convert light into electricity. In the case of concentrated UV energy, there must be large specular fields that collect sunlight on the central tower. Here, light turns into heat, and from it into electricity.
The interest in focusing light is justified by the fact that storing heat as a result is much cheaper than storing electricity using rechargeable batteries.
According to the project, concentrated solar power plants store thermal energy using large reservoirs. These containers are filled with molten salt heated to very high temperatures (around 1000 degrees Fahrenheit). When electricity is needed, the hot salt is passed through a heat exchanger and converts the heat of the salt into steam. A special turbine converts steam into electricity.
This technology was developed some time ago, but its cost will never be so low as to compete with the use of natural gas. This served as an incentive for a group of scientists to work further. In particular, they began to experiment with higher temperatures using an efficient heat engine to get a cost reduction.
As a result of the work done, it turned out that too hot salt simply corrodes stainless steel storage containers. Therefore, the research team began to look for another environment that could effectively store heat at much higher temperatures.
Scientists tried to work with liquid metal, but opted for silicon. Oto is one of the most abundant metals on planet Earth, with the ability to withstand really high temperatures – over 4000 degrees Fahrenheit.
Last year, the team developed a pump that can withstand this temperature and be used to pump liquid silicon through a storage system. This heat resistance of the unit was recognized as the maximum to date and entered into the Guinness Book of Records.
Sun in a box
Now scientists have outlined their idea for a new storage system for inexhaustible energy sources. The name of the system is TEGS-MPV, multi-contact photovoltaic.
In this case, there is no need to use the fields of the mirrors and the tower in the center of the field to collect heat. Scientists propose converting electricity from solar and wind renewable sources into heat by Joule heating when an electric current is passed through a heating element.
The system can be interfaced with existing renewable energy sources such as solar power plants. At the same time, excess electricity will be stored in such a container until later used.
For example, a small town that is partially powered by solar energy would need a fully insulated 10-meter tank. The material of its manufacture is graphite, and inside it is filled with liquid silicon capable of withstanding at a “cold” temperature of 3500 degrees Fahrenheit. Through a tubing system, this cold reservoir is connected to a second “hot” container. Electricity from solar cells enters the system and is converted by heating elements into heat.
Liquid silicon is pumped out of the “cold” container and heated by heating elements as it passes through the tube system. Once in a “hot” container, heat energy is stored at high temperatures of over 4000 ° C Fahrenheit.
When there is a need for electricity, for example, after sunset, very hot, luminous liquid silicon enters special photovoltaic devices that convert heat into electricity for further supply to consumers. The cooled silicon, in turn, is pumped back into the “cold” reservoir and the cycle continues. Researchers among themselves call this project “the sun in a box.”
Storage issues
An urgent issue is energy storage, since in this case the most insulated and strong container is required in order to safely store the molten liquid inside. At the same time, outside the container, the temperature should be kept within comfortable limits.
One of the suggested options is graphite containers. However, there was concern that at such high temperatures, graphite would react with Si to form silicon carbide, which could lead to wall erosion.
To check the version, a test version of a miniature graphite tank was made. It was filled with liquid silicium and heated to ultra-high temperatures. The results showed that after the liquid was heated to 3600 F and held at this level for about 1 hour, silicon carbide, instead of starting to corrode the walls of the container, began to form a thin protective layer, sticking to the graphite and preventing the process from spreading further.
Scientists have also demonstrated the possibility of completely sealed storage, eliminating the possibility of leaks. It is estimated that such conservation systems will power the small city of about 100,000 homes entirely from renewable energy sources. In addition, such structures can be placed anywhere, regardless of terrain and location.