Time: 2019/1/22 9:31:39 Source: China Electric Power News Author: Views: 3 times

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Engineers at MIT have come up with a conceptual design for storing renewable energy such assolar energyand wind energy, and send energy back to the grid as needed. The new design can not only power small cities when solar and wind energy is sufficient, but also power supply day and night. The study design was published in the journal Energy and Environmental Science.

New system costs half as much as pumped storage

The current mainstream energy storage methods are lithium-ion batteries and pumped storage power stations. Lithium-ion batteries are already considered a viable but expensive way to store renewable energy. Pumped-storage plants are by far the cheapest form of grid-scale energy storage.

Researchers at MIT have developed a new way of storing energy by storing excess electricity generated by solar or wind energy as heat in white-hot molten silicon containers, which are then converted into electricity when needed.

The researchers estimate that the system is much cheaper than lithium-ion batteries, at about half the cost of a pumped-storage plant.

"Even if we wanted to run the grid right now on pure renewable energy, we couldn't. Because you need fossil fuel turbines to compensate for the fact that renewable energy can't be distributed on demand." Asenger, associate professor in the Department of Mechanical Engineering Henry said. "We are developing a new technology that, if successful, will address the most important and critical problem in energy and climate change, which is energy storage."

Silicon plays a key role

The new energy storage system stems from a project in which researchers looked for ways to improve the efficiency of concentrated solar thermal power generation. Unlike traditional solar power plants, which use solar panels to convert light into electricity, concentrated solar thermal power requires large areas of giant mirrors that concentrate sunlight onto a central tower. There, light is converted into heat and ultimately electricity.

"The technology is interesting because once you get into this process of focusing light for energy, you're going to be much cheaper to store heat than to store electricity," Henry said.

Concentrated solar thermal power plants store solar energy in large tanks filled with molten salt, which are then heated to temperatures around 1,000 degrees Fahrenheit. When electricity is needed, the hot salt passes the heat through a heat exchanger into the steam, which is then turned by a turbine. Steam turns into electricity. "This technology has been around for a while, but it has been assumed that the cost will not be low enough to compete with natural gas," Henry said.

Therefore, if a way to operate at higher temperatures is found, more efficient heat engines need to be used and costs reduced. "However, if operators heat the salt to extremely high temperatures, the salt can corrode the stainless steel tanks in which it is stored.

Henry's team looked for a medium other than salt that could store heat at higher temperatures. The researchers initially experimented with liquid metals and eventually locked on silicon -- the most abundant element in the Earth's crust, which can withstand temperatures in excess of 4,000 degrees Fahrenheit.

In 2017, the research team developed a pump that can withstand high temperatures and deliver liquid silicon through a renewable storage system, a feat mentioned in the Guinness Book of World Records. Since that development, the team has been designing an energy storage system that could integrate such a high-temperature pump.

3500~4300 degrees Fahrenheit lap tour

Now, researchers have come up with the concept of a new renewable energy storage system, dubbed TEGS-MJP, that instead of collecting heat from traditional concave mirrors or central towers, they directly store the electricity generated by renewable energy ( such as solar and wind energy) into heat - the process of passing electricity through a heating element.

The system can be paired with existing renewable energy systems to capture excess electricity during the day and store it for later use. Henry said: "Suppose everyone comes home from get off work, although the sun is about to set, it is still very hot, so the air conditioner needs to be turned on. At this time, the photovoltaic power generation will not have much output, and then the stored energy will come in handy. ." The system consists of a tall, highly insulated tank made of graphite, filled with liquid silicon,

The tank is 10 meters wide and has a minimum temperature of almost 3,500 degrees Fahrenheit. A row of pipes exposed in the heating element connects this "cold water tank" to another "hot water tank". When electricity from the city's solar power enters the system, that energy is converted into heat for the heating elements. At the same time, the liquid silicon is pumped out of the cold tank and, when passing through a drain pipe exposed under the heating element, heats up further and then enters the hot tank. There, thermal energy is stored at high temperatures of about 4,300 degrees Fahrenheit.

When electricity is needed, hot liquid silicon is pumped into a tank, and specialized solar cells (multi-junction photovoltaics) convert its energy into electricity to feed into the grid. The cooled silicon can be pumped back into the cold water tank until the next round of storage - effectively acting as a large rechargeable battery.

"People are starting to call our design the 'sun in a box,'" Henry said. "It's a pretty metaphor, it's basically just a very strong light source, and all the light sources are put in a box, and this box can be Harvest heat."