One of the main hurdles for renewable energy is energy storage. Renewable resources have intermittency issues when it comes to energy production.
For example, solar panels can only produce electricity when the sun is shining or wind turbines will only spin when there is wind. This means that the energy from these resources is not always available to meet demand.
Currently, the way that the electricity grid functions is by maintaining a balance between supply and demand. Energy storage solutions could allow for excess supply during periods of low demand, such as at night when people are sleeping, to be saved for use when there is higher demand. Smart grid technology is one way in which renewable energies could be better integrated into the energy mix.
Here are some energy storage technologies that are currently being used, developed or considered:
Pumped hydroelectric storage relies on a system of reservoirs and pumps to store water for energy production. During times of low demand, electricity is used to pump water from a lower reservoir to an upper one, and then when it is needed, the water is released through a turbine to create electricity. Large amounts of energy can be stored for long periods of time, but lots of space is necessary for the reservoirs and the initial cost of infrastructure is expensive. Currently this is the most common energy storage system in use.
Compressed air energy storage (CAES)
This form of energy storage has been used by municipalities and mining companies for decades. At off-peak times, motors using natural gas or electricity pump air into an underground cavern or some other large enclosed space. When energy is needed, the air is released and heated up so that it expands, rotating a turbine and creating electricity. This form of energy storage, although relatively cheap, is limited by location because it requires an enclosed space in which air could be compressed.
Flywheels use kinetic energy to store electricity. This cylindrical device uses electricity to power a rotor, which spins at a high speed. To reduce friction inside, the container is vacuum sealed. The energy is discharged through the inertial energy of the rotations. Flywheel devices can be hooked up together to make a larger storage facility, a flywheel farm. The advantage of flywheel devices is that they can be set up anywhere. A basic flywheel device can’t store energy for very long periods of time, but there is progress being made in the United States on newer versions, which can discharge electricity over the course of four hours.
Electric vehicles could be plugged into the grid and used as batteries to store excess energy, such as at night. This energy could then be release back into the grid at peak times. The downside of this type of energy storage is that the car batteries could be worn out with constant use so this energy storage solution is still being debated. There would have to be extensive infrastructure to support this type of energy storage.
There are a variety of solid and liquid-based battery types that currently exist. The advantage of battery energy storage is that batteries can be placed anywhere and aren’t location-specific. For large-scale energy storage, there are sodium-sulfur, metal-air, lithium ion, and lead-acid batteries. However, cost is still an inhibiting factor. Safety risks with batteries include things like fire and leakage. With further technological innovation, it is expected that production costs will decline and make battery energy storage a more viable solution.
Rail energy storage
Rail energy storage is similar to the pumped hydroelectric storage system. When there is low demand, rail cars loaded with heavy materials, such as rocks and gravel, travel up a slope. When electricity is needed, the cars travel back down the slope and create electricity using a regenerative braking system (in a traditional braking system, energy is wasted and dissipate¬s as heat). This energy storage solution requires a hill and lots of space so its implementation is limited by location.
Molten salt energy storage
Using solar energy, sunlight is reflected by an array of mirrors onto tanks with molten sand. The heat from these tanks boils water and creates steam, which turns a turbine and creates electricity. The main downside of this storage is that it requires a lot of space for the array of mirrors and the tanks.
Thermal energy storage
This form of energy storage basically involves creating ice during off-peak times, such as at night, to use for cooling a building during high-peak times, such as during the day. This energy saving solution is only useful for cooling a building, which admittedly is a large drain on electricity usage in hot summer locations.
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