What are Flow Batteries and How do they Efficiently Store Wind and Solar Power?

What are Flow Batteries and How do they Efficiently Store Wind and Solar Power?

What are Flow Batteries and How do they Efficiently Store Wind and Solar Power?

Renewables have been around for a while now; for centuries in fact. However, it only became ubiquitous in recent times due to certain technological advancement in the areas of energy storage. You might ask, “Why are we talking about storage when we should focus on generating the energy” But with renewable energy generation, the capacity for storage will most likely determine how much energy can be exploited.

REDOX Flow Battery

REDOX Flow Battery

This is because the major drawback of the two major renewable energy sources (wind and solar) is their intermittent nature. They are not usually predictable and even when they are, the peak period of their supply doesn’t coincide with that of demand. This means that if we’re ever going to achieve a 100% renewable energy scenario, we must have facilities in place to store and quickly release the energy stored.

The Energy Storage Solution

As we mentioned earlier, the concept of generating electrical energy via renewable energy sources is not entirely new. Similarly, we have existing infrastructure for storing energy. Arguably the oldest and most common is the pumped storage.

Pumped Storage

In addition to being one of the oldest, it ranks as one of the means of storage that has the highest energy density. Thousands of megawatts can be stored via this technology.

How does it work? The system is equipped with a bottom reservoir of water and a top reservoir. During the peak supply hours or period of low demand, the excess electricity is used to pump water to the top reservoir. This process is known as “charging the battery” and the energy is stored in form of potential energy.

When the demand for energy peaks, the water from the top reservoir is released back to the bottom reservoir through turbines and this turbine turns a generator that then provides electricity. The drawback to this approach is quite glaring; it is only economically feasible for large-scale systems. Also, the construction of dams and reservoirs is a huge turnoff, leading to several abandoned projects.

Mechanism of Pumped Energy Storage

Mechanism of Pumped Energy Storage

Compressed Air Energy Storage

In this approach, electricity is used to pump ambient air into a storage container and then when the energy is needed, the compressed air is expanded to drive a turbine. This is another sophisticated technology requiring storage facilities that are expensive to implement.

Compressed Air Energy Storage System

Compressed Air Energy Storage System


Think of batteries and three related thoughts surface; the high cost, the low lifespan, and the toxic nature. But for many years, they have been our most utilized energy storage technology, becoming more prevalent with the solar industry boom.

The issue of batteries brings up to the subject matter in this post; flow batteries. We shall go over how it works and see why it is a technology to look out for.

What are Redox Flow Batteries?

In its simplest form, they are defined as batteries that charge and discharge via reduction-oxidation reactions. They work via electrolytes flowing into a common area and then interacting via a membrane to create an electrical charge. There are several electrolytes that can be used for the job; vanadium, zinc, chlorine, and even saltwater solutions.

Compared to lithium-ion batteries, they have a much lower energy density but then, they have several other advantages in their favor. Besides, compared to pumped storage, they are 1000 times denser. They are often used in large capacities and the capacity can simply be increased by adding more tanks. Also, even though they are not easy to move about, the system is such that there’s no need for mobility.

Flow Batteries

Working Mechanism

Advancement on Flow Batteries by Stanford University

Even though we knew that flow batteries are enormously important and that they have the potential to revolutionize the energy storage situation, the liquids required to make the change were either very toxic or there was a strict limitation on the temperature at which it could work.

But for William Chueh, an assistant professor of materials science and engineering at Stanford University tried a mix of sodium and potassium and they found that it has 10 times the energy available per gram. A ceramic membrane made of potassium and aluminum oxide was used to keep the positive and negative materials separate without inhibiting the flow of the current.

While this announcement heralds a breakthrough in the field, there is still work to be done. The effectiveness of the membrane is seen at temperatures above 200 degrees Celsius and the researchers are working on a room-temperature battery. A thinner membrane that boosted the power output is already being designed and this offers a bit of promise.

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