Homes, businesses, and cities powered by the sun are not free from the power grid because solar panels cannot store all the energy they collect for later use. The most popular form of renewable energy storage that dominates the solar photovoltaic and electric car industry is a solid-state lithium-ion battery. The most recent competitor to take the top dog spot is the Tesla Power Wall. A relatively new kid on the block that may bump that dominance down a few bars is Solar Flow technology.
Can flow batteries solve the electricity storage problem?… “Flow batteries can make grid-scale energy storage economical and boost the use of intermittent energy sources.” – Prof. Werner Antweiler, Ph.D., Sep. 2014
What is a flow battery? Solid-state batteries such as lithium-ion accumulate energy within a solid electrode material like metal, but flow batteries store their energy in external electrolyte liquid tanks. Flow batteries are much easier to scale up than solid-state systems because there is no need for huge batteries. With a flow battery system you simply make the tanks bigger. Timothy Cook is a chemist at the University at Buffalo and an expert on flow battery technology. Cook explains: “you really simplify how to make the battery grow in capacity… we’re not making flow batteries to power a cell phone, we’re thinking about buildings and industrial sites.”
A flow battery is made of the following components:
- Two separate liquids containing electroactive chemicals
- A membrane to prevent the chemicals from mixing while allowing for ion exchange to occur through it
- An electrochemical cell enables extraction of stored energy in the solutions for use as electricity
- Storage tanks and the pumps to cycle solutions through the cell
When the chemicals are cycled through the cell, an ion exchange (current flow) occurs between them and through the membrane. Power is extracted by contacting electrodes used to drive the energy to an external circuit. Flow batteries are also called “redox flow batteries,” which reference the reduction and oxidation that occurs in the chemical solution during operation. To recharge, the process reverses, which causes the charge to move in the opposite direction.
Solid-state lithium-ion batteries are great for mobile high-power needs like cell phones and laptop computers, but flow batteries can store power for a much longer time period, and they last for decades before requiring any replacement. That makes them an excellent option for providing power to large utility grids, large data centers, military bases, electric vehicles, and micro-grid/off-grid applications where space is not a constraint.
Manufacturers of flow batteries offer a selection of chemistries including iron chromium, vanadium, zinc bromine, zinc iron, and others. Flow batteries can be manufactured as redox, hybrid, or membrane-less. With a true redox setup, energy is stored in the chemical liquid at all times. In hybrid redox, a portion of the energy is stored in a solid metal during the charge. In membrane-less systems, the liquids self-separate within one tank. Depending on the chosen chemistry to employ, flow batteries are usually less reactive, easily disposed of, have no fire risk, and are often recyclable.
Chemical solutions in the majority of flow batteries can be recharged indefinitely, and they can be rapidly recharged by exchanging spent solutions with a fresh fill. The easy and fast refueling method is very attractive for applications such as electric cars. While the chemicals have an indefinite lifetime, the individual components must be maintained like any other system. Flow batteries also require more complicated electronics compared to basic solid-state lead-acid batteries.
Researchers are in the process of refining solar cells to integrate with a battery that works three different ways. It can function like a typical solar cell, which converts sunshine into electricity immediately, stores the energy, or charges like a solid-state battery. It combines the two existing technologies of solar cells that harvest light and a flow battery. The technology has the advantage of bringing a power source to rural, remote, and undeveloped areas in the world where no power grid exists or access to a grid is not reliable.
14.1% Efficient Monolithically Integrated Solar Flow Battery… “Because of the intermittent nature of sunlight, the design of practical round-trip solar energy utilization systems requires both efficient solar energy conversion and storage. Compared with separated solar energy conversion and storage devices, combining the functions of separated devices into a single device allows us to bypass the intermediate step of electricity generation, which represents a more efficient, compact, and cost-effective approach to utilizing solar energy. Here, we present a monolithically integrated solar flow battery device that builds on III-V solar cells and organic redox species. The excellent performance of this device and the general design principles proposed here promise a general approach for storing the intermittent solar energy electrochemically with high storage capacity and efficiency, which will accelerate the large-scale deployment of solar energy technologies, especially in remote locations, to enable practical off-grid electrification.” – Chem, Sep. 27
Do due diligence on flow battery technology and identify investment opportunities just around the bend.
Go with the flow. Kelly McGarry, Red Bull Rampage 2013.
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