Energy storage will be a huge part of the renewable energy revolution. Electricity doesn’t keep like cheese or barley. It has to be used more or less instantaneously or it is lost forever. Curtailment is the polite phrase the utility industry uses to describe the process of selling excess electricity. In some cases, the energy producer has to pay energy consumers or distributors to take it off their hands. Giving stuff away or paying others to get rid of it is a really poor business model. You can’t buy apples for 10 cents an piece, sell them for a dollar a dozen, and hope to make a profit based on volume.
At the present time, there are three main ways to store electricity — lithium ion batteries, pumped hydro storage, or redox flow batteries. There are some other technologies out there like compressed air or lifting a pile of enormous concrete blocks over and over but they are on the margins of the energy storage field.
Lithium ion batteries are very good at storing electricity but they are still expensive, even though prices have come down significantly in the past 5 years. One of their strengths is they can respond to changes in frequency or voltage very quickly. Pumped hydro is also very good at storing energy but it takes a lot of real estate and cannot react as swiftly as batteries.
Redox flow batteries have a unique advantage. The amount of power and the amount of energy they store can be adjusted to meet the needs of any particular use case. They also have a small footprint compared to batteries and pumped hydro, so they can be sited almost anywhere — within city limits, next to a renewable energy installation, or in an existing utility substation. They can store electricity for long periods of time, which means electricity generated by solar panels in the summer can be saved for a cold, cloudy winter day. The energy density of a hybrid flow battery, especially a polysulphide/air system, is about 500 times higher than pumped hydroelectric storage.
Despite their advantages, until now redox flow batteries have not had a significant cost advantage over batteries and had a shorter service life. But researchers at Warwick University in the UK, in cooperation with colleagues at Imperial College London, say they have found a way to dramatically reduce the cost of redox flow batteries to £20 per kWh or less using inexpensive materials like manganese and sulfur which are found in abundance nature. They claim the cost of materials for their new battery is about 1/30th that of the materials needed for a lithium ion battery, which may use expensive elements like cobalt. Their research was published recently in the journal Applied Materials & Interfaces.
What makes the new battery so special? According to Science Daily, the technology combines carbon based electrodes with economically sourced electrolytes — manganese or sulphur — by means of a simple and yet highly effective electrophoretic deposition of nano-carbon additives (nitrogen-doped graphene) that enhances the electrode durability and performance in highly acidic or alkaline environments significantly. If the words “electrophoretic deposition of nano-carbon additives” make your eyes glaze over, you probably should not pursue a career as a scientific researcher.
Dr Barun Chakrabarti, one of the lead authors on the paper, says “This EPD technique is not only simple but also improves the efficiencies of three different economical hybrid flow batteries thereby increasing their potential for widespread commercial adoption for grid-scale energy storage.” If what the researchers say holds up in real world use, the world of renewable energy and energy storage just took a big step forward.