The energy storage saga



I have long held the opinion that energy storage was the next big hurdle to be overcome in the transition to a secure and reliable energy future. It seems that storage has finally come into its own, and is being actively considered by all sectors of the industry, from consumer installations to utility scale generation plant. Other developments such as micro-grids and smart grids, which depend on storage have also increased the awareness of the value of storage.

Mike Rycroft

Until fairly recently, any mention of storage was avoided. Ironically the sector that avoided the possibility of using storage the most was renewable energy. Any mention of storage in conversations with people in that sector was met with the cliché that storage was “too expensive”. The underlying fear could have been that adding storage would cause the cost of renewables to be far less attractive than what the industry would have liked. The turning point in this argument came a few years back, when a speaker at an international conference held here posed the question “too expensive for what?”

It is now widely accepted by all sectors of the industry that energy storage is necessary, if we are to advance to more secure, efficient and reliable electrical power systems. The move has been assisted by several factors, the main of which must be the rapidly dropping cost of the technology. Cost reduction is driven by demand, so there is evidence of demand developing in the market. The expanding electric vehicle market has contributed much to the price reduction.

The realisation that storage is necessary has also been brought about by several spectacular grid failures, such as that in Australia, where there are plans to install the worlds biggest network storage unit, and also extreme weather events around the world. The proposed move to distributed generation will be dependent on storage for its success. The change in the RE industry is the biggest though, and supporters are coming to realise that it is better to have something that could be controlled than to rely on the vagaries of nature.

Storage of electrical energy is nothing new. The first electrical storage device, the lead acid battery, was invented in 1859 by Gaston Plante and is still widely used 158 years later. The chemistry has not changed much although the physical design has undergone several major changes. My contact with lead acid batteries occurred during my career in the telecoms industry, which was probably one of the largest users of industrial batteries in the country at the time. Every telephone exchange had a battery bank to provide back-up power in the case of mains failure.

One of the problems with lead acid batteries is that they produce hydrogen when being charged. Models in use at the time, had an enclosed case with a vent to allow the gases to escape. This also meant that, depending on the electrolyte level, a significant amount of hydrogen could be trapped inside the case. Hydrogen is a very explosive gas, and a concentration of only 4% in air will explode if ignited. It is also a very light gas that can find its way into any corner or crevice. In the case of the batteries, if a spark ignited the hydrogen exiting the vent, the flame would flash back through the vent and cause the gases inside the battery to explode, with sufficient force to destroy the battery and splash acid on anyone unlucky enough to be in the vicinity. Explosions often occurred when the batteries were being serviced, static electricity being blamed.

The explosion problem resulted in a move to valve regulated lead-acid (VRLA), more commonly known as sealed batteries, which did not require servicing, and did not explode. Although more expensive, they offered a reliable and safer alternative. The development of VRLAs went through several stages, and some very strange designs emerged, some requiring to be bolted tightly together in a steel case to work properly. Many of the early products did not survive the market. Sealed batteries also did away with the need for a separate battery room, and allowed batteries to be placed next to equipment, which was a great advantage for small remote sites. This move was strongly opposed by the technical staff, who did not want “dirty” batteries next to their highly sophisticated digital equipment, although the equipment depended on the batteries.

Today batteries have moved out of the back room and are available in units that can be installed in your living room, if you want to. Lithium and other technologies dominate, and the development seems to be following the same path as with the lead acid, with some solutions succeeding and others falling by the wayside. There are a huge selection of new technologies that claim breakthroughs or quantum leaps in performance, but most opinions are that they are at least a decade away from commercialisation, and many of them may prove not viable or commercially unsuitable. So for the moment we are stuck with using the current range of products, with all their limitations.

Fortunately, the development of batteries has been tracked by the development in energy management systems and storage controllers, which allow the properties of batteries to be leveraged to the best advantage, making storage units much more efficient and even intelligent. With reduced prices, the products available today offer possibilities that were unthinkable a decade ago, and storage will continue to find more and more applications and acceptance in the industry.

Send your comments to energize@ee.co.za

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