Innovations in Energy Storage – Key to Renewable Energy Adaptation

Renewable energy (RE) is the source of energy that are naturally replenished and thus don't deplete. The most common types of RE are solar and wind. These are the ones that are predominantly used around the world today. While wind turbines harness the kinetic energy of the wind to convert it into electricity, solar technology has more variants. Both heat and light from the sun can be utilized to generate energy. Solar thermal and concentrated solar power use the sun’s heat to produce energy and work while Solar photovoltaics (PV) or commonly known as solar panels use the sunlight to produce electricity.

All those who have been fairly accustomed to the proceedings in the renewable energy technology understand the pros and cons. While significantly lower levels of environmental impact is a major advantage of RE, it still hasn’t picked up well enough and hasn’t quite been able to compete with the conventional sources (Coal, Gas, etc.). RE technology, or at least the two most popular ones, Solar and Wind have a major drawback. The sun doesn’t shine all the time and the wind doesn’t blow continuously. This makes the energy produced by these technologies intermittent. Add frequent weather changes and it can be observed that one cannot solely depend on these technologies for their energy needs. These cannot serve the base load. We still need coal, gas or nuclear powered plants to serve a steady, continuous base load.

Energy storage is considered as the answer to this problem. It is a well-known concept and the most widely used method of electrical energy storage are batteries.

Batteries have been used for many years now in a variety of applications. They have been improved significantly over the years, from bulky lead acid batteries to sleek and powerful Li-Ion batteries that are light weight. Batteries are a topic that has been subject to tremendous research. They may look like a simple device but they are quite complex in the sense that they get affected by too many parameters. The charging current, discharging current, operating temperature, depth of discharge, the duration for which it has been kept unused and the amount of variation in load are some factors that affect the life and efficiency of a battery. It is nearly impossible to get the best of everything and as a result, a typical battery works well for not more than 3-4 years. In the case of renewable energy, where a power plant lasts for about 25 years, a battery bank to store the energy is a great idea but it also means a recurring expense of replacing the batteries every 3 years. This increases overall project costs over the lifetime. That being said, a well-designed battery bank connected to a solar power plant will ensure a steady supply of power thus eliminating the intermittent nature of the energy generated. In order to do that, the batteries need to be lighter, cheaper and have a higher energy density (more storage in reduced space). Many organizations are currently researching batteries, from mobile phone manufacturers to electric car makers.

Li-Ion battery (left) and lead acid battery (right)

While batteries are capable of storing electrical energy, thermal energy storage requires a completely different arrangement. In a solar thermal device, which is equally intermittent, the heat generated while the sun shines may be stored in special arrangements for later usage. It is in some way like a thermos flask that traps the heat in the coffee and keeps it warm for a long time. There have been many materials and compounds that have been explored which can store heat or cold and release it according to the user needs. These are primarily Phase Change Materials (PCMs) that change phase (solid – liquid –gas) when subject to heat or cold and stay in the new phase for a considerable time till the energy is removed externally. Salts have been researched for this purpose. Excess heat from say an oven can be pumped into an insulated chamber of salt using conventional heat transfer methods. This melts the salt (solid to liquid). Due to insulation of the chamber, the heat that has been put in remains in for a considerable time. The heat from the molten salt can be extracted later using conventional methods and utilized for various processes. A technology like this will enable solar water heaters to provide hot water even during the night. Phase change materials are various compounds that work in different temperature ranges. They can be selected according to the application whether it is heating or cooling. PCMs have found niche uses in a wide spectrum ranging from lunch boxes to Neonatology. PCMs last for about 3-4 years which again leads us to a recurring expense every 4 years when integrated with a RE setup. A lot of effort is being put to improve the cyclic performance and durability of PCMs.

We might have also noticed that stone and concrete floors tend to get really warm during summers. For example, anyone who has been to the Taj Mahal will remember the hot marble floor on which one has to walk barefoot. Getting inspired from these, research is being done on thermal energy storage in concrete and stone blocks.

In conclusion, it is evident that a breakthrough in energy storage, whether thermal or electrical is the key factor that will lead to extensive adaptation of renewable energy systems. By addressing the core disadvantage of RE, i.e. intermittent nature of RE, energy storage technology might make all the difference in the years to come.