Energy storage technologies are a strategic and necessary component for the efficient utilization of renewable energy sources and energy conservation. There is a great potential to replace fossil fuels by using renewable generation resources, which do not all produce energy continuously, and storing energy that would otherwise be wasted. Renewable energy sources can be used more effectively through the addition of short- and long-term energy storage. All kinds of energy storage systems enable greater and more efficient use of these fluctuating energy sources by matching the energy supply with demand. To find the right direction for the development of energy storage, let us briefly discuss the law of conservation of energy.
The law of conservation of energy, first formulated in the nineteenth century, is a law of physics. It states that the total amount of energy in an isolated system remains constant over time. Thus, the total energy is said to be conserved over time. For an isolated system, this law means that energy can change its location within the system and that it can change form within the system. For instance, chemical energy can become kinetic energy, but that energy can be neither created nor destroyed within a defined system. Keeping this in mind, we have to consider keeping energy within a system and how to transform it into the best form for use. This law is the basis for the call to develop effective energy storage. From the perspective of this law, we can examine all areas of natural science and find energy storage possibilities in every area.
Storage methods examples:
– Liquid nitrogen
– Hydrogen peroxide
– Flow batteries
– Fuel cells
– Superconducting magnetic energy storage (SMES)
– Compressed air energy storage (CAES)
– Flywheel energy storage
– Hydraulic accumulators
– Hydroelectric energy storage
– Gravitational potential energy (device)
– Ice Storage
– Molten salt
– Cryogenic liquid air or nitrogen
– Seasonal thermal stores
– Solar ponds
– Hot bricks
– Steam accumulators
– Fireless locomotives
– Eutectic systems
The list is long, and these are only a few energy storage possibilities, but all of these examples are already being used today. Thus, I think there are a lot of possibilities for storing energy. We now have the task of developing the storage possibilities in ways that assure low costs and small energy losses during the transformation from one energy form to another.
Let us take, for example, the Nokia Li-ion battery for powering a mobile phone:
A lithium-ion battery (sometimes Li-ion battery or LIB) is a family of rechargeable battery types in which lithium ions move from the negative electrode to the positive electrode during discharge.
Specifications for the Nokia Li-ion battery for powering a mobile phone:
Specific energy 100-250 W·h/kg (0.36-0.90 MJ/kg)
Energy density 250-730 W·h/L (0.90-2.23 MJ/L)
Specific power ~250-~340 W/kg 
Charge/discharge efficiency 80-90% 
Energy/consumer-price 2.5 W·h/US$
Self-discharge rate 8% at 21 °C /15% at 40 °C /31% at 60 °C (per month) 
Cycle durability 400-1200 cycles
Nominal cell voltage NMC 3.6/3.7 V, LiFePO4 3.2 V
Looking at the data, we see that the transformation of electrical energy to chemical energy and back to electrical energy costs 10 to 20% in energy loss. This energy is not lost, but it changes into heat energy, which we can normally not fully use. This heat energy will increase the temperature of the battery, which provokes higher self-discharge. Furthermore, we have to take price into account.
We have to develop energy storage further. The system solution will become, in the future, a combination of storage strategies, different energy forms, and smart management of the system. For example, we have described an example for a hybrid power plant in a previous article:
The following picture shows an example of how “Frauenhofer Institutes” are seeing the future of energy supply:
All the elements in the above picture are already known and somehow usable today. We have to develop them further in terms of performance and cost efficiency. Such systems will be the future in becoming independent of fossil energy, reducing CO2 emissions, and preventing energy wars.