Energy storage systems

The efficiency of the use of global energy resources depends not only on the ways of their use, but also on the methods of the generated energy storage. According to the projection of the analysts of GMT Research, the energy storage market size grows rapidly and already in 2020 will be twenty-six times larger than it was in 2014. In 2015, the home energy storage systems comprised about 16% of total market size. This is due to the fact that it is desirable to install the energy storage systems in addition to wind or solar power plants, because the energy is unevenly generated by renewable sources during the day. For example, the solar energy is generated only during the daylight, but it is consumed all day long, or a cloudy day takes place and total volume of the generated energy is less than the volume of daily power consumption of your household. The energy storage systems are designed for use in such cases.

Energy storage technologies

The lithium-ion energy storage technologies are the most widespread on the market of energy storage systems today. For example, lithium-ion batteries were used in 95% of all cases in 2015. They are also widely used in the consumer market and on the car market, where they are set into electric or hybrid propulsion systems. The prices of lithium-ion batteries become lower, their reliability increases, they prove their worth in the systems (propulsion systems) needed to consume much power during a short period and in the systems needed to consume less power during a longer period. Lithium-ion batteries therefore are used by all kinds of consumers: from large utilities specialising in power distribution and supply to individual business entities and accommodation facilities for the storage of energy.

Nevertheless, it is necessary to specify the usability of lithium-ion energy storage systems. Firstly, it is very important that the performance characteristics of different types of lithium-ion batteries shall be appropriate for the specific purposes. For example, the use of a certain type of lithium-ion batteries can be 80% more efficient for big power plants than the application of other types because of rapid charging and discharging. Secondly, other technologies of energy storage can be more applicable in some particular cases. For example, lead-acid batteries can be more suitable for the management of the energy storage in order to satisfy the needs of residential areas. Alkaline batteries are more economical for large-scale power plants, but only in the cases of short charging and discharging periods (less than one hour).

Main characteristics of the energy storage systems

One of the main characteristics of any system of energy storage is effective capacity. The value of this characteristic of the energy storage system depends on nominal capacitance, allowed rate of depth of discharge and the decrease of the battery capacitance over time. For example, Adara Power offers the energy storage system for households with the battery nominal capacitance 8.6 kWh. Besides, specified allowed rate of depth of discharge equals to 75%. It follows that the value of the effective capacity of Adara batteries is equal to 6.45 kWh. At the same time, Tesla, a direct competitor of Adara Power produces the energy storage systems “Powerwall” and their allowed rate of depth of discharge is 100%. The value of effective capacity of these energy storage systems is equal to their nominal capacitance (7 or 10 kWh).

However, the value of nominal capacitance of the batteries is actual only for the first day of their cycle life. Their effective capacity will slowly decrease in the course of time because of battery wear. The cycle life of the energy storage system is the characteristic, which determines the durability of the battery. The service life of the battery depends strongly on the conditions of use. For example, the producer calculates that the lifetime of one and the same battery shall comprise 400 battery cycles under the condition that the rate of the depth of discharge is 70%, or 300 battery cycles under the condition that the rate of the depth of discharge is 85%. These calculations shall be accessible to the clients, but it is almost impossible to find them put into practice.

It is important for the client to know the changes in the battery cycle life under different conditions of use in order to ensure the maximum efficiency of the batteries. For example, Sonnen guarantees that the lifetime of all energy storage systems “SonnenBatterie” is calculated as 10000 battery cycles or 10 years. When such a system is used under standard operating conditions, you get only near 3650 battery cycles per 10 years. That is why you shall realise about 3 battery cycles per day to accomplish near 10000 battery cycles during the guarantee period. The special conditions of use are necessary for this purpose. The energy storage system can be used not only for own consumption, but also for the power supply to the grid.

Business models of energy storage systems

There are some economic scenarios for the owners of energy storage systems. They are described below.

Stand-alone home power stations

In this case, you use your energy storage system to store the generated power for your own needs and ensuring energy independence of your household. The excess of the generated power is stored in the battery system during the day in order to be consumed at night-time. However, these systems need additional control over the amount of the generated power; the presence of a standby power supply is also desirable. As a matter of fact, this energy storage system shall calculate the power consumption by households in real time for the optimisation of power generation. Besides, the system shall reduce power generation, when the amount of the generated power exceeds the capacity of energy storage system. This way of the solar power plant installation is profitable when the client strives for a full energy independence or in the regions with the high cost of power.

Backup home power stations

This type of energy storage systems is beneficial to the households, which are situated in the regions of power supply problems. The plants generate power until the energy storage system is completely filled. Then it stops. Your battery system, subsequently, is always charged up to the moment of power supply shutdown. By necessity, you can also generate electricity individually. In this case, you shall calculate the amount of power that is necessary for the supply of the household during blackout periods and install the energy system storage of the appropriate dimensions.

Grid-connected home power stations

In this case, you aim to sell the generated power for a higher price, than the price for which you purchase power from the government. Taking into considerations the conditions in Ukraine, it is a highly lucrative enterprise, as the government is obliged to buy the power from you at the rate of green tariff correlated with the euro. You do not need to install the energy storage system to sell the generated power directly to the government. It allows you to get considerable cost savings.

Phenomenon of negative electricity price

Negative price of electricity is a relatively new feature of wholesale electricity markets. Negative prices of daily electricity were noticed for the first time in Germany in 2007 and they occur enough rarely at present, but in 2012, within 56 hours per 15 different days, the prices of power decreased to negative values in the process of the determination of power price for the next day. It means that the electricity suppliers should pay for the supplied power consumption by the customers. This phenomenon appears when there is exclusively a low demand for power supply and the supplier decides that the expenses related to the shutdown and reset of a whole power supply system are higher than the costs paid for the generated power consumption by external parties. Negative prices of electricity prove the inflexibility of existing conditions and their appearance conditions the necessity of the use of energy storage systems. The presence of negative prices of electricity stimulates the market of energy storage: instead of purchasing power from the suppliers and selling it later, the owner of the energy storage system can be paid by the suppliers for the consumption of power and sell the power later, getting double profit in this way. Besides, the installation of energy storage systems will cause the increase of the electricity price and a large market of energy storage, on its own, will make negative electricity prices disappear.

The information provided in the given article allows for some important conclusions:

Firstly, the energy storage systems already have the economic potential under certain conditions. One often forgets about it without taking into consideration the government grants for the implementation of energy storage projects and economic losses resulting from power supply interruptions.

Secondly, it is necessary to decide on the technology (lithium-ion, lead-acid, alkaline or other) for the project of energy storage system, which ensures the best realisation of your objectives. The use of several technologies will be more expensive, but it will allow your system to be more flexible.

At last, the most important conclusion is the next: the development of the market of energy storage systems is able to transform the existing standards of power supply worldwide. Today, unconventional energy sources are used in most of the cases for current needs. Energy storage systems help to smooth out the variations between the periods of power generation and line load period. Renewable sources of energy will increasingly replace conventional ones (coal and gas).

Due to the fact that the electric power generation by wind generators or solar modules makes some inconstancy, energy storage subsystems became the important part in energy supply systems. The electric power accumulated for a day is delivered in a network at evening hours or at moments of peak consumption, when energy amounts, generated by a solar power-station, appear to be not enough for consumer needs. Thus, it is necessary to understand that system of energy accumulation and storage is not simply an accumulator, leading global companies understant this concept in some other words. Manufacturers offer complex solutions that include both actual accumulators (storage units) and software solution that provide control over accumulator condition and optimal load balancing.