Building hybrid solutions for energy storage systems

One of the ways to increase the technical and economic efficiency of energy storage devices is their hybridization, i.e., the creation of storage devices consisting of blocks of different types of batteries. This approach is justified to reduce the initial investment in batteries due to the use of cheaper lead-acid batteries in the main module.

A variety of energy storage technology solutions are currently available, including lead-acid, lithium-ion, nickel-based, sodium-based, and others. All of which have the potential to be used in a variety of conditions. Selection parameters: performance, security, price.
Recently, in the most authoritative energy magazine in the Republic of Belarus «Energy. News of Universities and Energy Associations of the CIS» published a series of articles prepared with the participation of the head of the SSE development project of the center for scientific and technical competencies 1AK-GROUP, Professor K. V. Dobrego. A series of articles is devoted to building effective hybrid solutions for energy storage systems (ESS).

In article [1], from a technical and methodological point of view, the issue of the feasibility of hybridization of energy storage systems is considered. The concepts of the degree of hybridization (the share of an additional module in the total capacity of a hybrid energy storage system), the coefficient of the synergistic effect of hybridization, and the degree of internal buffering of electricity are defined. Indicators of the cost of buffering electricity with lithium-ion, lead-acid batteries and supercapacitors are given. Data are provided on the component composition of the total investment cost of energy storage systems built on lead-acid and lithium-ion technologies.
A method for determining the economic efficiency of ESS hybridization is presented. It is shown that, in the general case, adding lithium-ion batteries with a block of supercapacitors does not lead to a reduction in the cost of power buffering due to the high cost of power buffering with a supercapacitor. The economic feasibility of using supercapacitors to compensate for high pulse loads can be determined based on an analysis of the frequency spectrum of the load graph of the storage unit.

In article [2], there are three types of hybrid storage potential: lead-acid batteries (batteries) supplemented with lithium-ion batteries; lead-acid batteries supplemented with supercapacitors; lithium-ion batteries supplemented with supercapacitors. Several options for organizing interaction between blocks are being considered — connecting an additional block using a threshold approach, nonlinear-functional load current difference and load independence by an L-filter. As a load, the ESS accepts: 1 — an electric forklift, 2 — a 30-apartment residential building, 3 — a 300-apartment residential complex. The efficiency of hybridization of measurements is achieved due to the comparative cost of buffering electricity with the main type of battery and a hybrid storage device. Calculations show that the effectiveness of hybridization depends on the type of battery connection, on the nature of the graphic load, and on the algorithm for the interaction of blocks. The economic effect of hybridization of lead-acid and lithium-ion batteries can arise in the presence of a high-frequency component of the load on the consumer and high standard deviations of the load. Hybrid solutions are advisable in case of a shortage of available funds in small industrial enterprises characterized by a «variable» load schedule, electric forklifts, stackers, and in farms using light stations and wind generators. On the other hand, there is a positive economic effect of observation at low values of the degree of hybridization.
The threshold load limiting method turns out to be the most effective for working according to the electric forklift schedule and the most effective for a smoothed load (residential complex). However, none of the load limiting methods has universal advantages over coronaviruses for all types of loads and typical hybrid systems. Thus, when designing an ESS and the efficiency of its hybridization, it is necessary to have information not only about the cost of the battery and the corresponding cost of buffering electricity, but also about the expected load schedule of the ESS and the cost of the power equipment necessary to organize the connection of the units.
The developed models and methods are considered by 1AK-GROUP in the design of ESS and economic development of ESS hybridization.

Article [3] highlights the practical aspect of implementing power coupling of hybrid ESS blocks. Namely, the possibility of the simplest passive coupling of lead-acid and lithium-ion batteries. The operating modes of a hybrid electric energy storage system (ESS) were simulated with a simple parallel connection, as well as with switching blocks using a threshold algorithm. It is shown that to equalize the rate of discharge of the main and additional units, it is necessary to coordinate the ESS capacity, the degree of hybridization, the type of load and the electrical parameters of the batteries.
With threshold switching of blocks, it becomes possible to change the discharge rate of an additional block and increase the economic efficiency of a hybrid ESS.
Examples are given of calculating the threshold switching voltage of a lithium-ion block for three typical loads: an electric forklift, a 30-apartment residential building and a 300-apartment residential complex.
The results obtained can be used to design hybrid ESS for small power systems, including solar and wind power plants.

1. Dobrego K. V. On the issue of creating hybrid electricity storage systems. Energy. Izv. higher uch. establishments and energy CIS associations. 2023, v. 66, no. 3, p. 215-232.
2. Dobrego K. V., Koznacheev I. A. Modeling the functional interaction of hybrid energy storage units. Energy. Izv. higher uch. establishments and energy CIS associations. 2023, v.66. No. 5, p. 405-422.
3. Dobrego K. V., Koznacheev I. A. Modeling of passive coupling of blocks of a hybrid electricity storage system. Energy. Izv. higher uch. establishments and energy CIS associations. 2024, v.67. No. 3 (in published).