Power Engineering Consulting Joint Stock Company 3 - The best solution for the best choice


In Vietnam for recent years, the development of Renewable Energy (RE) has been strongly promoted, especially in the Southern and Southern Central areas. In which, the ratio of capacity of Solar Power increases gradually over the years (8% in 2019, 14% in 2020, 21% in 2021 & 2022).

Data from Office of Gas and Electricity Market – UK in Vietnam researching
Distribution of Solar rooftop and Solar farm projects

Currently, solar power plants face a problem that the generation time is only available in a certain time frame (specifically, from ~7 AM to nearly 5 PM, peaking capacity between 11 and 14:30 depending on geographical location). Meanwhile, the peak load hours in Vietnam occur in the time frame of 9 – 11 AM in the morning, in the afternoon from 14 – 16h in summer and 17 – 19h in winter.

This leads to a large amount of power during the power generation peak time of the solar plants becoming redundant and very wasteful. To solve this problem, the application of BESS has been considered to solve the issue of economics and system stability. This is also evident in the Prime Minister’s orientation: to install 300MW of BESS system by 2030, to install 30650 to 45550MW of storage power by 2050. Realizing that the trend of installing BESS will soon be applied to renewable energy projects, especially in solar ones, PECC3 presents the following analysis on the application of BESS for floating solar projects.

Battery energy storage system (BESS or ESS) is a system that uses cells (cells) made of common compounds used in batteries such as Lithium-ion, Nickel, Sodium … as energy storage elements. A BESS system usually consists of a battery storage system (BSS), a battery management system (BMS), ancillary systems and a power conversion system (PCS) housed in containers.


Commonly used batteries for BESS systems can be listed as follows:



By the commitment to reduce CO2, the future development trend of power sources: coal-fired power will gradually be replaced, hydro power is difficult to develop due to almost all exploitation, waste and hydrogen power plants are still in the potential stage and need to research more, promote the development of wind and solar power sources… With the increasing proportion of renewable energy sources in the structure of Vietnam’s power sources, it is a big challenge for the operation of the power system. Therefore, the development of BESS to be able to store energy for transmission at the necessary time frames, at the time of weather incidents or when the generating power on the power system decreases suddenly is an issue which would be interested in recent years.

PECC3 has done research on the application of BESS for RE projects and has made designs for a number of projects. The article presents one of the BESS applications for floating solar projects – a type of renewable energy being promoted in areas with hydro power reservoirs.


The BESS installation alternatives are presented as follows:

  • Alternative (G): connect to MV busbar. Need to install more transformer for BESS connection.
  • Alternative (S1): connect to LV busbar (at LV side of LV transformer)
  • Alternative (S2): BESS installed location is on resevoir. BESS needs to be divided into several parts ® take up surface space and O&M is more complex
  • Alternative (C1): connect to LV busbar (at LV side of LV transformer)
  • Alternative (C2): modern technology of Central Inverter allows BESS connection without separated inverter for BESS. Still need to divide BESS into several parts.

The alternatives for DC or AC connecting (LV side) have better efficiency but need to divide BESS into several parts.

The alternative for AC connecting (MV side) has benefit that BESS is centralized locating into one specific area, and has ability to be expanded in future.


BESS capacity is calculated and selected based on many factors as the following formula:


*DoD – Depth of Discharge: capacity of the battery to discharge to a level without affecting battery life and performance. The higher this number, the better the battery quality. DoD of lead batteries is about 50%, Lithium-ion is about 80-90%, Vanadium flow reaches 100%

Another very important factor when choosing a BESS capacity is the rated charge/discharge cycle and the lifespan of the battery. With today’s advanced technologies, the lifespan of Lithium-ion batteries can be up to 10 – 12 years depending on usage and maintenance conditions, charge/discharge cycles up to 6000 – 7000 times. When one of these two indicators reaches a critical level, it is necessary to replace the battery, so it must be calculated to optimize the battery capacity to avoid these two indicators being too different.

For example, at the end of 10 years of lifespan, the charge/discharge cycle is at only 4000/6000 times, so the battery must be replaced ® wasted, in this case, if the battery capacity is reduced, the actual number of charging/discharging times could be increased. When these two indicators approach the critical together, it is an ideal case in optimizing the installed battery capacity.


High installation cost is one of the leading reasons why very few projects dare to invest in BESS. Currently, the investment rate of 01 set of BESS ranges from 360 – 420 USD/kWh. In the case of optimization of installed capacity, the break-even selling price of power is still high (18.08 – 20.91 cents/kWh, equivalent to 4,264 – 4,934 VND/kWh). If the number of charging/discharging times can be increased to 2 times/day, the break-even price of power will be significantly reduced (see picture below).

In case of 01 time/day charging/discharging, Investment rate 360$/kWh, BESS capacity 2MWh
In case of 02 time/day charging/discharging, Investment rate 360$/kWh, BESS capacity 2MWh

The second issue is that to accurately calculate the capacity of the BESS to be installed, plant operating data is required as an input basis. For projects where the amount of capacity is reduced irregularly or projects that want to install BESS from the beginning, there will be difficulties in optimizing BESS capacity.


Around the world, BESS is also installed with wind power plants, helping to store excess energy when the amount of power produced exceeds demand, or in the case of reducing the power generated to the grid.

BESS centralized installation for Wind power plants

In addition, BESS is also used at substations to increase reliability for special loads.

The application of BESS for RE projects brings a lot of benefits to both the Owners and the dispatching agencies. However, the lack of a mechanism/policy for the installation of BESS is a big barrier because procurement costs are high and there is still no FIT price for this type, which prevents investors/owners from stepping up their investment. . In the future, if there is a good power price mechanism, the development of BESS is very suitable and effective with the strongly growing trend of renewable energy as well as reducing CO2 emissions in Vietnam.

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