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BESS Basics: Battery Energy Storage Systems for PV-Solar

Jul. 29, 2024

BESS Basics: Battery Energy Storage Systems for PV-Solar

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By Nashvinder Singh and Jigeesha Upadhaya

Energy storage systems capture surplus energy during times of high production/low demand and store it for use during times of low production/high demand. While not a new technology, energy storage is rapidly gaining traction as a way to provide a stable and consistent supply of renewable energy to the grid.

The energy storage system of most interest to solar PV producers is the battery energy storage system, or BESS. While only 2&#;3% of energy storage systems in the U.S. are BESS (most are still hydro pumps), there is an increasing move to integrate BESS with renewables.

What is a BESS and what are its key characteristics?

Largely, BESS systems use lithium-ion batteries to store electricity. They can be used either as stand-alone or coupled with renewable energy sources.

Main characteristics used by the industry and which vary with different BESS chemistries are:

Rated Power Capacity
Rated Energy Capacity
Depth of Discharge (DOD)
Storage Duration
Cycle Life
State of Charge (SOC)
Round-Trip Efficiency
System Life
Safety Monitoring and Control

What are the major parts of a BESS?

A typical BESS includes:

Battery modules &#; connected in series and parallel for required capacity.
Storage enclosure with thermal management.
Power conversion system (PCS) &#; All the clusters from the battery system are connected to a common DC bus and further DC bus extended to PCS.
Battery management system (BMS), which continuously monitors the voltage, temperature, fire warning and state of charge (SOC) of the battery. It regulates the charging and discharging power depending on input signal.
Energy management system (EMS) &#; The control logic is executed at EMS. It will provide input signal to PCS for charge/discharge depending on control logic requirement.

A BESS is an energy source, and like any energy source that feeds the grid, it must be managed and controlled. At Nor-Cal, we provide SCADA and EMS solutions for monitoring and controlling BESS per site requirements.

Why is integration of BESS gaining traction?

BESS systems are gaining traction for both technical and commercial reasons. Technically, they provide immense benefits to the grid:

Use in emergency response systems or for storm outages
Frequency regulation
Grid stability
Reduction of grid congestion
Ramp rate control
Energy arbitrage
Peak shaving
Black start &#; providing quick energy or stabilizing energy to get the grid started at a good response rate

What's most exciting is the use of BESS in helping the world transition to renewable energy.

Renewables are intermittent in nature&#;production goes up when the sun is shining and the wind is blowing, but goes down when the day is overcast or the winds die down. On the current grid, on-demand gas power is still needed to fill in the gaps. As more renewables come online and begin contributing to the grid in order to meet ambitious clean energy goals, energy storage technologies, including BESS, can help ensure a stable, steady supply of energy.

Being able to store excess energy is also a financial benefit to renewable energy producers. Instead of having to curtail production, at the request of the grid or utility, that curtailment can be stored. When production later goes down, that stored energy is available for sale to fill in the gaps.

Another reason for the rise in BESS systems is the affordability of lithium-ion batteries. The prices for this technology are going down and are expected to go even lower. This is moving the needle away from older existing energy storage systems and towards BESS.

How important is the siting of BESS?

The siting of any power generation resource is important, but the immense flexibility of BESS systems mean they can be installed and utilized in any number of ways:

Front-of-meter or behind-the-meter
Near to the loads/energy sources or independent/standalone
Co-located with variable renewable energy resources
Used to augment traditional power generation

There are exciting residential, commercial and industrial behind-the-meter applications. Consumers with rooftop solar panels can store excess energy using a BESS, and then have that power available as a backup. The California Solar & Storage Association (CALSSA) estimates behind-the-meter battery deployments in the 2&#;2.5 GW range through the end of .

What are the possible configurations?

There are a variety of configurations available for BESS depending on siting. BESS can be utilized in a standalone setup, in which the BESS takes electricity from the grid when the supply is high and sends it back when the demand is high. For PV + Storage systems, four types of configurations are used.

Independent

In this, both PV and storage systems are not physically co-located and do not share common components or control strategies. Being independent, storage responds to overall grid conditions to provide peak capacity, shift energy from off-peak to on-peak periods and provide ancillary services. Although the storage could charge from PV energy, it would only do so when grid conditions made this an economic option.

DC Coupled (Flexible Charging)

In this case, the PV and storage is coupled on the DC side of a shared inverter. The inverter used is a bi-directional inverter that facilitates the storage to charge from the grid as well as from the PV.

DC Coupled (PV-Only Charging)

This configuration is similar to DC coupled, but the storage can be charged using PV only, not from grid electricity. This is also known as the DC tightly coupled configuration.

AC Coupled

In this case, PV and storage are co-located with two separate inverters. BESS is charged by converting the PV electricity from DC to AC and then back to DC at the BESS inverter for the BESS to store it. Since there are no shared components, the storage can still act independently of the PV system.

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AC coupled configurations are typically used for existing PV systems, because it's easier to just add on a second inverter, add a BESS, and then use the existing circuitry to integrate the BESS into that. DC coupled systems are more common for new PV + Storage installations.

How are battery applications typically categorized?

Battery applications are typically categorized on the basis of energy and power.

Energy supply interactions happen on a slower timescale, where large amounts of energy are supplied or pulled from the grid. These are referred to as "energy" applications. These applications include energy arbitrage and energy time-shift. Since energy response typically has a deeper depth of discharge on a consistent basis, these applications have a steeper degradation curve for some chemistries.
Power applications normally transpire on a much faster timescale and are employed to support real-time control of the power grid. Power applications include frequency response, load ramping and voltage support.

Each BESS has a rated energy capacity measured in kilowatt-hours (kWh) or megawatt-hours (MWh), as well as rated power capacity measured in kilowatts (kW) or megawatts (MW). Most BESS manufacturers also provide Depth of Discharge (DOD), which indicates the percentage of the battery that has been discharged relative to the overall capacity of the battery. Staying within maximum recommended DOD is important for optimal performance and lifespan of the battery.

For example, if the manufacturer of a 100 kWh battery recommends a maximum DOD of 80 percent, you shouldn't use more than 80 kWh from the battery without recharging.

These ratings, the internal chemical structure of the battery itself, the cycle frequency, and battery health all play a critical role in determining if a BESS is suitable for a specific application. For energy applications, you will need to pay attention to different parameters than you would when using a BESS system for power applications.

How can Nor-Cal help with integrating BESS systems for PV projects?

Energy storage is the future of solar PV, and we are right there to help our customers with the latest developments. We coordinate with BMS manufacturers and integration companies to implement the necessary EMS requirements into our SCADA systems. We can also ensure that the BESS meets utility and ISO requirements.

If you need a PV-Solar SCADA provider who can help you take advantage of all the benefits BESS systems have to offer, contact us today. Whether you have a PV + Storage integration or a standalone BESS, we'd be happy to talk with you about your options. Schedule a call with us today.

"Photovoltaic + Energy storage + Charging"

With the clear promotion of new energy vehicles, the market for EV Chargers has expanded, but the operation of EV Chargers alone is not ideal for corporate income. The storage and charging system can cut the peaks and fill the valley and save part of the electricity price. It is also a reflection of the sustainable development of energy. Nowadays, the optical storage and charging project has gradually become the target of many domestic enterprises.

Recently, a number of &#;light storage and charging&#; projects have been successfully put into operation, and Fujian, Shaanxi, Hubei and other provinces and cities have successively achieved zero breakthroughs in the &#;light storage and charging&#; project.

The optical storage and charging integrated power station can solve the problem of insufficient power distribution capacity of the new energy vehicle charging station. It uses the night low valley electricity price for energy storage, and supplies power to the charging station through energy storage and utility power during the peak charging period to meet the peak power consumption. Demand has not only achieved peak cutting and valley filling, but also saved power distribution capacity, increased consumption of new energy, and made up for the lack of solar power discontinuity. It is a sustainable energy utilization method.

According to statistics, among the 31 provinces and cities that have adjusted the general industrial and commercial electricity prices nationwide, a total of 18 provinces and municipalities have issued peak-to-valley electricity price lists to encourage users to use electricity in a time-sharing manner by reducing electricity prices during the night low valley period and increasing the peak daytime electricity prices. Recently, Shandong Province has implemented an electric energy substitution incentive policy. The electric bus centralized charging and replacing facilities use a kilowatt hour of electricity consumption for each kilowatt hour, and the electricity is used to deduct the peak (priority) peace. Segment electricity, reduce the cost of electricity for electric buses. The Guizhou Provincial Development and Reform Commission also said that it will explore the use of price signals to guide the power to cut peaks and fill valleys, and to test the peak and valley time-sharing electricity prices for electric vehicles and electric storage.

According to the data, the peak-to-valley spread of the provinces in the country is distributed at 0.4~0.9 yuan/kWh, while for the two provinces in Jiangsu and Guangdong, the peak-to-valley spread is higher than 0.8 yuan/kWh, which is the user side. The use of energy storage to arbitrage peak and valley spreads provides considerable space.

The &#;light storage and charging&#; integrated charging station integrates multiple technologies such as photovoltaic power generation, energy storage and EV Chargers. It can not only supply green electric energy for electric vehicles, but also realize auxiliary service functions such as power peak clipping and valley filling, which can effectively improve system operation effectiveness. The energy storage system stores electric energy when the electricity is low at night, and is released to the EV Charger during the peak of the daytime power consumption. On the one hand, the impact of the large current on the regional power grid is relieved on the one hand, and the charging electricity cost difference is brought to the charging station through the difference between the peak and the valley. A considerable amount of income.

For traditional charging station construction, grid access and land resources are two major problems. The &#;light storage and charging&#; integrated solution achieves a basic balance between local energy production and energy consumption through power storage and optimized configuration. It can flexibly interact with the public power grid and operate relatively independently according to needs, alleviating the impact of EV Charger power on the power grid. In terms of energy consumption, using an energy storage system to charge the power battery can improve energy conversion efficiency.

Not only that, the &#;light storage and charging&#; integrated charging station is a new mode for the exploration of micro-grid. The use of photovoltaic power generation clean energy, combined with energy storage technology is advanced in many aspects.

At present, China's "light storage and charging" integrated charging station is concentrated in Jiangsu, Shaanxi, Zhejiang, Fujian, Guangdong and other places, and most of these provinces have implemented peak and valley electricity prices.

As we all know, China has become the world's largest electric vehicle market, but China's charging infrastructure construction is seriously inadequate. This problem has also become a major bottleneck for the rapid development of electric vehicles and the rapid development of charging infrastructure.

Such a huge EV Charger gap, if built into a light storage charging station, will greatly improve the "electric vehicle long-distance travel", inter-city traffic "mileage anxiety" problem, while saving the operating costs of EV Charger enterprises, new energy The consumption has provided more favorable conditions and will also provide important demonstrations for the sustainable development of energy.

Faced with such a huge market, there are more and more enterprises that are keenly aware of the big cake of the optical storage market. Most of them are mainly industrial enterprises such as electric power and charging infrastructure. The favor of energy companies.

However, the high cost of energy storage is a difficult problem for the integrated development of &#;light storage and charging&#;. At present, some &#; PV + electric vehicle battery+ charging&#; projects are implemented, and the energy storage unit is postponed. The fundamental reason is that the energy storage cost is too high.

In addition, the photovoltaic installed capacity can only meet the charging demand of electric vehicles only when it reaches a certain scale, and large-scale photovoltaic construction requires a large area. Therefore, the &#;light storage and charging&#; integrated charging station is largely restricted by the site, and most of them have localized construction in the public areas of the city with distributed photovoltaic and energy storage system layout conditions, such as commercial parks, industrial parks, commercial residential buildings, etc.

When the energy storage cost is too high, the corresponding industrial incentive policy is very important. At present, in the mainstream market for overseas energy storage applications, although the electricity price is relatively high, there is a subsidy policy for the energy storage industry, which has boosted the development of the local energy storage industry. After the implementation of China's energy storage policy, it is believed that the optical storage system will also usher in a larger market.

At present, the &#;light storage and charging&#; integrated charging station is more profitable by using the peak-to-valley electricity price difference, and the &#;light storage and charging&#; integration scheme can better realize the investment income in the area where the peak-to-valley electricity price difference is relatively large. Photovoltaic power generation is self-sufficient, and surplus power storage combines the energy-storage peak-valley electricity price arbitrage. With energy storage systems, it will inevitably increase the cost of the power station and extend the investment return period.

Therefore, despite the continuous implementation of the project, the number of &#;light storage and charging&#; integrated charging stations is still small. The number of EV Chargers in the &#;light storage and charging&#; integrated charging station accounts for a very small proportion of the total number of EV Chargers in the country. At present, there are many demonstration application stations, and large-scale promotion has not yet been carried out.

Internationally, the &#;light storage&#; model has been operated in many countries and regions. Residents use their own roofs to build photovoltaic arrays. The stored electricity is used for electric vehicle charging or household electricity, and the remaining energy can be sold to the grid.

In China, with the maturity of the photovoltaic industry, the boost of the new energy automobile industry, and the advancement of energy storage technology, the &#;light storage and charging&#; integrated power station has also landed smoothly. At present, many domestic companies are actively promoting the construction of &#;light storage and charging&#; integrated charging stations. It is the starting point for many enterprises to build a 'light storage and charging' integrated charging station to build a high-power charging facility in social public places, to solve the pain points of new energy vehicle charging infrastructure, and to match the scarcity peaking resources of power grid dispatching.

The cost of photovoltaic + energy storage + charging micro-grid system is gradually decreasing. The "light storage and charging" mode is flexible and friendly, and has broad application prospects in the long run.

At the same time, energy storage services in charging facilities, safety issues can not be ignored, to prevent the occurrence of heat, short circuit and other phenomena in the process of charging and discharging.

The popularity of new energy vehicles, users' demand for fast charging, the city's electricity load will far exceed the existing power supply capacity, and urban expansion has become a reality. In the future, centralized charging of electric vehicles is likely to lead to urban power shortage. Distributed energy storage can not only solve the problem of urban expansion, but also provide backup power for commercial complexes and intelligent buildings to avoid temporary power outages during peak hours.

The optical storage and replacement power station has a far-reaching impact on the development of new energy vehicles. It is of great significance. Photovoltaic self-use, green economy, energy storage can alleviate the expansion of power grid investment, and optical storage charging stations will become the mainstream of charging infrastructure development.

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