A Battery Energy Storage System (BESS) captures energy from both renewable and non-renewable sources. It then stores this energy in rechargeable batteries for later use.
When needed, the stored electrochemical energy is released from the battery. This discharge helps balance energy demand and generation.
The growing emphasis on renewable energy sources and the urgent goal of achieving net-zero carbon emissions position Battery Energy Storage Systems (BESS) as essential technology for commercial and industrial organizations. By adopting BESS, you can have a vital pathway in the transition to green energy and expedite your journey toward net zero.
How does a battery storage system work?
A BESS collects energy from renewable energy sources, such as solar PV Module or from the electricity network and stores the energy using battery storage technology. The batteries discharge to provide energy when necessary, such as during peak demands, power outages, or grid balancing. In addition to the batteries, BESS requires additional components that allow the system to be connected to an electrical network.
A bidirectional power conversion system (PCS) is the main device that converts power between the DC battery terminals and the AC voltage and allows for power to flow both ways to charge and discharge the battery. The other primary element of a BESS is an energy management system (EMS) to coordinate the control and operation of all components in the system
Advantages of battery energy storage systems
Battery storage systems have several advantages when paired with renewable energy and non-renewable forms of generation. Solar can be unpredictable, so battery storage systems are a key component in steadying energy flow by providing a steady supply whenever required, irrespective of weather conditions. Additionally, BESS can protect users from potential supply interruptions that could threaten the energy supply. Here are some of the benefits of battery storage systems:
BESS Applications
Battery energy storage can be beneficial for several reasons due to the flexibility of co-locating with other renewable energy sources or non-renewable sources. Battery energy storage also requires a relatively small footprint and is not constrained by geographical location. Let’s consider the below applications and the challenges battery energy storage can solve.
Peak Shaving / Load Management (Energy Demand Management)
A battery energy storage system can balance loads between on-peak and off-peak periods. The electricity demand fluctuates depending on the day of the week, time of day, and seasonality. As such, when there is peak electrical demand, prices are at their highest. Alternatively, the power price is at the standard rate when demand is low during off-peak periods. Peak shaving allows users with battery energy storage systems the assets to store power during off-peak periods and discharge during peak times to reduce electricity costs.
Energy Time Shifting / Arbitrage
Energy time shifting or arbitrage allows users with BESS solutions to store their purchased power during off-peak times to use on-site when the imported power price is high. Alternatively, users can trade their stored electricity via the flexibility markets (Energy Markets, Ancillary Services, and Capacity Market) for income generation.
Frequency Response
A BESS has a frequency response which allows it to provide active power output when there is a change in the electrical grid’s frequency. A deviation from the nominal frequency indicates a mismatch between power supply and demand, which can destabilise the grid, causing outages or blackouts. To restore balance quickly, the BESS can adjust its active power output by reacting to deliver sub-second frequency response to stablise and balance supply and demand within the network. The growing share of renewable generation and decentralised power plants connected to the network, means battery storage will continue to play a critical role in our energy transition.
Grid Connected
In Front-of-the-Meter applications battery storage systems are typically referred to as utility or grid-scale battery storage and can be connected to transmission or distribution networks to reduce congestion management whilst also controlling voltage and providing reserve and ancillary services. A BESS can also support power generation assets.
Commercial and Industrial
BESS is typically Behind-the-Meter, and applications include avoiding electricity network charges, benefiting from tariff differences, delivering value-added balancing services, or enhancing on-site resilience and energy consumption when paired with on-site solar PV, thus saving money and optimizing the sustainability benefits.
Why is Energy Storage needed?
Most energy systems have a varying demand with some short-term but significant peak power requirements, which results in a capacity requirement which might only be used for a fraction of the time. Energy storage allows energy to be saved for later use.
Energy storage creates capabilities and efficiencies low-cost energy for the electric grid and assists in mitigating climate change.
Renewable energies are intermittent in nature, i.e., their capacities to produce energy vary with time and climate. Energy storage from renewable energies can avoid any curtailment of renewable energies during favourable weather conditions when excess wind or solar energy gets generated.
The four main solar battery system types
1. AC-coupled battery systems (grid-tied)
These systems are increasingly popular for grid-connected properties. They enable energy storage capacity to be quickly and relatively cost-effectively added from scratch, or to an existing solar setup.
2. DC-coupled hybrid systems (grid-tied)
These systems offer the highest levels of efficiency when charging batteries and using battery power, making them a popular choice for many homeowners and businesses.
3. DC-coupled systems (off-grid)
DC-coupled off-grid systems are popular for small-scale setups, such as for individual homes, motor homes, and boats. They are highly efficient at charging batteries and powering DC appliances.
4. AC-coupled systems (off-grid)
These systems are ideal for large-scale off-grid solar setups and are efficient when powering high AC loads while solar power production is high (during the day). An off-grid AC-coupled system can be a useful addition to a grid-tied AC-coupled system. Since they are disconnected from the grid, off-grid systems usually rely on batteries to power their loads. However, Hoymiles AC-coupled solutions allow you to connect your system directly to a diesel generator, so that your PV modules continue running, even if the main grid shuts down.
What are the advantages of AC-coupled battery systems?
There are several benefits to using an AC-coupled BESS for your solar plant, including:
- Retrofitting: AC-coupled batteries are easy to install on an existing solar panel system, and more can be added to expand capacity.
- Flexibility: Installers are not restricted in where the inverters and batteries can be located. AC coupling works with any type of inverter.
- Resiliency: The flexibility to install multiple inverters and batteries in different locations helps risk of an outage if an inverter fails. Having multiple inverters provides more combined power and battery faults do not have an impact on power generation.
- Versatility: AC-coupled systems enable batteries to charge from the grid as well as the solar panels and the grid, so if the solar panels are not generating enough electricity, the battery can still charge from the grid.
What are the disadvantages of AC-coupled battery systems?
- Cost: AC-coupled systems cost more than DC-coupled systems as they use multiple inverters.
- Lower efficiency: The stored energy is converted three times, from the DC current to AC current to supply the building and then back to DC current to the battery and again back into AC. Each conversion results in a small amount of energy loss.
- Supply limitations: AC BESSs are not designed to be used off-grid and as they are transformer less, they cannot manage the surge loads from multiple appliances.
What are the advantages of a DC-coupled system?
Where AC-coupled systems suffer in terms of efficiency and cost, DC-coupled systems have the advantage:
- Affordability: DC-coupled systems tend to be cheaper than AC-coupled systems as the solar panels and battery use a single inverter and less extra equipment such as voltage transformers and switchgear.
- Higher efficiency: Unlike AC systems which convert the current multiple times, DC BESSs only convert the current once, reducing energy losses and making them more efficient.
- Oversizing: DC-coupled systems allow solar panels to generate more electricity than the inverter rating. The excess energy can be used to charge the battery, an EV charger or a water heating system, whereas in an AC-coupled system the energy is lost.
What are the disadvantages of a DC-coupled system?
- Limited flexibility: Installers have less flexibility than with an AC system, as the inverter needs to be located close to the battery.
- Less resiliency: With a single inverter in a DC-coupled system, if the inverter fails, the solar power as well as the battery capacity is lost