Know the risks associated with energy storage systems

Renewable energy technologies such as wind and solar PV can only generate power on an intermittent basis. Established technologies such as coal fired power generation can generate power continuously however they can take time to respond to changes in demand. This means that power generated from renewable sources may not be available during periods of peak demand or that a coal fired power station may not be able to respond to a rapid change in demand. Energy Storage Systems (ESS) are emerging as a solution to this problem. They enable the storage of excess power for later use to help manage short term peaks in demand (eg. ‘peak shaving’) and to assist with grid load balancing. ESS technologies such as batteries can dispatch power in seconds, compared with minutes or hours for established power generation technologies.

The use of ESS for tasks such as peak shaving helps with reducing carbon emissions by managing fossil fueled power generation when the electrical grid is taxed with short term peaks in demand. Load balancing helps smooth the intermittent nature of renewable energy sources such as solar and wind thus making the grid more stable, reliable and resilient. As more renewable generation capacity is installed, and renewables represent an increasing proportion of total generation capacity, grid stability becomes an ever increasing issue.

ESS as a concept is not new. Batteries in various forms have been around for a long time, however in recent years battery technology has improved and there has been a marked increase in the deployment of higher energy density grid-scale systems based on Li-ion battery technology.

There are some well-documented risks associated with Li-ion batteries. The primary focus is on the fire hazards associated with Li-ion batteries and the potential for a condition known as ‘thermal runaway’. Thermal runaway results from internal shorts inside a battery cell which occur due to a variety of reasons and can ultimately lead to the battery catching fire.

At its most basic level an ESS is a set of batteries which is charged from a renewable source or when surplus power is available and then discharged when required to meet demand. They can be used to supply utility grids, local microgrids (e.g. campuses and neighborhoods) and/or individual buildings. The ESS can be charged from a wide range of potential sources including the power grid (usually during low demand, low pricing periods), solar and wind installations, conventional generators or other sources.

Li-ion battery-based systems are a common ESS design due to the inherent energy density advantages of lithium battery chemistry. However, it should be noted that ESS and Li-ion batteries should not be considered synonymous; Li-ion batteries are only one type of ESS technology. Other chemistries, including traditional lead acid batteries, can be used as well as other technologies such as a “flow” ESS using chemicals such as vanadium. ESS can be located inside a building or, in the case of larger systems, outdoors in appropriate weatherproof enclosures.

When located within a building, the ESS is usually installed in cabinets within mechanical and electrical rooms, and will rely on the base building support systems. When installed outside a building, the enclosures usually contain thermal management systems, supporting electrical and fire protection equipment.

Results from recent free burn tests combined with ongoing research and development have reinforced the following best practices for safety and property protection associated with ESS:

• Lithium-ion, and lithium metal polymer battery systems should be provided with an approved device to preclude, detect, and control thermal runaway (generally found within the Battery Management System).
  
• ESS should incorporate appropriately certified inverters/inverter systems. An inverter is the hardware and embedded software that converts DC battery output to AC electricity for use on the power grid. An ESS should also comply with other recognised safety standards which address risk assessment and controls.
  
• Most ESS will be remotely configurable and connected to the Internet. In order to prevent an intentional or inadvertent cyber-induced failure to the ESS, electrical grid, etc., robust cybersecurity controls must be incorporated within ESS. Security cannot be an afterthought and it needs to be “baked into” the system design. Furthermore, cyber risk assessments need to be conducted and vulnerabilities routinely patched/updated on a regular basis as threats evolve. An appropriate standard to reference is the International Society of Automation (ISA) 99.
  
• Battery systems inside buildings should be housed in a noncombustible, locked cabinet, or other enclosure to prevent access by unauthorised personnel unless located in a separate equipment room accessible only to authorised personnel. In addition, the room housing the batteries should comply with local building codes and other appropriate regulatory requirements. In most cases it is recommended that the batteries be located in a room which is configured as a separate fire compartment from the remainder of the building. The room should be externally accessible for manual firefighting operations.
  
• An ESS located outdoors should be well away from critical buildings or equipment and located in a non-combustible enclosure. Sufficient clearance should be maintained around the installation to provide for fire service access.
  
• Lithium-ion, lithium metal polymer, or other types of sealed batteries with immobilised electrolyte do not require spill control.
  
• Battery ventilation should comply with recognised regulatory, industry and manufacturers’ standards.
  
• Advisory and warning signage in accordance with recognised regulatory, industry and manufacturers standards should be installed.
  
• It is recommended that an approved, monitored, automatic smoke detection system be installed in Li-Ion ESS areas. Sprinkler protection or clean-agent gas fire suppression within the room or enclosure should be designed and installed to the relevant code requirements.
  
• Portable fire extinguishers should be provided in the room or in close proximity to the enclosure. In seismically active areas, battery systems should be seismically braced in accordance with the building code.
  
• A comprehensive operations and maintenance programme is necessary to ensure all monitoring and protective devices are in good working order. Regular inspections should be undertaken to ensure the battery systems are not overheating, or show signs of malfunction. Annual thermographic scanning can help ensure the ESS system is operating within normal parameters.
  
• All ESS systems should have online condition monitoring systems for battery room temperature, and battery modules for charging, temperature, state of charge, state of health, resistance, capacitance, and alarm. The system should be fitted with temperature monitoring which incorporates a high temperature alarm for the battery room and container. Temperatures should be monitored at a constantly attended location.
  
• Installations should have emergency power disconnects to ensure manual, remote, and local disconnect is possible adjacent to the unit.

ESS are here to stay and the number and capacity of installations can be expected to grow exponentially over time in parallel with the grow of renewable power generation technologies such as Solar PV. In fact, they are expected to play a key role as the world transitions to a clean energy future.

These systems fill some of the gaps, and compensate for some of the shortcomings of both conventional power generation and renewable energy production. They can help to lessen the burden on an aging electrical grid and reduce our carbon footprint by reducing short term peaks in demand, managing grid instability and smoothing the intermittency issues associated with renewables. Therefore, it is crucial to build and install the most reliable and effective systems possible by designing and protecting them with the best available technology and practices.