BOSS – Installation, Operation and Maintenance Manual
A l e n c o n S y s t e m s L L C - P a g e
|
10
Introduction
Energy Storage Systems Benefits
Energy Storage Systems (ESS) is actively advancing into the portfolio of equipment being
offered by the Renewable Energy Industry. In both new and existing PV installations, ESS helps
to overcome intermittency – a major shortcoming of solar and wind as sources of energy. With
ESS, solar power becomes available on demand, just the same as conventional generation
means such as coal and gas. Today, the majority of ESS deployed and being deployed utilize
Lithium Ion battery technology. The cost of batteries has significantly fallen in the past few years
while the need for energy storage capacity has increased due to the increased levels of
renewables on the Grid. These dynamics have made the case for ESS adoption very attractive.
Energy Storage Systems Challenges
Many megawatt-hours of alternative energy can be stored in large containers filled with Lithium
Ion batteries. Individual battery cells are assembled into modules, modules into racks (stacks)
and racks into containers. A large amount of energy is packed in one space and presents a
danger of a potential explosion if conditions of safe charge and discharge are violated or general
deterioration of battery condition is not detected.
Potential Hazards
Each high voltage battery rack has a positive and negative terminal isolated from the battery
case. If all the positive terminals are connected together and all the negative terminals are
connected together then in the case of a short on one of the battery racks, the rest will rapidly
discharge their stored energy into a shorted component causing a huge current reaching tens of
thousands of amperes and risking an explosion. The isolation deterioration of the battery cells to
the grounded case is one of the major factors of fault in the battery rack that may cause fault
current.
State-of-Charge and State-of-Health
The capacity of lithium ion batteries to store and discharge electrical energy is measured in MWh
or KWh. The amount of
releasable
charge the battery contains at any given time relative to full
capacity of a battery is called State-of-Charge (SOC) and is measured in percentiles:
𝑆𝑂𝐶 =
100%
As batteries age over time as they experience a number of charge/discharge cycles. As such,
their capacity to hold charge diminishes. The degree of degradation of the battery measured as
a percentage of current full capacity to the initial rated capacity is called State-of-Health (SOH)
and is measured in percentiles:
𝑆𝑂𝐻 =
100%
To prevent overcharge of full discharge all battery racks should maintain the same SOC. This
means that charge/discharge current should be controlled according to their SOH.
