Page 71 - Energize July 2022

TECHNICAL

manufacturer has a successful track record with the reduction of the depth of discharge to approximately 15% or 30% DOD, tubular
of experience with the production of long lead-acid batteries can present a solid, lower cost business case while providing a predicted
cycle durability cells. When daily discharges 10-years or more of reliable duty-cycle performance.
greater than 50% DOD are required, lead- There are many other interesting alternatives on the way, especially if we talk about
acid will not perform as well as Li-ion. This seasonal storage by power-to-heat or power-to-gas. Meanwhile, it should be understood
is mainly due to conversion of the active that such energy market requirements need standards and regulation. An electrochemical
mass during the charge and discharge storage installation can be extremely expensive if we talk about pure energy storage, and the
reaction and the corresponding active business case for many of these alternatives will take time to justify.
mass softening while the charge/discharge
process takes place. This does not occur Operation and other considerations
with Li-ion cells. Li-ion batteries are limited in their operational temperature range. The most applicable
That means for solar systems with temperature range is 10 to 30°C. Higher temperatures can influence the ageing rate in a
3
smaller capacities (like at-home solar similar manner to lead-acid batteries. At lower temperatures, the risk of overcharging the
rooftops) Li-ion technology may easily cells can lead to the batteries becoming unusable. 4
fulfil the demand at an interesting price Sulphuric acid-based lead-acid batteries are influenced at lower temperatures by the
point when the DOD and the potentially internal resistance of the acid. The charging behaviour can be positively influenced by
better cycle lifetime is taken into account. changes in the charging voltage or additives to the active mass and/or electrolyte.
It should be noted that a lead-acid battery By comparison, Li-ion cells can demonstrate a negative charging behaviour due to the nature
using a tubular plate design (VLA or gelled of the organic electrolyte. This can result in an increase of internal resistance which is several
electrolyte VRLA) can be a good alternative times faster in comparison to lead-acid batteries. The resulting adjustment of the performance
if the DOD is limited to a maximum of 50%. is very challenging and has not been totally solved. Modifying the charging behaviour by voltage
In certain energy storage systems (ESS) adjustment may lead to accelerated ageing and is normally counterproductive.
both lead-acid and Li-ion batteries can play An operation with high currents below 10°C may lead to irreversible capacity loss, driven
a role, especially for areas where 1 to 3 by lithium plating at the anode and possible development of dendrites which can lead to
MWh of energy is required. For example, the danger of a short circuit inside the cell. Figure 8 shows the potential rise in internal
in frequency regulation applications where
the availability of power is required for
short periods to ensure stability of the
power flow on the grid, lead-acid batteries
as well as Li-ion technologies are well
suited for these applications where short
time durations are required (see Figure 7).
In Germany, the installation of power
generation from renewables has led to
serious problems in the regulation of
voltage and frequency with unpredictable
introduction of both demand for and
supply of power into the grid. Thus,
storage of this energy is needed when
Figure 7: Typical profiles for Frequency, battery power demand and SOC
in oversupply and then instantaneously
needed when the supply is gone. Lead-
acid tubular and Li-ion batteries are being
used in many instances to handle this
requirement due to the reduced cost and
capacity requirements.
BAE has engaged in a partnership with
Belectric, an international renewables and
energy storage integrator headquartered
in Germany, to provide a containerized
battery energy storage solution in
Kitzingen, Germany. Used originally as
a pilot, it is now going into commercial
operation and Belectric is engaged in
installing these in multiple sites throughout
Europe. What this example shows is that Figure 8: Development of DC resistance on dependence on SOC high power Li-ion cell (5,9 Ah softpack)

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