RESDAS Renewable Energy Systems Design
Assistant for Storage
General recommendations for selection and usage of batteries
|
Battery application types: |
| SLI: |
car battery (Starting, Lighting and Ignition) |
| Heavy duty SLI: |
car battery for more cycling, typically for taxis |
| Industrial: |
stationary standby applications |
| Traction: |
fork-lift trucks |
|
Battery technology types: |
| VRLA: |
(valve-regulated lead-acid) where the electrolyte is immobilized in a gel or
absorptive glass mat (AGM). |
| Flooded: |
where the electrolyte is liquid, and the cells are freely vented. |
| Flat (pasted) plate: |
where the lead grid is pasted with the active material. Always used for the
negative plate, sometimes used for positive plate. |
| Tubular plate: |
where the electrode consists of small lead rods, surrounded with active
material, held within tubes. Used only for the positive electrode. In a tubular
plate battery, the negative plate is always flat (pasted) plate. |
Recommendations:
-
The battery technology (VRLA-GEL, VRLA-AGM, or flooded) should be selected
using this
table.
-
From a performance standpoint, tubular plate batteries are preferred, as they
will probably last longer than flat (pasted) plate batteries.
-
Within technology types it is preferable to choose batteries which are labelled
"solar" or "deep cycle", in that order. “Solar” batteries have been designed
for renewable energy applications while “deep cycle”, although more general,
are designed for usage profiles that are similar to ones that are expected in
renewable based applications.
-
In flat plate batteries thick plates are a better choice than thin plates.
-
In flooded batteries, the ratio of electrolyte volume to nominal capacity
should be as high as possible.
-
In general the ratio of battery mass to nominal capacity (kg/Ah) should be
high.
-
In most renewable energy systems, industrial batteries will perform better than
car batteries, even in systems where cycling is shallow.
-
It is preferable to avoid the use of car batteries for renewable energy
applications if there is an alternative. The common car battery (SLI) battery
is not able to withstand many deep cycles and long periods at low SoC, as
required by many renewable energy applications. As a consequence the common car
battery is likely to fail within a short time (about 1 - 2 years) due to
sulphation, corrosion, or shedding of the active mass from the plates.
-
If the use of a common car battery (SLI) in the renewable energy system cannot
be avoided, the following points should be considered:
-
SLI batteries for taxis, lorries or heavy-duty applications usually have
thicker plates and are more suitable.
-
It is essential to keep an SLI battery close to a fully charged condition and
not to discharge more than 30% of its capacity. This generally requires the use
of a battery with a higher capacity than would normally be called for.
-
Recommended maximum Depth Of Discharge (DoD):
The following table provides a maximum discharge threshold below which
different batteries should not be discharged. This Depth Of Discharge (DoD)
value is general in nature and battery manufactures should be consulted for
specific battery types or brands. As discussed previously, expected battery
life is a factor of many different issues, specifically the aging mechanisms.
Given normal operation, battery life is represented as a curve of the number of
discharge and charge cycles to a specific DoD that the battery can supply
against that specific DoD. This curve, called a cycles to failure curve, is
available from manufactures for most common batteries. Generally speaking, as
the DoD of a cycle increases, the number of times the battery can withstand
that cycle decreases. This curve is not linear, meaning that five cycles to a
90% DoD does not do the same damage as one cycle to 50% DoD, but it is close
and in some models it is assumed to be linear. Generally speaking, limiting the
discharge a certain maximum DoD will increase the life of the battery bank but
it will also increase the initial cost since a larger battery will have to be
used to keep the same available battery capacity.
Maximum discharge thresholds for different battery types.
| Battery type |
Maximum DOD |
| Industrial, tubular plate |
80% |
| Industrial, flat plate |
80% |
| SLI |
30% |
-
To achieve proper life and performance, batteries must be carefully treated:
-
Do not short-circuit the battery terminals. This can cause or the plates to
buckle and the battery to explode, which may expose people to battery acid.
-
The battery should be transported carefully and not subjected to sharp
movements as the case or active plate matter may be damaged)
-
Do not subject a battery to temperatures above 30 °C when in storage or during
operation. Efforts should be made to be sure that batteries are stored and
operated in the temperature range specified by the manufacturer. If no detailed
information by the manufacturer is given, 15 - 20°C should be used for RES
batteries.
-
Do not subject batteries to excessive overcharge, specifically VRLA batteries
that will vent and dry out. Flooded batteries will require more distilled water
and excessive overcharge will damage the battery plate active material.
-
Do not tamper with the vents on a VRLA battery (gassing may then occur rather
than recombination, and the battery may dry-out more quickly).
-
If a battery is stored, then it should be recharged every 6 months, and kept in
a cool place below 25°C.