19.3.4
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•
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increased grid resistance due to high positive potentials. Further, the electrolyte can dry
out. At high charging voltages, gassing can occur, which results in the loss of water. Thus,
demineralised water should be used to refill the battery from time to time.
Lead acid batteries used in PV applications
One can distinguish lead acid batteries based on the type of plates being used:
In flat plate lead acid batteries the plates are significantly thicker than in the case
of starter batteries, implying a cycle life of 1,000 cycles for a daily depth of
discharge (DDoD) of 20% at 25 ο C.
The positive plates of tubular plate lead-acid batteries are made of porous tubes,
which contain the active mass. These tubes prevent the loss of active mass as a
result of changes in volume, which occur in cyclic operation. The negative plates
in tubular plate batteries are flat plates. The cycle life of this type of battery is
considerably longer than for batteries with flat plates described above. For real
traction applications, such as in forklift trucks, tubular plates with a fairly high
antimony content are used. These batteries have an excellent cycle life, but their
self-discharge is far too high for most PV applications. For these, tubular plates
are used with an antimony content such that the cycle life is still fairly good, but
with a low self-discharge. A typical value for the cycle life is 3,000-4,000 cycles
for a daily depth of discharge of 20%.
In rod plate lead acid batteries the positive plate is made up of rods with the
active mass between them. The plates have a low antimony content. The
construction height of the battery is fairly low, so there is almost no stratification
of acid. This battery has superior properties for PV applications, but is rather
expensive.
One can also distinguish open (vented) and sealed (maintenance-free) lead acid batteries.
In order to make lead acid batteries maintenance-free, all or part of the antimony in the
plates is replaced by calcium. A calcium alloy with a very low antimony content (< 1%)
has a very low self-discharge (approximately 1% per month at 25 °C) and reduces the
splitting of water into oxygen and hydrogen. In most maintenance-free lead acid batteries
the electrolyte is contained either in a gel between the plates or in a micro porous
separator. Oxygen produced at the positive plate can diffuse through the gel or the micro
porous separator and reach the negative plate, where it reacts with hydrogen to form water
again. Maintenance-free lead acid batteries frequently used for PV applications are flat
plate batteries with a gel or micro porous separator, and tubular plate batteries with a gel.
•
•
•
increased grid resistance due to high positive potentials. Further, the electrolyte can dry
out. At high charging voltages, gassing can occur, which results in the loss of water. Thus,
demineralised water should be used to refill the battery from time to time.
Lead acid batteries used in PV applications
One can distinguish lead acid batteries based on the type of plates being used:
In flat plate lead acid batteries the plates are significantly thicker than in the case
of starter batteries, implying a cycle life of 1,000 cycles for a daily depth of
discharge (DDoD) of 20% at 25 ο C.
The positive plates of tubular plate lead-acid batteries are made of porous tubes,
which contain the active mass. These tubes prevent the loss of active mass as a
result of changes in volume, which occur in cyclic operation. The negative plates
in tubular plate batteries are flat plates. The cycle life of this type of battery is
considerably longer than for batteries with flat plates described above. For real
traction applications, such as in forklift trucks, tubular plates with a fairly high
antimony content are used. These batteries have an excellent cycle life, but their
self-discharge is far too high for most PV applications. For these, tubular plates
are used with an antimony content such that the cycle life is still fairly good, but
with a low self-discharge. A typical value for the cycle life is 3,000-4,000 cycles
for a daily depth of discharge of 20%.
In rod plate lead acid batteries the positive plate is made up of rods with the
active mass between them. The plates have a low antimony content. The
construction height of the battery is fairly low, so there is almost no stratification
of acid. This battery has superior properties for PV applications, but is rather
expensive.
One can also distinguish open (vented) and sealed (maintenance-free) lead acid batteries.
In order to make lead acid batteries maintenance-free, all or part of the antimony in the
plates is replaced by calcium. A calcium alloy with a very low antimony content (< 1%)
has a very low self-discharge (approximately 1% per month at 25 °C) and reduces the
splitting of water into oxygen and hydrogen. In most maintenance-free lead acid batteries
the electrolyte is contained either in a gel between the plates or in a micro porous
separator. Oxygen produced at the positive plate can diffuse through the gel or the micro
porous separator and reach the negative plate, where it reacts with hydrogen to form water
again. Maintenance-free lead acid batteries frequently used for PV applications are flat
plate batteries with a gel or micro porous separator, and tubular plate batteries with a gel.