Lead acid batteries are the oldest and most mature technology available. They will be
discussed in detail later in this section.
Other examples are nickel-metal hydride (NiMH) and nickel cadmium (NiCd)
batteries. NiMH batteries have a high energy density, which is comparable to that of
lithium-ion batteries (discussed below). However, NiMH batteries suffer from a high rate
of self discharge. On the other hand, NiCd batteries have much lower energy density than
lithiumion batteries. Furthermore, because of the toxicity of cadmium, NiCd batteries are
widely banned in the European Union for consumer use. Additionally, NiCd batteries
suffer from what is called the memory effect: the batteries loose their usable energy
capacity if they are repeatedly charged after only being partially discharged. These
disadvantages make NiMH and NiCd batteries unsuitable candidates for PV storage
systems.
Lithium-ion batteries (LIBs) and lithium-ion polymer batteries, which are often
referred to as lithium polymer (LiPo) batteries, have been heavily investigated in recent
years. Their high energy density has already made them the favourite technology for light
weight storage applications, for example in mobile telephones. However, these
technologies still suffer from high costs and low maturity.
The last and most recent category of batteries that we will discuss in this treatise are
redox flow batteries. Lead acid batteries and LIBs, the two main storage options for PV
systems, are similar in the sense that their electrodes undergo chemical conversion during
charging and discharging, which makes their electrodes degenerate with time, leading to
inevitable ‘ageing’ of the battery. In contrast, redox flow batteries combine properties of
both batteries and fuel cells, as illustrated in Figure 19.20. Two liquids, a positive
electrolyte and a negative electrolyte are brought together, separated only by a membrane,
which is only permeable to protons. The cell can thus be charged and discharged without
the reactants being mixed, which in principle prevents the liquids from ageing. The
chemical energy in a redox flow battery is stored in its two electrolytes, which are stored
in two separate tanks. Since it is easy to make the tanks larger, the maximal energy that
can be stored in such a battery is therefore not restricted. Further, the maximal output
power can easily be increased by increasing the area of the membrane, for example by
using more cells at the same time. The major disadvantage is that such a battery system
requires additional components such as pumps, which makes it more complicated than
other types of batteries.
discussed in detail later in this section.
Other examples are nickel-metal hydride (NiMH) and nickel cadmium (NiCd)
batteries. NiMH batteries have a high energy density, which is comparable to that of
lithium-ion batteries (discussed below). However, NiMH batteries suffer from a high rate
of self discharge. On the other hand, NiCd batteries have much lower energy density than
lithiumion batteries. Furthermore, because of the toxicity of cadmium, NiCd batteries are
widely banned in the European Union for consumer use. Additionally, NiCd batteries
suffer from what is called the memory effect: the batteries loose their usable energy
capacity if they are repeatedly charged after only being partially discharged. These
disadvantages make NiMH and NiCd batteries unsuitable candidates for PV storage
systems.
Lithium-ion batteries (LIBs) and lithium-ion polymer batteries, which are often
referred to as lithium polymer (LiPo) batteries, have been heavily investigated in recent
years. Their high energy density has already made them the favourite technology for light
weight storage applications, for example in mobile telephones. However, these
technologies still suffer from high costs and low maturity.
The last and most recent category of batteries that we will discuss in this treatise are
redox flow batteries. Lead acid batteries and LIBs, the two main storage options for PV
systems, are similar in the sense that their electrodes undergo chemical conversion during
charging and discharging, which makes their electrodes degenerate with time, leading to
inevitable ‘ageing’ of the battery. In contrast, redox flow batteries combine properties of
both batteries and fuel cells, as illustrated in Figure 19.20. Two liquids, a positive
electrolyte and a negative electrolyte are brought together, separated only by a membrane,
which is only permeable to protons. The cell can thus be charged and discharged without
the reactants being mixed, which in principle prevents the liquids from ageing. The
chemical energy in a redox flow battery is stored in its two electrolytes, which are stored
in two separate tanks. Since it is easy to make the tanks larger, the maximal energy that
can be stored in such a battery is therefore not restricted. Further, the maximal output
power can easily be increased by increasing the area of the membrane, for example by
using more cells at the same time. The major disadvantage is that such a battery system
requires additional components such as pumps, which makes it more complicated than
other types of batteries.