19.3.1
realizing storage of energy. Therefore it is important to make an optimal choice.
Figure 19.19 shows a Ragone chart, where the specific energy is plotted against the
peak power density. Because it uses a double logarithmic chart, storage technologies with
very different storage properties can be compared in one. Solar energy applications require
a high energy density and – depending on the application – also a reasonably high power
density. For example, we cannot use capacitors because of their very poor energy density.
For short to medium-term storage, the most common storage technology of course is the
battery. Batteries have both the right energy density and power density to meet the daily
storage demand in small and medium-sized PV systems. However, the seasonal storage
problem at large scales is yet to be solved.
Figure 19.19: A Ragone chart of different energy storage methods. Capacitors are indicated with ‘cap’.
The ease of implementation and efficiency of the batteries are still superior to that of
other technologies, such as pumping water to higher levels, compressed air energy storage,
conversion to hydrogen, and flywheels. Therefore we will focus on battery technology as a
viable storage option for PV systems.
Batteries are electrochemical devices that convert chemical energy into electrical
energy. We can distinguish between primary and secondary batteries. Primary batteries
convert chemical energy to electrical energy irreversibly. For example, zinc carbon and
alkaline batteries are primary batteries.
Secondary batteries or rechargeable batteries, as they are more commonly known,
convert chemical energy to electrical energy reversibly. This means that they can be
recharged when an over potential is used. In other words, excess electrical energy is stored
in these secondary batteries in the form of chemical energy. Typical examples of
rechargeable batteries are lead acid or lithium ion batteries. For PV systems, only
secondary batteries are of interest.
Types of batteries
realizing storage of energy. Therefore it is important to make an optimal choice.
Figure 19.19 shows a Ragone chart, where the specific energy is plotted against the
peak power density. Because it uses a double logarithmic chart, storage technologies with
very different storage properties can be compared in one. Solar energy applications require
a high energy density and – depending on the application – also a reasonably high power
density. For example, we cannot use capacitors because of their very poor energy density.
For short to medium-term storage, the most common storage technology of course is the
battery. Batteries have both the right energy density and power density to meet the daily
storage demand in small and medium-sized PV systems. However, the seasonal storage
problem at large scales is yet to be solved.
Figure 19.19: A Ragone chart of different energy storage methods. Capacitors are indicated with ‘cap’.
The ease of implementation and efficiency of the batteries are still superior to that of
other technologies, such as pumping water to higher levels, compressed air energy storage,
conversion to hydrogen, and flywheels. Therefore we will focus on battery technology as a
viable storage option for PV systems.
Batteries are electrochemical devices that convert chemical energy into electrical
energy. We can distinguish between primary and secondary batteries. Primary batteries
convert chemical energy to electrical energy irreversibly. For example, zinc carbon and
alkaline batteries are primary batteries.
Secondary batteries or rechargeable batteries, as they are more commonly known,
convert chemical energy to electrical energy reversibly. This means that they can be
recharged when an over potential is used. In other words, excess electrical energy is stored
in these secondary batteries in the form of chemical energy. Typical examples of
rechargeable batteries are lead acid or lithium ion batteries. For PV systems, only
secondary batteries are of interest.
Types of batteries