Page 101 - Alternative Energy Systems in Building Design

STORAGE BATTERY TECHNOLOGIES 77

Storage Battery Technologies

One of the most significant components of solar power systems is the battery backup
system frequently used to store electric energy harvested from solar PV systems for
use during the absence of sunlight, such as at night and during cloudy conditions.
Because of the significance of storage battery systems and the fact that they represent
a notable portion of the overall installation cost, it is important for design engineers
to have a full understanding of the technology. More important, the designer must be
mindful of the hazards associated with handling, installation, and maintenance.
To provide an in-depth knowledge about the battery technology, this section covers
the physical and chemical principles, manufacturing, design application, and main-
tenance procedures of the storage battery. This section also attempts to analyze and
discuss the advantages and disadvantages of different types of commercially available
solar power batteries and their specific performance characteristics.

HISTORY

In 1936, while excavating the ruins of a 2000-year-old village near Baghdad known as
Khujut Rabu, workers discovered a mysterious small jar identified as a Sumerian arti-
fact dated to 250 BC. This jar, which was identified as the earliest battery, was a 6-in-
high pot of bright yellow clay that included a copper-enveloped iron rod capped with
an asphalt-like stopper. The edge of the copper cylinder was soldered with a lead-tin alloy
comparable with today’s solder. The bottom of the cylinder was capped with a
crimped-in copper disk and sealed with bitumen, or asphalt. Another insulating layer
of asphalt sealed the top and also held in place the iron rod that was suspended into
the center of the copper cylinder. The rod showed evidence of having been corroded
with an agent. When the jar was filled with vinegar, it produced about 1.1 V of electric
potential.
A German archaeologist, Wilhelm Konig, who examined the jar came to the surprising
conclusion that it was nothing less than an ancient electric battery. It is stipulated that
the Sumerians made use of the battery for electroplating inexpensive metals such as
copper with silver or gold. Figure 3.38 shows the actual Baghdad battery, and
Fig. 3.39 is an illustration of the elements of the Baghdad battery.
Subsequent to the discovery of this first battery, several other batteries were unearthed
in Iraq, all of which dated from the Parthian occupation between 248 BCE and 226 CE. In
the 1970s, German Egyptologist Arne Eggebrecht built a replica of the Baghdad battery
and filled it with grape juice, which he deduced ancient Sumerians might have used as
an electrolyte. The replica generated 0.87 V of electric potential. Current generated from
the battery then was used to electroplate a silver statuette with gold.
However, the invention of batteries is associated with the Italian scientist Luigi
Galvani, an anatomist who, in 1791, published works on animal electricity. In his
experiments, Galvani noticed that the leg of a dead frog began to twitch when it came
in contact with two different metals. From this phenomenon he concluded that there
is a connection between electricity and muscle activity. Alessandro Conte Volta, an