Surgery and Healing in the Developing World - Dartmouth-Hitchcock

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72 Surgery and Healing in the Developing World
Figure 1. A 10 cm crystalline silicon
solar cell before encapsulation in a
module. (Photo by R. Mitchell, courtesy
NREL/PIX.)
(less than one kilowatt) photovoltaic systems at small rural health clinics. Perhaps
the most important application for PV at these clinics is that of reliable and stable
electric power for vaccine refrigeration and maintenance of the vaccine cold chain.
Vaccines must be consistently stored at temperatures between 0 o and 8 o C to retain
their potency. There are now over 5000 PV-powered vaccine refrigerators in use
worldwide. Unlike absorption refrigeration, fueled by propane or kerosene,
PV-powered refrigerators are compressor-based and allow enhanced temperature
stability for long-term vaccine storage. The technology is mature and endorsed by
the Expanded Programme on Immunization of the World Health Organization. 2
The next most important applications of PV in these clinics are lighting and water
disinfection. The need for lighting is obvious. But the water issue is often over-looked.
The World Health Organization attributes thousands of deaths daily to water borne
illnesses. 3 While there are several commonly used chemical methods for small-scale
water disinfection, e.g., chlorine and iodine compounds, they often produce unwanted
taste and odor and require long processing times. Faster, more effective, and
more agreeable water disinfection processing can be obtained by electrical methods.
These include ozone treatment and ultraviolet light exposure. Ultraviolet light irradiation
easily deactivates bacteria and viruses, and there is no risk of over-dosage.
Water disinfection systems specifically designed for use with PV are readily available
and quite inexpensive.
Photovoltaic systems use photovoltaic cells (commonly known as solar cells) to
convert sunlight directly into electric current (Fig. 1). The PV technology is inherently
noiseless, pollution-less, and involves no moving parts. Others candidates for
providing stand-alone remote electric power include wind turbine (windmill) systems
and small hydro-powered (micro-hydro) systems. There have been a number of
successful deployments of these technologies to power remote clinics. This is particularly
true with wind power coupled to a diesel or PV system to form a hybrid
power system. However, both wind and hydro systems are electromechanical in nature
and require the upkeep of rotating machinery including electric generators.
Additionally, their applicability is highly geographically dependent—many areas of
the world do not have the required wind or running water resource. For these reasons,
they are not as elegant a solution for many remote clinic-size energy requirements
as that provided by the photovoltaic option. Indeed, many remote clinics will
not need more than 2000 watt-hours (2 kWh) of electric energy per day. With this in
mind, the present chapter will focus on the description and explanation of small
stand-alone photovoltaic power systems suitable for remote health care facilities.
The sun radiates immense power, i.e., energy per unit time. Most of the sunlight
reaching the earth’s surface has a wavelength between 300 and 2000 nm. (By com-