IEEE Power & Energy Magazine - July/August 2014 - 72

table 1. Typical component life spans and associated costs.
Typical Life Span

<1 year

3-5 years

5-10 years

>10 years

>20 years

Components

Lightbulbs
(incandescent)

Lead-acid batteries

Inverter

Charge controller

PV panels

figure 1. PV panels at the Sabongari CCS in Cameroon
(photo courtesy of Michael Wilson).

the sustainability of a system is not a simple univariate,
time-independent binary condition. Rather, it is a continu-
ous, multidimensional dynamic state variable. technical,
environmental, economic, social, and organizational aspects
all influence the sustainability of a project. these key ingre-
dients are all important and interrelated. Careful attention
to each at the planning stages of project can maximize the
potential for sustainability.

Technical Sustainability
Technical sustainability refers to the ability of a system
to meet technical specifications and service expectations
throughout its life span. at the outset of a project, a designer
makes several key decisions and assumptions that either
encourage or jeopardize the prospects for sustainability.

figure 2. Installation of the CCS in Thiou, South Sudan
(photo courtesy of Mou Riiny).
72

ieee power & energy magazine

one assumption that must be made but is subject to wide
uncertainty is how the system will be used postinstallation.
once electricity is available, people often begin climbing the
"energy ladder"-purchasing additional lighting and mov-
ing on to luxury items such as televisions and portable DVD
players that drive up their energy usage. initial expectations
of energy use, therefore, may no longer hold.
the authors once worked on a project to add a micro wind
turbine to a farmer's small PV system. the extra energy
would have allowed the farmer to earn additional income for
his family by recharging his neighbors' mobile phones. the
next morning it was discovered that the charge controller
had disconnected the loads due to low battery voltage. the
battery was drained. after some investigation, it was found
that in anticipation of increased energy, the farmer had pur-
chased additional lighting. he purchased less efficient and
less expensive incandescent bulbs (approximately uS$1
each) rather than the compact fluorescent bulbs (approxi-
mately uS$4.50) he had previously used. in a single day, his
demand increased by a factor of four.
this natural appetite for electricity can and should be
planned for. educating the end user in understandable terms
about basic concepts of efficiency and the system's limita-
tions, as well as designing for future expansion and scalabil-
ity, can guard against failure due to overconsumption.
another important design consideration is the replace-
ment or repair and maintenance of the system. Components
will inevitably fail (see table 1), and the system designer
should plan for this. there are two philosophies about how
this should be done. the first is to select high-end, highly
durable and ruggedized components that offer superior per-
formance in terms of reliability and thus reduce replacement
and repair as well as maintenance frequency. the disadvan-
tages of this approach are that components of this quality
are usually expensive and not easily obtained or supported
locally. the logistics of importing equipment are not trivial.
it is an endeavor potentially rife with corruption and long
delays, and steep duties make already expensive equipment
even more so. the added expense may not be a barrier dur-
ing implementation, but postinstallation-unless the project
has continuing donor support or, better, is financially self-
supporting-a failed component may never be replaced.
the second approach is to use locally available and less
expensive components whenever possible. these may be of
inferior quality but can be less burdensome to replace and
repair. the disadvantages of this approach include more fre-
quent and sometimes more complex maintenance. flooded
lead-acid batteries are less expensive than their sealed
july/august 2014



Table of Contents for the Digital Edition of IEEE Power & Energy Magazine - July/August 2014

IEEE Power & Energy Magazine - July/August 2014 - Cover1
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IEEE Power & Energy Magazine - July/August 2014 - Cover3
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