Reliable Vaccine Refrigerators
Kerosene-powered refrigerators have been widely used throughout the world to
provide cold storage for vaccines. In locations where there is a reliable supply
of high-quality kerosene, these systems have provided a valuable service.
However, this type of refrigerator is subject to a high percentage of
lost vaccines due to unsati8factory temperature control and excessive downtime
when the supply or quality of the fuel is poor. In regions where bottled gas is
readily available at reasonable prices, gas-powered refrigerators are providing
a dependable alternative to kerosene because of the higher quality fuel.
Until recently, kerosene and bottled gas refrigerators were the only practical
means of storing vaccines. Now a newer power system
technologyPhotovoltaicsoffers an alternative. Photovoltaic-generated
electricity is used to power conventional vapor-compression refrigerators, the
type most of us have used all of our lives, units familiar to refrigeration
mechanics all over the world. The benefits of photovoltaic-powered units are
causing decision makers to reconsider their use of kerosene and gas-powered
This document provides information on which to base a decision about procuring
vaccine refrigerators. Photovoltaic systems make good sense where refrigeration
is required and there is no access to reliable grid electricity, and where
previous use of kerosene refrigeration has proven to be troublesome because the
fuel is of poor quality or there are problems with delivery.
Photovoltaic modules convert sunlight
directly into electricity in a process that is both elegant and simple.
The cells in the modules are made from silicon, the most abundant
element on earth after oxygen. Photovoltaic modules have no moving
parts, which makes them inherently more reliable than other energy
sources. They are appropriate for many applications, especially where
conventional electric utility service is not available.
Rural Health Clinic Needs
the advantages of Photovoltaics, a number of factors are slowing the
rate at which the technology is being used. They include:
of knowledge about and familiarity with photovoltaic technology and
its advanced state of development for many applications.
and uncertainties associated with procuring photovoltaic systems,
including sizing and specification of appropriate components.
of problems developing after the systems have been purchased and
uncertainty concerning their resolution.
initial cost, which is often considered more heavily than the
extremely low operating cost.
that occurred when photovoltaic refrigeration systems were a new
technology; most of them have been eliminated.
National Laboratories, through its Photovoltaic Systems Design
Assistance Center, offers technical support to minimize the risk
associated with procurements and to help ensure that only reliable and
long-lasting systems are purchased. The Design Assistance Center is part
of the U.S. Department of Energys National Photovoltaic Program.
rural health clinic often has needs for electricity other than vaccine
refrigeration, and they can be met by photovoltaic systems. Lighting and
communications are commonly powered by photovoltaic systems because they
are the most economic for small energy needs. Photovoltaic lighting
systems supply reliable, high-quality light without the soot and
possible danger of kerosene or other flame-based illumination. Batteries
can be counted on to provide required energy for emergency
communications when they are kept charged by a photovoltaic system. In
addition, a health clinic could use photovoltaic-generated electricity
to power a television set and videocassette recorder for health-related
is easy to envision the situation in which electricity supplied by a
photovoltaic system to a rural health clinic could dramatically increase
the importance of the clinic in the community, enhancing its ability to
perform its function. In such a case, a photovoltaic- powered vaccine
refrigerator would simply be part of the health clinic power usage.
The systems initial capacity to generate power can be
increased simply by adding modules and batteries.
a vaccine has made the often lengthy journey to a village health clinic,
it is imperative that the refrigerator maintain the vaccine at the
proper temperature to ensure its viability. Spoiled vaccines not only
are uselessthey can undermine local confidence in the entire
immunization program. Thus, refrigerators used for vaccine storage must
be able to maintain a constant temperature. The ability to control the
temperature precisely distinguishes a refrigerator powered by
Photovoltaics from one powered by kerosene or bottled gas.
systems use vapor-compression refrigerators, and their temperature is
thermostatically controlled. This means that their internal temperature
is maintained constant no matter how the external temperature changes.
The vapor-compression process also responds rapidly when conditions
change inside the refrigerator, for example when the door is opened, or
items are added to the shelves. The time required to compensate for most
changes is about 10 minutes.
absorption refrigerators used with kerosene and bottled gas do not at
present have thermostatically controlled interior temperatures. This
means that as external temperatures change, so do the internal
temperatures. The internal temperature is adjusted by altering the
intensity of the flame. Typically, the user monitors the internal
temperature with a thermometera good practice for any kind of vaccine
refrigeratorand then adjusts the flame accordingly. In practice, this
usually means turning the flame down in the evening and up in the
morning. In addition, the time required for the refrigerator to respond
to door openings and added internal load is significantly longer than
for vapor-compression units.
change in thermostat setting will be realized in 10 or 15 minutes in a
vapor-compression refrigeratora similar change in flame for an
absorption refrigerator may take 8 to 10 hours to achieve.
Characteristics of Vapor-Compression
precise and stable temperature control of vapor compression
refrigerators makes them particularly well suited for vaccine
storage, provided reliable electricity can be supplied.
compressor drives the vapor-compression process and requires either
electrical or mechanical power input.
mechanical power can be used, as in automotive air conditioners, an
electric motor is the most common device to power the compressor.
for the motor can be supplied from an electric utility company,
photovoltaic modules, batteries, or other electric generators.
powered vapor-compression refrigerators are by far the most common
type refrigerator in the world; they are also the most reliable,
durable, and easiest to maintain.
of Absorption Refrigeration
control of heat transfer processes is less precise than electrical
control, and it takes much longer to produce a desired temperature
change within an absorption refrigerator.
precise and stable temperatures requires user attention at least
systems rely on heat transfer, chemical processes, and gravity flow
of fluids rather than on electrical or mechanical power.
bottled gas, solar thermal, or electric power can be used, the heat
for absorption systems is most often supplied from burning kerosene.
vapor-compression refrigeration has the advantages of control and
response time over absorption refrigeration for all small refrigeration
applications, including vaccine storage. Absorption refrigeration should
only be used when a reliable power source for a vapor-compression system
is unavailable, or when it can be shown that costs of absorption systems
are lower than vapor-compression alternatives and the absorption system
can provide an equivalent degree of cooling for the vaccines.
Photovoltaic-Powered Vaccine Refrigeration
photovoltaic-powered vaccine refrigeration system has four major
components, as illustrated.
photovoltaic modules in the array convert sunlight directly into
electricity to power the compressor of the vaccine refrigerator. Because
sunlight is not available at nighttime or during periods of poor
weather, rechargeable batteries are used to store electric energy. A
properly designed and maintained battery subsystem will allow the
refrigerator to operate a week or more without sunlight.
charge controller regulates the flow of electricity to protect the
batteries from overcharging and over-discharging, either of which will
shorten the lifetime of the battery.
Powered by a Photovoltaic System
Photovoltaic systems require little preventive maintenance and demand
little of the users time. As with all systems, however, it is
important to perform a minimal amount of maintenance to ensure the
system will function properly.
Daily maintenance for photovoltaic systems involves checking the
refrigerators temperature and operating lights; no adjustments
are normally required.
Weekly maintenance for photovoltaic systems involves checking for
excessive ice buildup and defrosting if necessary. Usually
defrosting is only necessary several times a year.
Monthly maintenance for photovoltaic systems involves checking for dirt
buildup on the array and refrigerator condenser, checking the level
of electrolyte in the battery, and checking the battery terminals
for corrosion. The
above items only require action when a problem is noted, and the
maintenance required is simple.
Photovoltaic systems are inherently reliable, but as with anything,
improper use can reduce their reliability, It is important that
users be educated about their systems and trained in their use. This
will allow them to realize the high level of reliability that is
possible with these systems.
Installation, Service and Repair
skills involved in installation, service and repair are few and can
be learned readily with appropriate education and training programs.
Once the systems are installed, the amount of time the
photovoltaic refrigerators are not running because of planned or
unplanned service and repair is small, as long as repairmen with
adequate training are available.
possible, materials used in the systems design should be
available locally, or at least in the region. This will probably
include mounting hardware and wiring devices. The design should not
be too rigid and should allow for possible substitutions for
specified components when necessary.
The vapor-compression refrigerator is known world-wide and in
most places can be serviced locally.
subsystem for energy storagethe battery and charge
controlleris critical to the proper operation of the photovoltaic
refrigeration subsystem. Without
energy storage, the refrigerator will not function at night or in
poor weather. Unfortunately, this subsystem is often taken for
granted, with the thought that a battery is just a battery.
Consequently, battery problems are the most frequent cause of
failure in a photovoltaic system.
battery must be designed for many cycles of deep discharge. The
current EPI recommendation is for 1000 cycles to 50% discharge,
which will provide a life for the battery of roughly two to three
years. A requirement more consistent with the lifetime of the array
and the refrigerator is 1500 cycles to 80% discharge, which would
provide a battery life of eight to ten years. The cost of such a
battery is only slightly more than for the former type.
is important that the charge controller be designed for the specific
battery being used, because various types of batteries have
different requirements regarding the upper and lower voltage limits
and the charge rate as the battery approaches full charge. A
properly designed and maintained energy storage subsystem will
provide years of trouble-free operationbut its design and
maintenance are crucial to this operation.
Kerosene-Powered Vaccine Refrigeration Systems
kerosene-powered vaccine refrigeration system has the components
wick inside the burner is in contact with kerosene in the fuel tank. The
flame from the wick provides heat energy which drives the absorption
process. The exhaust gases and particulates from the burning process
pass through the flue and are exhausted in the surrounding air (often
inside the health clinic).
winder rod is used to adjust the flame height. A person controls the
temperature within the refrigerator by manually raising and lowering the
height of the flame. The rate of heat transfer from the burner to the
generator, which determines the amount of cooling produced, is affected
by the condition of the burner, wick, flue and kerosene. As soot builds
up on the generator, heat transfer through the generator is slowed, and
it becomes increasingly difficult to maintain temperatures within the
prescribed 00C to 8~C range.
temperature in a kerosene system is manually controlled by
adjustment of the flame. Temperature control is not precise, and the
time for the system to respond to a change in setting is several
systems require frequent preventive maintenance.
maintenance for kerosene systems involves adjusting the flame
setting to maintain proper temperatures, usually twice a day.
maintenance for absorption systems involves checking for excessive
ice buildup and defrosting if necessary, filling the fuel tank,
cleaning the flue and baffle,
disassembling and cleaning the burner, and trimming the
maintenance for kerosene systems involves checking for dirt buildup
on the condenser and absorber and cleaning them when necessary, and
thoroughly cleaning the fuel tank.
kerosene refrigerators have no thermostat, control of the interior
temperature is dependent on inspecting a thermometer and manually
adjusting the temperature. Control of the temperature is, therefore,
less reliable than in thermostatically controlled vapor-compression
refrigerators. Also, the reliability of a kerosene refrigerator is
strongly affected by the availability of fuelas well as its
qualityand by how the refrigerator is used.
Installation, Service and Repair
of kerosene systems is straightforward. However, downtime for both
scheduled and unscheduled service is more frequent than for
Economic Comparison of Photovoltaic and
procuring a vaccine refrigerator, the primary goal is long-term reliable
cold storage of vaccines so that increased immunization coverage and
improved health care can be attained. Another goal is to do this at the
least cost over the life of the refrigeration system. Before considering
the economics of photovoltaic refrigeration systems, examine the
following flowchart to help in making a decision about this technology.
simple yes/no decisions may clearly favor photovoltaics or
The following discussion is for those who determine that
examining economic trade-offs makes sense.
the characteristics of the two types of systems are so different,
economic comparisons are often confusing. For example, the lifetime of a
kerosene-powered vaccine refrigerator is typically about five years. For
a photovoltaic system, on the other hand, the array has an expected
lifetime of more than 20 years, and the vapor-compression refrigerator
has an expected lifetime of about ten years. Using current EPI
guidelines, batteries will last only two to three years, but this can be
extended at little cost to as much as ten years by specifying batteries
designed for long cycle life and deep discharge.
initial cost for installed kerosene systems is about $1500 (late 1988).
The installed cost for a system powered by photovoltaics is higher. A
complete photovoltaic-powered system with a 30-liter refrigerator and no
ice-making capability currently sells for less than $1800. The
WHO/UNICEF EPI Technical Series indicates that a volume of 25 liters is
sufficient to store 100,000 doses of vaccine. A larger photovoltaic
system with a 30-liter freezer and a 50-liter refrigerator currently
sells for about $3400. Because fuel, service, repair, and replacement
costs are high for kerosene systems, the cost per delivered dose of
vaccine over the life of the system may still be less for the system
powered by photovoltaics than for one using kerosene.
Criteria for Making Decisions
number of criteria may be used to make procurement decisions involving
vaccine refrigerators. Representative criteria include the following:
first cost. Decisions based on this criterion use a short-term
perspective. Unfortunately, the short-term nature of budget cycles,
the partitioning of budgets into restrictive categories, and
procurement policies often result in the use of this criterion only.
life-cycle cost. This may be expressed as either total cost over the
systems lifetime, or cost per effective dose of vaccine over the
same time period. All costs must be included, especially an estimate
of the value of lost vaccines.
reliability. For vaccine refrigeration systems, reliability means a
minimum of downtime, ability to continuously maintain stable
temperatures, and components with long lifetimes.
convenience and productive use of time. The more simple and
convenient the unit is to operate and maintain, the more likely it
is that maintenance will be performed and the more time the health
professional can devote to health-related matters.
factors. Other criteria that might be considered include
susceptibility to energy shortages and reductions in operating
budgets, environ mental concerns, etc.
the criteria discussed above, the only one that typically favors a
kerosene system procurement is lowest first cost. First costs are often
poor measures of longer term cost effectiveness. Consequently,
procurement officers are encouraged to give consideration to the other
criteria, especially as they apply to improving and sustaining the cold
WHO/UNICEF EPI Technical Series provides documents in English, French,
and Spanish covering
EPI product information sheets
Guides on the implementation of solar energy for the EPI
EPI training information sheets.
documents provide information on available hardware and suggestions on
designing systems and specifying components for procurement actions.
They can be obtained from
Nations Childrens Fund
New York, NY 10017
Telex 234292 UNICEF New York
should be given to options for specifications in the EPI Technical
Current EPI Recommendation
set capable of 1000 cycles to 50% depth of discharge. Battery can
be housed beneath refrigerator.
charge regulatoronly specifies performance.
deals with transportation to central receiving facility.
types are approved, and all freeze ice.
1500 cycles to 80% depth of discharge, housed separately from
refrigerator (for ease of maintenance and replacement).
a multi-year field life regulator to be matched to battery.
size, weight, assembly requirements, and safety constraints to put
the system in the field.
refrigerator only, one without a freezer, may be adequate.
suggestions are offered to avoid problems in the field. The systems
chosen following them will be low in maintenance and cost-effective. A
recommendation for all refrigerators, and the first step in solar
design, is to minimize the power requirements. Over sizing increases
fuel requirements, the size of the power system, and maintenance. The
hints for saving energy and minimizing the size and cost of a vaccine
storage refrigerator are the same for all types: buy only the size that
is required for a given use, do not make ice unless it is needed, open
the refrigerator as infrequently as possible, and only store essential
items in the unit.
an aid to the design specification, we have constructed a one-page form
that contains much of the information specific to photovoltaics. It is
included at the end of this report.
Technical and Procurement Assistance Available
National Laboratories, through its Photovoltaic Systems Design
Assistance Center, is now offering unique support services that smooth
the procurement process, minimize any risk, and help ensure the
reliability of photovoltaic-powered vaccine refrigeration systems.
support services are offered with the realization that there have been
some less than optimal experiences with photovoltaic systems in the
past. Most of these problems have been minor from a technical
standpoint, but major from that of the user. Through these support
services, it is Sandias goal to avoid such problems with future
procurements. In this way, buyers can take advantage of the excellent
match that exists between photovoltaic technology and vaccine
refrigeration needs throughout the world.
specific technical support and procurement services offered by Sandia
in the use of appropriate technical specifications, including the
proper combination of functional requirements for the system and
design requirements for components.
results of on-going laboratory evaluations of both photovoltaic and
kerosene-powered vaccine refrigeration equipment.
education and training programs, materials, and instructors for
recommendations on the appropriateness of photovoltaics for specific
applications and conditions.
information and publications on the use of photovoltaics for water
pumping, water purification, lighting and rural electrification.
additional technical assistance for projects with high impact