Solar (PV) refrigeration of vaccines
Practical Action
Batteries
The battery most commonly used is the lead acid type, long life, deep cycle batteries are
preferred. A capacity to run the refrigerator for five days without sun is recommended.
Charge regulator
The charge regulator maintains the power supply within the current and voltage range tolerated by
the refrigerator and prevents overcharge of the battery. Some models include an audible alarm or
warning light to signal when battery voltage becomes low. Lightning surge protection must be
provided for tropical areas.
Array and support structure
The solar array can be for roof or ground mounting. The array size for a refrigeration system is
calculated to meet the power requirements of the system, given the solar irradiance data for the
proposed site. The typical requirement is 150 - 200 Wp of photovoltaic modules.
Performance
The energy consumption of a photovoltaic vaccine refrigerator is typically 400 - 800 watt-hours
per 24 hours for a 100-litre refrigerator without icepack freezing and at +32°C ambient
temperature. At +43°C ambient temperature and freezing 2kg of ice packs per 24 hours the
energy consumption of the same refrigerator would rise to about 900 - 1900 watt-hours per 24
hours. It is very important not to overload a solar refrigerator as this increases energy consumption
considerably.
A good vaccine refrigerator should be able to maintain correct internal temperatures for at least
ten hours in the event of being disconnected from the battery and solar array.
Costs
The output of a photovoltaic array will vary according to the location at which it is to be installed
and the refrigerator energy consumption will depend on local climate. Therefore the size of the
solar array, the battery storage capacity and hence the system cost will vary depending on
location. Typical system costs are in the range of US $3,500 - 7500 excluding transport and
installation.
Products available
The Department of Vaccines and Biologicals of the World Health Organisation, in its
Immunisation Systems Series publishes, every two years, a document entitled 'Product
Information Sheets'. This catalogues equipment that has undergone tests to verify their
performance is of a standard acceptable to the World Health Organisation (WHO) and United
Nations Children Fund (UNICEF). The document may be obtained from: The V & B Document
Centre, Department of Vaccine and Biologicals, World Health Organisation, CH-1211 Geneva 27,
Switzerland. (Website: http://www.who.int/vaccines-documents, email: vaccines@who.int )
Suppliers
Note: This is a selective list of suppliers and does not imply Practical Action endorsement or
promotion.
Dulas Ltd., Dyfi Eco Park, Machynlleth, Powys
SY20 8SX
United Kingdom
Tel: +44 1654 705 000
Fax: +44 1654 703 000
E-mail: solar@dulas.org.uk
Website: www.dulas.org.uk/
Bright Light Solar
The Old School
Eglwysfach
Machynlleth
SY20 8SX
United Kingdom
Tel & Fax: +44 (0)1654 781 241
E-mail: ian.tansley@brightlightsolar.com
Website: http://www.brightlightsolar.com
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