Using the Sun to Keep Vaccines Cool
A collaboration to develop an environmentally-friendly, affordable, battery-free refrigeration system: Solar Direct Drive Technology
For safe storage of vaccines in countries with limited or unstable power supplies, uninterrupted refrigeration of vaccines is vital. Maintaining the required cold chain from the manufacturer to the child is an enormous challenge, particularly in communities off the main grid or with intermittent electric supply. Weak links in a system can result in the loss of millions of doses of vaccines.
UNICEF, UN partners, academia and industry have collaborated to develop an environmentally-friendly, affordable, battery-free refrigeration system. In March 2010, the World Health Organization (WHO) prequalified the Solar Direct Drive, a refrigeration system which utilises the solar array to directly drive a compressor which cools or freezes a liquid (we now have different designs) which in turn cools the vaccine. As such, the refrigeration cycle does not rely on electric battery to provide energy to run the compressor.
The temperature in kerosene refrigerators is almost impossible to maintain between the required +2 and +8 Celsius, putting at risk freeze-sensitive and expensive vaccines.
UNICEF procures more than 2.5 billion doses of vaccines annually
Successful public health programs rely on the availability of high-quality vaccines to protect children from disease. Every year, UNICEF procures more than 2.5 billion doses of vaccines. These vaccines must be continuously maintained at the correct temperature to remain effective. The system of cooling equipment that ensures that vaccines are kept at the proper temperature as they are distributed from the manufacturer to the locations where they are administered is called the cold chain. Weak links in the current cold chain in remote areas or in places with intermittent power supply results in large quantities and millions of dollars worth of spoiled vaccines each year.
For more than 20 years, kerosene absorption refrigerators and very expensive solar-powered refrigerators have been the only viable solution for storing vaccines. However, the temperature in kerosene refrigerators is almost impossible to maintain between the required +2 and +8 Celsius, putting at risk freeze sensitive and expensive vaccines. They also have many consumable components that are attractive for other uses, making the fridges inoperable, and emit significant levels of carbon. While conventional solar powered refrigeration using lead- acid batteries are costly due to batteries needing to be replaced every 5-7 years, and used batteries are difficult to dispose.
Most Sub-Saharan countries and middle and low income countries have been adversely affected by climatic changes that contribute to power outages. In many countries reliant on hydro energy generation, droughts result in low power generation, while in other areas, floods effect energy infrastructure.
CONTEXT AND ORIGIN
A key impetus for the project was ensuring the sustainable and safe storage of vaccines in hard to reach areas without electricity and other sources of energy, as was climate change and the possible application for safe food storage.
The United Nations Environment Programme Division of Technology Industry and Economics (UNEP-DTIE) invited partners including Greenpeace, UNICEF and industry to the table in 2001 to work to find a better refrigeration solution.
SYSTEM OR PROCESS EXPLANATION
Partners convened and commitments for funds and resource contribution (both information and expertise) were provided. For example, UNICEF provided guidance in the product’s development, performance requirements as well as technical expertise.
An important element of the project was that industry had to agree that the complete technology would be open-source and made available free of charge to any interested party with the goal of encouraging other suppliers to refine and develop similar products. This in turn would ensure a healthy market.
The project partners had no commercial interest in the project, with the sole mandate being to develop a technology, make it freely available to interested manufacturers worldwide, and promote its uptake internationally.
Industry partner, Vestefrost, developed a 19.5 litre prototype unit utilising Solar Direct Drive technology. A unique feature of the technology is that the energy of the sun is stored in ice instead of in batteries. The equipment is powered by renewable energy from the sun collected via photovoltaic solar panels. This is converted into direct current electricity which starts a compressor that in turn runs the refrigeration cycle and the ice bank maintains a consistent temperature in the unit. At night, the ice compartment keeps the vaccines at the required temperature.
The World Health Organization (WHO) prequalified the Solar Direct Drive technology in 2010, prior to which UNICEF Supply and cold chain programme experts, in conjunction with partners did 18 months of field testing in Senegal, Indonesia and Cuba, the goal of which was to test the unit in different climatic conditions to determine performance.
The WHO prequalification process allowed the system to be further tested in a laboratory setting at different climatic conditions – temperate, moderate and hot zone ranges. Based on these results, the first generation Solar Direct Drive technology was prequalified for use in moderate zones (up to 27C). However since the development of the first model, there has been an avalanche of research and development from the cold chain industry, with several new suppliers receiving prequalification for units utilising the Solar Direct Drive technology, notably Palfridge in Swaziland, True energy UK and SunDanzer in the USA.
The second generation equipment is suitable for temperatures of up to 32C, and work is currently underway on a third generation for regions with temperatures up to 43C.
As well as temperature specific alternatives, larger units are coming to market including a 21 litre unit from a Chinese manufacturer, and testing will also commence on a 100 litre model.
The estimated cost per unit is $USD 2500 but unlike absorption and solar powered battery units, there are no recurring costs after the initial investment in units utilising Solar Direct Drive technology.
• Eliminates use of fossil fuels by relying on solar energy
• Eliminates the use of fluorocarbons by using hydrocarbons.
• Eliminates the use of kerosene. Average kerosene cooler uses 292-365 litres of kerosene each year. There are about 100,000 kerosene coolers in the world.
• Kerosene is a dirty fuel, harmful to human health.
Ice bank ‘batteries’ versus lead batteries
• Batteries are vulnerable due to degradation and theft.
• Analysis shows that the energy content in ice and in lead batteries is of the same order of magnitude.
In the first year after pre-qualification more than 60 units were purchased by UNICEF country offices including Kenya, where units have been installed in a very remote region, Haiti, Papua New Guinea, Indonesia, Vanuatu and Rwanda as part of a UNICEF pilot. The general feedback on the technology has been positive.
The next step is looking at larger storage capacities, as well as refining the technology. As part of the pilot, Cold Chain Logistics information is being collected and shared between UNICEF Supply and Programme Division. Partners in various sites in the world also continue tests on operation suitability in varying climatic condition.
The expectation and preliminary indication of demand over the next 5-10 years is significant as all countries currently using absorption refrigerators move toward Solar Direct Drive technology.
Thanks to this technology, millions of children will have access to safe vaccines in these unfortunate and disadvantaged locations of the world. It also has great potential in emergency circumstances, such as natural disasters or war conditions, where power infrastructure has been interrupted or destroyed.