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Solar Refrigerators Store Life-Saving Vaccines

NASA’s battery-free solar technology powers vaccine refrigerators in hot, rural communities.

NASA’s photovoltaic (PV) technology has advanced many of its missions. This renewable source of energy is produced when certain photo-emissive materials, such as silicon, eject electrons upon absorbing photons from sunlight. These free electrons can be captured, and the resulting current can be used as electricity. NASA first used solar power in 1958 when Vanguard 1 was successfully launched into space.

Since then, NASA has harnessed the Sun’s energy to power many other satellites, probes, rovers, and even the International Space Station (ISS). The ISS’s iconic 115-foot solar array wings, each of which contains 32,800 solar cells that produce 32 kilowatts of electricity, were developed under the management of Glenn Research Center.

David Bergeron, who formerly headed the Advanced Refrigerator Technology Team at Johnson Space Center, sought to apply the innovations he helped develop — PV solar heat pumps for cooling lunar bases — here on Earth. After licensing the NASA technology, in 1999 he founded Solus Refrigeration — now called SunDanzer Refrigeration in El Paso, TX — and developed what became the company’s signature solar-powered refrigeration units, which have gone on to benefit many industries. One of the company’s models — a battery-free unit called the PV Direct-Drive model refrigerator — is now making another important contribution by ensuring that lifesaving vaccines are available in rural communities all over the world.

SunDanzer’s PV Direct-Drive refrigerator was designed in the early 2000s for off-the-grid users who are located where the Sun shines at least five hours per day. The unit connects directly to the solar panel, thereby eliminating the need for a charge controller or batteries, which can be tedious to replace and add extra cost over the lifetime of the unit. A key technology is the solar-powered vapor compression heat pump that circulates refrigerant throughout the interior and removes heat. In response to that process, a nontoxic, water-based phase change material freezes, creating an “ice pack” that enables temperature maintenance inside the enclosure.

In 2009, the refrigerator caught the attention of the Program for Appropriate Technology in Health (PATH), a global health nonprofit organization. PATH had established the Battery-Free Solar Refrigerator challenge, a contest where companies could apply for funding to qualify their refrigerators as suitable for vaccine storage with the World Health Organization (WHO). SunDanzer applied and won the funding. In 2010, the company renewed its license with NASA for the battery-free technology, then started modifying the unit’s specifications to meet the WHO’s standards.

The task of making its refrigerator vaccine-friendly wasn’t easy, especially in maintaining a consistent degree of cold. Vaccines thrive in a very specific temperature range, between around 35-46 °F, so the refrigerator had to be configured to meet that level of precision. A fan was used to circulate the air more evenly, and areas near the top and bottom of the unit where the temperatures often fell out of the acceptable range were closed off.

In 2011, the WHO prequalified the Solar Direct-Drive Vaccine Refrigerator, powered by NASA technology, as safe to use in hot zones around the world. SunDanzer’s vaccine refrigerator is an attractive option for clinics that operate in sunny, rural areas with little or inconsistent access to electricity. Battery-free construction also means that fewer things can malfunction that would require an expert to fix. The refrigerators require minimal maintenance and are intended to run for at least 15 years.

The company’s proprietary phase change materials, which are adept at storing thermal energy, can sustain the unit’s internal temperature during bouts of heavy cloud cover. For instance, the refrigerator can withstand 3½ days during combination cloudy weather and outside temperatures of 109.4 °F. In addition, the corrosion-resistant steel exterior and the lockable top-opening door provide increased durability and security.

The refrigerators have been used in rural areas such as in West African Senegal, where the company has installed 15 units. The United Nations Children’s Fund, which buys 40% of the global purchases of these refrigerators every year, is the company’s number-one customer.

Visit http://spinoff.nasa.gov/Spinoff2013/hm_4.html for the full story.