Imagine life without a refrigerator. It's such an accepted norm for us, but for a large portion of the world the ability to keep anything fresh for days at a time is beyond reach.
The International Energy Agency and World Bank report that 1.2 billion people around the world live off-grid, where the only likely source of electricity is from diesel-powered generators that are dirty, unreliable and increasingly expensive to run.
Dulas, a renewable energy technology company based in Machynlleth, Wales, has a solution. Its VC-150-2, VC-65-2 and VC-200-1 chest fridges - all powered by solar panels - are designed specifically to store vaccines and can work for five days without any kind of charge.
"They're all specifically manufactured for the safe storage of vaccines," says Catherine McLennan, a customer sales and marketing executive at Dulas.
McLennan says the fridges are used for many polio immunisation campaigns, mostly in Africa. "We provide a complete a complete stand-alone fridge system and they're expected to last as long as a domestic refrigerator, around 10 years, and they don't need any electricity from the grid."
Dulas, an ethically driven co-operative owned by its employees, supplies the fridges as a kit with solar panels, battery, charge controller and all cables and accessories.
Designed to work in up to 43 degrees Celsius ambient temperatures, the three solar fridges are found worldwide, usually as part of a vaccine drive by NGOs and humanitarian organisations such as Unicef, Goal, Save the Children and Merlin. Countries with life-saving projects featuring a solar fridge range from Peru and across sub-Saharan Africa to Myanmar, Laos, Indonesia and remote Pacific islands such as Vanuatu, Kiribati and the Solomon Islands.
The VC-65-2 and VC-150-2 also have freezer compartments, while the former also works as a blood bank.
"We make sure that we size every system according to the solar data in the area to ensure maximum efficiency," McLennan says. "Once you've set it up you do need a good day of sunshine, but if it's then stormy for five days the vaccines will remain cold enough."
Engineers at Dulas try to customise the solar arrays according to the sunshine in the destination country - a task that's harder than it sounds. Sunshine in the north and south of Vietnam, for example, varies as dramatically as in the deserts and mountains of Peru.
"The UN agencies usually tell us the nearest large town, then we use meteorological data from Nasa data systems to size the panels, battery and charger control and small components - we work from the solar panels backwards," says Chris Coonick, international technical engineer at Dulas, adding that the systems rely on their owners being careful.
"It's all about educating people on how to use the solar power they have for things they truly need it for," she says. "Just because the power is there it doesn't mean you should to use it for things that aren't important. We try to get people to prioritise and think about energy in a different way."
The company's current project is to provide a large 15kW solar system, including several solar refrigerators, to a hospital on the island of Likoma in Lake Malawi, which is being funded by the charity African Steps.
"At the moment they have a diesel generator and a gas turbine on the island, but they only have electricity every other day for three or four hours. It was all about whether diesel could be shipped to the island."
For now the island's hospital can't function 24 hours a day, but this month Dulas will replace that diesel generator and create a solar-based system that should last more than 25 years. The idea is to safeguard essential power for life-saving equipment.
"Solar power isn't the solution to everything," says Coonick, citing air conditioning as an example. "It's best for equipment that doesn't use a lot of power, and that you don't need that often - but when you do, it's vital."