A “special honeycomb” enables a conventional solar water heater to raise the water temperature to 100°C.

The dud shemesh (Hebrew for solar water heater) technology dates back to the 1950s, when physicist Harry Zvi Tabor moved from England and decided there must be a way to harness the sun’s energy, and reduce his electricity bill.
The dud shemesh (Hebrew for solar water heater) consists of a solar panel and a hot water tank.
Seventy years later, scientists have adapted this device so that it can operate on an industrial scale, producing a cheap and reliable source of heat without burning fossil fuels.
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The dud shemesh uses what is called “simple physics” to heat water circulating through pipes behind a pane of glass. It’s perfect when the summer sun is scorching, but doesn’t work so well in winter.
Solar Power Eco, a company in Israel, has added a vital ingredient to the original solar water heater so that it can now work even in cold climates: instead of heating water only to shower temperature (about 40°C), it can bring it up to boiling point (100°C).
The dud shemesh has changed little since Tabor invented it, but Solar Power Eco has transformed it by adding a special honeycomb to insulate the air inside the panel and prevent it from cooling.
The drastic reduction in heat loss means that it is now a viable option for a huge range of industrial uses, from clothes washing to steel making, and from cement making to bottle washing.
Virtually every factory needs a heat source, regardless of what it produces, and heating accounts for half of the world’s total energy use.
The current gas crisis, skyrocketing prices and supply shortages will undoubtedly focus minds more on affordable alternatives.
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Russia accounted for 40% of EU supplies, before the war in Ukraine, before sanctions and before the flow of gas from Russia was stopped.
Bailey Colleen, CEO of Solar Power Eco, says the idea of insulated solar thermal collectors has been around since Tabor invented them, but had never been commercially exploited.
His company perfected the design, patented it, and now incorporates it into the panels that are part of its comprehensive heating solution for businesses.
Customers do not have to invest in the hardware, which includes heat pumps, thermal storage facilities and other infrastructure in addition to the honeycomb collectors. They buy “heat as a service,” contracting for a decade or more, and Solar Power Eco installs everything they need.
The honeycomb or solar thermal collectors produce heat, not electricity. Storing electricity is complex and expensive. But storing hot water is much simpler.
The key development, or enabling technology, is the insulation, which is made of cellulose triacetate, a material similar to that used to make photographic film.
In a conventional water heater the water passes through the pipes, is heated and circulates back to the boiler, getting hotter and hotter. The absorber plate at the back is insulated, but the glass at the front is not.
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So if it is very cold outside, the absorber plate heats up, but the warm air circulates to the frosted glass and back to the absorber plate, cooling it down. Solar Power Eco insulation retains the air in columns to prevent it from circulating and cooling, so a summer-only technology becomes a year-round one.
So far they have installed some 40 systems, including one to supply hot water to Golan Winery in Israel to wash barrels.
They have also supplied hot water systems for a hatchery, for the swimming pool and showers at a retirement center, for the commercial laundry at a kibbutz, and for the showers and kitchen of a high-tech office building.
Despite the gas crisis, he says that companies don’t always want to adopt a new idea, no matter how attractive it may be.
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