Honeycomb Twist Transforms Israel’s 1950s Solar Water Heater

All-weather devices provide industry with a cheap, sustainable alternative to gas

Millions of homes in Israel rely on rooftop solar devices for their hot water.

The technology dates back to the 1950s when physicist Harry Zvi Tabor relocated from England and decided there must be a way of harnessing the sun’s power – and cutting his electricity bill.

He invented the dud shemesh (Hebrew for solar water heater) comprising a solar panel and a hot water tank.

Seventy years later, scientists have adapted his device so it can operate on an industrial scale, producing a cheap and reliable source of heat, without burning fossil fuels.

The dud shemesh uses what Tabor called “simple physics” to heat water circulating in pipes behind a glass panel. It’s perfect when the summer sun is blazing, but as any Israeli will tell you, it doesn’t work so well in winter.

Tigi, a company based in Hod Hasharon, central Israel, has added a vital ingredient to the original solar water heater so it can now operate even in cold climates – and instead of heating water just to shower temperature (around 40C), it can bring it up to boiling point (100C).

The dud shemesh has changed little since Tabor invented it, but Tigi has transformed it by adding a special honeycomb to insulate the air inside the panel, and prevent it from cooling.

The dramatic reduction in heat loss means it’s now a viable option for a huge range of industrial uses, from clothes laundering to steel making, and from cement-making to bottle washing.

Virtually every factory needs a source of heat, no matter what they produce, and heating accounts for half of the world’s total energy use.

The current gas crisis – soaring prices and supply shortages – will undoubtedly focus minds more sharply on affordable alternatives.

Russia accounted for 40 per cent of EU supplies – before war in Ukraine, before sanctions, and before whatever stopped the flow of gas through the Nord Stream pipelines.

Zvika Klier, Tigi’s CEO, says the idea of insulating solar thermal collectors – the glass panels in a dud shemesh – has been around since Tabor invented them, but had never been commercially exploited.

His company refined the design, patented it and now incorporates it into the panels that form part of its end-to-end heating solution for businesses.

“We build an entire solution for companies, which includes a very important building block, our unique solar thermal collector,” Klier tells NoCamels.

Customers don’t 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,” signing up for a decade or more, and Tigi installs everything they need.

“We install it at our expense, and they buy the heat from us at a lower cost than if they were burning fossil fuels, so they start saving immediately, from the first day,” says Klier.

“Also, part of our solution is storage. You heat water during the day, and you use it 24/7. You heat water during the weekend, when the factory doesn’t work, and you use it on Monday.”

As Klier is keen to emphasize, the honeycomb, or solar thermal collectors produce heat, rather than electricity. Storing electricity is complex and expensive. But storing hot water is a lot more straightforward.

“We developed a new type of solar thermal collector, which works very efficiently, like a dud shemesh, even in very cold climate conditions,” he says.

“We heat buildings in Norway with it in the winter, not just to 40 or 50 degrees Celsius that we’re used to with showers, but to 100 degrees Celsius, which is now workable for multiple commercial and industrial applications.

“The problem is that if it’s very cold outside, you lose a lot of the energy back to the environment, it cools off back to the environment. This is what we have solved. We discovered that there was a gap in system design.”

The key development – or enabling technology – is the insulation, which is made of cellulose triacetate, similar to the material used to make photographic film.

In a standard dud shemesh water passes through pipes, warms up and circulates back to the boiler, getting hotter and hotter. The absorber plate at the back is insulated, but the glass at the front isn’t.

So if it’s freezing outside the absorber plate still heats up, but hot air circulates to the freezing glass and back to the absorber plate, cooling it down. Tigi’s insulation holds the air in columns to prevent it circulating and cooling, so that a summer-only technology becomes one that works all year round.

“Until recently, we were focusing on finalizing stabilizing a solution and working primarily in Israel,” says Klier.

“Right now the focus is in the United States, but more importantly in Europe, where gas supplies are a real problem.”

They’ve installed around 40 systems so far, including one to supply hot water to the Golan Wineries, in Israel, to wash barrels at 85 degrees Celsius.

They have also provided hot water systems for a hatchery, for the swimming pool and showers at a senior retirement center, for the commercial laundry at a kibbutz, and for the gym showers and kitchen at a hi-tech office building.

Despite the gas crisis, he says companies don’t always rush to embrace a new idea, however attractive it is.

“This is a new situation and some people have not reacted yet. Factories move slowly, the sales cycle is long and some people are waiting to see how the cost of gas is going to evolve,” he says.

“So people are trying not to make an immediate decision. But we have just come back from Germany speaking with potential partners and energy companies. I think the general understanding is that people need to move away from gas.”

Germany bought more than half of all Russia’s gas exports before the invasion of Ukraine, and has been struggling ever since.

“Approximately 40 per cent of Europe’s natural gas came from Russia,” says Klier. “That’s no longer the case, so the cost of gas has gone up worldwide, but most sharply in Europe.

“Some of the people I’ve spoken with see 10 times the price from a year ago, and we’re talking about people shutting down their business because it’s not working.

“The other issue is that there is simply not enough gas. The industry is telling you that you will get very expensive gas, but not on Tuesdays and Thursdays, where you will not get gas at all.”

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