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Solar Boilers for Hot Water (Israel)

Credits: ©Sept Clean Techies/Karin Kloosterman

Israeli solar energy companies such as Solel Solar, Aora, Ormat technologies, and a host of others are now world leaders in the development of sun power to produce electricity. But Israel, a small country of 7 million, with more than half its land area being desert, has been a solar energy pioneer virtually since its beginning in 1948. What is now fondly known to many Israelis as a “dude shemesh” or sun boiler, was invented by a guy named Levi Yissar back in the early 1950’s, when electricity was very expensive due to a severe energy shortage. His innovation consisted of a modified electric water boiler that was erected on the roof of a building and attached by pipes to two simple glass faced collector plates that heated water running through them from the boiler, when the sun’s rays struck them during certain hours of the day. The heated water then returned by gravity feed to the insulated boiler, where it was stored for later use in kitchens and bathrooms.


Sun Boilers on Roof in Jerusalem

Solar boiler on a rooftop in Israel provides domestic hot water ©Apri Gila Brand

Yissar, an engineer, and entrepreneur, soon opened the first company selling such devices, the Neryah Company, in 1953. The device soon became so popular that people waited for weeks to purchase their own “dude shemesh”; and it wasn’t long before other companies got into the act. By the mid 1960’s, one in every 20 households already had their own sun boiler, and more than 50,000 had been sold.

Israeli companies also began exporting the device, particularly to other Mediterranean countries such as Greece, Turkey and Italy. More modified versions included an auxiliary electric heating device to heat water at night or on cloudy days. More modern versions have also been developed for large apartment buildings, where large collecting plates send water to either individual private water tanks or to large condominium ones where the heated water is shared by tenants in the building.

Nowadays, residents of most private dwellings or smaller apartment buildings in Israel have these sun boilers installed; which reduces electricity consumption considerably – by an estimated two million barrels of oil a year.

And it must be noted that all of this came into being long before the invention of photovoltaic solar energy cells and panels (PV) that are now being used to produce thousands of megawatts of electricity.

The old “dude shemesh” is still very much in use, however, even in many homes in the USA, Australia, and other countries. Middle Eastern countries like Jordan and Egypt, which has more than 500,000 solar collectors, are also availing themselves to this simple, yet efficient way of harnessing the sun’s power.

Egypt uses them in hotels and commercial buildings, as well in apartment blocks and private homes. Jordan has more than 200,000, many of them purchased from Israel. And even North African countries like Tunisia have also gotten into the act (110,000) with the assistance of the Global Environment Facility (GEF) to which more than 170 countries now belong.

The credit for much of this can be given to Israeli pioneer innovator Levi Yissar, who had the idea that the sun’s power could be harnessed, almost like a genie in a bottle. Appearing courtesy of Green Prophet.

Selection from Article from Wikipedia
Solar Water Heating

Flat-plate collectors for solar water heating were popular in Florida and Southern California in the 1920s. Levi Yissar built the first prototype Israeli solar water heater and in 1953 he started NerYah Company, Israel's first commercial manufacturer of solar water heaters. Despite the abundance of sunlight in Israel, solar water heaters were used by only 20% of the population by 1967. Following the energy crisis in the 1970s, in 1980 the Israeli Knesset passed a law requiring the installation of solar water heaters in all new homes (except high towers with insufficient roof area). As a result, Israel is now the world leader in the use of solar energy per capita with 85% of the households today using solar thermal systems (3% of the primary national energy consumption).

Israel's use of solar water heaters is estimated to save the country two million barrels of oil a year, and the country has the highest per capita use in the world. In the 1950s there was a fuel shortage in the new Israeli state, and the government forbid heating water between 10 p.m. and 6 p.m. As the situation worsened, engineer Levi Yissar proposed that instead of building more electrical generators, homes should switch to solar water heaters. He built a prototype in his home, and in 1953 he started NerYah Company, Israel's first commercial manufacturer of solar water heaters. By 1967 around one in twenty households heated their water with the sun and 50,000 solar heaters had been sold.[5] However, cheap oil from Iran and from oil fields captured in the Six Day War made Israeli electricity cheaper and the demand for solar heaters dropped. With the 1970s oil crisis, Harry Zvi Tabor, the father of Israel's solar industry, developed the prototype solar water heater that is now used in over 30%-40% of Israeli homes.

In 1980, the Israeli Knesset passed a law requiring the installation of solar water heaters in all new homes (except high towers with insufficient roof area). As a result, Israel is now the world leader in the use of solar energy per capita (3% of the primary national energy consumption).

As of the early 1990s, all new residential buildings were required by the government to install solar water-heating systems, and Israel's National Infrastructure Ministry estimates solar panels for water-heating already satisfy 4% of the country's total energy demand. Israel and Cyprus are the per capita leaders in the use of solar water heating systems with over 30%-40% of homes using them.

In order to heat water using solar energy, a collector is fastened to the roof of a building, or on a wall facing the sun. In some cases, the collector may be free-standing. The working fluid is either pumped (active system) or driven by natural convection (passive system) through it.

The collector could be made of a simple glass topped insulated box with a flat solar absorber made of sheet metal attached to copper pipes and painted black, or a set of metal tubes surrounded by an evacuated (near vacuum) glass cylinder. In some cases, before the solar energy is absorbed, a parabolic mirror is used to concentrate sunlight on the tube. Some systems are capable of converting light to heat and therefore are not as reliant on outside temperature.

A simple water heating system would pump cold water out to a collector to be heated, the heated water flows back to a collection tank. This type of collector can provide enough hot water for an entire family.

Heat is stored in a hot water tank. The volume of this tank will be larger with solar heating systems in order to allow for bad weather, and because the optimum final temperature for the absorber is lower than a typical immersion or combustion heater.

The working fluid for the absorber may be the hot water from the tank, but more commonly (at least in pumped systems) is a separate loop of fluid containing anti-freeze and a corrosion inhibitor which delivers heat to the tank through a heat exchanger (commonly a coil of copper tubing within the tank). Another lower-maintenance concept is the 'drain-back': no anti-freeze is required; instead all the piping is sloped to cause water to drain back to the tank. The tank is not pressurized and is open to atmospheric pressure. As soon as the pump shuts off, flow reverses and the pipes empty by the time when freezing could occur.

When a solar water heating and hot-water central heating system are used in conjunction, solar heat will either be concentrated in a pre-heating tank that feeds into the tank heated by the central heating, or the solar heat exchanger will be lower in the tank than the hotter one. However, the main need for central heating is at night when there is no sunlight and in winter when solar gain is lower. Therefore, solar water heating for washing and bathing is often a better application than central heating because supply and demand are better matched.

The water from the collector can reach very high temperatures in good sunshine, or if the pump fails. Designs should allow for relief of pressure and excess heat through a heat dump.