Sun water heaters on the rooftops of apartments and houses in Israel are a common characteristic of the skyline of Israeli cities and towns. In a country, where nearly every day in the spring and summer is a sunny day with barely a cloud in sight, and the winters are fairly short, with more than six months of the year rainless, the installation of sun water heaters (dudei shemesh in Hebrew) is cheap, simple and the the most common form of water heating in Israel.
Solar-heated boiler systems involves the installation of simple black panels on the roof of the home, which attract sunlight and become hot. The installation consists of a boiler into which cold water enters from the household faucet (the entrance is located on the bottom side of the boiler), from which it passes into black, glass-covered pipes called koltim. The hot water then enters the household’s faucets from the upper part of the boiler, where the water is hotter.
Water storage tanks range from 30 to 300 liters. The tank size for the daily hot water needs of an average family is 150 liters. Typical domestic units consist of a 150 liter insulated storage tank and a 2 square meter flat panel, which collects solar radiation, heats the water and passes it to storage in a pumpless, gravity-driven loop.
The cost of a system depends on the size of the water storage tank and the number of collectors installed. A system consisting of a 150 liter storage tank and two collectors is around NIS 2,800 – 3,500. This includes installation. The warrenty (from selected vendors) for the system is around 8 years for the collectors and storage tank.
Solar water heating systems require periodic inspections and routine maintenance to keep them operating efficiently. Also, from time to time, components may need repair or replacement. On an annual basis, it should be checked if visually any new construction or objects are blocking the collectors. Shading can greatly affect the performance of solar collectors. Dusty or soiled collectors will perform poorly. Periodic cleaning may be necessary in dry, dusty climates. Storage tanks and piping may also need checking for cracks, leaks, rust, or other signs of corrosion. In such cases the installation company should be contacted to clean the storage tank and the heating element inside.
One of the main advantages of a dud shemesh is that it saves electricity costs. The installation of a unit can save its owner some 2,000 kWh per year in electricity costs. The electrical backup heating coil of the dud shemesh, which all storage tanks contain, is commonly used in the winter for heating water. In the summer and on sunny days in the winter there is no need to employ the electric element in order to ensure that the water is warm enough for washing. During cold and cloudy winter it may be neccessary to turn on the boiler 20 to 40 minutes – depending the usage – prior to showering or other uses in order to have hot water. Solar water heating systems can also be bought with the function of a timer. If an apartment does not have a dud shemesh, an electric boiler is in place, which needs to be turned on regularly for hot water, unless usage can be regulated with a timer.
Flat plate solar systems were perfected and used on a very large scale in Israel in the 1950s when there was a fuel shortage in the country, and the government forbade heating water between 10 p.m. and 6 a.m.. The first prototype solar water heater was developed by an Israeli in 1953, which led to the launch of the NerYah Company, Israel’s first commercial manufacturer of solar water heating.
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