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Calculations of solar collector hourly thermal energy output as part of central solar water heating system with individual 150 liters storage tanks for each apartment in high rise multi-apartment residential building in Tel Aviv. The energy output at noon is 758 kcal/hr in January and 1,221 kcal/hr in April. Solar collectors supply 2,647 kWh/year of thermal energy to each apartment, minimum 5.41 kWh/day on average day in December, maximum 8.53 kWh/day in August. Hot water supply equivalent at 40°C is 30 liter/hr in December and 81 liter/hr in August at noon, 192 liter/day in January to 500 liter/day in August.

Today, solar thermal systems are well established worldwide with an enormous potential for energy production and for high contribution to the future green energy system. Solar domestic hot water systems with natural circulation are most favorable in areas with a mean annual sum of global radiation on a horizontal surface above 1800 kWh− 2 year− 1 and with collector areas up to 10 m2. Forced circulation systems for flat-type solar collectors could be useful in colder climates and for large systems. The application of more complex solar collector technologies depends on the possible demands for higher temperature levels. Several examples concern some industrial applications, whose heat demands could now be met through solar energy. In all the cases, the next challenge is to swiftly make cost-effective all such devices and technologies.