How does a solar water heater work?

A solar water heater, or in professional parlance an ‘open thermosiphon system’, is the most common water heating system in Israel. It is composed of a solar panel and a tank connected together on the roof of the house. The water is heated in the panel and stored in the tank for household use. Each tank includes an electric heater that is used to heat the water on days when the sun’s rays are not sufficient.

The water tank is built from an internal metal tank with sides coated with enamel. This coating prevents the formation of rust that reduces the amount of hot water and shortens the life of the boiler.

At the bottom of the tank there are cold water inlet pipes and hot water outlet pipes, as well as a pipe to the panel. At the top of the tank there is a return pipe from the panel to the tank.

The inner container is inserted into a white-painted outer shell that is painted on both sides with oven-cured paint and is therefore durable for years.

High-quality polyurethane insulation is injected in the space created between the outer shell and the inner tank, which saves energy and effectively prevents heat loss from the water.

Each water tank is equipped with an electrical system built from a heating element and a thermostat. Vertical solar water heaters have a heat accelerator.

The panel is built from an outer frame made of corrosion-resistant galvanized steel and a polypropylene back resistant to ultraviolet radiation with aluminum foil and polyurethane insulation that prevents heat loss and leads to maximum utilization of the energy absorbed by the panel.

Inside the panel, there is a copper pipe system and a heat absorption surface made of corrosion-resistant aluminum, made by an automatic laser machine with no human contact. This high-tech manufacturing process is considered the most advanced such process worldwide. This technology ensures the efficiency and high heat output of the panel.

In areas prone to extreme  climatic conditions (frost), the pipe system is made of seamless galvanized steel Schedule 40 pipes. Schedule pipes have lifespans that are several times longer than ordinary pipes that are prone to rusting. These pipes are fitted with unique attaching wings painted with a two-layer oven-cured paint that are used as absorption surfaces. Each panel is protected by a high-transparency glass panel or a tempered solar glass panel that can withstand particularly harsh weather conditions such as strong winds and hail.

The thermosiphon solar water heater system utilizes the physical principle that hot water rises upward and the cold water remains at the bottom of the tank.

Therefore, the water tank is installed significantly higher than the panel, usually with the bottom of the tank parallel to the top of the panel, unless a nonreturn valve is installed, preventing the return of hot water to the panel (reverse thermosiphon).

Cold water enters the solar water heater from the home network to the bottom of the tank. During the winter the electric heating element heats the water and as a result of the molecular expansion of the water, the water rises and concentrates in the upper part of the tank from where hot water is drawn for use.

On summer days when there is sun, the water flows from the bottom of the tank to the bottom of the panel. The sun’s rays heat the panel’s absorption surface, which transfers the heat to the water inside the panel’s pipes. As a result of the molecular expansion of the water, the water rises to the top of the panel and from there to the top of the tank through a return pipe,

and collects at the top of the boiler. This cyclic action is called a thermosiphon.

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