Solar Hot Water Heaters

Types, tips and benefits

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Solar hot water heaters and "green" heating systems are more attractive than ever before, because they are more competitive, reliable, using free renewable energy and providing high efficient operation.

This is the reason why we are writing about solar heating, panels, how to build solar water heater, about different systems including active and passive systems, the main parts, books and much more. Here are the highlights of the article:

Cost benefits for the solar hot water heaters that utilize the "green" technology are better that before, government tax credits and utility rebates are available, and value is added to your home by stepping further toward environment protection, renewable energy utilization and your energy independence.

Either you are doing home improvements with the "green" technology, or have a new house; solar powered water heaters, because of its flexibility in installation, can be added to your old heating system and combine it with a new system.

Note: Renewable energy is green, clean, pollution free and protects the environment. So why not to use the sun when it is free.

Solar hot water heaters can be used in any climate, especially if you live in southern regions. Solar water heating may be a cost-competitive with the natural gas, propane, electricity and oil, but it depends on your location and fuel prices.

How they work

solar hot water heatersSolar hot water systems are simple, reliable and cost-effective method of harnessing the sun's energy for the energy needs of your home.

Solar hot water heaters use panels, flat plate collectors, mounted on the roof, or installed on a freestanding frame. The purpose of solar collectors is to capture sun's heat and transfer it further.

As the fluid circulates, either naturally or forced by pumps, it transfers the energy to a storage tank, directly or indirectly. These tanks are usually located either on the roof or in the technical room and garage.

There are two types of solar hot water heaters, open-loop and closed-loop.

The open-loop, when used in cold climate, needs to be drained, as the water can freeze up. Closed-loop heating system, or indirect, have the antifreeze solution. This system has a piped loop of water or antifreeze separated from the hot water supply by a heat exchanger.

If you live in a colder climate environment, the drain-back solar water system is what you want to use. The water that is in the collector and pipes drains into an insulated tank each time when the pump shuts off. This is the safe way of removing water when not collecting solar heat, and to prevent freezing.

If your home is located in the warmer climates, probably you will use direct solar water heating system. The potable water from your home plumbing system circulates directly through the solar collector into the storage tank.

With active solar hot water heaters, pumps and controls are used to move the hot water from the collector to the storage tank. For passive systems, usually called thermosyphon, there are no pumps and other electrical components.

Tip 1: For solar water heaters to be energy efficient, the storage tank has to have the right size, to match the solar panels area and family needs.

Tip 2: Collector pipes and storage tank must be well insulated.

Many solar heating systems have a back-up heater, so your hot water needs are met even when there is no sufficient sunshine.

emergency plumber

Solar water heating systems

Several main types of solar water heating systems are popular and sold today as the most efficient, reliable, simple and long lasting.

  • Direct systems

  • Indirect systems

  • Active system

  • Passive system

  • Open loop

  • Closed loop

  • Integral Collector Storage system

  • Thermosyphon system

  • Drainback system

Direct vs. indirect

When domestic water is heated directly inside the solar collector from the sun's heat energy, we are talking about direct solar water heating system. If water inside the tank is heated by the solar fluid that circulates through the heat exchanger, we are referring to the indirect heating systems.

Active vs. passive

When cold and heated water moves through the solar hot water heaters by utilizing the electrically powered pump this is called an active system.

On the other side solar hot water heaters that do not require external energy for its parts (no moving parts), where hot and cold water circulates by using the principle of the law of physics, are called passive systems.

Open-loop vs. closed-loop

All open-loop systems are direct and active. Domestic water circulates directly through the solar panels/collectors utilizing the circulating pump for this operation. Closed-loop systems are also indirect as the water is heated indirectly; first sun heats the solar fluid that circulates through the heat exchange where it transfers the heat to domestic water.

ICS or Batch

Integral Collector Storage, ICS, systems are also known as batch systems. Batch ICS solar heating systems do not require pumps as they are passive and they don't have storage tanks as the domestic water is heated directly in the collector.


Thermosyphon systems are using the natural low where the hot water naturally rises, so the solar hot water heaters tank is positioned above the collector. They can also be divided on direct and indirect solar water heating, and get the direct exposure to the sun or to get the heat from the solar fluid.


Drainback systems are known as active, indirect and closed-loop solar heating systems. They can be used for both water and home space heating and in any climate region except where is extremely cold. The main advantage is its capability to drain all the fluid out of the collector when the system turns off. That means they require continuous drop between the solar collector and the storage tank.

Pressurized glycol

Pressurized glycol system is used if the continuous fall is not possible, like with the drainback systems. With the pressurized system piping can go in any direction without concerns. Fluid used to absorb the solar heat is the mixture of water and antifreeze. The mixture circulates from the collectors through a coil of pipe in the solar tank, and then is pumped back through the collectors.

Main parts

  • Support structure

  • Storage tank except batch systems

  • The pump

  • Controller

  • Freeze protection

  • Other safety features


  • Solar hot water heaters utilize free renewable, solar energy.

  • Since solar water heating systems are using free sun energy, they can supply up to 50% of the energy needed for your home and therefore greatly reduce the heating costs (depends on climate conditions, water use...).

  • Some heaters do not require electricity to operate.

  • Can be used to directly heat the swimming pool.

  • Easy to maintain.

  • Solar water heating is reliable and effective way of heating.

  • Government incentives for using green energy.

  • Increased energy independence.

  • You are contributing to a cleaner environment by reducing greenhouse gases.


  • Higher start up cost than electrical or gas heaters.

  • High installation cost.

  • With colder temperature solar energy use drops.

  • Has to be supplemented it by other fuel source.

  • Collector due to its small pipe size is subjected to the mineral buildup.

Popular Brands / Manufacturers

  • Stiebel Eltron

  • Lochinvar

  • Bock

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(All pictures are courtesy of Rheem)

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