Solar Hot Water Heaters Buying Guide - Types, Advantages and Benefits

Solar water heaters - evacuated tubes

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

This is the reason why we are writing about solar heating, panels, how to build a solar water heater, about different systems including active and passive systems, main parts, advantages, benefits, and much more.

Here are the highlights of the article:

Why owning a solar water heater is a good thing

The cost benefits of the solar hot water heaters that utilize the "green" technology are better than before. The government tax credits and utility rebates are available, and value is added to your home. All of us using these systems will take a role in the environmental protection, renewable energy utilization, and energy independence.

Either you are planning the improvements on the existing home with the "green" technology, or you have bought a new house; solar-powered water heaters because of its flexibility in installation, can be easily added to your existing heating system or combined with a new system.

Solar hot water heaters can be used in any climate, especially if you live in the southern regions, as the efficiency will be the highest. 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 solar water heater works

Solar hot water systems are simple, providing a reliable and cost-effective solution for harnessing the sun's energy for the energy needs of your home.

These systems use solar panels such as flat plate collectors or evacuated tubes, which are mounted on the roof, or installed on a freestanding frame. The purpose of the solar collectors is to capture the sun's heat and use it for water heating.

The fluid inside the collectors is heated by the sun and transferred either naturally or forced by the pumps, to a water storage tank, directly or indirectly. These tanks are usually located either on the roof or in the utility room.

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 to reduce the heat loss.

Many solar heating systems have a backup heater, so your hot water needs are met even when there is no sufficient heat from the sun.

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Solar water heating systems - Types

There are several popular types of solar water heating systems which are considered as efficient, reliable, simple and long-lasting.

  • Direct system
  • Indirect system
  • 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 with the sun's heat energy, we are talking about the 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.

If your home is located in the warmer climates, the recommendation is to use the direct solar water heating system. The potable water from your home plumbing system circulates directly through the solar collector and the storage tank.

Active vs. passive

An active system is when the cold and heated water are moved through the solar hot water heaters and to the storage tank, utilizing the electrically powered pump and controllers.

On the other side, solar hot water heaters that do not require pumps and the external energy for its parts (no moving parts), where hot and cold water circulate by using the law of physics, are called passive systems. These are also known as thermosiphon 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. When it is used in cold climates, it needs to be drained, as the water can freeze up.

Closed-loop systems are also indirect as the water is heated indirectly; first, the sun heats the solar fluid, then it circulates to the heat exchanger, where it transfers the heat to domestic water (no direct contact between the fluid and water).

The 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.

ICS or Batch

Integral Collector Storage system or ICS 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 law of physics where the hot water naturally rises, so the solar hot water heaters tank is positioned above the collector. They can also be divided into 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 it 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.

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 the solar heat, and to prevent freezing.

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. The 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

  • Collectors or panels
  • Support structure
  • Storage tank except for batch systems
  • The pump
  • Thermal expansion tank
  • Controller
  • Freeze protection
  • Other safety features


  • Solar hot water heaters utilize free, renewable solar energy.
  • Since solar water heating systems are using free sun’s 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 directly to heat the swimming pool.
  • Easy to maintain.
  • Solar water heating is a reliable and effective way of heating.
  • Government incentives for using green energy.
  • Increased energy independence.
  • Provides cleaner environment by reducing the greenhouse gases.


  • Higher start-up cost than electrical or gas heaters.
  • High installation cost.
  • With the lower temperature, the efficiency drops.
  • Has to be supplemented it by other fuel sources.
  • Due to the small pipe size inside the collector, it is subjected to the mineral buildup.

Related articles

Solar types
DIY design and build tips
Build solar WH
Problems and troubleshooting
Swimming pool solar water heater
Solar panels
Passive systems
Active systems

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