Solar Hot Water Heaters: Advantages and Disadvantages of Various Types

Solar-powered water heater

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

Cost benefits of the solar hot water heaters utilizing "green" technology are better than before. Government tax credits and utility rebates are available, and value is added to your home by stepping further toward environmental protection, renewable energy utilization, and your energy independence.

Solar hot water heaters are ideal systems for heating water

Either you are making home improvements with the "green" technology or building a new house, solar-powered water heaters can be added to your old heating system and combined with a new system. This is possible due to their installation flexibility.

Note: Renewable energy is green, clean, pollution-free, and protects the environment. So why not use solar energy 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 cost-competitive with natural gas, propane, electricity, and oil, but it depends on your location and fuel prices.

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

In this article:

• How solar water heaters works
• Types
• Main parts
• Advantages
• Disadvantages

How solar water heaters work?

Solar hot water systems are simple, reliable, and efficient systems of harnessing the sun's energy for the energy needs of your home; water, space, or pool heating.

Solar water heaters (SWH) mostly use flat plate collectors known as panels or evacuated tubes mounted on the roof of a house or installed on a freestanding frame (racking system). The purpose of solar collectors is to capture the sun's heat and transfer it further to the air or water.

As the fluid circulates, either naturally or forced by the pump, the energy is directly or indirectly transferred to a storage tank. These tanks are usually located either on the roof or in the utility room and garage.

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 tanks must be well insulated to reduce heat loss.

Many solar heating systems have a backup heater, so your hot water needs are met even with insufficient sun exposure.

Solar hot water heater types

Several main types of solar water heating systems are popular and sold today, as the most 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 from the sun's heat energy, we are talking about direct solar water heating systems. We refer to the indirect heating systems, if the water inside the tank is heated by the solar fluid that circulates through the heat exchanger.

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

Active vs. passive

With active solar hot water heaters, pumps and controls move hot water from the collector to the storage tank. 

On the other side, they do not require external energy for their parts (no moving parts) and where hot and cold water circulate thanks to convection and gravity, are called passive systems. A great example is the thermosiphon system.

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, the sun heats the solar fluid that circulates through the heat exchanger, where it transfers the heat to domestic water.

The open-loop needs to be drained, when used in cold climates, as the water can freeze up if left in the tubing.

The closed-loop heating system, or indirect, has the antifreeze solution in the pipes. This system has a piped loop of water or antifreeze separated from the hot water supply by a heat exchanger.

ICS

Integral Collector Storage or ICS systems are found as batch and thermosyphon systems, and since they are passive, they do not require pumps. These are built as a single unit, consisted of the collector and hot water tank.

Batch

Batch water heaters are very simple - they consist of a cylindrical tank, painted in black, where water is heated, placed inside the insulated box, and covered with glazing (tempered glass). Domestic water is heated directly inside the storage tank, and it is recommended for mild and warm climates.

Thermosyphon

Thermosyphon systems use natural convection where hot water naturally rises, so the tank of the solar hot water heaters is positioned above the collector without using a pump.

They can also be divided into direct and indirect solar water heating and get direct exposure to the sun or to get the heat from the solar fluid. As long as there is a temperature difference (hot and cold water), water will circulate. According to experts, thermosiphon systems are more effective than batch.

Drainback

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

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

Antifreeze systems - pressurized glycol

The antifreeze or 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 (propylene glycol due to low freezing point and lack of toxicity). The mixture circulates from the collectors through a pipe coil in the solar tank and then is pumped back through the collectors.

Main parts

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

Solar collectors are designed to collect the heat from the sun. As can be seen in this article, there are several types; unglazed and glazed solar panels, evacuated tubes, and concentrators.

Advantages

• Solar hot water heaters utilize free, renewable solar energy.
• Since these systems utilize free solar 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, and others).
• Some heaters do not require electricity to operate.
• It 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 a cleaner environment by reducing greenhouse gases.

Disadvantage

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

Summary

What is common for all types of solar water heating systems is that they depend on sun exposure and solar energy usage.

That is why it is vital to know the basics, such as the solar altitude angle, to orient the collector at the correct tilt angle. For example, solar collectors are most effective when the surface of the panel is normal (perpendicular) to the sun's rays and south orientation.

If you would like to know more about collectors, evacuated tubes, batch systems, how to build an SWH system, click on the provided links.