Solar Water Heater: A Complete Guide for Beginners & Experts

Before you buy a solar water heater (SWH), it is important to know the working principle, parts, and technology involved, among other vital aspects.

Once you have the right information, choosing the right SWH will be a simple process – let’s dive right in.

What is a Solar Hot Water Heater?

A solar water heater is a system that warms or heats water to a suitable temperature. It uses solar energy for the entire heating process.

These water heating systems come in different configurations, as you will discover shortly in this guide.

SWH

Inside Solar Water Heater Tank

How to find your trusted solar heater supplier?

You can always trust Kesun solar which is one of the biggest solar heater supplier in China. Kesun solar is dedicated to supply you highest quality products with competitive price by increasing the production technology. In Kesun Solar, every connections are welded by argon protected welding. Argon protected welding can effectively avoid of oxidation reaction during high temperature of welding. So you can rarely found rusted leakage on connections from Kesun solar heater.

Some other solar heater suppliers are still using normal welding or even rubber sealing on connections of solar heater. When the water leak out from the connections, they even not understand why it will happen.

So after you read this, you will know who is your trusted solar heater supplier.

Solar-Powered Water Heater Benefits

• Cost-effective solution for heating water – once you install the heating system, you will not incur additional energy costs since the system depends on the sun’s energy.
• Low maintenance – most solar waters will save you the maintenance costs
• Fuel savings – it is a perfect replacement for the electrical geyser or other eating technologies that use fuel.
• Eco-friendly – they do not produce any emissions. Solar energy is clean and sustainable
• Short pay-back period – although the initial investment can be high, the payback period be 2 to 4 years.
• It reduces carbon footprint
• The initial installation cost can be low, especially where the local authorities offer incentives for adopting sustainable water heating solutions.

Parts of Solar Water Heating Systems

Storage Tanks

Solar Thermal Water Heater

Whenever you are considering tanks for solar panel water heaters, it is important to note:

• 1-tank system: some have unique designs with an option for a backup heating system
• 2-tank system: water is preheated before the normal heating takes place. Today, you will find many pre-heated solar thermal heating systems in the market.

At times, a thermosyphon system is necessary. Ideally, this system helps in energy management, making it a perfect backup plan in solar water heating systems.

Thermosyphon Systems for Solar Panels Water Heater

In most cases, these storage tanks are made from welded steel with an internal heat exchanger system. At the same time, they may have heating elements as a backup. This will ensure the tank retains its temperature even when there is no sufficient sunlight.

Among the key factors you should consider when choosing a solar hot water heater storage tank include:

• Double wall with proper insulation
• The inner section of the tank should be stainless steel or rust-resistant metals
• The outer section can be made from stainless steel, aluminum, or other material. If possible, it should be painted to prevent corrosion
• Heating element is an option but they should have a thermostat to help regulate the temperature
• Tank capacity – it varies depending on where you plan to use the water tank. For instance, bathing may require about 10 to 15 liters, while shaving will require 7 to 10 liters.

Remember, there are the solar tankless water heaters. Usually, these systems only heat water when you need it. Additionally, these systems require small installation space.

Tankless SWH

However, the solar tankless water heater may not supply many users simultaneously. Besides, integrating this system in the existing building with solar powered water heaters can be cumbersome.

Insulation Material

The insulation will prevent possible heat loss. Although there are many options to control heat loss, the most popular insulation material is thick polyurethane.

Solar Thermal Panel

Thermal vs PV Solar Panel

Most people tend to confuse PV solar panel technology and solar thermal. Ideally, these are two different technologies.

Solar photovoltaics produce electrical energy. On the other hand, solar thermal technology is specifically designed to produce heat. The heat can be stored and transformed into electrical energy.

In most cases, solar thermal work hand in hand with the solar collector systems.

With the help of a solar collector, the system automatically traps, transforms, and transfers the energy to the fluid transfer system.

Generally, there are 3 main collectors for water heating systems:

Flat Plate Collector	Integral Collector Storage (ICS)	Evacuated Tube Collector
Glazed flat plate collectors have dark absorbers with plastic or glass cover. These systems are usually insulated. Unglazed flat plate collectors – they don’t have an enclosure. However, the absorber plate is either polymer or metal.	Depending on the design, ICS has either one or more black tanks. Alternatively, they may have insulated glazed boxes with tubes. Heating takes place in two stages – the preheating phase and the conventional heating stage Suitable for mild-freeze areas	It has transparent glass tubes with a metal absorber on the fin Usually, the fin provides a large surface area for solar energy absorption while limiting heat loss through radiation

Flat Plate Water Heaters

Additionally, there is the compound parabolic collector for solar hot water heating systems. They feature a reflective geometry for optimal concentration of solar energy for heating water.

Compound Parabolic Collector

In most cases, the thermal solar collector for water heating is arranged in a combination of parallel and series. Ideally, this maximizes the amount of energy it can get from the sun hence an efficient heating process.

Piping System

They are conduits that transport heating fluid and water throughout the system.

Electric Element

An electric heating element that heats rapidly guarantees significant cost savings. It helps to generate heat energy.

Temperature Sensor

Most water heating systems are equipped with thermostats. It helps to control the temperature within the tank thereby preventing possible overheating.

Heat Transfer Fluid

The fluid provides a medium for heat energy transmission from the thermal solar water heater collector to the heat exchanger system. Many factors determine the efficiency of heat transfer fluid such as:

• Coefficient of expansion
• Viscosity
• Thermal capacity
• Safety
• Boiling and freezing point
• Compatibility with the system i.e. it should be non-corrosive

Let’s explore some common fluids for these systems:

Type of Heat Transfer Fluid	Main Characteristics
A mixture of water and propylene glycol	The ratio is usually 1:1 Non-toxic Excellent freeze protection Should be changed after 3 to 5 years For better corrosion resistance, add some inhibitors
Water	Non-toxic High specific heat Low viscosity Does not protect against freezing Can be corrosive if proper PH is not maintained Possibility of mineral deposit when water with high mineral content is used.
Air	Neither freezes nor boils Leaks out easily Require large heat exchanger system which is expensive

Heat exchanger

Heat Exchanger for Thermal Water Heater

The heat transfer fluid and water do not mix. The heat exchanger allows for heat transfer from fluid to water. A larger surface area will guarantee an efficient and reliable heat transfer process.

However, most thermal water heating systems heat exchangers are made from copper due to superior thermal conduction properties. Stainless steel is also an option.

In most heat exchangers, the heat transfer takes place between liquid to liquid. The heat transfer fluid is mainly propylene glycol mixed with water.

Of course, there are SHWs with air-to-liquid heat transfer systems. In such situations, there is no heat transfer fluid.

Additionally, you can opt for coil-in-tank, shell-and-tube, or tube-in-tube systems.

Pump

They are common in active solar heating systems. They help circulate water throughout the systems. Other related components include water heating system valves, pumps, etc.

At the same time, you can use the pumps in the heat transfer fluid circulation.

Water Heating System Valve

Control System

These are electronic devices helping to control various systems in the solar thermal water heating system. Additionally, they also ensure the overall safety of the system.

Working Principle of Solar Powered Water Heater

The thermal water heater working principle may vary slightly depending on the design and configuration. However, the fundamental principle is mainly:

• Thermal collectors convert radiation from the sun into heat energy
• With the help of special heat transfer fluid, it “passes” the heat to water
• Thermal regulators help in the heat exchange process
• As the water heats up, its density reduces hence moving to the top of the tank ready for use. At the same time, cold water with high-density move at the bottom of the tank for heating.

Although the fundamental working principle of solar hot water heaters remains the same, there could be some variations. Usually, this depends on the SWH system design.

Active Solar Water Heater

Let’s compare the two:

Indirect Circulation	Direct Circulation
Suitable for areas where freezing is rampant A pump circulates heat transfer fluid	Best for areas that rarely experience freezing The pump mainly circulates water

Let’s discuss these two systems in detail:

Direct Circulation

Usually, this system is also called the open-loop system. Normally, you can use these systems in areas that:

• Experience less freezing – it is a perfect system for moderate to mild climates
• Have single application requirements such as domestic hot water systems

That is, water flows to other parts of the building from the solar collector system with the help of a pump.

At times, we also refer to these water heaters as Drainback systems.

Direct Circulation System

However, in case you wish to install the open loop water heating in areas that are susceptible to mild freezing, then go for recirculation systems.

The recirculation systems use heating pipes whenever they approach freezing temperatures. That is, the water flows from the tanks, through the collector, and to the piping system.

Remember, when you activate anti-freezing protection in the recirculation systems, you will incur additional energy costs. It is because you will use electricity.

However, in case there is a power outage, you must install a freeze valve.

Advantages of Open Loop System

• Easy to integrate with an existing system
• Simple design makes it the most affordable
• Ensures efficient heat transfer
• Expanding the water heating system is easier

Limitations of Open Loop System

• Anti-freezing system increases the operational costs
• Not suitable for areas that are prone to freezing

Indirect Circulation System

If you are looking for a water heating system suitable for regions known for freezing then choose indirect circulation water heating systems. Owing to their unique designs, you can refer to these systems as closed-loop active solar hot water heaters.

The closed loop is suitable for multiple applications. For instance, using a single water heating system, you can use the system for:

• Swimming pool water heating
• Hot tub water heating
• Shower water heating, etc.

These systems have anti-freeze fluid that prevents possible freeing. The pumping system ensures a consistent flow of:

• Ant-freezing fluid
• Heat transfer fluid

The mixture of heat transfer fluid and anti-freeze liquid flows through the collector, and to the heat exchanger system. Currently, closed-loop glycol water heaters are effective when it comes to freezing protection. To maintain this efficiency, you must change the glycol after 3 years, depending on the quality.

Advantages of Closed Loop Systems

• A perfect choice for areas prone to freezing
• Allowing for easy integration with multiple systems

Limitations of Closed Loop Systems

• Compared to open loop systems, they are more complicated
• Changing the anti-freeze adds additional maintenance cost

Passive Solar Water Heater

There are two options:

Integral Collector Storage Systems	Thermosyphon system
Suitable for areas whose need for hot water during the day is high Best for areas whose temperatures do not go below freezing temperature ·         Water heating takes place in the storage tank	It heats water in the solar collector Their capacity is limited to 40 gallon

Due to their simple construction, these water heating systems remain simple and affordable. Broadly, you will find integral collector storage and convection heat storage.

Apart from these, there are other common terms describing these SWH systems:

• Pressurized solar water heater
• Non-pressurized solar water heating systems.

Of course, this classification mainly depends on the solar thermal water heater working principle.

Let’s compare the two:

Pressurized Solar Water Heater Panels

Non-pressurized Solar Water Heating System

Another name is high pressure solar hot water heater Pressure in the tank is usually high – nearly equal to the tap pressure They retain the pressure throughout the water heating process They have an evacuated tube alongside Also present are the heat pipe collectors for absorbing solar energy The best part, it can work with an existing system and they are more robust On the flip side, these systems are more expensive  and may require a temperature differential controller

Commonly referred to as a low-pressure solar-powered water heater Pressure in the solar panel water heater tank is lower (water losses pressure as it enters the solar thermal water heater system) Mostly characterized by vacuum glass tube collectors which are exposed to the sun for sufficient heating These systems are simple, affordable, long-lasting, light-weight However, the main drawbacks include limitations when it comes to installation, susceptibility to scaling without proper installation, in case any glass tube breaks the entire system must be shut-down

Heat Pipe Collector System

U Pipe Collector System

Solar Powered Water Heater Maintenance

Maintenance is the only sure way of ensuring your system serves you optimally for a long time.

Remember, only certified contractors should conduct the solar water heater repair and maintenance process.

Although these water heating systems are known for nearly zero maintenance, certain practices will ensure this equipment serves you for a long time. The following solar water heater panels maintenance practices increase service lifespan:

• Check the anti-freeze – you can top it up or replace and increase the fluid that has served for a long time.
• Check for possible leakages which may be due to mechanical damage
• Inspect if there are damages to solar heater frames
• Ensure the mountings and valves are working properly
• Remove any possible vegetations or dirt that are on the solar water heating system
• Periodically inspect all parts and components
• Descale the plumbing systems in case you are using hard water

Sizing Solar Systems for Water Heating

Sizing solar thermal water heaters can be the most challenging process. Remember, the solar water heating system should match the practical application requirements.

However, for the scope of this guide, we will focus on some fundamental aspects that can act as your perfect guide.

Solar Collector Size

Collector size will determine the amount of thermal energy the system can generate. Of course, this is an important aspect of the water heating capability.

Applications requiring high water volume will require a larger solar collector. Of course, this should also go hand in hand with the technology.

Water Storage Volume

Even as you consider these two, you should determine the following:

• Fluctuations in temperature – this is critical in areas that experience varying climates (i.e. summer and winter).
• Portability of the solar power water heater

At any given point during the water heating process, there could be two scenarios:

Possibility of Freezing

Your system must have anti-freeze protection. Remember, freezing can damage the solar water heater due to unregulated expansion and contraction.

A mixture of water and propylene glycol transfer fluid solves this problem. However, this is possible with indirect water heater systems.

In case you have a direct water heating system, you may drain the pipes whenever you anticipate freezing.

Alternatively, some systems feature special silicone rubber pipes. These pipes can expand during freezing. This practice is usually referred to as freeze tolerance.

Overheating

In most cases, this is never an issue in the drain backwater heater systems. The pump will stop automatically thereby preventing possible overheating.

In a non-drain back system, there is always the possibility of overheating in case there are no proper precautions.

In some active water heating systems, hot water may continue to circulate within the collector. The net effect is cooling in the solar thermal heat storage tank.

Additionally, pressure relief valves also play a fundamental role in high-pressure systems. At the same time, the low-pressure or vented water heater systems have an open vent. This is an effective safety control.

Apart from these, you must pay attention to any other safety measures during the solar water heater installation. By doing so, you will increase the service lifespan of the solar powered water heater.

Expected Heat Energy

In most cases, the thermal energy will depend on the panel’s efficiency and the sun’s intensity. Therefore, it will vary depending on the weather condition.

Take for example;

• Tropics you should expect 7kWh/m² every day
• In temperate regions, the average heat energy is about 3.27 kWh/m² every day

Apart from the weather condition, the technology in the thermal solar panel plays an integral role here.

Solar Panels for Water Heaters

Let’s compare the table below courtesy of Wikimedia:

SWH Energy Estimates

Both technology and configurations determine the net thermal energy you can use for your heating systems.

For instance, designing solar water systems for cold weather will be costly. This is due to the complexity of these systems.

The payback period will depend on the design complexity.

Price of Solar-Powered Water Heater

Solar water heater prices depend on the quality, features, and technology.

For example, the prices vary from say 200 USD to over 6000 USD. Therefore, it is quite difficult to estimate the exact price of SWHs.

Simply contact a solar thermal water heating system manufacturer for an accurate quotation.

Of course, they will also help you in the solar panel water heater design process.

Uses of Solar Powered Water Heaters

Ideally, we use solar thermal systems in vary many aspects such as:

Rooftop Water Heating Systems

• Solar panel water heater for homes – common applications include solar pool water heaters, solar water trough heaters, solar livestock water heaters, solar water heaters for chickens, solar power water heating for bathrooms, etc.
• Commercial solar water heating systems – some common applications include hostels, dormitories, hospitals, or hotels that use the systems to heat water.
• Industrial applications – they play an important role in various preheating processes, cleaning or washing

Even if you intend to use solar water heating systems, it is important to comply with the set rules and regulations. Let’s briefly summarize the main standards for SWH:

Region	Standards when using SWH
Europe	EN 806 EN 1717 EN 60335 UNE 94002:2005
United States	OG-300
Canada	CSA-F378 CSA-F379 SRCC
Australia	Renewable Energy Acts/Regulations

Of course, you should also consider the solar panel water heater systems which are ENERGY STAR certified.

Conclusion

Before choosing any solar water heater system, you must specify where you intend to install the equipment and its specific use.

From this information, you will choose the perfect solar thermal heater size and type. For any questions or inquiries, contact us now.

More Resources:

Solar Water Heating System – Source: DOE

Thermal Water Heating System – Source: McCoy Mart

Solar Panel Water Heater – Source: Wikipedia

Type of Water Heaters (SWH) – Source: PENNSTATE

SWH Systems – Source: Britannica

Solar Thermal Water Heater – Source: HAREDA