A Comprehensive Guide to Solar Water Heater Panels

Solar collectors, particularly solar water heater panels, play a crucial role in harnessing the power of the sun for efficient water heating systems.

In this comprehensive guide, you will explore various types of solar collectors, gaining valuable insights into their functionalities and advantages.

Additionally, you will discover essential information about sizing and installing, ensuring optimal performance and efficiency.

solar panels used to heat water
Solar water heater and solar panels

Solar Water Heater Panels: Things to Look For

Importance of Harnessing Solar Power for Water Heating

Harnessing solar power for water heating is of paramount importance in today’s world. As the global population continues to rise and energy demands surge, finding sustainable and eco-friendly alternatives to conventional energy sources becomes crucial.

Solar power offers a remarkable solution by utilizing the sun’s abundant and renewable energy to heat water. By employing solar thermal systems, we can significantly reduce our dependence on fossil fuels and decrease carbon emissions, mitigating the adverse effects of climate change.

The ingenious design of solar panels allows them to absorb the sun’s heat energy, which is derived from solar radiation. This heat absorption capability enables their application in various domains, including water and space heating, and even electricity generation.

Moreover, solar panels for water heaters offer versatility, making them suitable for both residential and commercial settings. They provide free energy for small-scale or large-scale applications, demonstrating their practical use in meeting diverse energy needs.

Types of Solar Water Heater Collectors

You can buy or build several types of solar collectors for water heating, and the specific type you choose to install will depend on factors such as the region, climate, application, operating temperature, installation availability, and other considerations. In addition to domestic water heating, solar collectors can also be used for pool heating.

The following are some common types of solar collectors:

  • Glazed flat-plate solar panels
  • Unglazed flat-plate solar panels
  • Evacuated tubes
  • Parabolic-through collector
  • PV panels

Each of these types of solar collectors is used for various applications due to their different operating temperatures.

For instance, unglazed collectors are known as low-temperature collectors because they operate at temperatures below 110°F. They are primarily used for heating swimming pools.

Solar panels and evacuated tubes operate at medium temperatures, reaching up to 180°F, and can be used for heating pools, spaces, and domestic water.

Parabolic-through collectors are designed to work at temperatures above 180°F and are mainly used in commercial applications.

Evacuated Tubes

Evacuated tubes are cylindrical collectors designed to minimize thermal losses by utilizing a vacuum-sealed environment. These tubes exhibit superior heat retention capabilities, making them particularly suitable for colder climates.

PV Panels

PV panels (Photovoltaic) differ from the previously mentioned collectors as they are specifically designed to convert solar radiation into electricity. In the context of solar water heating systems, PV panels can be utilized to power the pumps and controllers, rendering the system both energy independent and cost-effective.

The following two types of panels are also worth mentioning:


Monocrystalline solar panels are constructed using a single (mono) crystal structure, which is evident by the uniform and flat color of the solar cells. Despite utilizing older technology, they remain highly efficient.


Polycrystalline solar panels feature newer technology and are typically more cost-effective than monocrystalline panels. As a result of the cooling process of the silicon cells, they display a less uniform appearance compared to the aforementioned type

Glazed Flat Panels

The solar water heating panels we are discussing are known as glazed flat panels. They consist of a flat-plate absorber coated for high absorption ratio, with tubing installed within a framed structure.

The design of flat plate collectors can vary in several aspects, such as the type of absorber plate, coating, tubing configuration, and connection to the absorber.

Glazed collectors are particularly suitable for moderate temperature applications, including domestic water heating, space heating, or pool heating.

Sizing Tips

The sizing of a solar water heater panel depends on the specific region where you reside. If you live in the colder northern parts of the US, a larger collector square footage is required compared to the warmer southern areas. It is always advisable to consult with a local plumber and adhere to relevant code requirements.

As an example, if you have a daily hot water requirement of 20 gallons for a family of four or more, the water heater tank should provide a minimum of 80 gallons of hot water. For such a demand, the recommended collector size would be around 40 square feet or a surface area of 4’x10′.

For a more accurate estimation, online sizing tools can be utilized.

While sizing is crucial, it is important to consider several other factors during the installation, including:

  • Weather conditions
  • Panel orientation
  • Location of the installation site
  • Shading obstructions 

Orientation Tips

The orientation of solar water heater panels is of paramount importance to maximize their efficiency and harness the benefits of free solar heating. Roughly 30% to 65% of the sun’s heat energy passes through the panel cover and heats the water circulating within the tubing housed in the panel box.

This underscores the necessity of utilizing efficient solar panels or collectors. Ideally, the collector should be positioned perpendicular to the sun’s rays to achieve optimal orientation.

Experts recommend setting the tilt angle of the solar panel equal to the latitude of the location. This approach aims to maximize the annual utilization of solar energy.

To optimize solar energy capture during summer (primarily for pool heating), the panel tilt angle should be set 15 degrees lower than the latitude of the site. Conversely, during winter (for space heating), it should be set 15 degrees higher than the latitude of the site.

Most solar water heater panels are typically installed facing south (the ideal direction), southeast, or southwest, at the designated angle. This positioning ensures maximum exposure during peak sunlight hours, typically occurring approximately two hours after sunrise and two hours before sunset when the sun is around 30 degrees above the horizon.

When selecting a site for panel installation, it is crucial to choose an unshaded area between 9 a.m. and 3 p.m. as any shading significantly impacts the panel’s performance.

Note: Direct sun exposure yields the highest efficiency. Even on overcast days, solar panels receive diffuse radiation, albeit approximately 60% less than on clear days.

For those interested in automation, it is possible to invest in equipment that continuously orients the panels toward the sun, maintaining an angle close to perfection. However, such a system requires a significant investment in terms of cost, time, and professional installation.

Required Tools

Here is a list of tools required for DIY solar panel installation:

  • Soldering kit, which includes a torch, tubing cutter, brushes, acid flux, and other related items.
  • Assorted wrenches.
  • Various types of drills and saws.
  • Multimeter and other electrical components for electrical work.
  • Garden hose.
  • Screwdrivers.
  • Hammer.
  • Level.
  • Bucket.

Tips When Building a Solar Panel

The building materials for solar panels are commonly available in standard sizes, such as the length of pipes, tempered glass, and metal sheets for the absorber. To optimize efficiency, facilitate handling, and simplify installation, it is advisable to construct multiple panels and connect them in parallel.

The essential components of a solar panel encompass the frame, absorber plate, tubing, glazing, insulation, valves, sensors, pumps, and other necessary elements.


The frame box for solar panels is typically constructed using aluminum, wood, or fiberglass materials and features insulation on one side and the back. It is recommended to prioritize aluminum as the preferred choice due to its aesthetic appeal, corrosion resistance, and longevity.

Additionally, the panel box should incorporate drainage holes at its lowest point to facilitate the removal of rainwater, condensation, and other moisture.


The top of the solar panel should be composed of a material that is transparent to sunlight while minimizing heat loss. Typically, the cover consists of low-iron tempered glass, either as a single or double-layer, creating a greenhouse effect. This design feature aids in prolonging the retention of heat within the collector. Additionally, the glass cover acts as a protective barrier against cold weather and wind, preventing the dissipation of accumulated heat. For cost-saving purposes in DIY projects, lower-quality tempered glass or plastic glazing can be considered.

Compared to plastic, the glass panel cover offers benefits such as enhanced durability, heat resistance, and greater resilience to external conditions, despite being susceptible to breakage.

In colder regions, utilizing double-layer glass is recommended to maximize heat retention within the solar water heater panel.


To minimize heat dissipation, the solar panel frame incorporates the pipework. Two options for tubing configuration are commonly used: a single long pipe that zigzags back and forth within the panel, moving from left to right, or multiple straight tubes (risers) connected to the manifolds (headers).

When selecting piping materials, it is recommended to utilize copper tubing, which can be joined through soldering or brazing, and properly supported by hangers at appropriate intervals. Copper is favored over PEX (cross-linked polyethylene) due to its ability to withstand higher temperatures and UV radiation.

Maximizing the contact between the copper pipes and the absorber plate is crucial for optimizing heat transfer.

Absorber Plate

The absorber is a crucial component of the solar panel responsible for receiving solar energy and converting it into heat energy. Typically, it is constructed using aluminum or copper sheet material, which is painted in a dark color to enhance absorbance.

The tube system is connected to the absorber plate and facilitates the passage of water, allowing it to absorb heat from the absorber plate.

Other Components to Consider

To construct an efficient solar water heating system, careful attention must be given not only to the selection of the solar panel and box but also to the incorporation of various essential components. These include pumps, valves, expansion tank, thermostat, sensors, and controls.

Circulation pumps are employed to facilitate the movement of thermal fluid within the tubing.

Check valves play a crucial role in preventing thermosiphoning during nighttime. They ensure that cold water from the panel does not flow back to the water storage tank, while allowing hot water to rise to the collectors, where it dissipates heat.

To protect the system, a pressure relief valve (PRV) is utilized to prevent excessive pressure, while a temperature and pressure relief valve (TPR or T&P valve) offers protection against both high temperature and pressure conditions.

The inclusion of an expansion tank is essential to prevent high pressures and minimize the risk of component failures.

Sensors are designed to monitor the system temperature, enabling effective control and regulation.

As mentioned earlier, a photovoltaic module can be employed to harness solar energy for powering the pump and other electronic components.

How to Increase Efficiency and Reduce Heat Loss

When it comes to harnessing solar power for water heating, maximizing energy efficiency is crucial. By optimizing your system, you can make the most of the sun’s energy and reduce energy consumption. Here are some key considerations to help you maximize energy efficiency:

  • Insulation and system optimization: Proper insulation of your water storage tank and pipes minimizes heat loss, ensuring that the heated water remains hot for longer periods. Additionally, regular system maintenance, such as cleaning panels and checking for leaks, helps maintain optimal performance.
  • Surface coating: For optimal absorption and efficiency, it is advisable to paint the exposed surfaces, particularly the tubing, with flat black paint. In colder climates, an even better option is to employ selective surface coating, known for its effectiveness. However, it is important to be cautious as this coating can potentially cause overheating during hot weather.
  • Integration with existing systems: Integrating your solar water heater panels with existing water heating systems, such as backup heaters or heat pumps, allows for flexibility and efficient use of energy. This ensures a continuous supply of hot water even during periods of low solar radiation.
  • Smart controls and timers: Utilizing smart controls and timers allows you to schedule water heating based on your usage patterns. This prevents unnecessary energy consumption and ensures hot water availability when needed.
  • Regular monitoring and adjustment: Monitor your system’s performance regularly to identify any inefficiencies or issues. Adjust settings as needed to optimize performance and energy usage.

Installing Tips

Installing solar panels for water heating on the roof is generally the most suitable option. It ensures convenient access to the storage tank, minimizing heat loss due to long pipe runs. Additionally, installing insulation is recommended to mitigate weather-related elements and reduce heat loss.

Efficient operation of the solar transfer fluid requires it to travel from the coolest to the hottest area.

For drainback systems, the pipe slope plays a critical role in facilitating functional operation, allowing water to drain from the collectors when the pump is not running.

In drainback systems, distilled water is used as the solar transfer fluid to minimize the risk of scaled build-up. On the other hand, antifreeze systems utilize propylene glycol to protect against freezing.

In modern home construction, solar panels for water heaters are often integrated into the design of the house, blending with the exterior. These built-in solar panels are typically installed flush or nearly flush with the roof surface. In the case of unglazed collectors without frames, they are always flush-mounted to the roof or another surface.

Standard solar water heater panels should have a sturdy structural frame securely mounted on the roof to withstand snow and wind loads. Adequate roof drainage is also important. If the solar panels are not flush with the roof surface, it is recommended to install them 3-5 inches above.

Mounting hardware for solar panels, such as rails, clamps, brackets, and bolts, is typically provided by the manufacturer based on the collector type, roof type, and orientation. It can be purchased along with the solar heating system or separately as a kit or individual items.

When installing solar collectors on the roof, it is crucial to seal every drilled hole and ensure watertight joints on the pipes to prevent roof leaks.

Accessibility for maintenance and service is an important factor to consider when installing solar collectors. Ground and wall installations are the most suitable options in this regard.

Ground-mounted solar panel installations are convenient, easier than roof mounts, safer, do not affect the aesthetics of the home, and minimize the risk of roof leaks. As long as they receive ample sun exposure throughout the day, ground mounts are a viable option.

Solar panels can also be installed on walls, provided they have a southern orientation and are unshaded.

Whether installing panels on the ground or roof, it is important to secure the area and panels to reduce the risk of breakage. During winter, it is advisable to drain the pipes completely to prevent bursting in freezing temperatures.

For glazed solar panels, due to their size and weight, several people are typically required for carrying and installation. Vacuum tubes and unglazed types can be handled by a single person.

When deactivating the solar heating system, it is recommended to cover the collectors with materials like cardboard or other sturdy, light-blocking materials.


In conclusion, incorporating solar water heater panels into your home or business offers numerous benefits, ranging from cost savings to environmental protection. By reducing your carbon footprint and embracing a greener lifestyle, you contribute to a cleaner and more sustainable future for generations to come.

Embracing solar power for water heating is not only a practical choice but also a powerful statement of your commitment to the planet and its well-being.


How Long Do Solar Water Heater Panels Last?

Solar water heater panels typically last for 20 to 30 years or more, depending on factors like quality, installation, maintenance, and local conditions. Regular upkeep and using high-quality components can extend their lifespan.

Should Solar Panels Be Washed?

Yes, it is advisable to periodically wash solar panels to maintain their optimal performance. Over time, dirt, dust, leaves, bird droppings, and other debris can accumulate on the surface of the panels, reducing their efficiency. Regular cleaning helps ensure that sunlight is effectively absorbed by the panels and converted into usable energy. Use a soft brush or cloth with water to remove dirt and debris. Follow manufacturer guidelines and exercise caution during cleaning to avoid damage.

When Do Solar Panels Need to Be Replaced?

Solar panels have a long lifespan, but replacement may be necessary in certain situations. Factors such as age, physical damage, degradation, technology advancements, and warranty coverage can indicate the need for panel replacement. If your panels are nearing the end of their lifespan or have severe damage compromising their performance, replacement may be worth considering. Upgrading to newer panels with higher efficiency can maximize energy production. If your panels are under warranty and experiencing issues, contact the manufacturer or installer for potential replacement or repair options.

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