Solar Water Heater Panels: Sizing and Installing Tips

Solar water heaterSolar water heater

Solar collectors, including water heating panels, are the most important elements of the sun-powered water heating system.

Find out about different types, check out sizing and installing tips, how to build a panel, about panel kits and mounting hardware, and more.

Solar collectors are designed to absorb heat energy from the sun (solar radiation) and are used in water and space heating, even to produce electricity. They can be used in residential and commercial applications, providing free energy either in small or large applications and are especially beneficial when combined in an array to meet high-demanding tasks.

Depending on the design and applied materials, some collectors are better than others. For example, with the selective high-quality coating applied on the absorber plates, the absorption efficiency of the solar heat increases. Inside the solar panel, thermal fluid circulates and absorbs the heat energy and, further through the plumbing system, transfers to the storage tank for water heating.

The quality of the hot water storage tank is also an important feature as it should operate with minimal heat loss.

Solar water heater panels: Things to look for


You can buy or build several types of solar collectors for water heating. Which type you will install depends on the region, climate, application, operating temperature, installation availability, and other factors. Except for domestic water heating, solar collectors can also be used for pool heating.

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

The above types of solar collectors, due to different operating temperatures, are used for various applications.

The above types of solar collectors, due to different operating temperatures, are used for various applications.

For example, the unglazed collectors, as the operating temperatures are below 110 F, are called low-temperature collectors and are used for heating swimming pools.

Solar panels and evacuated tubes operate at medium temperature, up to 180 F, and are used for the pool, space, and domestic water heating.

Parabolic-through collectors work with temperatures above 180 F and are mainly used in commercial applications.

Evacuated tubes

Evacuated tubes are collectors that utilize cylindrical tubes filled with vacuum to control the thermal losses. As they have better heat retention than flat collectors, they are mostly used in colder climates.

PV panels

PV panels (Photovoltaic) are different from those mentioned here as they are designed to produce electricity from solar radiation. In solar water heating systems, they can be used to run the pumps and controllers, making the system energy independent and cost-effective.

The following two types of panels are also worth mentioning:


Monocrystalline solar panels are made from a single (mono) crystal structure and can be recognized by the uniform flat color of the solar cells. While they use older technology, they are still efficient.


Polycrystalline solar panels are newer technology and are more affordable than mono panels. As the silicon cells cool unevenly, they give a less uniform appearance than the above type.

Glazed flat panels

Solar water heating panels that we will cover here are actually glazed flat panels, consisting of the flat-plate absorber with the coating for high absorption ratio and tubing installed in a frame (box).

The design of the flat plate collectors can also vary. What can be different are the type of the absorber plate and coating, the tubing configuration, and its connection to the absorber.

Glazed collectors are ideal for moderate temperature applications for domestic water heating, space heating, or pool heating.

Sizing tips

Note: Professional installation and repair are recommended.

Sizing a solar water heater panel depends on the area where you live. If you live in the northern and colder parts of the US, you need more collector square footage than if you live in the southern warmer areas. Always consult the local plumber and code requirements.

Example: If you need 20 gallons of hot water per day, and for a family of four or more, the water heater tank should provide at least 80 gallons of hot water. The recommended collector size for such a demand will be around 40 square feet or 4'x10' surface area.

If you want to be more accurate, you can use an online sizing tool.

While sizing is important, several other factors should be considered during the installation;

  • Weather
  • Orientation
  • Location of the site
  • Shading obstructions 

Orientation tips

The orientation of solar water heater panels is very important for solar panel efficiency and free solar heating. Between 30% and 65% of the sun's heat energy goes through the cover of the solar panel and heats the water that circulates through the tubing installed inside the panel box.

This is the reason why you need an efficient solar panel or collector. The perfect orientation for the collector is when it is perpendicular to the sun's rays.

Also, some experts say that the optimal tilt angle for the solar panel is at an angle equal to the latitude of the location. This recommendation is to maximize usable solar energy annually.

To maximize the solar energy in the summer, when the panel is mainly used for pool heating, the panel tilt angle should be 15 degrees less than the latitude of the site, while in winter, when it is used for space heating, it should be 15 degrees more than the latitude of the site.

The majority of the solar water heater panels are installed facing the south (the best), southeast or southwest - at the specified angle, and with the goal to have a full exposure during the major sunlight hours, which is two hours after the sunrise and two hours before the sunset, and when the sun is approximately 30 degrees above the horizon. 

Install a solar panel at a not-shaded site between 9 in the morning to 3 in the afternoon. Any shading will greatly affect the performance of the solar panel.

Note: Direct sun exposure is the best to maximize efficiency. Even during the overcast days, solar panels receive diffuse radiation but approximately 60% less than on a clear day.

You can always try to automate the system by investing in the necessary equipment. Such control will always orient panels toward the sun, keeping the angle close to the perfect, but it requires lots of money, time, and professional installation.


Here is the list of the tools needed for DIY solar panel installation.

  • Soldering kit, including the torch, tubing cutter, brushes, acid flux…
  • Wrenches – different types
  • Drills and saws – different types
  • Multimeter and other elements for electrical work
  • Garden hose
  • Screwdrivers
  • Hammer
  • Level
  • Bucket

Tips when building a solar panel

The building material comes in standard sizes; length of the pipes, tempered glass, the metal sheet for the absorber. So, rather than building one large and heavy panel, make several panels and connect them in parallel for maximum efficiency, easy handling, and installation.

The main components of the solar panel are; frame, absorber plate, tubing, glazing, insulation, valves, sensors, pumps, and others.


The frame box is usually made of aluminum, wood or fiberglass, and has insulation on a side and back. The preference should be given to the aluminum as it looks better, doesn't corrode, and lasts longer.

The panel box should have drainage holes at the lowest point to drain the rain, condensation, etc.


The top of the panel should be made of material that is transparent to the incoming sunlight and, at the same time, can reduce heat loss. The cover is usually made of low-iron tampered single or double-layer glass for the greenhouse effect (to keep the heat inside the collector longer). It also prevents cold weather and wind from carrying away the collected heat. If you build your own, and in order to reduce the costs, you can use lower quality tempered glass or even plastic glazing.

The advantage of the glass panel cover over the plastic is its durability, heat resistance, it can deteriorate less due to the outside conditions, but it is breakable.

If you live in a colder area, use double-layer glass to keep the heat longer inside the solar water heater panel.


In order to avoid heat dissipation, the pipework is fitted into the solar panel frame. The tubing can either utilize one long pipe which snakes through the panel, back and forth as it moves from left to right, or several straight tubes (risers) connected to the manifolds (headers).

For the piping, the recommendation is to go with the copper tubing, joined by soldering or brazing and supported by appropriate hangers at the right spots. Copper is a favorable material over PEX because copper can withstand higher temperatures and UV radiation.

The copper pipes should contact the absorber plate as much as possible to maximize the heat transfer.

Absorber plate

The absorber is part of the solar panel that receives solar energy and transforms it into heat energy. It is usually made of aluminum or copper sheet and painted in a dark color to increase absorbance.

Attached to the absorber plate is the tube system through which the water passes while absorbing the heat from the absorber plate.

How to increase efficiency and reduce heat loss

When you build your solar panel, make sure to insulate it well to reduce heat loss, ensure efficient heat transfer, and protect the inside (tubing) from weather conditions. The trapped heat will then transfer heat to the incoming fluid passing through the tubing more efficiently.

The collector will get the maximum absorption and efficiency if the exposed surfaces (tubing) are painted flat black paint. In colder climates, an even better option is to use selective surface coating due to its effectiveness, but it can result in overheating during hot weather.

Other components to consider

Building an efficient solar water heating system doesn't require only the right selection of the solar panel and the box but includes other components such as; pumps, valves, expansion tank, thermostat, sensors, and controls.

Circulation pumps are used to move the thermal fluid inside the tubing.

Check valves prevent thermosyphoning at night when the cold water from the panel goes back to the water storage tank while the hot water rises to the collectors, where it loses heat.

A pressure relief valve (PRV) protects the system from excessive pressure, while the temperature and pressure relief valve (TPR or T&P) valve from both high temperature and pressure.

The expansion tank is used to prevent high pressures and potential element failures.

Sensors are designed to monitor the system temperature.

As mentioned above, a photovoltaic module, when using solar energy, can be used to power the pump and other electronics.

Installing tips

A roof is the best place for installing solar panels for water heating. The location should allow short and easy access to the storage tank, so the heat is not lost if the pipes are too long. Moreover, as they are exposed to weather elements and heat loss, installing the insulation is recommended.

The solar transfer fluid must travel from the coolest to the hottest area for the most efficient operation.

The pipe slope is especially critical in the case of the Drainback systems as it will provide the functional operation – so water can drain from the collectors when the pump is not running.

In the case of the Drainback systems, the piping system is filled with distilled water (to reduce the danger of scaled build-up), while the Antifreeze system, with the propylene glycol, protects the system from freezing.

In modern home construction, the panels are an integral part of the house, as they are designed to blend with the exterior. These built-in solar panels are installed flush or nearly flush with the roof surface. As they do not have the frame, the unglazed collectors are always flush-mounted to the roof or some other surface.

Standard solar water heater panels should have a structural frame that is securely mounted on the roof (bolted), so they can resist the snow and wind loads, for example. At the same time, it is important to allow proper roof drainage. If the solar panels are not flush with the roof surface, install them 3-5" above.

The solar panel mounting hardware (mounting rails, clamps, brackets, bolts...) is available with a purchase of any solar heating system or as a separate kit or item. The mounting hardware allows you to install the panels on the roof, ground, top, and side of the pole, RV... Mounting hardware is usually provided by the manufacturer and is based on the collector type, roof type, and orientation.

Keep in mind that the roof installation increases the possibility of roof leaks. This is why it is important to seal every drilled hole and secure all the joints on the pipes to be watertight.

Another important factor to consider when installing solar collectors is to have them accessible for maintenance and service.

This is where the ground and wall installation are the most suitable.

Solar panel ground mount is convenient, easier than the roof mount, and much safer, doesn't affect the look of your home and possible roof leak, and as long as it has the sun exposure majority of the day, go for it.

Solar panels can also be installed on the wall – side of the building, but as long as it has a southern orientation and is unshaded.

Either installing the panels on the ground or the roof, secure the area and panels to reduce the risk of breakage. During the wintertime, drain the pipes dry to keep the pipes from bursting during the freezing temperatures.

Due to its size and weight, several people are needed to carry and installed the glazed solar panels, while one person could handle vacuum tubes and unglazed types.

When deactivating the solar heating system, always cover the collectors with material like cardboard or other sturdy light-blocking material.

Panel kits, mounting hardware, portable RV panels and DIY solar panel books

An online giant - amazon.com is my favorite online store where you can buy water heating equipment like collectors and PV panels, solar panel kits, books that describe in detail how to build panels, flexible panels for pools, small portable for RVs, roof and ground mounting hardware for installation ... or in short the whole solar panel systems.

Most manufacturers provide a 25-year warranty, and their panels are designed for easy installation and maintenance-free service.

Solar charging kits are designed to provide free and clean power and are perfect for your RV, cabin, boat, battery charging, and even home. The kit usually comes with solar panels, mounting frames, power inverter, and controllers.

Foldable or flexible solar panels are a convenient way of converting solar power into electrical current, even in low light. Solar cells are high-efficient and are mainly used for charging electronics when camping, hiking, during power outages, and whenever a portable power source is needed. Due to their multi-section design, they can be easily folded and stored.

RV solar panel kits are designed with solar charging kits, inverter, DC installation kit, transfer switch, and other components, making them ready for a complete plug and play installation.

As can be seen, there are many types of solar collectors for space and water heating. No matter which one you choose to buy or build, you are getting a great alternative to widely used electric and gas heating, but with one important advantage – the use of solar energy from the sun is free.

If your solar panel is leaking, not heating water, the pump is not working, check out this troubleshooting guide to find the cause and solution.

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