Solar Water Heater Panels
Sizing and Installing Tips
(updated 2018)

Solar water heating panel

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 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 the minimal heat loss.

In the article

Types

There are several types of solar collectors for water heating you can buy, or build, and 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 different 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 are operating at the medium temperature, up to 180 F, and are used for the pool, space, and domestic water heating.

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

Evacuated tubes

Evacuated tubes are collectors that utilize the 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 the ones mentioned here as they are designed to produce electricity from the solar radiation. In solar water heating systems, they can be used to run the pumps and controllers, for example, making the system energy independent and cost-effective.

The following two types of the panels are also worth mentioning:

Monocrystalline

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 an older technology they are still efficient.

Polycrystalline

Polycrystalline solar panels are newer technology and are more affordable that 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 for pool heating.

Sizing tips

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 square footage of the collector 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 the 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, there are several other factors that 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 the 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 mostly 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.

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 site that is not shaded 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 the efficiency. Even during the overcast days, solar panels receive the 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 a 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.

Tools

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

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

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

Frame

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

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

Glazing

The top of the panel should be made of the material which is transparent to the incoming sunlight and at the same time can reduce the heat loss. The cover is usually made of the 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 to carry away the collected heat. If you build your own, and in order to reduce the costs, you can use the 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 the colder area, use the double layer glass so it can keep the heat longer inside the solar water heater panel.

Piping

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. The reason why the copper is a favorable material and not PEX is that copper can withstand higher temperatures and UV radiation.

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

Absorber plate

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

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

The collector will get the maximum absorption and efficiency if the exposed surfaces (tubing) are painted in the 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 to include 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 are used to 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 an 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 the solar energy, can be used to power the pump and other electronics.

Installing tips

A roof is the best place for installing the 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. And as they are exposed to weather elements and heat loss, the recommendation is to install the insulation.

For the most efficient operation, the solar transfer fluid must travel from the coolest to the hottest area.

The pipe slope is especially critical in a 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.

The piping system in a case of the Drainback systems is filled with distilled water (to reduce the danger of scaled build-up), while in the Antifreeze system, with the propylene glycol, protecting 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. The unglazed collectors, as they do not have the frame, are always flush-mounted to the roof or some other surface.

Standard solar water heater panels should have a structural frame which 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 the 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 the separate kit or items. 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 the 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 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 the breakage. During the winter time 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 vacuum tubes and unglazed type could be handled by one person.

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

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

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

Amazon.com is my favorite online store where you can buy water heating equipment like collectors and PV panels, solar panel kits, books that are describing in details 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 of the manufacturers are providing 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 the solar panels, mounting frame, power inverter, and controllers.

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

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

As it 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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